GCSE Astronomy - Pearson Edexcel 2.0 Flashcards
What is the mean diameter of the Earth?
13,000 km
Name the 4 terrestrial planets:
- Earth
- Mercury
- Venus
- Mars
Which is the largest of the terrestrial planets?
Earth
How much smaller is Earth’s polar diameter than its equatorial diameter?
42 km
What is the shape of the Earth?
Earth is an oblate spheroid.
Why is the Earth an oblate spheroid?
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.
How much of the Earth’s surface is covered by water?
Over 70%
Name some of the diverse features displayed by the landforms on Earth:
- mountain ranges
- volcanoes
- deserts
- rainforests
- grasslands
- glaciers
How many major internal divisions does the Earth have?
4
Name the Earth’s 4 major internal divisions:
- crust
- mantle
- outer core
- inner core
Which is the thinnest layer of the Earth’s 4 major internal divisions?
The crust
How thin is the Earth’s crust?
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.
What do the tectonic plates float on top of?
The silicate mantle
How far through the Earth’s internal structure does the silicate mantle extend?
The silicate mantle extends half-way to the Earth’s centre, making up ~80% of the Earth’s volume.
What drives the movement of the tectonic plates?
The upper mantle is semi-molten, allowing thermal convection currents to rise and fall, driving the sideways motions of the tectonic plates.
True or False: the lower mantle is semi-molten.
False. The lower mantle is solid.
What is the temperature of the outer core?
The temperature of the outer core is ~5000 K.
What does ‘~’ mean?
Approximately
What does ‘K’ stand for in terms of temperature?
Kelvin
What is the outer core made of?
The outer core is made of liquid iron with some nickel.
Which layer of the outer core is responsible for the Earth’s magnetic field?
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).
What is the temperature of the solid inner core?
The temperature of the solid inner core is ~5500 K, which is about the same temperature as the Sun’s photosphere.
Despite the high temperatures, what stops the iron and nickel in the Earth’s inner core from melting?
Despite the temperature of ~5500 K, the inner core has such a high pressure that this prevents the iron and nickel from melting.
What actually are latitude and longitude?
Latitude and longitude are actually angles subtended at the centre of the Earth by imaginary curved lines (arcs) on the Earth’s circumference.
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.
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.
What is longitude measured from?
Longitude is measured East or West of the Prime Meridian.
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.
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.
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.
When is the spring equinox?
On or close to March 21st
When is the autumnal equinox?
On or close to September 23rd
What happens during the spring and autumnal equinoxes?
The Sun lies directly over the equator.
When is the summer equinox?
On or close to June 21st
When is the winter equinox?
On or close to December 21st
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.
What is the latitude of the Tropic of Cancer?
23.5 degrees North
What is the latitude of the Tropic of Capricorn?
23.5 degrees South
What is the latitude of the equator?
0 degrees
What is the latitude of the Arctic Circle?
66.5 degrees North
What is the latitude of the Antarctic Circle?
66.5 degrees South
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’).
What is the mean temperature of Earth as regulated by the atmosphere?
15 degrees Celsius
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
What are the drawbacks of the atmosphere for astronomers?
- The sky is blue, restricting observations to night time
- Air in the atmosphere is continuously in turbulent motion - these adverse seeing conditions make the stars appear to twinkle
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.
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’.
What is skyglow?
Skyglow is the rusty orange haze cast by light near urban conurbations. It illuminates the sky, making most stars invisible.
What are the 2 types of light pollution which are a problem for astronomers?
- Skyglow
- Local glare from sports grounds, supermarket car parks, streetlights and security lights that ruin our eyes’ night vision (dark adaptation)
What is an observer’s zenith?
The point in the night sky directly (90 degree angle) above the observer is their zenith.
What is the Earth’s exact equatorial diameter?
12,756 km
What is the Earth’s exact polar diameter?
12,714 km
How many constellations are there in the sky?
88
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.
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.
Which 3 stars make up the Winter Triangle asterism?
- Procyon
- Betelgeuse
- Sirius
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.
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.
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.
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.
How many supernova have been observed with the naked eye in our Galaxy in the last 1000 years?
3
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.
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.
What are the Northern Lights also known as?
Aurora Borealis
What are the Southern Lights also known as?
Aurora Australis
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.
Which star from Cassiopeia must you be able to identify?
Schedar
Which star from Cygnus, the Swan, must you be able to identify?
Deneb
Which 2 stars from Crux, the Southern Cross, must you be able to identify?
Mimosa and Acrux
Which 3 stars make up the Summer Triangle asterism?
- Deneb
- Vega
- Altair
What is an optical double star?
Two stars, physically unrelated, that happen to lie roughly in the line of sight.
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.
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.
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.
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).
What is the ecliptic on the celestial sphere?
The path taken by the Sun on the celestial sphere during one year.
What is the symbol used to denote the First Point of Aries?
♈︎
What is the First Point of Aries?
The point where the ecliptic cuts the celestial equator on its ‘journey’ from South to North.
What are the celestial equivalents of latitude and longitude on the celestial sphere?
Declination and right ascension
What is the abbreviation for declination?
dec
What is the abbreviation for right ascension?
RA
What is the symbol for declination?
δ
What is the symbol for right ascension?
α
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)
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).
How many degrees in 1 h (hour) when measuring right ascension?
15 degrees
How many min in 1 h when measuring right ascension?
60 min = 1 h
How many degrees in 1 min (minute) when measuring right ascension?
0.25 degrees
Which star is closest to the North Celestial Pole?
Polaris
What are the equatorial coordinates of Sirius?
6h 45 min, -17 degrees
What are the equatorial coordinates of Betelgeuse?
5h 55 min, +7 degrees
What are the equatorial coordinates of Fomalhaut?
22h 58 min, -30 degrees
What are the equatorial coordinates of Deneb?
20h 41 min, +45 degrees
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
True or False: Since we on Earth are ‘inside’ the celestial sphere looking ‘outwards’ to the sky, right ascension increases to the left.
True
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.
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).
What is a cardinal point when measuring bearings? (GIVE THE EXAMPLES)
North, East, South, West
What is an intercardinal point when measuring bearings? (GIVE THE EXAMPLES)
North-West, South-East, North-East, South-West
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.
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.
During diurnal motion, the highest point the stars reach is called their…
Culminate (highest point)
Like the Sun, the stars rise in the East and set in the ……..
West
How long is one sidereal day?
23 h 56 mins
How long does it take the Earth to rotate 360 degrees?
23 h 56 mins - this is one sidereal day.
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.
How long is one solar day?
24 h 0 min
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.
What does GMT stand for?
Greenwich Mean Time
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.
What does LST stand for?
Local Sidereal Time
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.
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.
What is the equation for a star’s hour angle?
Hour Angle = Local Sidereal Time - Right Ascension
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).
What does NCP stand for?
North Celestial Pole
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.
True or false: Altitude of NCP (or SCP) = observer’s latitude
True.
What does SCP stand for?
South Celestial Pole
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.
The altitude of Polaris (or the NCP or SCP) is equal to…
The observer’s latitude
What is another word for a star’s polar distance?
A star’s co-declination
What is a star’s polar distance?
The angular distance of a star from the NCP.
What is the angular declination of the NCP?
+90 degrees
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
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.
The larger the declination of a star, the ………….. its polar distance.
The larger the declination of a star, the smaller its polar distance.
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.
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
The upper transit of a star is also the point at which a star……
Culminates (reaches the highest point in its cycle).
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.
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.
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).
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.
Calculate the polar distance for Capella: (dec = +46 degrees)
44 degrees
Calculate the polar distance for Dubhe: (dec = +62 degrees)
28 degrees
Calculate the polar distance for Vega: (dec = +39 degrees)
51 degrees
Calculate the polar distance for Acrux: (dec = -63 degrees)
27 degrees
An astronomer observes a star with RA = 05 h 35 min crossing their meridian. What is the astronomer’s LST?
05:35
For an observer, the hour angle of Sirius is -0h 45 min. In how many minutes will Sirius be due South?
45 min
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
Why should you fit a torch with a red filter before going observing?
Red light does not destroy the eyes’ dark-adapted state.
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.
How long does it take for your eyes to become fully dark adapted?
20 - 30 minutes of darkness.
The eye contains 2 types of photoreceptive cell. Name these 2 types of photoreceptive cell:
Rods and cones
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.
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.
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.
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’.
What is averted vision?
Averted vision is looking slightly to the side of an object.
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.
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.
Name some factors that may affect the visibility of objects in the night sky:
- Landscape (e.g. trees, high buildings)
- Cloud
- Light pollution (e.g. skyglow, local glare)
- Transparency of atmosphere (recent rain removes dust particles)
- Seeing conditions relating to the ‘steadiness’ of the atmosphere on the I - V Antoniadi Scale.
How does recent rain improve observing conditions?
Recent rain removes dust particles in the atmosphere.
True or False: The Moon is 100X closer to us than Venus.
True.
True or False: Half of the Moon’s surface is in permanent darkness.
False
True or False: Lunar ‘seas’ are covered in water.
False
Why is it that during a ‘supermoon’ the lunar disc appears larger?
The Moon is slightly closer to the Earth than usual.
Name the 7 principal lunar features which you may be asked to identify:
- Ocean of Storms
- Copernicus crater
- Kepler crater
- Sea of Crises
- Apennine mountains
- Sea of Tranquillity
- Tycho crater
Which out of the Earth, the Moon and the Sun is the most spherical in shape?
The Sun
What is the difference between the Moon’s polar diameter and the Moon’s equatorial diameter?
4 km
What is the Moon’s mean diameter?
3500 km
What is the shape of the Moon?
Oblate spheroid (same as the Earth).
True or False: The Moon’s far side is almost devoid of maria.
True.
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.
What is the Sun’s mean diameter?
1.4 million km
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.
What is the latin name for the Moon’s large, dark-grey, relatively smooth seas?
Maria (singular = Mare, pronounced ‘mah-ray’)