GCSE Astronomy - Pearson Edexcel 2.0 Flashcards
1
Q
What is the mean diameter of the Earth?
A
13,000 km
2
Q
Name the 4 terrestrial planets:
A
- Earth
- Mercury
- Venus
- Mars
3
Q
Which is the largest of the terrestrial planets?
A
Earth
4
Q
How much smaller is Earth’s polar diameter than its equatorial diameter?
A
42 km
5
Q
What is the shape of the Earth?
A
Earth is an oblate spheroid.
6
Q
Why is the Earth an oblate spheroid?
A
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.
7
Q
How much of the Earth’s surface is covered by water?
A
Over 70%
8
Q
Name some of the diverse features displayed by the landforms on Earth:
A
- mountain ranges
- volcanoes
- deserts
- rainforests
- grasslands
- glaciers
9
Q
How many major internal divisions does the Earth have?
A
4
10
Q
Name the Earth’s 4 major internal divisions:
A
- crust
- mantle
- outer core
- inner core
11
Q
Which is the thinnest layer of the Earth’s 4 major internal divisions?
A
The crust
12
Q
How thin is the Earth’s crust?
A
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.
13
Q
What do the tectonic plates float on top of?
A
The silicate mantle
14
Q
How far through the Earth’s internal structure does the silicate mantle extend?
A
The silicate mantle extends half-way to the Earth’s centre, making up ~80% of the Earth’s volume.
15
Q
What drives the movement of the tectonic plates?
A
The upper mantle is semi-molten, allowing thermal convection currents to rise and fall, driving the sideways motions of the tectonic plates.
16
Q
True or False: the lower mantle is semi-molten.
A
False. The lower mantle is solid.
17
Q
What is the temperature of the outer core?
A
The temperature of the outer core is ~5000 K.
18
Q
What does ‘~’ mean?
A
Approximately
19
Q
What does ‘K’ stand for in terms of temperature?
A
Kelvin
20
Q
What is the outer core made of?
A
The outer core is made of liquid iron with some nickel.
21
Q
Which layer of the outer core is responsible for the Earth’s magnetic field?
A
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).
22
Q
What is the temperature of the solid inner core?
A
The temperature of the solid inner core is ~5500 K, which is about the same temperature as the Sun’s photosphere.
23
Q
Despite the high temperatures, what stops the iron and nickel in the Earth’s inner core from melting?
A
Despite the temperature of ~5500 K, the inner core has such a high pressure that this prevents the iron and nickel from melting.
24
Q
What actually are latitude and longitude?
A
Latitude and longitude are actually angles subtended at the centre of the Earth by imaginary curved lines (arcs) on the Earth’s circumference.
25
Where is latitude measured from?
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.
26
Where is the equator (and what is its latitude)?
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.
27
What is longitude measured from?
Longitude is measured East or West of the Prime Meridian.
28
How and when was the Prime Meridian's exact location decided?
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.
29
At what angle is the Earth's polar axis tilted to?
The Earth's polar axis is tilted at 23.5 degrees to the vertical.
30
The Earth's polar axis is tilted at 23.5 degrees to the vertical. Name a consequence of this for observers:
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.
31
When is the spring equinox?
On or close to March 21st
32
When is the autumnal equinox?
On or close to September 23rd
33
What happens during the spring and autumnal equinoxes?
The Sun lies directly over the equator.
34
When is the summer equinox?
On or close to June 21st
35
When is the winter equinox?
On or close to December 21st
36
What happens during the summer and winter equinoxes?
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.
37
What is the latitude of the Tropic of Cancer?
23.5 degrees North
38
What is the latitude of the Tropic of Capricorn?
23.5 degrees South
39
What is the latitude of the equator?
0 degrees
40
What is the latitude of the Arctic Circle?
66.5 degrees North
41
What is the latitude of the Antarctic Circle?
66.5 degrees South
42
What are the Arctic and Antarctic circles?
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').
43
What is the mean temperature of Earth as regulated by the atmosphere?
15 degrees Celsius
44
What are the benefits of the atmosphere?
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
45
What are the drawbacks of the atmosphere for astronomers?
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
46
Why is the sky blue?
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.
47
Why do stars appear to 'twinkle'?
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'.
48
What is skyglow?
Skyglow is the rusty orange haze cast by light near urban conurbations. It illuminates the sky, making most stars invisible.
49
What are the 2 types of light pollution which are a problem for astronomers?
1. Skyglow
2. Local glare from sports grounds, supermarket car parks, streetlights and security lights that ruin our eyes' night vision (dark adaptation)
50
What is an observer's zenith?
The point in the night sky directly (90 degree angle) above the observer is their zenith.
51
What is the Earth's exact equatorial diameter?
12,756 km
52
What is the Earth's exact polar diameter?
12,714 km
53
How many constellations are there in the sky?
88
54
What are constellations?
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.
55
What are asterisms?
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.
56
Which 3 stars make up the Winter Triangle asterism?
1. Procyon
2. Betelgeuse
3. Sirius
57
Where in the sky is the Orion Nebula?
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.
58
Where in the sky is the Pleiades cluster?
One of Orion's neighbouring constellations, Taurus, the Bull, boasts one of the most beautiful open clusters of stars, the Pleiades.
59
How do meteors and shooting stars appear in the night sky?
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.
60
How do comets appear in the night sky?
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.
61
How many supernova have been observed with the naked eye in our Galaxy in the last 1000 years?
3
62
How do supernova appear in the night sky?
A supernova would appear as a bright new star, be visible for possibly a few weeks and then slowly fade.
63
How do planets appear in the sky?
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.
64
What are the Northern Lights also known as?
Aurora Borealis
65
What are the Southern Lights also known as?
Aurora Australis
66
Where are Northern and Southern Lights generally visible from?
Aurora are generally visible from the polar regions, although they have been observed on rare occasions from mid-UK latitudes.
67
Which star from Cassiopeia must you be able to identify?
Schedar
68
Which star from Cygnus, the Swan, must you be able to identify?
Deneb
69
Which 2 stars from Crux, the Southern Cross, must you be able to identify?
Mimosa and Acrux
70
Which 3 stars make up the Summer Triangle asterism?
1. Deneb
2. Vega
3. Altair
71
What is an optical double star?
Two stars, physically unrelated, that happen to lie roughly in the line of sight.
72
What is the most distant object that can be seen with the naked eye?
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.
73
How do artificial satellites appear in the sky?
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.
74
How do aircraft appear in the sky?
Aircraft are easily identified by green and red right-of-way 'navigation' lights and flashing white identification lights.
75
What is the celestial sphere?
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).
76
What is the ecliptic on the celestial sphere?
The path taken by the Sun on the celestial sphere during one year.
77
What is the symbol used to denote the First Point of Aries?
♈︎
78
What is the First Point of Aries?
The point where the ecliptic cuts the celestial equator on its 'journey' from South to North.
79
What are the celestial equivalents of latitude and longitude on the celestial sphere?
Declination and right ascension
80
What is the abbreviation for declination?
dec
81
What is the abbreviation for right ascension?
RA
82
What is the symbol for declination?
δ
83
What is the symbol for right ascension?
α
84
What is declination?
Declination is simply the projection of latitude onto the celestial sphere; it is measured in degrees (+ and - signs indicate N and S)
85
What is right ascension?
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).
86
How many degrees in 1 h (hour) when measuring right ascension?
15 degrees
87
How many min in 1 h when measuring right ascension?
60 min = 1 h
88
How many degrees in 1 min (minute) when measuring right ascension?
0.25 degrees
89
Which star is closest to the North Celestial Pole?
Polaris
90
What are the equatorial coordinates of Sirius?
6h 45 min, -17 degrees
91
What are the equatorial coordinates of Betelgeuse?
5h 55 min, +7 degrees
92
What are the equatorial coordinates of Fomalhaut?
22h 58 min, -30 degrees
93
What are the equatorial coordinates of Deneb?
20h 41 min, +45 degrees
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).
True
95
True or False: Since we on Earth are 'inside' the celestial sphere looking 'outwards' to the sky, right ascension increases to the left.
True
96
What is azimuth in the amateur horizontal coordinate system?
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.
97
What is altitude in the amateur horizontal coordinate system?
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).
98
What is a cardinal point when measuring bearings? (GIVE THE EXAMPLES)
North, East, South, West
99
What is an intercardinal point when measuring bearings? (GIVE THE EXAMPLES)
North-West, South-East, North-East, South-West
100
What is diurnal motion a result of?
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.
101
Explain diurnal motion:
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.
102
During diurnal motion, the highest point the stars reach is called their...
Culminate (highest point)
103
Like the Sun, the stars rise in the East and set in the ........
West
104
How long is one sidereal day?
23 h 56 mins
105
How long does it take the Earth to rotate 360 degrees?
23 h 56 mins - this is one sidereal day.
106
How many degrees does the Earth move around the Sun in one sidereal day?
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.
107
How long is one solar day?
24 h 0 min
108
Why do the stars rise, culminate and set 4 min earlier (GMT) each day?
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.
109
What does GMT stand for?
Greenwich Mean Time
110
Why do astronomers use LST?
Most astronomers observe the stars as opposed to the Sun, and so astronomers use clocks based on LST rather than clock time.
111
What does LST stand for?
Local Sidereal Time
112
What is the LST of an observer?
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.
113
What is a star's hour angle?
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.
114
What is the equation for a star's hour angle?
Hour Angle = Local Sidereal Time - Right Ascension
115
What can an astronomer deduce if a star's hour angle is negative?
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).
116
What does NCP stand for?
North Celestial Pole
117
How do the stars appear to revolve around the NCP? HINT: THINK POLARIS
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.
118
True or false: Altitude of NCP (or SCP) = observer's latitude
True.
119
What does SCP stand for?
South Celestial Pole
120
Knowing that altitude of NCP (or SCP) = observer's latitude, what can we say about Polaris?
Since Polaris is only 0.5 degrees from the SCP, then to a good approximation: altitude of Polaris = observer's latitude.
121
The altitude of Polaris (or the NCP or SCP) is equal to...
The observer's latitude
122
What is another word for a star's polar distance?
A star's co-declination
123
What is a star's polar distance?
The angular distance of a star from the NCP.
124
What is the angular declination of the NCP?
+90 degrees
125
What is the equation for calculating a star's polar distance?
Since the declination of the NCP is +90 degrees, it follows that:
Polar Distance = 90 degrees - Declination
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.
True.
127
The larger the declination of a star, the .............. its polar distance.
The larger the declination of a star, the smaller its polar distance.
128
The larger the declination of a star, the ................ the chance of it being circumpolar.
The larger the declination of a star, the greater the chance of it being circumpolar.
129
What is a star's upper and lower transit?
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
130
The upper transit of a star is also the point at which a star......
Culminates (reaches the highest point in its cycle).
131
What are circumpolar stars?
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.
132
Stars are NOT circumpolar stars if they...
Stars are not circumpolar stars if they have a large polar distance and are due to set below the northern horizon before rising again.
133
Stars ARE circumpolar if they...
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).
134
What is the expression for determining whether or not a star is circumpolar?
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.
135
Calculate the polar distance for Capella: (dec = +46 degrees)
44 degrees
136
Calculate the polar distance for Dubhe: (dec = +62 degrees)
28 degrees
137
Calculate the polar distance for Vega: (dec = +39 degrees)
51 degrees
138
Calculate the polar distance for Acrux: (dec = -63 degrees)
27 degrees
139
An astronomer observes a star with RA = 05 h 35 min crossing their meridian. What is the astronomer's LST?
05:35
140
For an observer, the hour angle of Sirius is -0h 45 min. In how many minutes will Sirius be due South?
45 min
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?
30 min
142
Why should you fit a torch with a red filter before going observing?
Red light does not destroy the eyes' dark-adapted state.
143
When is the best time to observe celestial objects and why?
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.
144
How long does it take for your eyes to become fully dark adapted?
20 - 30 minutes of darkness.
145
The eye contains 2 types of photoreceptive cell. Name these 2 types of photoreceptive cell:
Rods and cones
146
Which out of rods or cones in the eye are colour-sensitive cells?
Rods are not colour-sensitive photoreceptive cells.
Cones are colour-sensitive photoreceptive cells.
147
What are rods in the eye sensitive to changes in?
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.
148
When might a star not be seen if looked at directly?
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.
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)?
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'.
150
What is averted vision?
Averted vision is looking slightly to the side of an object.
151
Where are cones in the eye relevant to the eye's optical axis?
Cones lie on or close to the optical axis - they are sensitive to colours when the light is bright enough.
152
Where are rods in the eye relevant to the eye's optical axis?
Rods are offset from the optical axis - they are sensitive to light/dark but not to colour.
153
Name some factors that may affect the visibility of objects in the night sky:
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.
154
How does recent rain improve observing conditions?
Recent rain removes dust particles in the atmosphere.
155
True or False: The Moon is 100X closer to us than Venus.
True.
156
True or False: Half of the Moon's surface is in permanent darkness.
False
157
True or False: Lunar 'seas' are covered in water.
False
158
Why is it that during a 'supermoon' the lunar disc appears larger?
The Moon is slightly closer to the Earth than usual.
159
Name the 7 principal lunar features which you may be asked to identify:
1. Ocean of Storms
2. Copernicus crater
3. Kepler crater
4. Sea of Crises
5. Apennine mountains
6. Sea of Tranquillity
7. Tycho crater
160
Which out of the Earth, the Moon and the Sun is the most spherical in shape?
The Sun
161
What is the difference between the Moon's polar diameter and the Moon's equatorial diameter?
4 km
162
What is the Moon's mean diameter?
3500 km
163
What is the shape of the Moon?
Oblate spheroid (same as the Earth).
164
True or False: The Moon's far side is almost devoid of maria.
True.
165
What is the difference between the Sun's polar diameter and the Sun's equatorial diameter?
10 km. However, this is insignificant compared with its mean diameter of 1.4 million km, so the Sun is almost perfectly spherical.
166
What is the Sun's mean diameter?
1.4 million km
167
The full disc of the Moon subtends an angle of just less than ..... degrees at the human eye.
The full disc of the Moon subtends an angle of just less than 0.5 degrees at the human eye.
168
What is the latin name for the Moon's large, dark-grey, relatively smooth seas?
Maria (singular = Mare, pronounced 'mah-ray')
169
What are the Moon's seas made up of?
The large, dark-grey, relatively smooth seas are made up of volcanic basalt rock.
170
What are the Moon's highlands made up of?
The lighter-grey, mountainous, highly-cratered highlands are made up of igneous rock called anorthosite.
171
What is the latin name for the Moon's lighter-grey, mountainous, highly-cratered highlands?
Terrae (singular = Terra)
172
Which English physicist made one of the earliest (c. 1600) naked-eye sketches of the lunar disc?
William Gilbert (better known for his contribution to our understanding of magnetism).
173
How many days does it take the Moon to rotate through an angle of 120 degrees?
9.1 days
174
How many astronauts have walked on the moon?
12 astronauts
175
What caused the formation of the Moon's cratered highlands and mare (sea) basins?
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.
176
How were the Moon's lunar craters formed?
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.
177
How many days does it take for the Moon to revolve around the Earth once?
27.3 days; this is also the time taken for the Moon to rotate on its axis by 360 degrees.
178
How many days does it take for the Moon to rotate once on its axis?
27.3 days; this is also the time taken for the Moon to revolve around the Earth once.
179
How long is a sidereal month?
27.3 days
180
How long is a solar month?
29.5 days
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.
59%
182
The Moon's equator is inclined to the plane of its orbit around the Earth by ...... degrees.
1.5 degrees
183
The plane of the Moon's orbit is inclined at ....... degrees to the ecliptic.
5.1 degrees
184
Give 2 reasons why the Moon appears really high in the sky at times:
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).
185
What causes a libration in the Moon's latitude (GIVE 2 CAUSES)?
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.
186
What causes a libration in the Moon's longitude?
Libration in longitude arises from the Moon's varying speed in its elliptical orbit around the Earth.
187
Why did Apollo astronauts deploy seismometers on the surface of the Moon?
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.
188
In which year did the Luna 3 spacecraft become the first spacecraft to photograph the Moon's far side?
1959
189
In 1959, which spacecraft photographed the Moon's far side for the first time?
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).
190
What are the 4 major internal divisions of the Moon?
1. crust
2. mantle
3. outer core
4. inner core
191
What is the mean thickness of the lunar crust?
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.
192
Give a possible explanation for why lunar maria are almost exclusively found on the Moon's near side:
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.
193
The radius of the Moon's core is less than ____% of the Moon's radius.
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.
194
On Earth, the core extends to more than ____% of its radius.
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.
195
True or False: The Moon's core is at the physical centre of the Moon.
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).
196
By how many kilometres is the Moon's core offset from the physical centre of the Moon?
2 km - it is offset by about 2 km towards the near side (i.e. towards Earth).
197
Prior to what year was the appearance of the Moon's far side unknown?
Prior to 1959, the appearance of the Moon's far side was unknown.
198
What is the name of the only noteworthy sea on the far side of the Moon?
Mare Moscoviense
199
Describe the technology Luna 3 was equipped with before being sent to photograph the far side of the Moon:
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.
200
Describe the surface features of the far side of the Moon:
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).
201
When did US President John F. Kennedy make his historic speech announcing the ambitious Apollo space programme?
In May of 1961.
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?
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'.
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:
1. The collection of lunar soil and rocks for analysis on return to Earth.
2. The deployment of scientific experiments on the lunar surface.
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:
1. Laser Ranging Retro Reflectors (to monitor the Earth - Moon distance).
2. Passive seismometers
3. Lunar dust collectors
4. Solar Wind Composition (SWC) experiments
205
At what date and time did Neil Armstrong become the first of total twelve astronauts to steep onto the Moon's surface?
2:56 GMT on July 21st 1969
206
Explain the Giant Impact Hypothesis theory about the origin of the Moon:
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.
207
Explain the Fission Theory about the origin of the Moon:
The Earth was spinning so rapidly that part of it (now filled by the Pacific Ocean) spun off and formed the Moon.
208
Explain the Capture Theory about the origin of the Moon:
The Earth and the Moon were formed at different places in the Solar System, but the Moon became 'captured' by Earth's gravitational force.
209
Explain the Condensation (Co-accretion) Theory about the origin of the Moon:
The Earth and Moon formed together at the same time out of material from the solar nebula.
210
Give 2 pieces of evidence which support Giant Impact Hypothesis Theory as the true origin of the Moon:
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.
211
Which planet in the Solar System could float on water?
Saturn
212
Which planet in the Solar System has a rusty surface and is known as the Red Planet?
Mars
213
Which planet in the Solar System can appear brighter than any other planet in the sky?
Venus
214
What is the name of the dwarf planet Pluto's largest moon?
Charon
215
How many planets are there in the solar system?
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.
216
How many terrestrial planets are there in our Solar System?
4
217
What are the properties of terrestrial planets?
Terrestrial planets are relatively small worlds of rock surrounding small iron cores.
218
What are the properties of gaseous planets?
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.
219
How many gaseous planets are there in our Solar System?
4
220
What are the names of the 4 terrestrial planets in our Solar System?
1. Mercury
2. Venus
3. Earth
4. Mars
221
What are the names of the 4 gaseous planets in our Solar System?
1. Jupiter
2. Saturn
3. Uranus
4. Neptune
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.
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.
223
What is the largest body on the main Asteroid Belt?
Ceres
224
Where in the Solar System are most dwarf planets located?
Most dwarf planets inhabit the cold outer limits of the Solar System - the Kuiper Belt.
225
Name 3 notable dwarf planets:
1. Pluto
2. Eris
3. Makemake
226
What are SSSOs?
Small Solar System Objects
227
Name 3 types of SSSOs:
1. Asteroids
2. Meteoroids
3. Comets
228
What are asteroids?
Small, irregular rocky objects with diameters < 1000 km.
229
What are comets?
'Dirty snowball' mixtures of compacted dust, rock and ice, found mainly in the outer regions of the Solar System.
230
Where in the Solar System are most asteroids located?
Most asteroids reside in the doughnut-shaped Main Belt between the orbits of Mars and Jupiter.
231
What is the size range for asteroids?
Asteroids range from ~10 m (the generally-accepted cut-off between asteroids and meteorites) to ~1000 km. Most have irregular shapes.
232
True or False: Comets can have their orbits 'modified' by the gravitational attraction of the massive planets.
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.
233
How do we classify comets?
Comets can be classified in terms of their orbital periods - short-period comets and long-period comets.
234
How long are short-period comets' orbital periods?
Short-period comets have orbital periods which are less than 200 years.
235
How long are long-period comets' orbital periods?
Long-period comets have orbital periods which are greater than 200 years.
236
Where in the Solar System are short-period comets thought to originate from?
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.
237
Where do long-period comets originate?
Long-period comets originate in the Oort Cloud, a spherical distribution of icy bodies about a half way to the nearest star.
238
What are the properties of long-period comets?
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.
239
What happens when a comet approaches the Sun?
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.
240
What is the approximate size of a comet?
~10 km
241
List the steps which take place as a comet approaches the Sun:
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.
242
Why do comet's tails generally point away from the Sun?
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.
243
Describe the appearance and properties of a comet's ion tail:
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.
244
Describe the appearance and properties of a comet's dust tail:
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).
245
What were the 2 main objectives of ESA's recent Rosetta mission?
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.
246
Name the 3 classifications for meteorites:
1. Iron
2. Stony
3. Stony-iron
247
What are iron meteorites?
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.
248
What are meteoroids?
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.
249
What are meteors/shooting stars?
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.
250
True or False: Meteors and shooting stars are the same thing.
True.
251
What happens during a meteor shower?
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.
252
What happens when larger meteoroids enter the Earth's atmosphere?
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.
253
Where do larger meteoroids which enter the Earth's atmosphere generally come from?
They probably come from the Asteroid Belt, but possibly from the Moon or Mars.
254
When is the famous meteor shower The Perseids visible?
Every year in mid-August.
255
When is the famous meteor shower Geminids visible?
Every year in November.
256
When is the famous meteor shower Quadrantids visible?
Every year in January.
257
Name 3 famous meteor showers:
1. The Perseids
2. Geminids
3. Quadrantids
258
What is the name of the constellation which the Quadrantids meteor shower is named after?
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.
259
What is the abbreviation for 'light year'?
l.y.
260
True or False: Light years are a unit of time.
False. Light years are a unit of distance.
261
What is a light year?
A light year is a unit of distance, which is equivalent to the distance travelled by light in one year.
262
What is the speed of light in km/s?
Light travels 300,000 km per second.
263
Distance travelled by light in 1 year = 1 _____ year.
Distance travelled by light in 1 year = 1 light year.
264
How far away are the nearest stars?
The nearest stars are a few light years away.
265
What is the abbreviation for 'parsec'?
p.c.
266
What is the abbreviation for 'astronomical units'?
AU
267
What are distances within the Solar System quoted in?
Astronomical Units (AU)
268
What is 1 AU?
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
269
What is the mean distance from the Earth to the Sun?
150 million km (1.5 x 10^8).
270
What unit do we use to compare the distances in the Solar System?
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.
271
Why are Mercury and Venus called inferior planets?
Mercury and Venus are called inferior planets because their orbits are closer to the Sun than that of the Earth.
272
Why are some planets called superior planets?
Superior planets are called this because their orbits are further away from the Sun than that of the Earth.
273
How many AU is the Moon from the Earth?
The Moon is ~1/400 AU from the Earth.
274
What is Edmond Halley famous for?
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.
275
What is transit?
On rare occasions, one of the inferior planets (Mercury or Venus) crosses thee solar disc. This is known as transit.
276
How did Edmond Halley devise his method to determine the absolute size of the Solar System?
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.
277
Name the 2 basic types of telescope:
1. refracting telescopes
2. reflecting telescopes
278
What type of lens does a refracting telescope use?
A refracting telescope uses a convex (converging) lens to capture and focus light.
279
What type of lens does a reflecting telescope use?
A reflecting telescope uses a parabolic concave (converging) mirror to capture and focus light.
280
What is the purpose of the objective element in a telescope?
The objective element collects as much light as possible and focuses the light to a small bright image.
281
What is the purpose of the eyepiece lens in a telescope?
The eyepiece lens magnifies the image focused by the objective element.
282
Explain how a telescope works:
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.
283
What is a telescope's aperture (size)?
A telescope's aperture, or size, is the diameter of its objective lens or mirror (usually quoted in cm, inches or metres).
284
Give 2 advantages of buying a telescope with a larger aperture/size:
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.
285
Give 2 factors which impact the resolution of the image produced by a telescope:
1. The size of the telescope.
2. The wavelength of light entering the telescope.
286
How does the wavelength of light entering a telescope impact the resulting image resolution?
The longer the wavelength of light entering the telescope, the poorer the resolution.
287
Why is it that, through the same telescope, red images are not as highly resolved as predominantly blue images?
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.
288
What is a telescope's light grasp?
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
289
What is the relationship between light grasp, area and the diameter of the objective element of a telescope?
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.
290
What is the equation for the magnification of a telescope?
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.)
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.
True.
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?
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.
293
Why is it that, under poor seeing conditions, high magnification is undesirable?
Under poor seeing conditions, high magnification is undesirable since turbulence in the air gives rise to unsteady images that lack clarity.
294
How does eyepiece focal length impact magnification?
The shorter the eyepiece focal length, the greater the magnification.
295
Why do we use eyepieces of different focal lengths?
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.
296
What is a Barlow lens?
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.
297
How does the magnification impact the field view of a telescope?
The greater the magnification, the smaller the field view of the telescope.
298
What does FOV stand for?
Field Of View
299
What is the field of view (FOV) of a telescope?
The field of view of a telescope is the circle of sky that is visible through its eyepiece.
300
What is FOV measured in?
FOV is measured in degrees or minutes of arc (abbreviation = arcmin or ') where 1° = 60'.
301
How many arcmin (abbreviation = ' ) in 1 degree?
1° = 60' (1° = 60 arcmin).
302
At what angle does the full Moon subtend an observer on Earth?
The full Moon subtends an angle of ~30' (0.5°) to an observer on Earth.
303
Who was the first scientist to use a telescope and interpret (sometimes incorrectly) what they saw?
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.
304
What is the ecliptic?
The plane of the Earth's orbit.
305
What is orbital inclination?
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.
306
True or False: The nightly positions of the planets can be shown on a planisphere.
False.
307
True or False: Of the 8 planets in our Solar System, Venus's orbit is the most circular.
True. Of the 8 planets in our Solar System, Venus's orbit is the most circular.
308
True or False: When a planet undergoes retrograde motion, the planet physically moves backwards in its orbit for a few weeks.
False.
309
Why do most astronomers prefer to use reflector telescopes?
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.
310
How does the Newtonian reflector work?
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.
311
Give 2 problems with refractor telescopes:
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.
312
What is chromatic aberration?
Chromatic aberration is where a lens focuses different wavelengths of light to slightly different points, making images blurred and unclear.
313
True or False: The Cassegrain reflector is a popular type of reflector which tends to be more compact than the Newtonian reflector.
True. The Cassegrain reflector is a popular type of reflector which tends to be more compact than the Newtonian reflector.
314
How does the Cassegrain reflector work?
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.
315
What are the 4 main types of probe?
1. fly-by
2. orbiters
3. impactors
4. landers
316
What do fly-by probes do?
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.
317
Give 2 examples of famous fly-by missions:
1. Voyagers I and II which visited the outer planets.
2. New Horizons which explored Pluto and the outer Solar System.
318
What do orbiter probes do?
Orbiter probes go into orbit around the target body.
319
What do impactor probes do?
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.
320
What do lander probes do?
Lander probes softly land on the surface - unlike impactor probes, the impact is controlled and the probe touches down intact on the surface.
321
Give 3 examples of famous orbiter missions:
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.
322
Give 2 examples of famous impactor missions:
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.
323
Give 2 examples of famous lander missions:
1. Huygens which landed on Saturn's moon Titan.
2. The Spirit and Opportunity rovers which were sent to Mars and Philae.
324
What was the New Horizons mission?
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.
325
What was the Juno mission?
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.
326
What was the Deep Impact mission?
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.
327
What was the Philae mission?
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.
328
Give 4 advantages of manned missions:
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.
329
Give 6 disadvantages of manned missions:
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.
330
What Greek word is 'planet' derived from?
Planetes
331
What does i stand for in astronomy?
Orbital inclination
332
What is the inclination of the Earth's orbit?
By definition, the inclination of the Earth's orbit is 0°.
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.
True. The small values of i (orbital inclination) confine the planets to a narrow Zodiacal Band in the sky centred on the ecliptic.
334
What is retrograde motion?
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.
335
What are the limits of the Zodiacal Band?
The limits of the Zodiacal Band are ~8° either side of the ecliptic due to the relatively large orbital inclination of Mercury.
336
The optimum place in a planet's orbit for it to be observed under the best (darkest) conditions depends on?
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.
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?
6.2 AU
338
When is an inferior planet (i.e. Mercury or Venus) best observed?
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°.
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.
1.72 AU
340
True or False: The planet Venus shines as the 'Morning Star' in the dawn sky shortly before sunrise.
True. The planet Venus shines as the 'Morning Star' in the dawn sky shortly before sunrise.
341
When is a superior planet best observed?
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.
342
What is an occultation?
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.
343
What may happen when an inferior planet is at inferior conjunction?
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.
344
True or False: The Sun is really moving.
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.
345
What is the First Point of Aries?
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.
346
What is the symbol which denotes the First Point of Aries?
♈︎
347
What is the symbol which denotes the First Point of Libra?
♎︎
348
What is the First Point of Libra?
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.
349
How often does the Moon repeat its cycle of phases?
Every 29.5 days.
350
True or False: The purpose of Stonehenge remains unknown.
True. The purpose of Stonehenge remains unknown.
351
When was Stonehenge built?
Stonehenge was built in stages between c.3000 BCE and c.1500 BCE.
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?
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.
353
What was astronomy originally used for?
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.
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).
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).
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?
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.
356
What is precession?
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.
357
How much time does it take for one complete rotation of the Earth's axis to take place?
~26000 years
358
Name the 5 'wandering' planets known to the ancient Greeks:
1. Mercury
2. Venus
3. Mars
4. Jupiter
5. Saturn
359
How long did Ptolemy's model of the universe last before becoming outdated?
~1500 years
360
What does 'geocentric' mean?
Earth-centred
361
What does 'heliocentric' mean?
Sun-centred
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.
True. Early models of the 'Universe' were based on the geocentric (Earth-centred) systems of ancient Greek philosophers such as Plato and Aristotle.
363
What were the 4 'elements' which the Aristotelian Universe was based on?
1. earth
2. air
3. fire
4. water
364
Describe the Aristotelian Universe:
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.
365
What was the major problem with the Aristotelian Universe model?
The Aristotelian Universe model was unable to explain the observed retrograde motion of the planets.
366
How did the Greeks initially modify the Aristotelian Universe to try and incorporate the retrograde motion which had been observed? Did this work?
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.
367
How did Egyptian astronomer and geographer Claudius Ptolemaeus (Ptolemy) further refine the universe model?
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.
368
How did Polish monk Nicholas Copernicus refine the Universe model after Ptolemy's model had been generally accepted for almost 1500 years?
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.
369
True or False: Nicholas Copernicus was the first person to propose a heliocentric (Sun-centred) Universe model.
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.
370
How did Tycho Brahe develop his 3 laws of planetary motion?
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.
371
Who built the Uraniborg Observatory on the island of Hven that lay between Denmark and Sweden?
Under the patronage of Frederick II, the King of Denmark, the eccentric and prominent astronomer Tycho Brahe built the Uraniborg Observatory.
372
In what year did Galileo Galilei first use his 'optick tube' (telescope) to observe the skies and make sketches of what he saw?
1609
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?
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.
374
What is the perigee for an object orbiting the Earth?
The closest point in the orbit to Earth.
375
What is the apogee for an object orbiting the Earth?
The furthest point in the orbit from Earth.
376
What does Kepler's first law of planetary motion state?
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).
377
What is the perihelion for a planet (or object) orbiting the Sun?
The point in the orbit at which a planet is closest to the Sun.
378
What is the aphelion for a planet (or object) orbiting the Sun?
The point in the orbit at which a planet is furthest from the Sun.
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:
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
380
What is the force responsible for the orbital motion of satellites and planets?
Gravitation (gravity). This is an attractive force between all bodies that have mass.
381
How did Isaac Newton discover gravity?
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.
382
What does Isaac Newton's law of universal gravitation state?
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.
383
List 4 things that gravitation is responsible for:
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.
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
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.
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.
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.
385
What does Kepler's third law of planetary motion state?
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
385
What does Kepler's second law of planetary motion state?
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).
386
In order to explain orbits, Newton devised a 'cannon thought experiment'. Explain this:
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.
387
The 2 best methods to obtain a large image of the Sun can be obtained by using...?
1. A H-alpha filter
2. Telescopic projection
388
What is a H-alpha filter?
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.
389
What is the telescopic projection method?
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.
390
What is the surface of the Sun called?
The photosphere.
391
What are sunspots?
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.
392
What is the approximate temperature of the photosphere (the surface of the Sun)?
~5800 K
393
What does K stand for?
Kelvin, which is a unit of measurement for temperature.
394
What is the approximate temperature of umbra on the surface of the Sun?
~3800 K
395
What is the approximate temperature of penumbra on the surface of the Sun?
~5600 K
396
How do we know that the Sun does not rotate as a solid body?
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.
397
How can you determine the solar rotation period of the Sun?
The solar rotation period can be determined by recording the position of a sunspot (or group) at approximately the same time every few days.
398
Explain how to calculate the solar rotation period of the Sun:
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.
399
What is the equation used when calculating the solar rotation period of the Sun?
T / Δt = 360° / ΔL
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°?
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).
401
At a different latitude, the Sun rotates through 60° in 5.5 days. Calculate the Sun's rotation period for this latitude.
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
402
What is the temperature in the central core of the Sun?
~15 million K.
403
How many million tonnes of mass does the Sun lose every second?
4 million
404
What is the Sun's total mass in tonnes?
2.0 x 10^27 tonnes
405
Why does the temperature in the central core of the Sun have to be so hot?
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.
406
What is the most common series of reactions in the Sun called?
The proton-proton chain.
407
What is the proton-proton chain?
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.
408
Where is the radiative zone?
The radiative zone is immediately above the Sun's core.
409
What happens in the radiative zone of the Sun?
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.
410
Where is the convective zone in the Sun?
The convective zone is the outer ~200,000 km of the Sun.
411
What happens in the convective zone of the Sun?
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.
412
How thick is the photosphere?
100 km thick.
413
In what form does the Sun's photosphere radiate energy?
The Sun's photosphere radiates energy in the form of visible light and, to a lesser extent, infra-red, ultra-violet and X-radiation.
414
How is thick is the chromosphere?
2000 km thick.
415
What are the Van Allen Belts?
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.
416
What is the Sun's corona?
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.
417
What is the solar wind?
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.
418
What is the solar wind responsible for?
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
419
