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GCSE Astronomy Revision Notes

Extracts from this document...




  1. What three features distinguish Earth from other planets in our solar system?
  • Liquid water, atmosphere, life
  1. Explain how Raleigh scattering makes the sky appear blue.
  • When blue light hits oxygen and nitrogen in the atmosphere, it is absorbed and reemitted in any direction. This is due to the shorter wavelength of blue light compared to other colours, meaning that it is scattered more often than other colours, which pass through more easily. This is why the sun appears more orange at sunset – the light passes through more atmosphere, so more light is scattered, so only the most red light passes through, as all of the blue light is scattered.
  1. Why is Earth’s atmosphere beneficial to humans?
  • The atmosphere keeps the Earth at a relatively warm temperature suitable for life. It also protects Earth’s surface from ultraviolet radiation. This is due to the ozone gas filtering out these rays. It contains oxygen and carbon dioxide, which are needed for life.
  1. Name three causes of light pollution.
  • Shopping centres, floodlights, street lights, etc
  1. Why is light pollution undesirable for astronomers?
  • It makes it difficult to see fainter stars and galaxies.
  1. What shape is the Earth?
  • Oblate spheroid (squashed sphere). The diameter is greater at the equator than it is at the poles.
  1. What is the diameter of the Earth?
  • 13,000 kilometres
  1. Describe how lunar eclipses show that the Earth is not flat.
  • During a lunar eclipse, the shadow of the Earth on the moon is curved.
  1. Describe how sailing ships show that the Earth is not flat.
  • They appear to disappear bottom-first over the horizon as they move away.
  1. Describe how shadows show that the Earth is not flat.
  • Using two places north and south of each other a few hundred kilometres apart, you can measure the angle of shadows cast by a vertical metre stick at each location. You can use the shadows to calculate the angle between the sticks. When you take the distance between the sticks into account, you can calculate the curvature of the Earth, because they are not parallel. Eratosthenes of Cyrene used this experiment to calculate the circumference of the Earth.
  1. How long is the rotation period of the Earth?
  • 23 hours and 56 minutes
  1. How long does it take the Earth to rotate by one degree?
  • 4 minutes
  1. What is one rotation of the Earth in relation to the stars called?
  • A sidereal day
  1. Define:
  • Equator – The line equidistant from Earth’s poles, parallel to Earth’s axis of rotation. The sun is directly above the equator at noon on the Equinoxes.
  • Tropics of Cancer and Capricorn – The Tropic of Cancer is 23°27′ North of the equator, and the Tropic of Capricorn is 23°27′ South of the equator. They represent the furthest north and south that the sun appears in the Zenith at noon on the solstices. In the summer solstice, it appears directly above the Tropic of Cancer.
  • Latitude – The angle between the equator, the centre of the Earth and the observer
  • Longitude – The angle of the observer east or west of the Greenwich Meridian.
  • Pole – The points on the Earth’s surface where the rotational axis passes through
  • Horizon – The circular boundary of part of Earth’s surface visible from a particular point. It is the line where the Earth’s surface appears to meet the sky.
  • Meridian – The imaginary line connecting the poles through the observer. The Prime Meridian passes through Greenwich and is used to determine longitude.
  • Zenith – The imaginary line passing through the centre of the Earth and the observer. The point in the sky directly above the observer.
  • Equinox – When the sun appears directly overhead at the equator at noon. This happens twice a year – on the autumn and spring equinoxes.
  • Summer solstice – When the sun appears directly overhead at the Tropic of Cancer at noon. This happens in the Northern Hemisphere summer.
  • Winter solstice – when the sun appears directly overhead at the Tropic of Capricorn at noon. This happens in the Northern Hemisphere winter.
  1. Why does the atmosphere cause problems for astronomers?
  • The atmosphere does not let all wavelengths of the electromagnetic spectrum to pass through, so we cannot observe all wavelengths. We can only observe visible light, microwaves and radio waves.
  1. Why do we put telescopes on mountains?
  • There is less atmosphere between the telescope and space, so less radiation is absorbed. There is also less light pollution as generally there are fewer people living in mountainous areas.
  1. Why do we send telescopes to space?
  • There is no atmosphere, so we can observe all wavelengths. However, this is very expensive and difficult to fix when things go wrong.
  1. What are the two types of telescope?
  • Reflecting and refracting
  1. How does a reflecting telescope work?
  • Light is reflected in a concave mirror at the back of the telescope, which focuses light onto the secondary mirror, which reflects it into the eyepiece.
  1. Who invented the reflecting telescope?
  • Isaac Newton
  1. How does a refracting telescope work?
  • Two convex lenses are placed so that their foci are in the same place. The larger lens is the Objective lens and the smaller one is the eyepiece. This focuses light to increase its intensity.
  1. What type of telescope are large telescopes and why?
  • Reflecting telescopes. They are easier and cheaper to make for the same magnifying power. They do not have the problems of chromatic aberration. They produce better quality images due to the large apertures.
  1. Give an advantage of larger telescopes.
  • They are not affected by Chromatic aberration.
  1. Which types of waves pass through the atmosphere?
  • Visual light, microwaves and some radio waves.
  1. What happens to infrared, ultraviolet and X-rays?
  • They are absorbed by the atmosphere.
  1. Where are observatories measuring these wavelengths located? Why?
  • In space, because there is no atmosphere to absorb these wavelengths.
  1. What are the Van Allen belts?
  • They are bands of radiation 1000 miles above the Earth’s surface. They can harm astronauts passing through them. Astronauts passing through the Van Allen belts see flashes with their eyes shut when passing through them.
  1. How were the Van Allen belts discovered?
  • They were confirmed when the Geiger counter on-board Explorer 1 was overwhelmed by strong radiation from a belt of charged particles trapped by Earth’s magnetic field.


  1. What do the highlands of the Moon look like?
  • The light areas of the Moon’s surface
  1. What do the lunar seas of the Moon look like?
  • The dark areas of the Moon’s surface
  1. Label this picture of the Moon with:
  1. Sea of Tranquility
  2. Ocean of Storms
  3. Sea of Crises
  4. Tycho
  5. Copernicus
  6. Kepler
  7. Apennine mountains


  1. What is the Moon’s diameter?
  • 3500 kilometres
  1. How far is the Moon from Earth?
  • 380000 kilometres
  1. What is the orbital period of the Moon?
  • 27.3 days
  1. What is the rotational period of the Moon?
  • 27.3 days
  1. What do the rotational and orbital periods mean for those observing the Moon from Earth?
  • We only ever see the near side of the Moon.
  1. Why is the far side of the Moon not visible from Earth?
  • The same side of the Moon is always facing the Earth.
  1. How do we know what the far side of the Moon looks like?
  • Space probes have captured images of it.
  1. How does the appearance of the far side of the Moon differ? What causes this?
  • There are fewer maria and more craters. This is due to thicker crust on the far side of the moon being thicker, so molten rock is less likely to flow to the surface. There are more craters because the far side of the Moon is not shielded from debris.
  1. What is the Latin name for seas on the Moon?
  • Maria
  1. What is Latin name for the highlands of the Moon?
  • Terrae
  1. How do lunar seas form?
  • Molten rock rises to the surface of the Moon.
  1. How do craters form?
  • Impact from debris
  1. How can we tell that the lunar seas were formed after the highlands?
  • There are fewer craters in the Maria.
  1. Describe rilles.
  • Rilles are trenches on the surface of the moon caused by the collapse of lava tunnels.
  1. Describe wrinkle ridges.
  • They are ridges up to 200m high which formed as the crust of the Moon cooled.
  1. Why does the Moon not have an atmosphere?
  • Its gravity is not strong enough to hold one.
  1. Describe the Apollo space programme.
  • The Apollo space programme used ALSEPS to learn about the geology of the Moon. This stands for Apollo Lunar Surface Experiments Packages, which consist of a data transmitter, a radioactive decay powered power supply and experiment modules. These measure seismic activity, charged particles in solar wind, the lunar atmosphere, the rate at which heat flows through the lunar rock and the strength of the Moon’s gravity. There is also a device to detect a laser from Earth to measure the distance between Earth and the Moon.
  1. What was the purpose of the Apollo space programme?
  • To learn about the geology and conditions on the Moon.
  1. How do astronomers think the Moon was formed?
  • 4.3 billion years ago, an object the size of Mars collided with the Earth, ejecting debris into a disc around Earth. The rocks in this disc were attracted to one another due to gravity, forming the Moon.
  1. What evidence is there to support the Moon formation theory?
  • Rocks found on the Moon by Apollo missions contained the same amount of an isotope of oxygen as those found on Earth suggesting a common origin. The surface of the Moon used to be molten – a giant impact could have provided the energy to melt it. Belts of warm dust similar to the one that the Moon could have formed from are found around other stars.


  1. Describe the use of a Sunspotter.
  • Point the gnomon in the direction of the sun until its shadow disappears. Adjust the sunspotter to ensure the dot of light is on the aiming dot. Trace the sunspots and the sun’s disc onto a piece of paper.
  1. Describe the use of a hydrogen alpha filter.
  • Attach the filter to the objective end of the telescope and aim the telescope at the sun. You can attach a camera to the telescope to browse the sun using a computer. This allows us to see a lot of detail.
  1. What is the diameter of the Sun?
  • 1.4 million kilometres – about 109 times the diameter of the Earth
  1. How far is the Sun from Earth?
  • 150 million kilometres – 1 Astronomical Unit
  1. What is the temperature of the photosphere?
  • 5800 Kelvin
  1. Which two parts of the Sun make up its atmosphere? Describe them.
  • The Chromosphere and the Corona. The Chromosphere is a dense layer of hydrogen and helium gas, around 5000 kilometres thick and with a red/pink tint. The Corona is millions of kilometres of thin, faint gas. When bubbles of billions of tonnes of gas erupt from the corona, the shockwaves are felt as solar wind.
  1. What is the temperature of the corona?
  • 2 million Kelvin
  1. What do sunspots look like?
  • Small dark spots on the photosphere.
  1. Why do sunspots occur?
  • They are cool areas on the sun, caused by strong localised magnetic fields preventing the upward convection of solar material from reaching the surface of the photosphere, resulting in lower temperatures.
  1. What do sunspots indicate?
  • Heightened solar activity
  1. What is the rotational period of the Sun at its poles?
  • 36 days
  1. What is the rotational period of the Sun at the equator?
  • 25 days
  1. How can we determine the rotational period of the Sun by observation?
  • Record the movement of sunspots over a period of time.
  1. Using this Butterfly Diagram, estimate the length of the solar cycle:


  •  11 years
  1. Using the diagram, predict the next solar maximum.
  • 2013
  1. Describe the long term latitude drift of sunspots.
  • The sunspots move nearer to the equator as the solar cycle continues.
  1. What process is the Sun’s energy generated by?
  • Nuclear fusion
  1. What element is created from what other element in the Sun?
  • Helium is created from hydrogen
  1. How can we observe the sun in different wavelengths?
  • By using filters and detectors for different wavelengths.
  1. What does the sun look like in the visible spectrum?
  • White light
  1. What does the sun look like in the hydrogen alpha spectrum?
  • Features such as prominences and filaments are visible in the hydrogen alpha spectrum. This is due to the increased contrast caused by looking only at a narrow range of wavelengths. H-alpha light is emitted by hot hydrogen gas and has a wavelength of 656 nanometres.
  1. What does the sun look like in the X-ray spectrum?
  • The corona is visible in the X-ray spectrum because it shows the hottest regions of the sun.
  1. Describe the structure and nature of solar wind.
  • Solar winds are made up of charged particles flowing from the corona at 400 kilometres per second. They escape the Sun’s gravity due to high temperatures.


  1. What size do the Moon and Sun appear in the sky?
  • About 0.5 degrees each
  1. Why do they appear the same size?
  • The Sun is 400 times bigger than the moon, but it is also 400 times further away.
  1. What is the period of the lunar phase cycle?
  • 29.5 days
  1. Draw diagrams to represent:
  • Full Moon image75.png
  • Waning Crescentimage02.pngimage11.png
  • Last Quarterimage11.pngimage15.png
  • Waning Gibbousimage11.pngimage16.png
  • New Moon
  • Waxing Crescentimage17.png
  • First Quarterimage18.png
  • Waxing Gibbousimage19.png
  1. Why do the phases of the Moon happen?
  • The phase of the Moon that is visible depends on the position of the Moon in relation to the Earth and sun.
  1. Why is the orbit period of the Moon shorter than the lunar phase cycle?
  • It takes longer for the Moon to return to the same position in relation to the Earth and Sun than it does to orbit 360 degrees, because the Earth is also orbiting the Sun.
  1. What do partial solar eclipses look like?
  • An arc is missing from the sun’s disc.
  1. What do total solar eclipses look like?
  • The moon obscures the photosphere, allowing the corona to be visible
  1. What do partial lunar eclipses look like?
  • Fuzzy shadow of Earth on the surface of the Moon, with a reddish hue.
  1. What do total lunar eclipses look like?
  • The Moon appears red
  1. Why are the durations of eclipses different?
  • The Earth’s shadow is bigger than the Moon’s shadow, so it takes longer for the Moon to pass through the Earth’s shadow than for the Earth to pass through the Moon’s shadow. This means that lunar eclipses can last for hours, whereas solar eclipses might be over in a few minutes.
  1. Why do eclipses not occur every new and full Moon?
  • The Moon does not orbit in the same plane as the Earth (about 5 degrees difference), so the Earth, Moon and Sun do not always line up exactly for an eclipse to occur.
  1. Describe a solar day.
  • The time taken for the Sun to reach the same point in the sky
  1. Describe a sidereal day.
  • The time taken for the stars to reach the same point in the sky
  1. How can we determine local noon?
  • Measure the shadows of an object. When the shadow is the shortest, it is local noon.
  1. How can we determine longitude?
  • Subtract local noon from Greenwich Mean Time noon
  1. How did sailors calculate their longitude and who invented the instrument?
  • They took a marine chronometer with them, which kept Greenwich Mean Time, then measured local noon by observation. The marine chronometer was invented by John Harrison in the 1700s with the help of his son, William Harrison.
  1. How can we determine time using a sundial?
  • The angle of the shadow on the sundial can be used to determine the local time. In order to convert this to GMT, we use the equation of time for a particular time.
  1. How does daylight length change throughout the year?
  • In the summer, daylight length is longer than in winter
  1. How do sunset and sunrise times change throughout the year?
  • In summer, sunset times are later and sunrise times are earlier than in winter. At the solstices, these times are at their most extreme and at the equinoxes these times are the same.
  1. State the equation of time.
  • Equation of time = Apparent solar time – mean solar time
  1. What does “apparent Sun” mean?
  • The movement of the Sun that we can actually observe on a day to day basis. All days are not equal in length – they can be 30 seconds either way. Over the course of four years, this adds up to where it started from.
  1. What does “mean Sun” mean?
  • Mean solar time is based on an imaginary sun that takes exactly 24 hours from noon to noon.
  1. What is an aurora?
  • Lights that appear to move across the sky
  1. Name the two aurorae.
  • Aurora Borealis and Aurora Australis
  1. Where are the aurorae most likely observed on Earth?
  • Close to the poles
  1. How are aurorae caused?
  • Charged particles of solar wind are deflected by the Earth’s magnetic  field. Some particles still enter the atmosphere at the poles, and strike molecules in the atmosphere, making them emit light.



  1. List the four rocky inner planets in order from centre.
  • Mercury, Venus, Earth, Mars
  1. List the four gas giants in order from centre.
  • Jupiter, Saturn, Uranus, Neptune
  1. Where are most asteroids found?
  • The Asteroid Belt, between Mars and Jupiter
  1. Name a dwarf planet in the Kuiper belt.
  • Pluto
  1. Where do comets come from?
  • Short period comets (those with orbital periods of 200 years or less) come from the Kuiper belt if they have orbital periods of less than 20 years, but some (like Halley’s comet) come from the Oort cloud. Long period comets (those with orbital periods of 200 years or more – some with periods of several million years) originate in the Oort cloud.
  1. What are centaurs?
  • A cross between a man and a horse a comet and an asteroid. They have crossed the orbits of one or more of the giant planets, and remain inside the solar system, only with fairly eccentric orbits. These include Hidalgo and Chiron.
  1. Where and what are TNOs?
  • Trans-Neptunian Objects – they orbit the Sun at a greater average distance than Neptune. They include Eris and Pluto, but there are over 1000 of them – all of the objects in the Kuiper Belt, Oort Cloud and Scattered Disk.
  1. Where is Ceres?
  • Asteroid belt
  1. Where is most of the matter in the solar system concentrated?
  • The Sun
  1. What is the ecliptic?
  • The plane which the Earth orbits the sun in, and which all of the planets lie approximately on.
  1. What is an Astronomical Unit?
  • Average distance between the Earth and the Sun – roughly 150 million kilometres
  1. What shape are the orbits of the planets?
  • Elliptical
  1. Do the planets orbit in the same plane?
  • Roughly – Mercury has the largest inclination from Earth’s plane – 7 degrees. Not Pluto, though
  1. What band of the sky do the planets appear in?
  • The Zodiac, which is a band following the ecliptic
  1. What is retrograde motion?
  • The apparent backwards motion of a superior planet in its path across the sky
  1. How does retrograde motion occur?
  • The Earth catches up to and then passes a superior planet in the sky.
  1. Define:
    ...read more.


    • Mercury – 90K to 700 K (due to slow revolution and thin atmosphere not trapping heat)
    • Venus – 740 K due to the greenhouse effect
    • Earth – About 290 K, or 15 C
    • Mars – 140 K to 290 K
    • Jupiter – 123 K
    • Saturn – 93 K
    • Uranus – 63 K
    • Neptune – 53 K
    1. Describe the composition of each of the eight planets.
    • Mercury – Rocky
    • Venus – Rocky, plus CO2 atmosphere
    • Earth –Rocky with an iron core
    • Mars – Rocky, with a lot of iron
    • Jupiter – 90% hydrogen, mostly liquid metallic hydrogen
    • Saturn – Mostly hydrogen and helium, especially liquid metallic hydrogen. Has two distinct rings, A and B, which are separated by the Cassini division, then C. The rings are made of small particles and are about 1 km thick.
    • Uranus – Same composition as Jupiter, but is blue due to methane. Axis is almost parallel to the ecliptic.
    • Neptune – Same as Uranus.
    1. What does the atmosphere of Venus tell us about dangers which face Earth?
    • It shows the extremes of the greenhouse effect
    1. Why could this be a problem for Earth?
    • Human activity is increasing the amount of Carbon Dioxide in the atmosphere
    1. How have space probes been used to explore Mars?
    • Mariner 2 and 4 completed fly-bys of Mars. There have also been landings on Mars, including Viking 1, Spirit, Opportunity and Curiosity.
    1. List three data samples that Curiosity has produced.
    • Colour photographs of the Martian landscape
    • Chemical ingredients for life
    • Evidence for ancient stream
    1. What types of equipment does Curiosity have?
    • Cameras, X-ray spectrometer, sample analysis , robotic arm, etc
    1. Why would exploring the solar system with a manned mission be impractical?
    • It would require a lot of supplies to be taken with the mission and would take a long time.
    1. What are Mars’ two moons called?
    • Phobos and Deimos
    1. How did these moons get there?
    • They are captured bodies from the Asteroid Belt
    1. What are their structures like?
    • About half the density of Mars, small, irregular and heavily cratered
    1. What are the structures of the moons of Neptune like?
    • Triton is the largest, and spins in the opposite direction to Neptune’s rotation, suggesting that it is a captured body. It is so large that it may be the result of a collision with Neptune or another moon. Proteus orbits around the equator of Neptune in the same direction, suggesting that it was formed at the same time as Neptune. Nereid has a highly eccentric orbit which takes 360 days, so it is probably captured from the Kuiper Belt.
    1. What do Saturn’s rings look like?
    • Coloured bands, highly reflective
    1. What are Saturn’s rings made of?
    • Small particles of rock, dust and ice


    1. What shape are the orbits of comets?
    • Very eccentrically elliptical – Halley’s comet is 35 AU from the Sun at aphelion and 0.5 AU at perihelion
    1. Why is the shape of cometary orbits created?
    • The orbits are stretched over long periods of time in the Oort Cloud
    1. Where is the Kuiper Belt?
    • 30 to 50 AU from the Sun
    1. Where is the Oort Cloud?
    • 50000 AU and up from the Sun
    1. What are the Kuiper Belt and the Oort Cloud made of?
    • Millions of small objects, made of rock, dust and ice
    1. How are the Kuiper Belt and the Oort Cloud related to comets?
    • Astronomers think that comets originate from here
    1. What evidence is there for the existence of the Oort Cloud?
    • There is no direct evidence, but:
    • Long period comets orbits are often inclined to the ecliptic, so they must come from a sphere surrounding the solar system
    • Long period comets orbit the sun
    • Long period comets originate from about 50000 AU
    1. Label on the image below:
    1. Coma
    2. Nucleus
    3. Dust Tail
    4. Ion Tail


    1. When do the tails of comets develop?
    • When the comet is near the Sun, due to the gas and dust heating up and coming away from the nucleus
    1. Which way does the dust tail point?
    • In an independent orbit of the Sun
    1. Which way does the ion tail point?
    • Away from the Sun
    1. Describe the difference between meteors, meteoroids and meteorites.
    • Meteoroids are lumps of debris in the Solar System that are smaller than 10 metres (anything larger is an asteroid). Meteors are meteoroids burning up in Earth’s atmosphere (shooting stars). Meteorites are the remains of meteors that have contacted the Earth’s surface.
    1. What is a micrometeorite?
    • A very small meteorite (grain of sand sized)
    1. What is a fireball?
    • A very bright meteor with a magnitude of -3 or brighter
    1. Name an annual meteor shower.
    • The Perseids, which happen in August
    1. Where is the radiant point for this meteor shower?
    • Perseus
    1. What is a radiant point?
    • The point which meteors appear to originate from
    1. What are PHOs?
    • Potentially Hazardous Objects – an object which orbit passes within 0.05 AU of Earth. There are roughly 1000 PHOs currently identified.
    1. What are the orbits of PHOs like?
    • Elliptical, not necessarily in the same plane as Earth
    1. Why do we need to monitor PHOs?
    • PHOs larger than 1 km in diameter could cause global catastrophe
    1. What could happen if  there is a collision with Earth and another object?
    • Land destruction, tsunamis, global climatic change – if the object is large enough. Otherwise not much.
    1. What happened in Russia?
    • The Chelyabinsk meteor entered Earth’s atmosphere on February 15th 2013. It was a small asteroid, of around 20 metres in diameter. It caused shockwaves which damaged buildings in the surrounding areas.
    1. How can we tell that there have been impacts between bodies within the solar system?
    • Craters. Also there are sometimes similar materials between bodies (e.g. Earth and Moon).


    1. What did Copernicus contribute to our understanding of the solar system?
    • Nicolaus Copernicus studied planetary motions and developed the first heliocentric model of the solar system. This allowed him to explain retrograde motion. He was reluctant to publish his findings because he feared being ridiculed.
    1. What did Tycho contribute to our understanding of the solar system?
    • Tycho Brahe took meticulous records of the skies to prove that the Earth orbits the Sun.
    1. What did Kepler contribute to our understanding of the solar system?
    • He used Tycho’s observations of Mars to formulate his laws of planetary motion. The first law states that planets move in an elliptical orbit around the Sun, with the Sun at one focus of an ellipse.
    1. Draw a diagram representing Kepler’s second law of planetary motion.








    1. What is the equation for Kepler’s secondary law of planetary motion?
    • A1 = A2
    • “An imaginary line from a planet to the Sun sweeps out equal areas in equal intervals of time”
    • When the planet is at perihelion, it travels faster than at aphelion. This means that it takes the same amount of time to travel from P to Q that it takes to travel from R to S.
    1. What is the equation for Kepler’s third law of planetary motion?
    • T2 = r3
    1. What are the units in Kepler’s third law of planetary motion?
    • T is the orbital period of a planet around the Sun in years
    • r is the mean distance of a planet from the Sun in Astronomical Units
    • For example, T for Earth is 1, and r is 1 – and 12 = 13
    1. What did Galileo discover about Venus?
    • Venus exhibits phases like the Moon, and its apparent size changes
    1. What did Galileo discover about the Moon?
    • It is not perfectly spherical – it has mountains and craters.
    1. Which are the four Galilean satellites of Jupiter?
    • Callisto, Europa, Ganymede and Io
    1. Who discovered Ceres? When and how?
    • It was discovered in 1801 by Giuseppe Piazza. He was observing over several nights, and noticed a feint star appear to move. It was the first asteroid discovered (recently renamed as a dwarf planet) and he thought that it was a comet.
    1. Who discovered Uranus? When and how?
    • William Herschel discovered it in 1781. He was recording the skies when one star appeared to be a small disc. He thought that it was a comet, but observing it further determined that it was a planet.
    1. Who discovered Neptune? When and how?
    • Neptune had been predicted by John Couch Addams and Urbain Le Verrier, because there were wobbles in the motion of Uranus that could only be explained by a planet pulling Uranus outwards. Johann Encke’s assistants discovered Neptune using the position predicted by Le Verrier.
    1. Who discovered Pluto? When and how?
    • Uranus’s orbit’s irregularities were still not explained fully. Edward Pickering and Percival Lowell suggested that there may be another undiscovered planet affecting its motion. This was incorrect, but using the prediction of its location in the sky, Pluto was recorded in 1930.
    1. What force maintains orbits?
    • Gravity
    1. What nature does this force have?
    • Inverse square law nature
    1. What does the inverse square law state?
    • If the distance between two objects doubles, the force between them is one quarter of the previous value.


    1. How can astrometry be used to detect exoplanets?
    • The gravity of large exoplanets causes the star to wobble. We can record the exact position of the star and the wobbles are detected.
    1. How can transit observations be used to detect exoplanets?
    • When an exoplanet moves across the disc of the star, there is a very small temporary drop in brightness. We can measure the amount of light over time to find exoplanets.
    1. How can Doppler shift be used to detect exoplanets?
    • The wobbling of a star due to exoplanets causes slight red-shift and blue-shift in a pattern, because the star moves towards us and away from us. We can detect this using spectroscopy.
    1. Why is it difficult to detect exoplanets?
    • The changes in light output, wobble and colour shift are very small, even for large planets. Current methods cannot detect Earth-like planets due to atmospheric turbulence and because their effect on stars is so small.
    1. What is probably an essential requirement for life?
    • Liquid water and carbon
    1. What is the present theory for water’s origin on Earth?
    • Volcanoes produced steam which condensed into water, and comets containing ice struck Earth
    1. How can astronomers determine the origin of water on Earth?
    • By detecting the water on comets to check if there are the same relative abundances of isotopes as water on Earth.
    1. What does the Rosetta probe do?
    • It will land on the nucleus of a comet to analyse the water and compare it to Earth’s water.
    1. What factors are in the Drake Equation?
    • Number of stars in our galaxy, fraction of stars with planetary systems, number of planets capable of sustaining life, fraction of life-forms that are intelligent, fraction of these that can and wish to communicate, fraction of a planet’s lifetime which can support civilisation… etc
    1. What does the Drake Equation tell us about the existence of life elsewhere in our galaxy?
    • We’re probably not alone
    1. What is the habitable zone?
    • The zone around a star where liquid water can exist.
    1. Which planets in our solar system fall into the habitable zone?
    • Earth
    1. What is the habitable zone also called and why?
    • The Goldilocks zone – it is neither too hot or too cold for liquid water to exist
    1. How are astronomers detecting for past or present life elsewhere in our solar system?
    • Space probes search for microbes and their bi-products
    • Spectral analysis of rocky exoplanets to find gases produced by living organisms
    • Trying to detect radio signals that intelligent forms have broadcast
    1. What benefits are there to discovering extra-terrestrial life?
    • Would help us to understand our place in the universe better
    • Would be one of the greatest discoveries of all-time
    1. What dangers are there to discovering extra-terrestrial life?
    • They may be more intelligent than us and view us as animals
    • Their microbes may be deadly to us (or vice versa)
    • We do not know the intent or capabilities of alien life forms



    1. Describe the appearance of a star in the night sky.
    • A point of light in the sky
    1. Name a star.
    • Betelgeuse
    1. Describe the appearance of a double star in the night sky.
    • Two stars, very close together
    1. Name a double star.
    • Albireo
    1. Describe the appearance of an asterism in the night sky.
    • Stars which form a pattern in the sky, often part of a constellation.
    1. Name an asterism.
    • The Plough
    1. Describe the appearance of a constellation in the night sky.
    • An area of the sky. There are 88 constellations with distinct boundaries as of 1930.
    1. Name a constellation.
    • Cassiopeia
    1. Describe the appearance of nebulae in the night sky.
    • Faint, fuzzy patches of light
    1. Name a nebula.
    • Orion Nebula
    1. Describe the appearance of a globular cluster in the night sky.
    • Fuzzy, with some brighter parts
    1. Name a globular cluster.
    • The Pleiades
    1. How are stars within a constellation labelled according to brightness?
    • Using Greek letters, alphabetically.
    1. How was the official list of constellations developed?
    • Using ancient constellations, then adding more for the southern hemisphere and then filling in gaps.
    1. What are some cultural differences between the constellations on the list?
    • Different cultures interpreted the same patterns in different ways – for example, the Aztecs thought of Capricornus as a whale and Indian astronomers associated it with an antelope.image39.png
    ...read more.


    1. What is Hubble’s Law?
    • More distant galaxies have greater redshifts
    1. What is the formula for Hubble’s Law?
    • v = Hd
    • Velocity (km/s) = Hubble’s Constant x distance (Mpc)
    1. What is the Hubble Constant?
    • About 77 km/s/Mpc
    1. What can we use the Hubble Constant for?
    • Determining the size and age of the universe
    1. How do astronomers use the Hubble Constant?
    • Multiply the distance by the constant to get velocity
    1. What does CMB stand for?
    • Cosmic Microwave Background Radiation
    1. What is CMB caused by?
    • The universe is still a few degrees above absolute zero – this energy is left over from the Big Bang
    1. How was CMB discovered?
    • By accident – two physicists found that there was uniform “noise” in all parts of the sky at all times.
    1. Describe the Wilkinson Microwave Anisotropy Probe.
    • WMAP detects and maps the distribution of CMBR
    1. Why is WMAP significant to cosmologists?
    • It allows us to learn more about the structure of the early universe
    • It shows that the rate of expansion is increasing
    1. What could dark matter be like?
    • It acts like a lens, bending light behind iit so it has gravitational effects
    1. Why is dark matter significant?
    • It makes up 23.3% of the Universe
    1. Why is dark energy significant?
    • It is what keeps the Universe expanding and makes up 72.1% of the Universe
    1. What evidence do we have for an expanding Universe?
    • Most galaxies are redshifted
    1. How has the universe evolved?
    • It is a lot bigger now
    • It is colder now
    • Wavelengths are longer now
    1. Give the main arguments in favour of the Big Bang.
    • The Universe is expanding, so it must have started from somewhere
    1. Compare two evolutionary models of the universe.
    • Big Bang Model states that there is a finite amount of matter moving apart
    • Steady State Hypothesis states that the universe is expanding and matter is created to maintain the same density throughout the universe.
    1. Why are cosmologists unable to agree on an evolutionary model?
    • Some cosmologists question the validity of the observations suggesting an accelerating expansion of the universe.
    ...read more.

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