GCSE Astronomy - Pearson Edexcel 2.0

Question 1

What is the mean diameter of the Earth?

Answer 1

13,000 km

Question 2

Name the 4 terrestrial planets:

Answer 2

1. Earth
2. Mercury
3. Venus
4. Mars

Question 3

Which is the largest of the terrestrial planets?

Answer 3

Earth

Question 4

How much smaller is Earth’s polar diameter than its equatorial diameter?

Answer 4

42 km

Question 5

What is the shape of the Earth?

Answer 5

Earth is an oblate spheroid.

Question 6

Why is the Earth an oblate spheroid?

Answer 6

The Earth is an oblate spheroid because its polar diameter is slightly smaller than its equatorial diameter (by 42 km) making the Earth more like a slightly squashed beach ball.

Question 7

How much of the Earth’s surface is covered by water?

Answer 7

Over 70%

Question 8

Name some of the diverse features displayed by the landforms on Earth:

Answer 8

1. mountain ranges
2. volcanoes
3. deserts
4. rainforests
5. grasslands
6. glaciers

Question 9

How many major internal divisions does the Earth have?

Answer 9

4

Question 10

Name the Earth’s 4 major internal divisions:

Answer 10

1. crust
2. mantle
3. outer core
4. inner core

Question 11

Which is the thinnest layer of the Earth’s 4 major internal divisions?

Answer 11

The crust

Question 12

How thin is the Earth’s crust?

Answer 12

The Earth’s crust ranges in thickness from 0 - 70 km. The older continental crust consists of low-density rocks such as granite. The oceanic crust is younger, thinner (up to 10 km thick) and consists of darker, denser rocks such as basalt.

Question 13

What do the tectonic plates float on top of?

Answer 13

The silicate mantle

Question 14

How far through the Earth’s internal structure does the silicate mantle extend?

Answer 14

The silicate mantle extends half-way to the Earth’s centre, making up ~80% of the Earth’s volume.

Question 15

What drives the movement of the tectonic plates?

Answer 15

The upper mantle is semi-molten, allowing thermal convection currents to rise and fall, driving the sideways motions of the tectonic plates.

Question 16

True or False: the lower mantle is semi-molten.

Answer 16

False. The lower mantle is solid.

Question 17

What is the temperature of the outer core?

Answer 17

The temperature of the outer core is ~5000 K.

Question 18

What does ‘~’ mean?

Answer 18

Approximately

Question 19

What does ‘K’ stand for in terms of temperature?

Answer 19

Kelvin

Question 20

What is the outer core made of?

Answer 20

The outer core is made of liquid iron with some nickel.

Question 21

Which layer of the outer core is responsible for the Earth’s magnetic field?

Answer 21

Currents of charged particles that flow in the outer core are responsible for the Earth’s magnetic field. (Rotating liquid iron core - iron being magnetic - gives us the Earth’s magnetic field).

Question 22

What is the temperature of the solid inner core?

Answer 22

The temperature of the solid inner core is ~5500 K, which is about the same temperature as the Sun’s photosphere.

Question 23

Despite the high temperatures, what stops the iron and nickel in the Earth’s inner core from melting?

Answer 23

Despite the temperature of ~5500 K, the inner core has such a high pressure that this prevents the iron and nickel from melting.

Question 24

What actually are latitude and longitude?

Answer 24

Latitude and longitude are actually angles subtended at the centre of the Earth by imaginary curved lines (arcs) on the Earth’s circumference.

Question 25

Where is latitude measured from?

Answer 25

Latitude is measured North or South of the Earth’s equator. This has a latitude of 0 degrees and is an obvious change for 0.

Question 26

Where is the equator (and what is its latitude)?

Answer 26

The equator is a line which ‘cuts’ the Earth in half across the middle. It has a latitude of 0 degrees, acting as the ground 0 for measuring latitude North or South of the equator.

Question 27

What is longitude measured from?

Answer 27

Longitude is measured East or West of the Prime Meridian.

Question 28

How and when was the Prime Meridian’s exact location decided?

Answer 28

Until 1884, seafarers used different meridians to define the 0 of longitude. In that year, the International Meridian Conference (held in Washington, DC) agreed that the meridian passing through the Observatory of Greenwich should be globally adopted as the 0 of longitude.

Question 29

At what angle is the Earth’s polar axis tilted to?

Answer 29

The Earth’s polar axis is tilted at 23.5 degrees to the vertical.

Question 30

The Earth’s polar axis is tilted at 23.5 degrees to the vertical. Name a consequence of this for observers:

Answer 30

One consequence of this is that during the Earth’s yearly orbit around the sun, observers at different latitudes on the Earth’s surface will ‘see’ the Sun at different altitudes in the sky.

Question 31

When is the spring equinox?

Answer 31

On or close to March 21st

Question 32

When is the autumnal equinox?

Answer 32

On or close to September 23rd

Question 33

What happens during the spring and autumnal equinoxes?

Answer 33

The Sun lies directly over the equator.

Question 34

When is the summer equinox?

Answer 34

On or close to June 21st

Question 35

When is the winter equinox?

Answer 35

On or close to December 21st

Question 36

What happens during the summer and winter equinoxes?

Answer 36

On 21st June and 21st December, the Sun lies directly over the Tropics of Cancer (lat. 23.5 degrees N) and Capricorn (lat. 23.5 degrees S); these dates correspond to the northern hemisphere’s summer and winter solstices.

Question 37

What is the latitude of the Tropic of Cancer?

Answer 37

23.5 degrees North

Question 38

What is the latitude of the Tropic of Capricorn?

Answer 38

23.5 degrees South

Question 39

What is the latitude of the equator?

Answer 39

0 degrees

Question 40

What is the latitude of the Arctic Circle?

Answer 40

66.5 degrees North

Question 41

What is the latitude of the Antarctic Circle?

Answer 41

66.5 degrees South

Question 42

What are the Arctic and Antarctic circles?

Answer 42

The Arctic and Antarctic Circles represent the most northern and southern latitudes from which the Sun can be seen to rise and set (weather permitting) on every day of the year.

For example, the Sun as observed from within the Arctic Circle during summer never rises or sets - giving 24 hours of daylight for several weeks (the ‘midnight sun’).

Question 43

What is the mean temperature of Earth as regulated by the atmosphere?

Answer 43

15 degrees Celsius

Question 44

What are the benefits of the atmosphere?

Answer 44

The atmosphere:
1. Provides us with oxygen to breathe
2. Absorbs harmful solar UV and X-radiation
3. Regulates our planet’s temperature to a mean 15 degrees C
4. Protects us from (most) meteoroid strikes

Question 45

What are the drawbacks of the atmosphere for astronomers?

Answer 45

1. The sky is blue, restricting observations to night time
2. Air in the atmosphere is continuously in turbulent motion - these adverse seeing conditions make the stars appear to twinkle

Question 46

Why is the sky blue?

Answer 46

Light is scattered by oxygen and nitrogen molecules in our atmosphere; most scattering occurs at the shortest (blue) wavelengths, and so the sky is predominantly blue.

Question 47

Why do stars appear to ‘twinkle’?

Answer 47

Air in the atmosphere is continuously in turbulent motion: different densities of air rise and fall on a variety of scales, causing light to refract and change direction as it passes through the different layers. These adverse seeing conditions make the stars appear to ‘twinkle’.

Question 48

What is skyglow?

Answer 48

Skyglow is the rusty orange haze cast by light near urban conurbations. It illuminates the sky, making most stars invisible.

Question 49

What are the 2 types of light pollution which are a problem for astronomers?

Answer 49

1. Skyglow
2. Local glare from sports grounds, supermarket car parks, streetlights and security lights that ruin our eyes’ night vision (dark adaptation)

Question 50

What is an observer’s zenith?

Answer 50

The point in the night sky directly (90 degree angle) above the observer is their zenith.

Question 51

What is the Earth’s exact equatorial diameter?

Answer 51

12,756 km

Question 52

What is the Earth’s exact polar diameter?

Answer 52

12,714 km

Question 53

How many constellations are there in the sky?

Answer 53

88

Question 54

What are constellations?

Answer 54

The entire sky is split up into 88 different constellations. With the exception of just a handful, each contains a pattern of stars that bears NO RESEMBLANCE to the name of the constellation. One of those exceptions is Orion.

Question 55

What are asterisms?

Answer 55

Asterisms are unofficial, popular patterns of bright stars that DO have a close likeness to their name; the stars in an asterism might belong to the same or different constellations and include: the Plough (in Ursa Major), Orion’s Belt, the ‘W’ (in Cassiopeia) and the Summer and Winter triangles.

Question 56

Which 3 stars make up the Winter Triangle asterism?

Answer 56

1. Procyon
2. Betelgeuse
3. Sirius

Question 57

Where in the sky is the Orion Nebula?

Answer 57

Orion itself contains a faint, rather fuzzy pink patch of light just below the Belt. This is a stellar nursery of young stars, gas and dust: the Orion Nebula.

Question 58

Where in the sky is the Pleiades cluster?

Answer 58

One of Orion’s neighbouring constellations, Taurus, the Bull, boasts one of the most beautiful open clusters of stars, the Pleiades.

Question 59

How do meteors and shooting stars appear in the night sky?

Answer 59

Meteors and shooting stars appear for a split second as a bright streak of light caused by a dust particle, probably from the tail of a comet, burning up in the atmosphere.

Question 60

How do comets appear in the night sky?

Answer 60

Comets are rare visitors to the inner Solar System, but may be seen as an extended fuzzy object (possibly showing 1 or 2 tails), moving slowly against the background stars from night to night.

Question 61

How many supernova have been observed with the naked eye in our Galaxy in the last 1000 years?

Answer 61

3

Question 62

How do supernova appear in the night sky?

Answer 62

A supernova would appear as a bright new star, be visible for possibly a few weeks and then slowly fade.

Question 63

How do planets appear in the sky?

Answer 63

On most evenings it is possible to observe 1 or more planets. Unlike the stars, planets do not appear to twinkle as they move slowly eastwards from night to night through an imaginary narrow strip of sky called the Zodiacal Band.

Question 64

What are the Northern Lights also known as?

Answer 64

Aurora Borealis

Question 65

What are the Southern Lights also known as?

Answer 65

Aurora Australis

Question 66

Where are Northern and Southern Lights generally visible from?

Answer 66

Aurora are generally visible from the polar regions, although they have been observed on rare occasions from mid-UK latitudes.

Question 67

Which star from Cassiopeia must you be able to identify?

Answer 67

Schedar

Question 68

Which star from Cygnus, the Swan, must you be able to identify?

Answer 68

Deneb

Question 69

Which 2 stars from Crux, the Southern Cross, must you be able to identify?

Answer 69

Mimosa and Acrux

Question 70

Which 3 stars make up the Summer Triangle asterism?

Answer 70

1. Deneb
2. Vega
3. Altair

Question 71

What is an optical double star?

Answer 71

Two stars, physically unrelated, that happen to lie roughly in the line of sight.

Question 72

What is the most distant object that can be seen with the naked eye?

Answer 72

The Andromeda Galaxy - it is close to the Great Square of Pegasus, visible just above to the left as a very faint, fuzzy patch of dim light.

Question 73

How do artificial satellites appear in the sky?

Answer 73

Artificial satellites appear to move slowly North to South as reasonably bright points of light in the twilight sky before fading from view as they enter the Earth’s shadow.

Question 74

How do aircraft appear in the sky?

Answer 74

Aircraft are easily identified by green and red right-of-way ‘navigation’ lights and flashing white identification lights.

Question 75

What is the celestial sphere?

Answer 75

The celestial sphere is an imaginary sphere concentric with Earth. It features a network of lines which are used to map stars and other objects in the sky (or more correctly, on the celestial sphere).

Question 76

What is the ecliptic on the celestial sphere?

Answer 76

The path taken by the Sun on the celestial sphere during one year.

Question 77

What is the symbol used to denote the First Point of Aries?

Answer 77

♈︎

Question 78

What is the First Point of Aries?

Answer 78

The point where the ecliptic cuts the celestial equator on its ‘journey’ from South to North.

Question 79

What are the celestial equivalents of latitude and longitude on the celestial sphere?

Answer 79

Declination and right ascension

Question 80

What is the abbreviation for declination?

Answer 80

dec

Question 81

What is the abbreviation for right ascension?

Answer 81

RA

Question 82

What is the symbol for declination?

Answer 82

δ

Question 83

What is the symbol for right ascension?

Answer 83

α

Question 84

What is declination?

Answer 84

Declination is simply the projection of latitude onto the celestial sphere; it is measured in degrees (+ and - signs indicate N and S)

Question 85

What is right ascension?

Answer 85

Right ascension is measured eastwards from the First Point of Aries; it is measured in hours and minutes (abbreviation h and min) where 1 h = 15 degrees and, just like time intervals, there are 60 min in 1 hour (so 1 min = 0.25 degrees).

Question 86

How many degrees in 1 h (hour) when measuring right ascension?

Answer 86

15 degrees

Question 87

How many min in 1 h when measuring right ascension?

Answer 87

60 min = 1 h

Question 88

How many degrees in 1 min (minute) when measuring right ascension?

Answer 88

0.25 degrees

Question 89

Which star is closest to the North Celestial Pole?

Answer 89

Polaris

Question 90

What are the equatorial coordinates of Sirius?

Answer 90

6h 45 min, -17 degrees

Question 91

What are the equatorial coordinates of Betelgeuse?

Answer 91

5h 55 min, +7 degrees

Question 92

What are the equatorial coordinates of Fomalhaut?

Answer 92

22h 58 min, -30 degrees

Question 93

What are the equatorial coordinates of Deneb?

Answer 93

20h 41 min, +45 degrees

Question 94

True or False: RA lines closer to the celestial equator are (almost) parallel to each other. RA lines closer to the poles converge (like lines of longitude on world maps).

Answer 94

True

Question 95

True or False: Since we on Earth are ‘inside’ the celestial sphere looking ‘outwards’ to the sky, right ascension increases to the left.

Answer 95

True

Question 96

What is azimuth in the amateur horizontal coordinate system?

Answer 96

Azimuth is a simple bearing (measured in degrees) from due north (GEOGRAPHICAL NORTH NOT MAGNETIC) moving round eastwards to the point on the observer’s horizon directly under the star; it ranges 0 - 360 degrees.

Question 97

What is altitude in the amateur horizontal coordinate system?

Answer 97

Altitude is found by the angle from the observer’s horizon upwards to the star or other celestial object; it ranges 0 to 90 degrees (the observer’s zenith - directly above).

Question 98

What is a cardinal point when measuring bearings? (GIVE THE EXAMPLES)

Answer 98

North, East, South, West

Question 99

What is an intercardinal point when measuring bearings? (GIVE THE EXAMPLES)

Answer 99

North-West, South-East, North-East, South-West

Question 100

What is diurnal motion a result of?

Answer 100

The apparent motion of the stars is called diurnal motion and is simply the result of the Earth rotating on its polar axis from West to East.

Question 101

Explain diurnal motion:

Answer 101

Like the sun, the stars rise in the East, reach their highest point when they are due South across the observer’s meridian, and later set in the West.

Question 102

During diurnal motion, the highest point the stars reach is called their…

Answer 102

Culminate (highest point)

Question 103

Like the Sun, the stars rise in the East and set in the ……..

Answer 103

West

Question 104

How long is one sidereal day?

Answer 104

23 h 56 mins

Question 105

How long does it take the Earth to rotate 360 degrees?

Answer 105

23 h 56 mins - this is one sidereal day.

Question 106

How many degrees does the Earth move around the Sun in one sidereal day?

Answer 106

1 degree. A sidereal day takes 23 h 56 mins (a sidereal day is how long it takes for Earth to rotate 360 degrees). Therefore, Earth needs to rotate a further 4 min to align a given point on Earth’s surface with the Sun once again.

Question 107

How long is one solar day?

Answer 107

24 h 0 min

Question 108

Why do the stars rise, culminate and set 4 min earlier (GMT) each day?

Answer 108

With respect to the stars, Earth rotates through 360 degrees in 23 h 56 min (one sidereal day). However, during this time the Earth has moved around the Sun by about 1 degree, so it needs to rotate a further 4 min to align a given point on its surface with the Sun again. 24 h 0 min is one solar day, so it follows that the stars rise, culminate and set 4 min earlier (GMT) each day.

Question 109

What does GMT stand for?

Answer 109

Greenwich Mean Time

Question 110

Why do astronomers use LST?

Answer 110

Most astronomers observe the stars as opposed to the Sun, and so astronomers use clocks based on LST rather than clock time.

Question 111

What does LST stand for?

Answer 111

Local Sidereal Time

Question 112

What is the LST of an observer?

Answer 112

The local sidereal time of an observer is the right ascension of a star that lies on the observer’s meridian at a given time.

For example, if a star with RA = 14 h 45 min lies on an observer’s meridian, the LST is 14:45.

Question 113

What is a star’s hour angle?

Answer 113

Observer’s often make use of a star’s hour angle. This is the time (in hours and min) since the object was last crossing the observer’s meridian.

Question 114

What is the equation for a star’s hour angle?

Answer 114

Hour Angle = Local Sidereal Time - Right Ascension

Question 115

What can an astronomer deduce if a star’s hour angle is negative?

Answer 115

If the hour angle is negative, its value tells an an astronomer how much time must elapse before the star or other celestial object will be crossing their meridian (the best time to observe it).

Question 116

What does NCP stand for?

Answer 116

North Celestial Pole

Question 117

How do the stars appear to revolve around the NCP? HINT: THINK POLARIS

Answer 117

The stars appear to revolve around the NCP in an ANTICLOCKWISE sense, from West to East ‘below’ Polaris and from East to West ‘above’ Polaris.

Question 118

True or false: Altitude of NCP (or SCP) = observer’s latitude

Answer 118

True.

Question 119

What does SCP stand for?

Answer 119

South Celestial Pole

Question 120

Knowing that altitude of NCP (or SCP) = observer’s latitude, what can we say about Polaris?

Answer 120

Since Polaris is only 0.5 degrees from the SCP, then to a good approximation: altitude of Polaris = observer’s latitude.

Question 121

The altitude of Polaris (or the NCP or SCP) is equal to…

Answer 121

The observer’s latitude

Question 122

What is another word for a star’s polar distance?

Answer 122

A star’s co-declination

Question 123

What is a star’s polar distance?

Answer 123

The angular distance of a star from the NCP.

Question 124

What is the angular declination of the NCP?

Answer 124

+90 degrees

Question 125

What is the equation for calculating a star’s polar distance?

Answer 125

Since the declination of the NCP is +90 degrees, it follows that:
Polar Distance = 90 degrees - Declination

Question 126

True or false: Each ‘small circle in the sky’ that a star traces out during one sidereal day has a radius equal to the star’s polar distance.

Answer 126

True.

Question 127

The larger the declination of a star, the ………….. its polar distance.

Answer 127

The larger the declination of a star, the smaller its polar distance.

Question 128

The larger the declination of a star, the ……………. the chance of it being circumpolar.

Answer 128

The larger the declination of a star, the greater the chance of it being circumpolar.

Question 129

What is a star’s upper and lower transit?

Answer 129

The points at which a star crosses the local meridian are called upper transit (highest point) and lower transit. The altitudes of a star at these 2 points enables us to link its equatorial and horizontal coordinates:
altitude at upper and lower transits = latitude +- polar distance

Question 130

The upper transit of a star is also the point at which a star……

Answer 130

Culminates (reaches the highest point in its cycle).

Question 131

What are circumpolar stars?

Answer 131

Circumpolar stars are stars which have a polar distance so small (and thus a ‘small circle in the sky’ so small) that these stars do not set and remain ‘visible’ all the time.

Question 132

Stars are NOT circumpolar stars if they…

Answer 132

Stars are not circumpolar stars if they have a large polar distance and are due to set below the northern horizon before rising again.

Question 133

Stars ARE circumpolar if they…

Answer 133

A star is circumpolar if its polar distance is less than the altitude of the NCP (which is equal to the latitude of the observer).

Question 134

What is the expression for determining whether or not a star is circumpolar?

Answer 134

Since polar distance = 90 degrees - declination, then for a star to be circumpolar:
90 degrees - declination < latitude of observer

For example, the star Thuban (declination +64 degrees) will be circumpolar from Ulaanbaaatar (latitude 48 degrees N) because 90 degrees - 64 degrees = 26 degrees, which is less than 48 degrees.

Question 135

Calculate the polar distance for Capella: (dec = +46 degrees)

Answer 135

44 degrees

Question 136

Calculate the polar distance for Dubhe: (dec = +62 degrees)

Answer 136

28 degrees

Question 137

Calculate the polar distance for Vega: (dec = +39 degrees)

Answer 137

51 degrees

Question 138

Calculate the polar distance for Acrux: (dec = -63 degrees)

Answer 138

27 degrees

Question 139

An astronomer observes a star with RA = 05 h 35 min crossing their meridian. What is the astronomer’s LST?

Answer 139

05:35

Question 140

For an observer, the hour angle of Sirius is -0h 45 min. In how many minutes will Sirius be due South?

Answer 140

45 min

Question 141

In the observatory of Frozentoze Astronomical Society, LST is 04:15. How long must elapse before a star of RA = 03 h 45 min crosses the observatory’s meridian?

Answer 141

30 min

Question 142

Why should you fit a torch with a red filter before going observing?

Answer 142

Red light does not destroy the eyes’ dark-adapted state.

Question 143

When is the best time to observe celestial objects and why?

Answer 143

When they are close to culmination; they are highest in the sky and at their brightest. This allows the colours of some stars to be detected and more detail to be resolved in ‘extended objects’ such as nebulae and star clusters.

Question 144

How long does it take for your eyes to become fully dark adapted?

Answer 144

20 - 30 minutes of darkness.

Question 145

The eye contains 2 types of photoreceptive cell. Name these 2 types of photoreceptive cell:

Answer 145

Rods and cones

Question 146

Which out of rods or cones in the eye are colour-sensitive cells?

Answer 146

Rods are not colour-sensitive photoreceptive cells.
Cones are colour-sensitive photoreceptive cells.

Question 147

What are rods in the eye sensitive to changes in?

Answer 147

The rods are very sensitive to changes in light intensity and are over-sensitised in daylight. Thus, they are ideal for night vision, but require time to ‘adapt’ to low light levels.

Question 148

When might a star not be seen if looked at directly?

Answer 148

If a star or nebula is insufficiently bright to stimulate the cones in the eye, said star or nebula will not be seen if looked at directly. This is because cones are not activated in dim light.

Question 149

How can you observe a star or nebula which is not bright enough to stimulate the cones in the eye (even if you are staring directly at said star/nebula)?

Answer 149

Since cones are not activated in dim light, it is necessary to stimulate the rods. Since the rods are offset from the optical axis, averted vision allows the star’s light to fall onto the rods and it to be ‘seen’.

Question 150

What is averted vision?

Answer 150

Averted vision is looking slightly to the side of an object.

Question 151

Where are cones in the eye relevant to the eye’s optical axis?

Answer 151

Cones lie on or close to the optical axis - they are sensitive to colours when the light is bright enough.

Question 152

Where are rods in the eye relevant to the eye’s optical axis?

Answer 152

Rods are offset from the optical axis - they are sensitive to light/dark but not to colour.

Question 153

Name some factors that may affect the visibility of objects in the night sky:

Answer 153

1. Landscape (e.g. trees, high buildings)
2. Cloud
3. Light pollution (e.g. skyglow, local glare)
4. Transparency of atmosphere (recent rain removes dust particles)
5. Seeing conditions relating to the ‘steadiness’ of the atmosphere on the I - V Antoniadi Scale.

Question 154

How does recent rain improve observing conditions?

Answer 154

Recent rain removes dust particles in the atmosphere.

Question 155

True or False: The Moon is 100X closer to us than Venus.

Answer 155

True.

Question 156

True or False: Half of the Moon’s surface is in permanent darkness.

Answer 156

False

Question 157

True or False: Lunar ‘seas’ are covered in water.

Answer 157

False

Question 158

Why is it that during a ‘supermoon’ the lunar disc appears larger?

Answer 158

The Moon is slightly closer to the Earth than usual.

Question 159

Name the 7 principal lunar features which you may be asked to identify:

Answer 159

1. Ocean of Storms
2. Copernicus crater
3. Kepler crater
4. Sea of Crises
5. Apennine mountains
6. Sea of Tranquillity
7. Tycho crater

Question 160

Which out of the Earth, the Moon and the Sun is the most spherical in shape?

Answer 160

The Sun

Question 161

What is the difference between the Moon’s polar diameter and the Moon’s equatorial diameter?

Answer 161

4 km

Question 162

What is the Moon’s mean diameter?

Answer 162

3500 km

Question 163

What is the shape of the Moon?

Answer 163

Oblate spheroid (same as the Earth).

Question 164

True or False: The Moon’s far side is almost devoid of maria.

Answer 164

True.

Question 165

What is the difference between the Sun’s polar diameter and the Sun’s equatorial diameter?

Answer 165

10 km. However, this is insignificant compared with its mean diameter of 1.4 million km, so the Sun is almost perfectly spherical.

Question 166

What is the Sun’s mean diameter?

Answer 166

1.4 million km

Question 167

The full disc of the Moon subtends an angle of just less than ….. degrees at the human eye.

Answer 167

The full disc of the Moon subtends an angle of just less than 0.5 degrees at the human eye.

Question 168

What is the latin name for the Moon’s large, dark-grey, relatively smooth seas?

Answer 168

Maria (singular = Mare, pronounced ‘mah-ray’)

Question 169

What are the Moon’s seas made up of?

Answer 169

The large, dark-grey, relatively smooth seas are made up of volcanic basalt rock.

Question 170

What are the Moon’s highlands made up of?

Answer 170

The lighter-grey, mountainous, highly-cratered highlands are made up of igneous rock called anorthosite.

Question 171

What is the latin name for the Moon’s lighter-grey, mountainous, highly-cratered highlands?

Answer 171

Terrae (singular = Terra)

Question 172

Which English physicist made one of the earliest (c. 1600) naked-eye sketches of the lunar disc?

Answer 172

William Gilbert (better known for his contribution to our understanding of magnetism).

Question 173

How many days does it take the Moon to rotate through an angle of 120 degrees?

Answer 173

9.1 days

Question 174

How many astronauts have walked on the moon?

Answer 174

12 astronauts

Question 175

What caused the formation of the Moon’s cratered highlands and mare (sea) basins?

Answer 175

Early in the Moon’s history, probably while still cooling and forming a primitive crust, its surface was bombarded heavily by left-over rocky debris - large meteoroids and asteroids - from the formation of the Solar System. This bombardment carved out the Moon’s cratered highlands and mare basins.

About 4000 million years ago, the storm of debris abated and molten lava was able to seep through the relatively-thin nearside crust where it solidified and formed the lunar maria; mountain ranges were thrust upwards near the edges of the maria, creating deep valleys in between mountains.

Question 176

How were the Moon’s lunar craters formed?

Answer 176

The lunar craters were formed by meteoroids striking the lunar surface. Each impact caused a shockwave that compressed the surface material to leave a large cavity. The subsequent ‘rebound’ splattered material - this is known as ejecta - out in all directions, creating the bright streaks that we see as rays.

Question 177

How many days does it take for the Moon to revolve around the Earth once?

Answer 177

27.3 days; this is also the time taken for the Moon to rotate on its axis by 360 degrees.

Question 178

How many days does it take for the Moon to rotate once on its axis?

Answer 178

27.3 days; this is also the time taken for the Moon to revolve around the Earth once.

Question 179

How long is a sidereal month?

Answer 179

27.3 days

Question 180

How long is a solar month?

Answer 180

29.5 days

Question 181

Although the Moon is in a synchronous orbit and only shows us its near side, over a period of time it is actually possible to observe up to ……% of the Moon’s surface from Earth due to various kinds of lunar libration.

Answer 181

59%

Question 182

The Moon’s equator is inclined to the plane of its orbit around the Earth by …… degrees.

Answer 182

1.5 degrees

Question 183

The plane of the Moon’s orbit is inclined at ……. degrees to the ecliptic.

Answer 183

5.1 degrees

Question 184

Give 2 reasons why the Moon appears really high in the sky at times:

Answer 184

1. The Moon’s equator is inclined to the plane of its orbit around the Earth by 1.5 degrees.
2. The plane of the Moon’s orbit is inclined at 5.1 degrees to the ecliptic.

This combination makes the Moon appear very high in the sky on occasions and results in libration in latitude. Consequently, from our vantage point on Earth, we can see ‘under’ the Moon’s south polar region to different extents (except twice a month when the Moon is crossing the plane of the Earth’s orbit).

Question 185

What causes a libration in the Moon’s latitude (GIVE 2 CAUSES)?

Answer 185

1. The Moon’s equator is inclined to the plane of its orbit around the Earth by 1.5 degrees.
2. The plane of the Moon’s orbit is inclined at 5.1 degrees to the ecliptic.

Question 186

What causes a libration in the Moon’s longitude?

Answer 186

Libration in longitude arises from the Moon’s varying speed in its elliptical orbit around the Earth.

Question 187

Why did Apollo astronauts deploy seismometers on the surface of the Moon?

Answer 187

To detect natural and artificial moonquakes (artificial = by deliberately crashing the Saturn V rockets’ third stages), which enabled scientists to study the internal structure of the Moon.

Question 188

In which year did the Luna 3 spacecraft become the first spacecraft to photograph the Moon’s far side?

Answer 188

1959

Question 189

In 1959, which spacecraft photographed the Moon’s far side for the first time?

Answer 189

In 1959, Luna 3 was the first spacecraft to photograph the Moon’s far side, showing a significant lack of maria in what was otherwise heavily-cratered lunar highlands. (Maria = darker grey smooth seas of volcanic basalt rock).

Question 190

What are the 4 major internal divisions of the Moon?

Answer 190

1. crust
2. mantle
3. outer core
4. inner core

Question 191

What is the mean thickness of the lunar crust?

Answer 191

The mean thickness of the lunar crust is 50-60 km - typically about 3 times that of the Earth’s crust. The thickness in the lunar highlands on the far side of the Moon can be as large as 160 km.

Question 192

Give a possible explanation for why lunar maria are almost exclusively found on the Moon’s near side:

Answer 192

The thickness of the lunar crust is greater on the far side of the Moon (as thick as 160 km compared with 50-60 km on the near side). This possibly explains why lunar maria are almost exclusively found on the Moon’s thinner near side.

Question 193

The radius of the Moon’s core is less than ____% of the Moon’s radius.

Answer 193

The radius of the Moon’s core is less than 25% of the Moon’s radius. On Earth, the core extends to more than 50% of its radius.

Question 194

On Earth, the core extends to more than ____% of its radius.

Answer 194

On Earth, the core extends to more than 50% of its radius. The radius of the Moon’s core is less than 25% of the Moon’s radius.

Question 195

True or False: The Moon’s core is at the physical centre of the Moon.

Answer 195

False. The Moon’s core is not at the physical centre of the Moon but is instead offset by about 2 km towards the near side (i.e. towards Earth).

Question 196

By how many kilometres is the Moon’s core offset from the physical centre of the Moon?

Answer 196

2 km - it is offset by about 2 km towards the near side (i.e. towards Earth).

Question 197

Prior to what year was the appearance of the Moon’s far side unknown?

Answer 197

Prior to 1959, the appearance of the Moon’s far side was unknown.

Question 198

What is the name of the only noteworthy sea on the far side of the Moon?

Answer 198

Mare Moscoviense

Question 199

Describe the technology Luna 3 was equipped with before being sent to photograph the far side of the Moon:

Answer 199

In 1959, the unmanned Soviet spacecraft Luna 3 successfully flew around the far side of the Moon. It was fitted with a dual-lens camera that took several photographs of the far side; the film was processed on-board, scanned and then transmitted back to Earth once Luna 3 was close enough.

Question 200

Describe the surface features of the far side of the Moon:

Answer 200

The Moon’s far side is almost completely covered in heavily-cratered highlands. The far side of the Moon has a significant lack of maria, possibly due to the lunar crust being significantly thicker (~160 km).

Question 201

When did US President John F. Kennedy make his historic speech announcing the ambitious Apollo space programme?

Answer 201

In May of 1961.

Question 202

In May of 1961, US President John F. Kennedy made his historic speech announcing the ambitious Apollo space programme. This was in response to what?

Answer 202

In May 1961, largely in response to the then-Soviet Union’s apparent supremacy in space, John F. Kennedy initiated the space race to land men on the Moon and return them back to Earth ‘before this decade [the 1960s] is out’.

Question 203

Besides competing with the then-Soviet Unions’ apparent supremacy in space, give 2 more objectives of the 1960’s race to the Moon as announced by John F. Kennedy in May of 1961:

Answer 203

1. The collection of lunar soil and rocks for analysis on return to Earth.
2. The deployment of scientific experiments on the lunar surface.

Question 204

One of the objectives for America going to the Moon as laid out in May 1961 was the deployment of scientific experiments on the lunar surface. Give 4 examples of technology/experiments deployed on the Moon:

Answer 204

1. Laser Ranging Retro Reflectors (to monitor the Earth - Moon distance).
2. Passive seismometers
3. Lunar dust collectors
4. Solar Wind Composition (SWC) experiments

Question 205

At what date and time did Neil Armstrong become the first of total twelve astronauts to steep onto the Moon’s surface?

Answer 205

2:56 GMT on July 21st 1969

Question 206

Explain the Giant Impact Hypothesis theory about the origin of the Moon:

Answer 206

A large body about the same size as Mars - astronomers call it Theia - struck a glancing blow with a nascent Earth. Theia was vaporised along with part of the Earth, and the debris slowly cooled and condensed to form the Moon.

Question 207

Explain the Fission Theory about the origin of the Moon:

Answer 207

The Earth was spinning so rapidly that part of it (now filled by the Pacific Ocean) spun off and formed the Moon.

Question 208

Explain the Capture Theory about the origin of the Moon:

Answer 208

The Earth and the Moon were formed at different places in the Solar System, but the Moon became ‘captured’ by Earth’s gravitational force.

Question 209

Explain the Condensation (Co-accretion) Theory about the origin of the Moon:

Answer 209

The Earth and Moon formed together at the same time out of material from the solar nebula.

Question 210

Give 2 pieces of evidence which support Giant Impact Hypothesis Theory as the true origin of the Moon:

Answer 210

The Giant Impact Hypothesis is supported by:
1. The Moon’s lack of substances that evaporate easily (‘volatiles’ such as water).
2. The Moon’s small iron core.
However, not all astronomers agree with this model and it remains a hypothesis.

Question 211

Which planet in the Solar System could float on water?

Answer 211

Saturn

Question 212

Which planet in the Solar System has a rusty surface and is known as the Red Planet?

Answer 212

Mars

Question 213

Which planet in the Solar System can appear brighter than any other planet in the sky?

Answer 213

Venus

Question 214

What is the name of the dwarf planet Pluto’s largest moon?

Answer 214

Charon

Question 215

How many planets are there in the solar system?

Answer 215

8

The 8 planets in our Solar System follow stable, almost circular, orbits around the Sun; they are all in the same sense and roughly in the same plane.

Question 216

How many terrestrial planets are there in our Solar System?

Answer 216

4

Question 217

What are the properties of terrestrial planets?

Answer 217

Terrestrial planets are relatively small worlds of rock surrounding small iron cores.

Question 218

What are the properties of gaseous planets?

Answer 218

Gaseous planets have liquid interiors and substantial atmospheres of hydrogen (H↓2) and helium (He) with traces of methane (CH↓4) and ammonia (NH↓3). They are also accompanied by complex ring systems and a large retinue of Moons; some of which are larger than our Moon and even the planet Mercury.

Question 219

How many gaseous planets are there in our Solar System?

Answer 219

4

Question 220

What are the names of the 4 terrestrial planets in our Solar System?

Answer 220

1. Mercury
2. Venus
3. Earth
4. Mars

Question 221

What are the names of the 4 gaseous planets in our Solar System?

Answer 221

1. Jupiter
2. Saturn
3. Uranus
4. Neptune

Question 222

True or False: Like true planets, dwarf planets have sufficient mass to be spherical, but lack the gravitational force needed to sweep their orbits clear of other debris.

Answer 222

True. Like true planets, dwarf planets have sufficient mass to be spherical, but lack the gravitational force needed to sweep their orbits clear of other debris.

Question 223

What is the largest body on the main Asteroid Belt?

Answer 223

Ceres

Question 224

Where in the Solar System are most dwarf planets located?

Answer 224

Most dwarf planets inhabit the cold outer limits of the Solar System - the Kuiper Belt.

Question 225

Name 3 notable dwarf planets:

Answer 225

1. Pluto
2. Eris
3. Makemake

Question 226

What are SSSOs?

Answer 226

Small Solar System Objects

Question 227

Name 3 types of SSSOs:

Answer 227

1. Asteroids
2. Meteoroids
3. Comets

Question 228

What are asteroids?

Answer 228

Small, irregular rocky objects with diameters < 1000 km.

Question 229

What are comets?

Answer 229

‘Dirty snowball’ mixtures of compacted dust, rock and ice, found mainly in the outer regions of the Solar System.

Question 230

Where in the Solar System are most asteroids located?

Answer 230

Most asteroids reside in the doughnut-shaped Main Belt between the orbits of Mars and Jupiter.

Question 231

What is the size range for asteroids?

Answer 231

Asteroids range from ~10 m (the generally-accepted cut-off between asteroids and meteorites) to ~1000 km. Most have irregular shapes.

Question 232

True or False: Comets can have their orbits ‘modified’ by the gravitational attraction of the massive planets.

Answer 232

True. For example, in 1994, Comet Shoemaker-Levy was captured by the gravitational field of Jupiter and torn apart. Fragments of the comet ‘crashed’ into the giant planet depositing dust and other debris into Jupiter’s clouds.

Question 233

How do we classify comets?

Answer 233

Comets can be classified in terms of their orbital periods - short-period comets and long-period comets.

Question 234

How long are short-period comets’ orbital periods?

Answer 234

Short-period comets have orbital periods which are less than 200 years.

Question 235

How long are long-period comets’ orbital periods?

Answer 235

Long-period comets have orbital periods which are greater than 200 years.

Question 236

Where in the Solar System are short-period comets thought to originate from?

Answer 236

Most short-period comets tend to hug the plane of the Solar System, and are thought to originate in the Kuiper Belt from where the gravitational influence of the planet Neptune might have ‘nudged’ some into elliptical solar orbits. A sub-set of short-period comets have orbital periods which are less than 20 years and do not venture much further away from the Sun than Jupiter.

Question 237

Where do long-period comets originate?

Answer 237

Long-period comets originate in the Oort Cloud, a spherical distribution of icy bodies about a half way to the nearest star.

Question 238

What are the properties of long-period comets?

Answer 238

Long-period comets have orbital periods greater than 200 years and originate in the Oort Cloud. They have unpredictable orbits - some are highly-inclined to the plane of the Solar System and some orbit in the opposite sense to that of the planets.

Question 239

What happens when a comet approaches the Sun?

Answer 239

As a comet approaches the Sun, a coma of rarefied gases and dust envelopes the small (~10 km) nucleus of rock and ice; eventually, one or more tails develop that can be several millions of kilometres long. As the comet rounds and begins to move away from the Sun, the tails and coma become less visible. Eventually the comet (now depleted of some of its content) ceases to be influenced by solar radiation, fades from view and returns to the outer Solar System.

Question 240

What is the approximate size of a comet?

Answer 240

~10 km

Question 241

List the steps which take place as a comet approaches the Sun:

Answer 241

1. A cometary nucleus is approaching the Sun.
2. Closer to the Sun, a coma of gas and dust develops.
3. Closer still, and one or more tails develop, pointing away from the Sun.
4. As the comet moves away from the Sun, the tail(s) diminish.

Question 242

Why do comet’s tails generally point away from the Sun?

Answer 242

It is the Sun that is primarily responsible for the formation of comets’ tails, and so it should be no surprise that these generally point away from it.

Question 243

Describe the appearance and properties of a comet’s ion tail:

Answer 243

A comet’s ion tail is long, straight and predominantly blue in colour; it consists of charged atoms (ions) that have been excited by particles in the solar wind and emit light by fluorescence when they de-excite.

Question 244

Describe the appearance and properties of a comet’s dust tail:

Answer 244

The broader, curved dust tail is produced by solar radiation pressure that pushes particles out of the comet’s nucleus; these reflect sunlight, making the tail visible. The curvature of the dust tail is due to the individual grains of dust following their own independent solar orbits (having now been ‘freed’ from the comet).

Question 245

What were the 2 main objectives of ESA’s recent Rosetta mission?

Answer 245

1. To study the activity of the icy surface of a comet (67P/Churyumov-Gerasimenko) as it approaches the Sun.
2. To land a small probe (Philae) onto the comet’s surface in order to perform a chemical analysis of its water content.

Question 246

Name the 3 classifications for meteorites:

Answer 246

1. Iron
2. Stony
3. Stony-iron

Question 247

What are iron meteorites?

Answer 247

Iron meteorites are rich in both iron and nickel. They probably originate from the metallic cores of asteroids that suffered huge impacts and broke apart.

Question 248

What are meteoroids?

Answer 248

Meteoroids are particles of dust, larger grit-sized chunks of rocks, and boulder-sized mixtures of stone, ice and metal that are in orbit around the Sun.

Question 249

What are meteors/shooting stars?

Answer 249

When meteoroids (particles of dust size) enter the Earth’s atmosphere - ranging in speed from 20-70 km/s - the air resistance converts kinetic energy into thermal energy, heating smaller particles into incandescence. The resulting streak of light visible in the night sky is called a shooting star or meteor.

Question 250

True or False: Meteors and shooting stars are the same thing.

Answer 250

True.

Question 251

What happens during a meteor shower?

Answer 251

When the Earth passes through a dusty meteoroid stream in the wake of a comet, many more meteors are visible; the event is known as a meteor shower. The individual meteors appear to diverge from a ‘vanishing point’ called the radiant, which is simply due to perspective. The shower is named after the constellation in which the radiant lies.

Question 252

What happens when larger meteoroids enter the Earth’s atmosphere?

Answer 252

When larger meteoroids enter the Earth’s atmosphere, they produce very bright meteors called fireballs; they survive their journey through the atmosphere, reaching the Earth’s surface as meteorites.

Question 253

Where do larger meteoroids which enter the Earth’s atmosphere generally come from?

Answer 253

They probably come from the Asteroid Belt, but possibly from the Moon or Mars.

Question 254

When is the famous meteor shower The Perseids visible?

Answer 254

Every year in mid-August.

Question 255

When is the famous meteor shower Geminids visible?

Answer 255

Every year in November.

Question 256

When is the famous meteor shower Quadrantids visible?

Answer 256

Every year in January.

Question 257

Name 3 famous meteor showers:

Answer 257

1. The Perseids
2. Geminids
3. Quadrantids

Question 258

What is the name of the constellation which the Quadrantids meteor shower is named after?

Answer 258

The Quadrantids meteor shower is named after the constellation of The Mural Quadrant. It is important to note that this constellation is now obsolete; the Quadrantids meteor shower was named before The Mural Quadrant failed to make the official list of 88 constellations.

Question 259

What is the abbreviation for ‘light year’?

Answer 259

l.y.

Question 260

True or False: Light years are a unit of time.

Answer 260

False. Light years are a unit of distance.

Question 261

What is a light year?

Answer 261

A light year is a unit of distance, which is equivalent to the distance travelled by light in one year.

Question 262

What is the speed of light in km/s?

Answer 262

Light travels 300,000 km per second.

Question 263

Distance travelled by light in 1 year = 1 _____ year.

Answer 263

Distance travelled by light in 1 year = 1 light year.

Question 264

How far away are the nearest stars?

Answer 264

The nearest stars are a few light years away.

Question 265

What is the abbreviation for ‘parsec’?

Answer 265

p.c.

Question 266

What is the abbreviation for ‘astronomical units’?

Answer 266

AU

Question 267

What are distances within the Solar System quoted in?

Answer 267

Astronomical Units (AU)

Question 268

What is 1 AU?

Answer 268

1 AU is defined as equal value to the mean distance from the Earth to the Sun:
1 AU = 150 million km = 1.5 x 10^8 km

Question 269

What is the mean distance from the Earth to the Sun?

Answer 269

150 million km (1.5 x 10^8).

Question 270

What unit do we use to compare the distances in the Solar System?

Answer 270

AU (Astronomical Units). For example, if somebody says that ‘Saturn is 9.5 AU from the Sun’, we know that the planet is 9.5 times further away from the Sun than we are.

Question 271

Why are Mercury and Venus called inferior planets?

Answer 271

Mercury and Venus are called inferior planets because their orbits are closer to the Sun than that of the Earth.

Question 272

Why are some planets called superior planets?

Answer 272

Superior planets are called this because their orbits are further away from the Sun than that of the Earth.

Question 273

How many AU is the Moon from the Earth?

Answer 273

The Moon is ~1/400 AU from the Earth.

Question 274

What is Edmond Halley famous for?

Answer 274

300 years ago, astronomers knew the relative distances between the planets and the Sun: the scale of the Solar System. In 1677, English astronomer Edmond Halley (of Halley’s Comet fame) formulated a plan to plant to determine the absolute distance between two planets: he devised a method to determine the absolute size of the Solar System.

Question 275

What is transit?

Answer 275

On rare occasions, one of the inferior planets (Mercury or Venus) crosses thee solar disc. This is known as transit.

Question 276

How did Edmond Halley devise his method to determine the absolute size of the Solar System?

Answer 276

It was known that the observed paths (Halley called them chords) taken by Venus would vary depending on the observer’s location on Earth because of parallax. Halley used geometry to show that the angle between 2 chords (α) could be calculated from the difference between their lengths; this in turn could be found by the difference between the times taken for Venus to cross the solar disc. Halley showed that if the latitude distance between the 2 observing locations was known, simple triangulation could be used to calculate the distance from Earth to Venus, and therefore from Earth to the Sun. In 1716, Halley urged astronomers to travel to different latitudes to observe and time the forthcoming transits in 1761 and 1769. His request was taken up by the global scientific community, eventually allowing the AU unit to be defined to withing 2.5% of its modern-day value.

Question 277

Name the 2 basic types of telescope:

Answer 277

1. refracting telescopes
2. reflecting telescopes

Question 278

What type of lens does a refracting telescope use?

Answer 278

A refracting telescope uses a convex (converging) lens to capture and focus light.

Question 279

What type of lens does a reflecting telescope use?

Answer 279

A reflecting telescope uses a parabolic concave (converging) mirror to capture and focus light.

Question 280

What is the purpose of the objective element in a telescope?

Answer 280

The objective element collects as much light as possible and focuses the light to a small bright image.

Question 281

What is the purpose of the eyepiece lens in a telescope?

Answer 281

The eyepiece lens magnifies the image focused by the objective element.

Question 282

Explain how a telescope works:

Answer 282

The objective element collects as much light as possible and focuses the light to a small bright image. This image is then magnified with an eyepiece lens so that astronomical objects such as double stars, lunar maria, globular clusters, nebulae and galaxies can be observed in much more detail (higher resolution) and are much brighter than when looking at them with just the naked eye.

Question 283

What is a telescope’s aperture (size)?

Answer 283

A telescope’s aperture, or size, is the diameter of its objective lens or mirror (usually quoted in cm, inches or metres).

Question 284

Give 2 advantages of buying a telescope with a larger aperture/size:

Answer 284

The larger the size/aperture:
1. The more light enters the telescope, making images brighter.
2. The ‘sharper’ the image, i.e. the higher the amount of detail that can be resolved.

Question 285

Give 2 factors which impact the resolution of the image produced by a telescope:

Answer 285

1. The size of the telescope.
2. The wavelength of light entering the telescope.

Question 286

How does the wavelength of light entering a telescope impact the resulting image resolution?

Answer 286

The longer the wavelength of light entering the telescope, the poorer the resolution.

Question 287

Why is it that, through the same telescope, red images are not as highly resolved as predominantly blue images?

Answer 287

The resolution partly depends on the wavelength of light entering the telescope: the longer the wavelength the poorer the resolution. Red has the longest wavelength of visible light.
So, in theory, the amount of detail visible in images of pink/red nebulae is not as good as that seen in blue nebulae surrounding young stars.

Question 288

What is a telescope’s light grasp?

Answer 288

A telescope’s light grasp is a measure of how much light is captured by the objective element; this depends on its cross-sectional area. Being circular, area depends on the square of the diameter of the objective lens/mirror, so:
light grasp α area α (diameter of objective element)^2

Question 289

What is the relationship between light grasp, area and the diameter of the objective element of a telescope?

Answer 289

Light grasp α area α (diameter of objective element)^2

This means that if one telescope has an objective that has twice the diameter of another, its light grasp will be 4 times (2^2) greater.

Question 290

What is the equation for the magnification of a telescope?

Answer 290

Magnification = focal length of objective lens / focal length of eyepiece lens

ie. Magnification = f↓o / f↓e

NOTE: THIS EQUATION IS ONLY VALID WHEN THE 2 FOCAL LENGTHS HAVE THE SAME UNIT: BOTH IN CM, BOTH IN MM, ETC.)

Question 291

True or False: A telescope’s size (the diameter of the objective element/mirror) is much more important than its magnification when observing astronomical objects.

Answer 291

True.

Question 292

Desmond has a 6.0-cm refracting telescope and Molly has a 15-cm reflector. How many times more is the light grasp of Molly’s telescope compared with Desmond’s?

Answer 292

6.25
SOLUTION:
light grasp ∝ area ∝ (diameter of objective element)^2
Molly’s telescope has an which is 2.5x the size of Desmond’s telescope (the size being the diameter of the objective lens). 2.5^2 = 6.25, so the light grasp will be 6.25 times greater.

Question 293

Why is it that, under poor seeing conditions, high magnification is undesirable?

Answer 293

Under poor seeing conditions, high magnification is undesirable since turbulence in the air gives rise to unsteady images that lack clarity.

Question 294

How does eyepiece focal length impact magnification?

Answer 294

The shorter the eyepiece focal length, the greater the magnification.

Question 295

Why do we use eyepieces of different focal lengths?

Answer 295

The focal length of the objective element is obviously fixed, and so different magnifications are achieved by using eyepieces of different focal lengths: the shorter the focal length, the greater the magnification.

Question 296

What is a Barlow lens?

Answer 296

A Barlow lens is a handy piece of kit for astronomers that is not actually in itself an eyepiece, but it allows eyepieces to be slotted into it. The optical elements of a Barlow lens increase the magnification by a factor of 2 or 3, effectively doubling the number of eyepieces available to the astronomer.

Question 297

How does the magnification impact the field view of a telescope?

Answer 297

The greater the magnification, the smaller the field view of the telescope.

Question 298

What does FOV stand for?

Answer 298

Field Of View

Question 299

What is the field of view (FOV) of a telescope?

Answer 299

The field of view of a telescope is the circle of sky that is visible through its eyepiece.

Question 300

What is FOV measured in?

Answer 300

FOV is measured in degrees or minutes of arc (abbreviation = arcmin or ‘) where 1° = 60’.

Question 301

How many arcmin (abbreviation = ‘ ) in 1 degree?

Answer 301

1° = 60’ (1° = 60 arcmin).

Question 302

At what angle does the full Moon subtend an observer on Earth?

Answer 302

The full Moon subtends an angle of ~30’ (0.5°) to an observer on Earth.

Question 303

Who was the first scientist to use a telescope and interpret (sometimes incorrectly) what they saw?

Answer 303

Italian astronomer and mathematician Galileo Galilei. His original telescope was a refractor with a convex lens as the objective and concave lens for the eyepiece. This design was modified by German mathematician Johannes Kepler who replaced the concave eyepiece with a convex one.

Question 304

What is the ecliptic?

Answer 304

The plane of the Earth’s orbit.

Question 305

What is orbital inclination?

Answer 305

Orbital inclination is the angle between the plane of a planet’s orbit and the pane of the Earth’s orbit (the ecliptic) around the Sun.

Question 306

True or False: The nightly positions of the planets can be shown on a planisphere.

Answer 306

False.

Question 307

True or False: Of the 8 planets in our Solar System, Venus’s orbit is the most circular.

Answer 307

True. Of the 8 planets in our Solar System, Venus’s orbit is the most circular.

Question 308

True or False: When a planet undergoes retrograde motion, the planet physically moves backwards in its orbit for a few weeks.

Answer 308

False.

Question 309

Why do most astronomers prefer to use reflector telescopes?

Answer 309

Astronomers generally prefer reflector telescopes because of the larger objective apertures that can be manufactured and supported (it is difficult for large lenses to keep their shape). Also, unlike lenses that absorb light, it is possible for mirrors to reflect light with almost no loss in intensity.

Question 310

How does the Newtonian reflector work?

Answer 310

Light is collected by a large parabolic mirror, reflected up the ‘tube’ and then sideways out of the telescope to a focus by a small plane mirror. The image is then magnified with the eyepiece lens.

Question 311

Give 2 problems with refractor telescopes:

Answer 311

1. Lenses tend to focus different wavelengths of light to slightly different points, making images blurred and unclear.
2. Refractors also tend to be longer in size (although this can be avoided using prisms as in pairs of binoculars) which makes viewing difficult at times.

Question 312

What is chromatic aberration?

Answer 312

Chromatic aberration is where a lens focuses different wavelengths of light to slightly different points, making images blurred and unclear.

Question 313

True or False: The Cassegrain reflector is a popular type of reflector which tends to be more compact than the Newtonian reflector.

Answer 313

True. The Cassegrain reflector is a popular type of reflector which tends to be more compact than the Newtonian reflector.

Question 314

How does the Cassegrain reflector work?

Answer 314

Light is collected by a large parabolic mirror, reflected up and then back down the ‘tube’ by a small convex mirror. Light then passes through a small hole in the primary mirror where the image is magnified with the eyepiece lens.

Question 315

What are the 4 main types of probe?

Answer 315

1. fly-by
2. orbiters
3. impactors
4. landers

Question 316

What do fly-by probes do?

Answer 316

Fly-by probes carry out fly-by missions, in which the space probe explores many targets. Fly-by probes do not land on or orbit the target - they just fly past taking images and measurements.

Question 317

Give 2 examples of famous fly-by missions:

Answer 317

1. Voyagers I and II which visited the outer planets.
2. New Horizons which explored Pluto and the outer Solar System.

Question 318

What do orbiter probes do?

Answer 318

Orbiter probes go into orbit around the target body.

Question 319

What do impactor probes do?

Answer 319

Impactor probes collide with the surface of the body. They can take measurements as they approach the body and measurements can be made of the plume of debris by telescopes.

Question 320

What do lander probes do?

Answer 320

Lander probes softly land on the surface - unlike impactor probes, the impact is controlled and the probe touches down intact on the surface.

Question 321

Give 3 examples of famous orbiter missions:

Answer 321

1. Magellan which mapped the planet Venus using radar.
2. Dawn which made detailed studies of asteroids Ceres and Vesta.
3. Juno which measured Jupiter’s composition and magnetosphere.

Question 322

Give 2 examples of famous impactor missions:

Answer 322

1. The third stages of Saturn V rockets were impacted onto the lunar surface to cause artificial moonquakes.
2. The Deep Impact probe which impacted on Comet Temple 1 to study the internal composition of a comet.

Question 323

Give 2 examples of famous lander missions:

Answer 323

1. Huygens which landed on Saturn’s moon Titan.
2. The Spirit and Opportunity rovers which were sent to Mars and Philae.

Question 324

What was the New Horizons mission?

Answer 324

New Horizons is a fly-by probe which was launched by NASA in 2006. It carried out a fly-by of Pluto in 2015, then went on to explore other Kuiper belt objects. New Horizons took the very first high quality images of the surface of Pluto.

Question 325

What was the Juno mission?

Answer 325

Juno is an orbiter probe which NASA launched in 2011. It arrived at Jupiter in 2016. It measured the atmosphere and magnetic field of Jupiter to help understand the origin and evolution of Jupiter.

Question 326

What was the Deep Impact mission?

Answer 326

Deep Impact was an impactor probe launched by NASA in January 2005. In July 2005, it successfully collided with the nucleus of Comet Temple 1 - this made it the first mission to look beneath the surface of a comet, finding evidence of ice and organic materials.

Question 327

What was the Philae mission?

Answer 327

Philae is a lander probe which the ESA launched in 2004 carried by the Rosetta spacecraft. Philae arrived at and landed on the comet 67P/Churyumov-Gerasiminko in 2014. It took images from the comets surface and analysed it directly.

Question 328

Give 4 advantages of manned missions:

Answer 328

1. Humans can cope with situations that robots cannot.
2. Humans are much more versatile than robots.
3. Humans are adaptable.
4. Manned missions are stepping stones towards human colonisation, e.g. of Mars.

Question 329

Give 6 disadvantages of manned missions:

Answer 329

1. Manned missions are much more expensive.
2. We need to keep the astronauts alive (e.g. food, water, air, warmth, etc.).
3. Being in space for a long time is not good for your health (low gravity and radiation).
4. We have to worry about bringing them back.
5. Human lives are at risk.
6. Training astronauts is expensive and takes a long time.

Question 330

What Greek word is ‘planet’ derived from?

Answer 330

Planetes

Question 331

What does i stand for in astronomy?

Answer 331

Orbital inclination

Question 332

What is the inclination of the Earth’s orbit?

Answer 332

By definition, the inclination of the Earth’s orbit is 0°.

Question 333

True or False: The small values of i (orbital inclination) confine the planets to a narrow Zodiacal Band in the sky centred on the ecliptic.

Answer 333

True. The small values of i (orbital inclination) confine the planets to a narrow Zodiacal Band in the sky centred on the ecliptic.

Question 334

What is retrograde motion?

Answer 334

From night to night the planets move slowly eastwards, but ancient astronomers noticed that occasionally they appeared to travel backwards from east to west in either a ‘loop-the-loop’ or zigzag motion. This is known as retrograde motion, and it can now be explained in terms of the faster-moving Earth ‘overtaking’ the superior planet on the inside of its orbit.

Question 335

What are the limits of the Zodiacal Band?

Answer 335

The limits of the Zodiacal Band are ~8° either side of the ecliptic due to the relatively large orbital inclination of Mercury.

Question 336

The optimum place in a planet’s orbit for it to be observed under the best (darkest) conditions depends on?

Answer 336

The optimum place in its orbit for a planet to be observed under the best (darkest sky) conditions depends on the planet’s orbital position compared with that of the Earth.

Question 337

When a superior planet is at opposition, it is 4.2 AU from the Earth. How far away is the planet when it is at conjunction?

Answer 337

6.2 AU

Question 338

When is an inferior planet (i.e. Mercury or Venus) best observed?

Answer 338

An inferior planet such as Mercury is best observed when it appears furthest from the Sun in the morning or evening sky; this is at, or close to, the greatest elongation when the angle Sun → inferior planet → Earth is 90°.

Question 339

When Venus is at inferior conjunction, it is 0.28 AU from the Earth. Calculate the furthest possible distance between the Earth and Venus.

Answer 339

1.72 AU

Question 340

True or False: The planet Venus shines as the ‘Morning Star’ in the dawn sky shortly before sunrise.

Answer 340

True. The planet Venus shines as the ‘Morning Star’ in the dawn sky shortly before sunrise.

Question 341

When is a superior planet best observed?

Answer 341

A superior planet is best observed at, or close to, opposition. At this point in its orbit, the planet is closest to the Earth, at its brightest and opposite the Sun in the sky; it is possible to observe the planet all night long and with the highest resolution.

Question 342

What is an occultation?

Answer 342

An occultation is an event in which a planet may temporarily obscure a distant star as it moves in front of the star for a few moments.

Question 343

What may happen when an inferior planet is at inferior conjunction?

Answer 343

When it is at inferior conjunction, an inferior planet may undergo a transit of the Sun’s disc. Transits, however, are extremely rare events due to the orbital inclinations taking the planet either ‘above’ or ‘below’ the Sun in the sky.

Question 344

True or False: The Sun is really moving.

Answer 344

False. The Sun’s apparent motion is due entirely to the orbital motion of the Earth and the constant 23.5° tilt of the Earth’s equator to the ecliptic.

Question 345

What is the First Point of Aries?

Answer 345

The point on the celestial equator from which right ascension is measured. It is the same as the vernal equinox. This point has zero right ascension and zero declination. It is defined as the point at which the Sun passes from south to north of the celestial equator, which happens on March 21st each year.

Question 346

What is the symbol which denotes the First Point of Aries?

Answer 346

♈︎

Question 347

What is the symbol which denotes the First Point of Libra?

Answer 347

♎︎

Question 348

What is the First Point of Libra?

Answer 348

The point on the celestial sphere diametrically opposite the first point of Aries. It is the same as the autumnal equinox. It has right ascension 12h and declination zero. It is the point at which the Sun passes from north to south of the celestial equator, which happens on September 23rd each year.

Question 349

How often does the Moon repeat its cycle of phases?

Answer 349

Every 29.5 days.

Question 350

True or False: The purpose of Stonehenge remains unknown.

Answer 350

True. The purpose of Stonehenge remains unknown.

Question 351

When was Stonehenge built?

Answer 351

Stonehenge was built in stages between c.3000 BCE and c.1500 BCE.

Question 352

The ancient Egyptians used the time at which the bright star Sirius rose after sunset to predict when the Nile would flood. Why did they do this?

Answer 352

The flooding of the River Nile was very important to ancient Egyptians because water, mud and silt were washed up onto the banks making fertile growing areas. As soon as the floods receded, the Egyptians ploughed the soil, sowed their seeds and used animals to push them into the ground. The Egyptians used the time at which the bright star Sirius rose after sunset to predict when the Nile would flood.

Question 353

What was astronomy originally used for?

Answer 353

Astronomy was born out of the basic need for human survival : when to sow and harvest crops, pick fruits and nuts, hunt for antelope and buffalo. The celestial calendars were key to the ancients’ very existence.

Question 354

True or False: As ancient civilisations flourished, stone monuments and temples were built to act as ceremonial and/or religious observatories. Many were aligned to the positions of key stars (for example the 3 stars in the Orion’s Belt) or to the rising of the Sun on key dates of the year (for example the summer solstice).

Answer 354

True. As ancient civilisations flourished, stone monuments and temples were built to act as ceremonial and/or religious observatories. Many were aligned to the positions of key stars (for example the 3 stars in the Orion’s Belt) or to the rising of the Sun on key dates of the year (for example the summer solstice).

Question 355

Many ancient monuments were built in alignment with the celestial alignments of the time (i.e. the 3 stars in Orion’s Belt). Why is it that the current celestial alignments of many ancient monuments differ from their original alignments?

Answer 355

The current celestial alignments of many ancient monuments differ from their original alignments because the Earth’s axis of rotation is not fixed but traces out a circular path against the stars.

Question 356

What is precession?

Answer 356

The Earth’s axis of rotation is not fixed but traces out a circular path against the stars. This relatively slow ‘wobbling’ of the Earth’s axis is called precession, and it arises from the gravitational pull of the Moon and the Sun on the Earth’s equatorial bulge; one complete rotation of the Earth’s axis takes ~26000 years. Precession is the reason why, as the Earth’s axis precesses, different stars can be found at the North Celestial Pole.

Question 357

How much time does it take for one complete rotation of the Earth’s axis to take place?

Answer 357

~26000 years

Question 358

Name the 5 ‘wandering’ planets known to the ancient Greeks:

Answer 358

1. Mercury
2. Venus
3. Mars
4. Jupiter
5. Saturn

Question 359

How long did Ptolemy’s model of the universe last before becoming outdated?

Answer 359

~1500 years

Question 360

What does ‘geocentric’ mean?

Answer 360

Earth-centred

Question 361

What does ‘heliocentric’ mean?

Answer 361

Sun-centred

Question 362

True or False: Early models of the ‘Universe’ were based on the geocentric (Earth-centred) systems of ancient Greek philosophers such as Plato and Aristotle.

Answer 362

True. Early models of the ‘Universe’ were based on the geocentric (Earth-centred) systems of ancient Greek philosophers such as Plato and Aristotle.

Question 363

What were the 4 ‘elements’ which the Aristotelian Universe was based on?

Answer 363

1. earth
2. air
3. fire
4. water

Question 364

Describe the Aristotelian Universe:

Answer 364

The Aristotelian Universe was based on 4 ‘elements’ - earth, air, fire and water - and a system of concentric crystalline spheres driven by a ‘prime mover’ that carried the Moon, Sun, planets and fixed stars around the Earth.

Question 365

What was the major problem with the Aristotelian Universe model?

Answer 365

The Aristotelian Universe model was unable to explain the observed retrograde motion of the planets.

Question 366

How did the Greeks initially modify the Aristotelian Universe to try and incorporate the retrograde motion which had been observed? Did this work?

Answer 366

In a modification, each planet was placed on a small rotating circle (an epicycle) whose centre revolved around the Earth on another circle (the deferent). So, in the Greek model, the planets revolved around epicycles whose centres revolved around Earth. However, these refinements were still unable to explain the exact positions and changing speeds (and directions) of the planets, and required further modification by Ptolemy.

Question 367

How did Egyptian astronomer and geographer Claudius Ptolemaeus (Ptolemy) further refine the universe model?

Answer 367

Ptolemy retained the epicycles but made 2 small adjustments that involved a slightly off-centred Earth and an imaginary point called the equant from which the angular motion of the centre of each epicycle was uniform. The model gained general acceptance for almost 1500 years until Copernicus advocated a heliocentric Universe.

Question 368

How did Polish monk Nicholas Copernicus refine the Universe model after Ptolemy’s model had been generally accepted for almost 1500 years?

Answer 368

Nicholas Copernicus applied some mathematical modelling to the problem and advocated a heliocentric (Sun-centred) Universe - unlike previous schemes, a model with the Sun at its centre could explain the observed motion of the planets without the need for an equant and epicycles. Copernicus was reluctant to present his model to the world - potentially because of fear of either ridicule or potential conflict with the Church. It was not until he lay on his deathbed in 1543 that he finally published his book - [ENGLISH TRANSLATED TITLE] On the Revolutions of the Heavenly Spires. The heliocentric model gained wider and wider acceptance in the late 16th century.

Question 369

True or False: Nicholas Copernicus was the first person to propose a heliocentric (Sun-centred) Universe model.

Answer 369

False. Aristarchus of Samos argued for a heliocentric Universe c.270 BCE based on his calculations that the Sun was much larger than the Earth.

Question 370

How did Tycho Brahe develop his 3 laws of planetary motion?

Answer 370

Tycho was particularly interested in the motion of Mars and plotted its position systematically and with great precision over 20 years. In 1600, Johannes Kepler joined him as an assistant. In 1601, Tycho died suddenly - the cause of death is speculated to be either excessive drinking or mercury poisoning. Kepler was now free to analyse Tycho’s positional data for Mars and formulated his 3 laws of planetary motion - Kepler’s laws - which he published in [ENGLISH TRANSLATIONS] The New Astronomy in 1609, and The Harmony of the World in 1619.

Question 371

Who built the Uraniborg Observatory on the island of Hven that lay between Denmark and Sweden?

Answer 371

Under the patronage of Frederick II, the King of Denmark, the eccentric and prominent astronomer Tycho Brahe built the Uraniborg Observatory.

Question 372

In what year did Galileo Galilei first use his ‘optick tube’ (telescope) to observe the skies and make sketches of what he saw?

Answer 372

1609

Question 373

In 1609, Galileo first used his ‘optick tube’ (telescope) to observe and sketch the skies. What were the 2 observations in particular which gave firm support to the heliocentric Universe and helped establish its acceptance?

Answer 373

1. The apparent size of the planet Venus changed and showed phases, meaning that it could not be orbiting a central Earth.
2. Four moons (Galileo called them ‘satellites’ orbited the planet Jupiter), proving that the Earth was not the centre of all heavenly motion.

Question 374

What is the perigee for an object orbiting the Earth?

Answer 374

The closest point in the orbit to Earth.

Question 375

What is the apogee for an object orbiting the Earth?

Answer 375

The furthest point in the orbit from Earth.

Question 376

What does Kepler’s first law of planetary motion state?

Answer 376

Kepler’s first law of planetary motion states that the planets move in elliptical orbits around the Sun, with the Sun at one focus (PLURAL: FOCI) of each ellipse (the other focus is empty).

Question 377

What is the perihelion for a planet (or object) orbiting the Sun?

Answer 377

The point in the orbit at which a planet is closest to the Sun.

Question 378

What is the aphelion for a planet (or object) orbiting the Sun?

Answer 378

The point in the orbit at which a planet is furthest from the Sun.

Question 379

Explain how Kepler’s third law of planetary motion can be applied to any system of orbiting bodies (i.e. artificial satellites, moons of Jupiter, etc.), not just the planets in our Solar System:

Answer 379

The only thing that we will change in different orbiting systems will be the ‘constant’ in the equation: T^2 / r^3 = a constant. Let’s call the constant k. It can be shown that k depends inversely on the mass (M) of the central body (the Sun, the Earth, Jupiter, etc.). This can also be written mathematically as:
k↓1 / k↓2 = M↓2 / M↓1

Question 380

What is the force responsible for the orbital motion of satellites and planets?

Answer 380

Gravitation (gravity). This is an attractive force between all bodies that have mass.

Question 381

How did Isaac Newton discover gravity?

Answer 381

In Lincolnshire in the summer of 1666, Newton made a connection between falling apples and the orbit of the Moon around the Earth: both moved in the way that they did because of the universal force of gravitation.

Question 382

What does Isaac Newton’s law of universal gravitation state?

Answer 382

Newton’s law of universal gravitation states that every body in the Universe attracts every other body with a force that is directly proportional to the product of their masses and inversely proportional to the square of their distance apart (separation).
Suppose that a comet orbits the Sun in an orbit where at the aphelion it is 20x further from the Sun than at the perihelion. This means that when the comet is passing through perihelion, the force of the gravity acting on it is 400x (20^2) greater than when it is at aphelion.

Question 383

List 4 things that gravitation is responsible for:

Answer 383

1. Creating stable elliptical (or circular) orbits of moons around planets and planets around stars.
2. Maintaining the motion of stars around the centre of our Galaxy.
3. Causing the Andromeda Galaxy to be on a direct collision course with ours.
4. Slowing down the rate at which the Universe is expanding.

Question 384

When an asteroid is at aphelion (A), it is 8 times further from the Sun than when it is at perihelion (P). Deduce the ratio:
force on asteroid at P / force on asteroid at A

Answer 384

64
SOLUTION:
Suppose that a comet orbits the Sun in an orbit where at the aphelion it is 20x further from the Sun than at the perihelion. This means that when the comet is passing through perihelion, the force of the gravity acting on it is 400x (20^2) greater than when it is at aphelion. SO if the asteroid is 8x further from the Sun at the aphelion than at the perihelion, the force on asteroid at the perihelion will be 64x (8^2) the force at asteroid A.

Question 385

True or False: The difference in speeds for planets (as stated by Kepler’s second law of planetary motion) is much less than the difference in speeds for bodies that have much more eccentric orbits such as comets.

Answer 385

True. The difference in speeds for planets (as stated by Kepler’s second law of planetary motion) is much less than the difference in speeds for bodies that have much more eccentric orbits such as comets.

Question 385

What does Kepler’s third law of planetary motion state?

Answer 385

Kepler’s third law states that the square of the orbital period (T) of a planet is proportional to the cube of its mean distance (r) from the Sun. This can be written mathematically as:
T^2 α r^3
or:
T^2 / r^3 = a constant

Question 385

What does Kepler’s second law of planetary motion state?

Answer 385

Kepler’s second law of planetary motion states that an imaginary line from the Sun to a planet sweeps out equal areas in equal intervals of time.
This law can be shown using a diagram, but it means that a planet will be travelling fastest when closest to perihelion and slowest when close to aphelion (i.e. CLOSER TO SUN = FASTER FURTHER FROM SUN = SLOWER).

Question 386

In order to explain orbits, Newton devised a ‘cannon thought experiment’. Explain this:

Answer 386

Imagine a cannon, which has been strategically placed on the summit of a high mountain, fired cannonballs at different horizontal velocities - A (the slowest) to E (the fastest). The velocities of cannonballs A and B are too slow to go into orbit around the Earth. The velocities of cannonballs D and E are too high for a circular orbit. But cannonball C has the exact velocity to go into a circular orbit. Newton was able to mathematically show that the cannonballs would follow different orbits whose shapes (circle, ellipse, parabola, etc.) depended on the initial horizontal velocities of each cannonball. Orbit C corresponds to a circular orbit: the cannonball’s horizontal velocity is ‘just right’ (slightly under 8 km/s) to cause the cannonball to ‘fall’ towards the Earth but by exactly the same amount that the Earth is curving away from it.

Question 387

The 2 best methods to obtain a large image of the Sun can be obtained by using…?

Answer 387

1. A H-alpha filter
2. Telescopic projection

Question 388

What is a H-alpha filter?

Answer 388

A H-alpha filter is a filter which can absorb all sunlight apart from a very narrow range of wavelengths centred on a particular spectral line of hydrogen (λ = 656 nm). It is used when trying to obtain a large image of the Sun safely.

Question 389

What is the telescopic projection method?

Answer 389

Telescopic projection requires the use of a ‘baffle’ card (card with a small hole) to absorb most of the solar radiation before entering the telescope. It is used when trying to obtain a large image of the Sun safely.

Question 390

What is the surface of the Sun called?

Answer 390

The photosphere.

Question 391

What are sunspots?

Answer 391

On most clear days, observers can see a number of sunspots on the ‘surface’ photosphere of the Sun. These are cooler areas of the photosphere that correspond to strong localised magnetic fields that inhibit the upward motion of convective solar material and prevent it from reaching the photosphere.

Question 392

What is the approximate temperature of the photosphere (the surface of the Sun)?

Answer 392

~5800 K

Question 393

What does K stand for?

Answer 393

Kelvin, which is a unit of measurement for temperature.

Question 394

What is the approximate temperature of umbra on the surface of the Sun?

Answer 394

~3800 K

Question 395

What is the approximate temperature of penumbra on the surface of the Sun?

Answer 395

~5600 K

Question 396

How do we know that the Sun does not rotate as a solid body?

Answer 396

By observing the apparent motion of sunspots across the solar disc, it is possible to determine the Sun’s rotation period at different latitudes and deduce that the Sun does not rotate as a solid body: its rotation period varies from 25 days at the solar equator to 36 days close to its poles.

Question 397

How can you determine the solar rotation period of the Sun?

Answer 397

The solar rotation period can be determined by recording the position of a sunspot (or group) at approximately the same time every few days.

Question 398

Explain how to calculate the solar rotation period of the Sun:

Answer 398

The longitudes of the sunspot (or group) on different dates can then be found with the aid of a transparent grid placed over a solar disc. If the difference in longitude (ΔL) of a sunspot occurs in a time interval Δt, then rotation period (T) can be calculated using the formula:
T / Δt = 360° / ΔL
This can be repeated for different times and longitude difference, from which the mean solar radiation period at the particular latitude can be calculated.

Question 399

What is the equation used when calculating the solar rotation period of the Sun?

Answer 399

T / Δt = 360° / ΔL

Question 400

At a particular latitude, the rotation period of the Sun is 30 days. How many days will it take the Sun to rotate by 120°?

Answer 400

10 days.
SOLUTION:
At this latitude, the full rotation period is 30 days. It takes 30 days to rotate 360°. So it takes 10 days to rotate 120° (divide by 3).

Question 401

At a different latitude, the Sun rotates through 60° in 5.5 days. Calculate the Sun’s rotation period for this latitude.

Answer 401

33 days.
SOLUTION:
T / Δt = 360° / ΔL
where ΔL = longitude, Δt = time interval, T = rotation period
SO Δt = 5.5, ΔL = 60
→ T / 5.5 = 360 / 60
→ T / 5.5 = 6
→ T = (6 X 5.5)
→ T = 33

Question 402

What is the temperature in the central core of the Sun?

Answer 402

~15 million K.

Question 403

How many million tonnes of mass does the Sun lose every second?

Answer 403

4 million

Question 404

What is the Sun’s total mass in tonnes?

Answer 404

2.0 x 10^27 tonnes

Question 405

Why does the temperature in the central core of the Sun have to be so hot?

Answer 405

The temperature in the central core of the Sun is hot enough for thermonuclear reactions involving the fusion of hydrogen (H) nuclei into helium (He) nuclei to occur. The temperature has to be high to overcome the mutual electrostatic repulsion of the positively-charged nuclei.

Question 406

What is the most common series of reactions in the Sun called?

Answer 406

The proton-proton chain.

Question 407

What is the proton-proton chain?

Answer 407

A proton–proton chain reaction is one of the ways by which stars fuse hydrogen into helium. It is the reaction that dominates in stars the size of the Sun.
1 H + 1 H → 2 H + 0 e^+ + 0 v
1 1 1 1 0

2 H + 1 H → 3 He
1 1 2

3 He + 3 He → 4 He + 1 H + 1 H
2 2 2 1 1
At each stage in the chain, mass (m) is lost and converted into energy (E) in accordance with Einstein’s equation E = mc^2, where c is the speed of light.

Question 408

Where is the radiative zone?

Answer 408

The radiative zone is immediately above the Sun’s core.

Question 409

What happens in the radiative zone of the Sun?

Answer 409

The radiative zone is where the energy in the form of photons (gamma-radiation) is transferred (in rather a random manner due to the scattering of photons by electrons) outwards.

Question 410

Where is the convective zone in the Sun?

Answer 410

The convective zone is the outer ~200,000 km of the Sun.

Question 411

What happens in the convective zone of the Sun?

Answer 411

The convective zone is where thermal energy is transported to the photosphere (surface of the Sun) by rising convection currents of hot plasma. At the base of this zone, the temperature is ~2 million K; at the top of the zone (photosphere), the temperature is 5800 K.

Question 412

How thick is the photosphere?

Answer 412

100 km thick.

Question 413

In what form does the Sun’s photosphere radiate energy?

Answer 413

The Sun’s photosphere radiates energy in the form of visible light and, to a lesser extent, infra-red, ultra-violet and X-radiation.

Question 414

How is thick is the chromosphere?

Answer 414

2000 km thick.

Question 415

What are the Van Allen Belts?

Answer 415

The Van Allen Belts are two doughnut-shaped rings of charged particles trapped in the Earth’s magnetic field. The inner belt has an altitude of 0.1-1.5 Earth radii (1500 km - 10,000 km) and contains mainly protons. The outer belt has an altitude of 3-10 Earth radii (15,000 km - 65,000 km) and contains mostly electrons.

Question 416

What is the Sun’s corona?

Answer 416

Above the Sun’s photosphere, the solar atmosphere consists of the spherical chromosphere and the tenuous, sometimes petal-shaped corona which extends outwards for millions of kilometres into space. The corona is only visible during a total solar eclipse.

Question 417

What is the solar wind?

Answer 417

The ‘slow’ solar wind is an outflow of charged particles (mostly protons and electrons) from the Sun’s corona that are ejected into space at speeds of ~400 km/s. There is also a ‘fast’ solar wind emitted from coronal holes and ‘gusts’ of radiation associated with coronal mass ejections and solar flares.

Question 418

What is the solar wind responsible for?

Answer 418

The solar wind is responsible for aurora and the creation, direction and visibility of cometary tails. In addition, it can trigger world-wide geomagnetic storms that:
1. overload power lines
2. add unwanted ‘noise’ to radio transmissions
3. affect the electronic components of instruments on orbiting satellites
4. add to the radiation risk to astronauts and air passengers