Astronomy GCSE Syllabus Explanations_opt

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Astronomy GCSE Syllabus

1.1 The Planet Earth

a Describe the features of the Earth that distinguish it from other planets. Including its water surface and

atmosphere.

Earth is different to many other planets because the Sun causes weather systems, and the exact distance that

we are from the Sun means that it is usually neither too hot or too cold for life forms to manage. We also have

water, so far unique from other known planets, and our atmosphere is of exactly the right composition for us

to be able to live off. These factors combined means that plants and animals are able to live on the Earth, but

so far as we know on no other surface.b Relate the blue sky to the preferential scattering of light in its atmosphere.

The sky is blue because of Rayleigh scattering- as it moves through the atmosphere, blue light becomes

scattered, and is radiated outwards and into our eyes, much more so than the other types of light. This is also

because the atmosphere absorbs many electromagnetic waves, including some of the red ones.

c Demonstrate an understanding of the benefits of the Earth's atmosphere to mankind.

Protects us from ultraviolet rays from the Sun and other harmful high energy particles

Climate can stay stable over long periods of time

The temperature can be regulated and kept within a narrow range

It traps heat and prevents most meteors from landing

The oxygen is essential to life

d Describe some of the major causes of light pollution and demonstrate an understanding of why it is

undesirable to astronomers.

Light pollution is mostly caused by things like flood, street or security lights that are left on on the outside of

buildings when most other things are dark. Astronomers find it undesirable because if our eyes are accustomed

to the bright light then they will not detect fainter ones like stars, and cameras work in the same way.

e Describe how Eratosthenes made the first accurate calculation of the circumference of the Earth.

Eratosthenes used trigonometry to work out that the distance between two cities was about 7 of the Earths

circumference. As he knew that this was about 5000 stadia (800km), then he calculated that the Earth in total

must be around 252000 stadia (39690km). This turned out to be surprisingly accurate, as we know that the

Earth is around 40075km, so he had a total error of less than 1%.

f Recall the shape (oblate spheroid/flattened sphere) and diameter (13,000 km) of the Earth.

g Describe the evidence that the Earth is approximately spherical.

Earth must be spherical because we can see it from space, the changing length of shadows, the fact that boats

disappear over the horizon, eclipses with their umbras and penumbras, the fact that we can go all the way

round, and the fact that the gravitational field strength is the same almost everywhere.

h Recall the rotation period of the Earth (23 h 56 min) and the time to rotate through 1 degree (4 min).

i Demonstrate an understanding of the terms: equator, tropics, latitude, longitude, pole, horizon, meridian

and zenith.

Zenith- The point directly above you.

Celestial meridian- The line joining north and south, via zenith and nadir.

Celestial equator- The line joining north and south, via east and west.

Horizon- As far as the eye can see in any direction.Longitude- How far east or west we go from the Meridian line.

Latitude- How far north or south we go from the Equator.

Equator- The (imaginary) line around the centre of the Earth

Tropic of Cancer- The (imaginary) line around the Earth at 23.5 degrees north of the Equator.

Tropic of Capricorn- The (imaginary) line around the Earth at 23.5 degrees south of the Equator.

Poles- The most northerly and southerly points of the Earth.

j Demonstrate an understanding of the drawbacks to astronomers of the Earth's atmosphere and relate these

to the need for optical and infra-red observatories to be sited on high mountains or in space.

The Earths atmosphere scatters some light coming in from outside, causing stars to twinkle, so that we

cannot take such good quality images from them, which is what makes the sky appear blue, so that

astronomers can no longer observe in the day. The atmosphere also prevents most types of things from theelectromagnetic spectrum from reaching ground level, so observatories have to be placed in space.

k Describe the features of reflecting and refracting telescopes (detailed ray diagrams are not needed).

Refracting telescopes work like a simple magnifying glass, the bigger the stronger, where as reflectors use

mirrors to bounce the light up and down, consequently magnifying it- the longer the telescope or the more

mirrors it has makes it have a better magnification here.


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l Demonstrate an understanding of why the world's largest telescopes are reflectors rather than refractors.

Refracting telescopes have to be bigger to be stronger, so if you want one ten times stronger, you must make a

lens ten times bigger, and a telescope for it to go in. However, reflecting telescopes can be made stronger

merely by inserting more mirrors, although making them longer makes them stronger too.

m Demonstrate an understanding that the Earth's atmosphere is transparent to visible light, microwaves and

some radio waves.

These can penetrate and pass through the Earths atmosphere because they are the longest of the

electromagnetic spectrum. Infra-red radiation is longer than visible light, but this is affected and absorbed by

water vapour and carbon dioxide, and consequently can only be detected from certain parts of the Earth.n Interpret data on the effect of the Earth's atmosphere on infra-red, ultra-violet and x-rays.

X-Ray: ROSAT Ultraviolet: ASTRO-2 Visible: Galileo Infrared: MSX Radio: NRAO/VLA

o Describe where infra-red, ultra-violet and x-ray observatories are sited and explain the reasons why.

Infrared, ultra violet and x-ray observatories are situated in space, so that the Earths atmosphere doesnt get in

the way and absorb/scatter the light.

p Describe the nature and discovery of the Van Allen Belts.

The Van Allen Belts are belts of radiation held in place by the Earth and its gravitational field. They are made of

billions of tiny particles, and are confined to where they are because of our atmosphere. There are two sections,

outer and inner, and whilst similar things have been found on other planets the term refers only to those around

the Earth.

1.2 The Moon

a Identify the Moon's principal features, including the Sea of Tranquillity, Ocean of Storms, Sea of Crisis, the

craters Tycho, Copernicus and Kepler, and the Apennine mountain range (Latin names are acceptable).

b Recall the Moon's diameter (3,500 km) and its approximate distance from Earth (380,000 km).

c Recall that the Moon's rotational period and orbital period are both 27.3 days.

d Demonstrate an understanding of why the far side of the Moon is not visible from Earth.

The moon spins on an axis, but much slower than the Earth, and only spins once every 27.32 days. As this is

roughly the same as the time it takes to orbit the Earth, only a little bit more than one side can ever be seen

from Earth.

e Describe how astronomers know the appearance of the Moon's far side and how it differs from the near side.

Astronomers first saw the far side of the moon when Apollo 8 flew round it in 1968, and when they took photos

of it. They found that the far side had next to no seas, and was almost all mountains and craters.

f Distinguish between the lunar seas (maria) and highlands (terrae).

Lunar seas are low, dark, flat patches of the moons surface, where as the highlands are very rugged and heavilycratered- whilst they have been bombarded the same amount by meteors over the years, the seas have since

been created over the top (see below).

g Demonstrate an understanding of the origin of lunar seas and craters.

Craters have been created over the years by different hitting the moon, but since many of these were formed

volcanoes have erupted on the moon. These caused massive lava flows, which while in liquid form flooded and
http://www.gb.nrao.edu/visitors/gbtour/radiomoon.jpghttp://antwrp.gsfc.nasa.gov/apod/ap970110.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap991222.htmlhttp://coolcosmos.ipac.caltech.edu/cosmic_classroom/multiwavelength_astronomy/multiwavelength_museum/images/moon_uv.gifhttp://wave.xray.mpe.mpg.de/rosat/publications/highlights/moon


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filled in much of the surrounding areas. These now look like large, flat, dark patches, which is how they became

known as seas.

h Demonstrate an understanding that the relative number of craters in the seas and highlands implies different

ages of these features.

The whole moon is likely to have been bombarded the same amount by meteors in total, yet the seas have

nowhere near as many craters as the highlands, which indicates that the seas were formed after the craters,

which were filled in.

i Describe the nature of rilles and wrinkle ridges.

Rilles on the moon are long trenches or grooves in the surface, thought to be caused by lava flows, where aswrinkle ridges are as a result of the forces from contracting and compressing lava causing the surface to buckle.

j Relate the lack of atmosphere to the Moon's low gravity.

The moon has no atmosphere because it is not massive enough to have enough gravity to stop it from escaping

back into space. The Earth is much more massive so it therefore escaped much more slowly, and the Earth is

also geologically active, so the moving rocks can help to replenish some of the lost gases.

k Describe the nature and purpose of the Apollo space programme and its experimental packages (ALSEPs).

The Apollo space program was designed to let the first humans go to the moon (achieved in 1969). The mission

left a range of experimental equipment designed to be operated from Earth, called ALSEPs, such as the LRRR to

measure distance from Earth, the Lunar Surface Magnetometer to measure the moons magnetic field, and the

ASE, to measure any seismic activity on the moon.

l Describe the likely origin of the Moon the giant impact hypothesis.The giant impact hypothesis suggests that a large object may have collided with the Earth when it was very

young, and when the surface had not completely solidified. It completely destroyed the object, but split the

Earth in two, to create the moon. Very soon after, the two objects took on their spherical shapes, and whilst the

moon remains in orbit of the Earth it is still very slowly moving away.

m Describe the evidence that allowed astronomers to develop the giant impact hypothesis.

Rocks on the moon are very similar or identical to those on Earth

The iron core of the Earth is very large, but the Earths is very small for its size

The moon was once closer to the Earth than it is now, suggesting that there may have been one collision

to form both

1.3 The Sun

a Demonstrate an understanding of how the Sun can be observed safely by amateur astronomers.

Special filters can be used to observe the Sun, but when used incorrectly can be just as dangerous as using

nothing. Therefore, the best way for amateur astronomers to observe it is to project an image through a

telescope onto a screen, or to cover part of the objective lens with some black card to reduce the amount of

light allowed to enter the telescope.

b Recall the Sun's diameter (1.4 million km) and its distance from Earth (150 million km).

c Recall the temperature of the Sun's photosphere (5,800 K).

d Describe the solar atmosphere (chromosphere and corona) and recall the approximate temperature of the

corona (2 million K).

As we move towards the outer edge of the chromosphere, it becomes less dense but also much hotter. It is inthis layer that Sunspots and granulation occur. The corona is most easily visible in an eclipse, and extends a long

way away from the Sun- in coronal mass ejections (cmEs) sometimes even as far as Earth. The corona is best

viewed in x-ray form, as it is much hotter than the chromo and photospheres.

e Describe the appearance and explain the nature of Sunspots.

Sunspots are cooler regions of the Sun (4000K not 6000K), which is what makes them look a lot darker against

the bright background of the hotter surface. They normally come in pairs, and have an umbra (the coolest

region) and penumbra (next coolest), as well as the normal granulations of the Sun around them.

f Recall that the Sun's rotation period varies from 25 days at the equator to 36 days at its poles.

g Demonstrate an understanding of how astronomers use observations of Sunspots to determine the Sun's

rotation period.

Astronomers assume that Sunspots stay on the same part of the Sun as it turns. They can therefore map the

progress of how far one particular Sunspot has moved around hour by hour, and therefore determine how long

different areas of the Sun take to rotate.

h Interpret data (for example a Butterfly Diagram) in order to describe the long-term latitude drift of Sunspots,

determine the length of the solar cycle and predict the year of the next solar maximum.

The butterfly diagram consists mostly of the same pattern repeated over and over. We can see that this


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happens about once every eleven years, which is known as a solar cycle, and also that the last solar maximum

was in about 2000, so that we can expect the next one in 2011. As the diagram also shows the latitudes at which

the Sunspots appear, we can see that they are slowly getting further away from the solar equator and less dense

in the middle.

i Demonstrate an understanding that the Sun's energy is generated by nuclear fusion reactions at its core,

converting hydrogen into helium.

The incredible heat created by nuclear reactions in the core of the Sun caused hydrogen atoms to fuse together

into helium atoms. While this is being done, four million tonnes of matter is lost every second, in the forms of

more light and heat energy that we expect from the Sun.j Describe how astronomers observe the Sun at different wavelengths.

Astronomers can observe the Sun at different wavelengths with things like h-alpha or x-ray filters on their

telescopes. Alternatively, for things like infra-red, they need special telescopes on high mountains in order to view

it. For safe methods of viewing on visible wavelengths, see 1.3a.

k Demonstrate an understanding of the appearance of the Sun at different wavelengths of the electromagnetic

spectrum, including visible, H-alpha and x-ray.

H-alpha filters help us to see prominences (cooler clouds), filaments (see prominences), Sunspots and the

chromosphere. X-ray images allow us to see which areas of the Sun are the hottest, as well as things like coronal

mass ejections which extend outside the main shape of the Sun. Visible wavelengths are the once we are all

familiar with, and when we use safe methods of observation we can do things like spot Sunspots, filaments or

prominences, though less clearly than with h-alpha.l Describe the structure and nature of the solar wind.

Solar wind is a stream of charged particles which flow from the solar corona, being able to escape the Suns

gravity mostly because of the intense temperatures of the corona, as well as other mechanisms. Other, faster

solar wind comes from coronal holes (cooler regions towards the poles of the Sun), where particles can escape at

speeds up to 850km/s (instead of 400km/s).

1.4 Earth-Moon-Sun Interactions

a Demonstrate an understanding that the Moon and Sun appear to be the same size when viewed from Earth.

The moon is about one four hundredth of the size of the Sun, but by coincidence it is also one four hundredth of

the average distance away from us as the Sun. Therefore the two appear to be the same size when viewed from

Earth.

b Recall the period of the lunar phase cycle (29.5 days).

c Demonstrate an understanding of lunar phases and deduce the lunar phase cycle from given data.

The moon has eight phases, with a full moon, then three waning (getting smaller) phases, then a new moon, then

three waxing (getting bigger) phases, before returning to a full moon again 29.5 says later. The phases in between

are waxing/waning gibbous, first/last quarter and waxing/waning crescent, working away from the full moon.

d Use diagrams to explain why the lunar phase cycle is (29.5 days) longer than the orbit period of the Moon.


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Above, we see that during the moons orbit of the Earth, the Earth has moved significantly in its own orbit of the

Sun, so the Moon therefore has further to travel to reach the same point, rather like the sidereal and solar days.

e Describe the appearance of partial and total solar and lunar eclipses.

Solar eclipses are when the moon obscures the Sun in a particular area for a short period of time. The areas with

no light at all are in the umbra (a total solar eclipse), but there is a much bigger area of land or sea where the Sun

is only partly obscured (a partial solar eclipse). Lunar eclipses are where the Earth blocks all light from getting to

the moon, and these are usually total, as the Earth is bigger than the Moon. We can still see the moon here

because of light reflecting from the Earth, and it appears as a copper colour.

f Describe, using diagrams, the mechanisms causing solar and lunar eclipses.

g Demonstrate an understanding that the duration of total solar and lunar eclipses are different and that they do

not occur every new and full Moon.

Eclipses do not occur every new and full Moon because the plane of orbit of the moon around the Earth is tilted

slightly (at about 5) to that of the Earth around the Sun. Therefore, it is only once every so many months that the

Sun, Earth and Moon are all in exactly the right positions for an eclipse. They also last for different amounts of

time to each other, because the Moon is not always the same distance from the Earth, and the Earth is not always

the same distance from the Sun. The longest total solar eclipse is 7m40s.

h Describe the terms 'solar day' and 'sidereal day'.

See below.

i Explain why a solar day is longer than a sidereal day.

A sidereal day is how long the Earth takes to do one complete turn on its axis. However, as in this time the Earthhas done a bit more in its orbit of the Sun, it takes an extra four minutes to turn so that the point that was facing

the Sun at the beginning of the day is facing it again. With this time added on, we get the solar day. Even then it is

not always the same length, so the 24 hours we use is mean solar day.

j Interpret simple shadow stick data to determine local noon and observer's longitude.

Local noon can be calculated by taking the lengths of shadow cast by a stick every few minutes for a period of

time, and the smallest is the closest to local noon. Longitude can then be calculated by taking or adding EOT to

the time, and then we find the difference between our time and 12:00, i.e. the local noon at Greenwich. When we

divide this by four, as we rotate a degree every four minutes around the Sun, then we know how many degrees

we are away from Greenwich in longitude. If we have noon later, we must be west, and if it is earlier, we are east

of the Meridian.

k Describe how a Sundial can be used to determine time.A Sundial is a stick on an angle of 23.5 (the tilt of the Earth), which is surrounded by a series of notches or lines

showing where the shadow will fall at different times of the day. Therefore, we can come at any time when the

Sun is up and see what time it is, although a Sundial is already corrected for EOT, unlike standard clocks.

l Interpret charts and diagrams showing the variation in daylight length during a year.


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m Demonstrate an understanding that there are seasonal variations in the rising and setting of the Sun.

There are seasonal variations in the rising and setting of the Sun because our orbit is slightly elliptical, so not in a

completely round circle. Also, the Earth is on a tilt to its plane of orbit, causing the Sun to appear higher in the sky

in summer to in winter.

n Demonstrate an understanding of the terms 'apparent Sun' and 'mean Sun'.

The apparent solar time is time corrected for EOT (Apparent solar time- mean solar time), which gets us the exact

time according to the Sun. However, in order to make clocks and other ways of telling the time quickly and easily

we standardise it, saying that each day is exactly twenty-four hours long, and therefore end up with a mean solar

time.

o Demonstrate an understanding of the term 'equation of time' (apparent solar time - mean solar time) and

perform simple calculations.

p Describe aurorae and recall from where on Earth they are most likely to be observed.

Aurorae are usually visible from between 65 and 70 degrees latitude (north or south) at night. They appear to

come in different colours, caused by different gases, with oxygen creating a green or brown effect and nitrogen a

blue or red one.

q Explain how aurorae are caused.

Aurorae are caused by the collision of charged particles from the Earths and Suns magneticfields. The charged

articles from the Sun hit our field and stretch or distort, then come off and speed towards the poles, creating the

aurora effect. The effect also occurs near the poles of Jupiter and Saturn, where the magnetic fields are alsostrong.

2.1 Our Solar System

a Describe the location and nature of the main constituents of our Solar System, including planets, dwarf planets,

asteroids, comets, centaurs and trans Neptune Objects (TNOs).

Planets: four of these are rocky, and four gas giants.

Dwarf planets: these are smaller than normal planets, and include Ceres, Pluto and Eris.

Asteroids: these are rocks between 10 and 400m in diameter, most of which are in the asteroid belt

between Mars and Jupiter. They include Vesta and Pallas.

Comets: these have a nucleus of ice, rock and dust, and they orbit the Sun either parabolically or

hyperbolically. They have gassy tails when close to the Sun.b Recall the names of planets and dwarf planets in order of their mean distance from the Sun.

Planets (in order): Mercury, Venus, Earth, Mars, Jupiter, Saturn, Neptune, Uranus

Dwarf Planets (NOT in order): Ceres, Pluto, Haumea, Makemake, Eris, and possibly Sedna.

c Demonstrate an understanding of the scale and size of our Solar System using scale models (for example balls

of different sizes at appropriate spacing, model Solar Systems such as the Spaced Out project).

d Recall that the ecliptic is the plane of the Earth's orbit around the Sun.


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e Demonstrate an understanding that one astronomical unit (AU) is the mean distance between the Earth and

Sun.

One AU is about 150 million kilometres in distance. As an example, Jupiter orbits the Sun at about 5.2AU on

average, meaning that it is 5.2x further away than us.

f Recall that planets move in elliptical orbits, slightly inclined to the ecliptic.

g Demonstrate an understanding that the planets appear to move within the band called the zodiac.

A band of the celestial sphere extending about 8 to either side of the ecliptic that represents the path of the

principal planets, the moon, and the Sun. It passes through twelve constellations, which is how we get the

astrological signs of the zodiac.h Demonstrate an understanding of the direct and retrograde motion of planets on a star chart.

Direct motion is the way that planets usually move across the sky, in the same direction as the stars, or forwards.

However, occasionally they appear to go backwards as the Earth overtakes them for a short period of time- see

diagram. This can only happen to exterior planets to the Earth.

i Demonstrate an understanding of the terms: perihelion, aphelion, greatest elongation, conjunction, opposition,

transit and occultation.

Perihelion- when an orbit is at its closest to the Sun.

Aphelion- when an orbit is at its furthest from the Sun.

Elongation- the angle between the Sun and a planet when viewed from Earth (only Mercury and Venus). The

greatest elongations are how big the angles are at their biggest.

Conjunction- When a planet is along the same line of sight as the Sun. Only the Mercury and Venus can be at

inferior or superior conjunction on either side of the Sun from us.Opposition- When the Earth is directly in between the Sun and an exterior planet.

Transit- When an interior planet passes across the Suns disc when viewed from Earth.

Occultation- When distant objects are obscured by nearer ones such as the exterior planets.

j Describe the main physical characteristics of the planets (including surface features, atmosphere, temperature

and composition).

Planet Mean distance

from the Sun

(AU)

Orbital period

(Earth years)

Average

temperature

(C)

Diameter

(1000km)

Rotation

period (Earth

days)

Mercury 0.38 0.24 170 4.9 59

Venus 0.72 0.62 470 12.1 243

Earth 1.00 1.00 15 12.8 1.00Mars 1.5 1.9 -50 6.8 1.00

Jupiter 5.2 11.9 -150 143 0.41

Saturn 9.5 29.5 -180 121 0.43

Uranus 19.1 84 -210 51 0.72

Neptune 30.0 165 -220 50 0.67

k Discuss how the atmosphere of Venus can be used to gain data on the danger of extreme global warming.

The atmosphere on Venus includes huge clouds of sulphur and carbon dioxide, which keep infra-red radiation

from the Sun in to bounce back and forth, making the surface temperature get hotter and hotter. This is known as

the runaway greenhouse effect and the worry is that one day ours may get this bad.

l Describe how astronomers use space probes to gain data on the characteristics of planets and other bodies in

the Solar System.There are four types of space probe that help exploration; flybys, orbiters, landers and rovers. The most famous

ones to conduct flybys are American Pioneers 10 and 11 in 1973 and 1979, which sent us pictures of Jupiter and

Saturn, and also Voyagers 1 and 2, which are still going deeper into the Kuiper Belt having sent through pictures

of Saturn, Uranus and Neptune. Orbiters are usually unmanned, and as the name suggests orbit bodies, sending

back more detailed pictures and information about weather and composition- the best were Galileo in 1995 with


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Jupiter and Cassini-Huygens in 2004 with Saturn. Landers take more close-up photos of surfaces while looking for

water and/or life for example Venera 3 in 1966 with Venus, Mariner 9 in 1971 with Mars, and Luna 2 to the Moon

in 1959. Finally there are Rovers, which are robotic missions designed to explore surface features- Apollo 15, 16

and 17 left these on the Moon in 1971 and 1972, and in 2003 Spirit and Opportunity were sent to explore Mars,

of which one is still working to send us information.

m Demonstrate an understanding of some of the problems that would be encountered by a manned exploration

of our Solar System.

Astronauts must live in conditions with no apparent up or down, no gravity and a risk of radiation from the Sun

for months at a time, not to mention the psychological strain of living and working in a tiny space with the samepeople, with limited and delayed communications to Earth. They can suffer from, among other things, Space

Adaptation Syndrome, brittle bones, muscle fatigue, low red blood cell counts, radiation sickness and just general

mental illness whilst in space.

n Demonstrate an understanding that some planets have satellite systems with a variety of origins and structures

(including Mars and Neptune).

Mars has two very small moons called Deimos and Phobos, which have very similar compositions to asteroids, are

heavily cratered and irregular in shape. This leads us to believe that they once were asteroids, captured by the

planets gravitational field at some point in the past. Neptune also has several unusual moons- Triton, which is the

only large one in the solar system to go around its planet in the opposite direction to how it spins, Nereid, most

likely a captured KBO due to its highly eccentric orbit, and Dark Proteus, the second largest moon in the solar

system which orbits extremely closely to Neptune itself.o Describe the appearance, physical nature and composition of planetary ring systems.

All four gas giants of Saturn, Neptune, Uranus and Jupiter have ring systems, although Saturns are by far the

most visible and the most famous. The exact compositions vary- Saturn has icy, reflective rings while Jupiters are

dusty and dark- they all contain billions of particles of ice, rock and dust which vary hugely in size. They can be

hundreds of thousands of kilometres wide, but less than 1.5km thick, with a lot of gaps in the structures. It is

unknown where they came from but, it seems probable that they are made from debris left over from planet

formation.

2.2 Comets and Meteors

a Describe cometary orbits and distinguish them from planetary orbits.

Comet orbits are highly elliptical, taking a long time- short period comets up to 200 years (aphelion being beyondNeptune, so they are scattered disc objects or KBOs), or into the thousands for long ones (believed to originate in

the Oort Cloud). Single apparition comets have para- or hyperbolic orbits.

b Describe the location and nature of the Kuiper Belt and Oort Cloud and show an appreciation of their

association with comets.

The Kuiper Belt is the region of the solar system between the orbit of Neptune (30AU) and 55AU. There are more

than 1000 known objects, which are usually methane, water or ammonia ices. KBOs include Pluto, Haumea and

Makemake, and it is believed than the Neptunian moon Triton and Saturns Phoebe were once KBOs. The Oort

Cloud is a spherical cloud of comets found at around 50000AU, several trillion of which are more than 1km in

diameter and which surrounds the solar system. Both the Kuiper Belt and Oort Cloud are believed to contain

objects left over from the formation of the Solar System, as does the Scattered Disc, which lies between them.

c Describe some of the evidence for the existence of the Oort Cloud.There is not yet any direct evidence for the existence of the Oort Cloud, but there is nothing yet to go against the

theory, and it helps to explain things like galactic tides and long period comets.

d Identify the nucleus, coma, dust and ion tails of comets.

e Demonstrate an understanding that the tails of comets develop when relatively close to the Sun.

The dust tails of comets are formed from solar wind having blown bits away from the nucleus, and these continue

to be gravitationally related to the nucleus, so follow it. The ion tail is most affected by solar wind, so always faces


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away from the Sun. After about 500 orbits all ice is knocked or blown off, so that a rocky core is all that remains of

the comet.

f Demonstrate an understanding of the mechanisms for the development of cometary dust and ion tails.

See above.

g Describe the nature and origin of meteoroids, meteorites and micrometeorites.

Meteoroid- a sand to boulder sized particle of debris in the solar system.

Meteor- a meteoroid which has entered our atmosphere, heated up and become visible.

Meteorite- a meteor which reaches the surface of the Earth.

Micrometeorite- a very small meteorite (less than a gram). h Demonstrate an understanding of meteors, fireballs and annual meteor showers.

Fireballs are meteors, but get their name from being slightly brighter than the usual ones, and can be up to -4 in

magnitude- brighter than some planets. Meteor showers occur when the Earths orbit crosses regions in areas

where there are large clusters of meteoroids, and in places this happens annually. These are named after the

constellation in which they are found, for example the Geminids or Orionids.

i Relate the occurrence of annual meteor showers to cometary orbits and account for their apparent divergence

from a radiant point.

When the Earth passes through the tail of a comet bits enter the atmosphere, and burn as they do so. These are

known as meteors and meteorites, or shooting stars in general. In some parts of the solar system more dust has

been left from passing comets than others, and when we pass through these then we get more than usual, known

as meteor showers.j Describe the orbits of Potentially Hazardous Objects (PHOs).

PHOs, or Potentially Hazardous Objects, are asteroids or comets with diameters of more than 150m that come

within 0.05AU of the Earth- in other words big enough to do serious damage in the case of an impact. They can

have any orbit, but usually parabolic or hyperbolic.

k Demonstrate an appreciation of the need to monitor the motion of PHOs.

PHOs need to be monitored for the sheer amount of damage that they could do to the Earth, although as yet

there is nothing we can do to stop them. Currently, there are over 1000 known PHOs, the most worrying of which

is Apophis; this will have a close approach to the Earth in 2029, and although it wont actually hit us then, we have

no way of knowing what the affect of our gravitational field will be, or if it will return several years later. In other

places, Venus spinning the wrong way and Uranus having a tilt of almost 90 could both be caused by collisions.

l Demonstrate an appreciation of the potential consequences of a collision between an impactor and the Earth.Obviously a PHO would kill any people which it happened to land on, but it could cause the same amount or more

if it were to land in the sea or desert, by beginning a dust storm or tsunami. If the object was large enough then

the Sun could even be blocked out, making an area uninhabitable, or the Earth could be knocked off course. There

is a one in 10000 chance that one could wipe out human civilisation completely.

m Describe how astronomers gather evidence of impacts between bodies within the Solar System and consider

their effects.

See 2.2k.

2.3 Solar System Discoveries

a Describe the contribution of Copernicus, Tycho and Kepler to our understanding of the Solar System.

Copernicus was the first person to suggest that we orbited the Sun rather than the other way around, a model

that had been accepted since Ptolemy and the Ancient Greeks. This model, among other things, explained

retrograde motion. However he was reluctant to publish the book and finally did so when he was on his

deathbed. In the late 16th

Century this was becoming more widely accepted and Tycho made more detailed notes

than ever before on the skies from an observatory on a secluded island. When he died, his assistant Kepler used

the notes to formulate the laws of planetary motion.

b Illustrate Kepler's second law of planetary motion with the aid of a diagram.

c Demonstrate an understanding of Kepler's third law relating planetary distances to orbital periods and perform


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simple calculations using the formula T2= R

3,where T is in years and R is in AU.

d Recall the main astronomical discoveries of Galileo related to the Solar System:

i) phases and apparent size of Venus.

ii) Relief features of the Moon.

iii) Principal satellites of Jupiter (Callisto, Europa, Ganymede and Io).

e Describe the discoveries of Ceres, Uranus, Neptune and Pluto and the techniques involved.

Ceres(and other asteroids)- Discovered by Giuseppe Piazzi in 1801, who found that it moved across the sky over a

long period of time between the orbits of Mars and Jupiter.

Uranus- Discovered by William Hershel in 1781, who thought that it was too big to be a star and moved over aperiod of several nights. He contacted other astronomers thinking it was a comet, but as it had no tail and grew

no larger or smaller it was decided to be a planet. Named after King George, but the German name of Uranus

later became more widely used.

Neptune- Uranus had an unusual orbit, suggesting the existence of another planted. John Adams made

predictions in 1845 as to where it may be, but was not taken seriously; however, the next year when Urbain

Leverrier independently calculated the same thing, Joham Galle in Berlin looked for it, and found it within a day of

trying. Credit is given jointly to Adams and Leverrier jointly. Named after God of the Sea.

Pluto- The unusual orbit of Uranus was still not explained, and Percival Lowell predicted where another planet

may be found. In 1930, when there were better telescopes and cameras, Clyde Tombaugh discovered and named

Pluto after God of the Underworld.

f Demonstrate an understanding that gravity is the force responsible for maintaining orbits and its inversesquare law.

The inverse square law means that if a small object is double the distance away from a larger one, then there is

half the amount of gravity affecting it, if it is four times then there is an eighth, and so on. Planets are held in

place by gravity, which is also responsible for things like everything falling to the ground when dropped- every

mass has some amount of gravity, including humans.

2.4 Exoplanets

a Describe how astronomers obtain evidence for the existence of exoplanets (including astrometry, transit

observations and use of Doppler-shifts).

The transit method- This relies on the fact that when a planet passes between us and another star then the

brightness of that star will decrease for the duration of the transit.Astrometry- The gravitational influence of a planet causes its star to wobble towards the common centre of

mass, although as stars appear to constantly change position in the sky then this can be difficult to detect.

Doppler shifts- These can be used to detect astrometry motion, by light appearing to be blue-shifted when the

star is moving towards us, and red when moving away, or other colours in between; speed can also be calculated.

b Discuss the difficulties associated with the detection of individual planets.

With all of the above methods size is a big problem; even Jupiter is only 9x10^-9 times as bright as the Sun, so we

can imagine what a tiny difference a transit would make. With the other two, it takes a huge planet to create a

wobble big enough for us to notice, especially since we cannot be watching every star at any one time.

c Demonstrate an understanding that the presence of liquid water is probably an essential requirement for life.

Water can come as a solid, liquid or gas, but only in its liquid form is it considered essential to life. Every plant or

animal is known to need water to survive, which is probably because of it being able to dissolve anything in someform. It also transports many nutrients, and makes hydrolysis and photosynthesis occur.

d Describe the present theories about the origin of water on Earth.

It is really unknown about how water originated on Earth to such an extent as it did, but we think that it was

partly from the melting of ice from comets landing, and also from the out-gassing of hydrogen and oxygen from

erupting volcanoes which then combine to make it. Ice is not uncommon as we journey further out into the solar

system, but only Earth is in the small zone where it can exist as a liquid.

e Describe methods used by astronomers to determine the origin of water on Earth (for example analysis of

water on a comet by the Rosetta probe).

Although it is not done by astronomers specifically, scientists often drill into the Earth to record from ice cores

how the Earths atmosphere has evolved over time. This can give us some clues, as can the study o f what

elements Earth has that other objects in the solar system does not. The Rosetta probe is also analysing the

composition of a comet, and will give us more information about the ice in there.

f Demonstrate an understanding of the individual factors contained in the Drake Equation and their implications

for the existence of life elsewhere in our Galaxy.


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g Demonstrate an understanding of the existence and significance of habitable zones/Goldilocks zones.

The golden zone is the distance away from each star where water can exist in liquid form, i.e. which could

potentially be habitable if other conditions were right.

h Describe some of the methods that astronomers use to obtain evidence for life (past or present) elsewhere inour Solar System.

There are several different research centres around the world dedicated to finding alien life- when pulsar stars

were first discovered scientists thought that the interference could be alien signals. There are lots of science

fiction films exploring the concept, and we are always on the lookout; the Voyager space probe, for example,

contained a plaque with a picture of humans and a diagram showing where Earth was, in case it should ever be

picked up by an alien lifeform when the probe went out into space.

i Discuss the possible benefits and angers of discovering extra-terrestrial life.

Whilst it might be exciting to think that we may not be alone in the Universe, do we really want to find out that

we arent? Could we be wiped out by other, better evolved creatures than ourselves? What would we do if we did

find other lifeforms? We really do not know, and it is yet another moral quandary for astronomers, as it would

certainly help to refine our understanding of the Universe, and be one of the greatest discoveries of all time.

3.1 Constellations

a Describe the appearance of stars, double stars, asterisms, constellations, open clusters, nebulae and globular

clusters in the night sky.

Nebulae- A cloud of gas or dust in space, which can be several light years across, or the size of 100,000 Suns. Some

can be where new stars are forming, others where stars are dying. They can also be stars in another galaxy, which to

us are only a light haze.

Star- A fixed luminous point in the night sky that is a large, remote incandescent body like the Sun.

Double Star- Two stars optically very close together, but which are not gravitationally related.

Asterism- A prominent pattern or group of stars, typically having a popular name but smaller than a constellation

Constellation- A group of stars forming a pattern that is traditionally named after its apparent form or identified with

a mythological figure, or areas of the sky, of which there are 88. Are not gravitationally related, and can physically be

hundreds of light years away from each other.

Open cluster- A group of stars formed from the same cloud, which are consequently fairly close to each other and

have roughly the same age.

Globular cluster- A collection of stars which orbit a galactic core spherically, tightly bound gravitationally.


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b Demonstrate an understanding of how stars within a constellation are labelled according to brightness (using

Greek a (alpha) to e (eta)).

Stars in constellations are measured in order of brightness, and are given letters from the Greek alphabet, with alpha

being the brightest. The following are the upper and lower case letters and names of the Greek alphabet:

c Demonstrate an awareness of how the official list of constellations became established and cultural differences in

this list.

The first list of constellations was published in 150AD by Ptolemy in Egypt, which was based on Ancient Greek

astronomy. Names probably date back to shepherds as far back as 2000BC, who used them navigationally and

named them after heroes in stories, eg Perseus or Andromeda. Since then, 16 southern ones were added by the

Dutch in the 16th

century along with another three for the northern hemisphere, and the final eleven were to fill up

the gaps in the sky by a Polish astronomer (Johannes Hevelius) a century later.

d Recognise and draw the Plough, Orion, Cygnus and Cassiopeia.

Ursa Major: Orion:

Cassiopeia: Cygnus and Lyra:

e Demonstrate the use of 'pointers' and other techniques to find other celestial objects, including:

i) Arcturus and Polaris from the Plough.


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ii) Sirius, Aldebaran and the Pleiades from Orion.

iii) Fomalhaut and the Andromeda Galaxy from the Great Square of Pegasus.

f Demonstrate an understanding that some constellations are visible from a given latitude throughout the year, butothers are seasonal.

Whilst from the same latitude there are the same constellations all year round, as we travel around the Sun the

times of day change, meaning that not all are in night-time hours. However, a few are circumpolar, meaning that

they are sufficiently far north to the Earth that they never set, and are always above us in the night sky when

viewed from the northern hemisphere on a clear night.

3.2 Observing the Night Sky

a Demonstrate an understanding of the terms 'right ascension' and 'declination'.

Right ascension- The equivalent of longitude in the sky. It is measures in hours, minutes and seconds- 24 hours is

360 degrees, so one hour is 15.

Declination- A north-south co-ordinate like latitude. Measured in degrees from celestial equator, symbol .

b Recall the declination of Polaris (+90 degrees) and explain why Polaris appears fixed in the night sky.

Polaris appears to be fixed in the night sky because it is as close to due north as we can get. For this reason, the

Earth spins on its axis, but because it is always above the Earth (as seen by us) it never seems to move.

c Demonstrate an understanding that the elevation of Polaris above the northern horizon is equal to the latitude

of the observer.

d Describe what is meant by the terms 'circumpolar stars' and explain the connection between the apparent

motion of stars and the Earth's rotation.

Circumpolar stars are those with a greater declination than 90 degrees minus your latitude, meaning that they are

in the night sky all year round when viewed from that place. As a night goes on, the sky appears to move in an east-

westerly motion- really, it is us that it is moving, and we rotate in the opposite direction to this when looking downon the Earth.

e Demonstrate an understanding that a star will be circumpolar from a given latitude provided declination is 90 -

latitude.

See above.


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f Analyse and interpret long exposure photographs of star trails to determine the rotation period of the Earth.

To the left is an example of long exposure photography of stars, which can help to

determine the rotational period of the Earth by using the below formula:

g Demonstrate the use of a planisphere, star chart or computer software in order to plan an observing session.

h Demonstrate an understanding of the terms 'ecliptic' and 'zodiacal band' on a star chart.

The ecliptic is the line which appears to be traced by the Sun and planets each year, passing through twelve

constellations, or the signs of the zodiac- traditionally, star signs show where the Sun was when we were born, but

as the Earth has changed this has become out of sync. The ecliptic is at a 23.5 degree angle to the celestial equator,

as this is how much the Earths axis is tilted by, thus the declination of the Sun varies from +23.5 (when it is directly

overhead for people on the tropic of cancer) to -23.5 (when it is directly overhead for people on the tropic of

Capricorn) throughout the year.

i Plan equipment needed for a naked-eye observation session (red torch, clipboard, pencil/rubber, warm clothes).

j Demonstrate an awareness of naked-eye observing techniques (dark adapted eye, relaxed eye and averted

vision).

Dark adapted eye- allowing the eyes to become completely sensitive to light (i.e. for about twenty or thirtyminutes) before making observations; red filters do not harm this.

Relaxed eye- closing one eye for a long period of time can become uncomfortable when looking through

telescopes, but after a while with both eyes open you will only begin to see out of the one you want, and will see

much more through being relaxed.

Averted eye- looking directly at a very faint object might not work, but by looking slightly to the side we see more in

black and white, and can therefore pick up fainter objects better.

k Demonstrate an awareness of, and use in a qualitative way, the Messier Catalogue.

The Messier catalogue was published by Charles Messier in 1781, and is a list of over a hundred nebulae and star

clusters so that they would not become confused with things like comets, which move. They were given numbers,

for example the Andromeda Galaxy is M31.

l Explain the apparent east-west motion of the night sky.As the Earth spins the sky appears to move as well, in the opposite direction (related to the occasional retrograde

motionof other planets). Consequently, everything moves east-westerly across the night sky, at a rate of one

degree every four minutes.

m Recall that stars cross the observer's meridian and culminate when they are due south.

n Use star data and charts to determine the time at which a star will cross the meridian.

Below is a chart for the Sun, with the red line being the ecliptic; it appears wavy as we are putting a three

dimensional sky onto a two dimensional piece of paper. As we move around the Sun, it appears to move, and the

chart shows at what declination we would expect to find it at different times of the year.

3.3 Physical Properties of Stars

a Demonstrate an understanding that stars in a constellation are not physically related but that stars in a cluster

are associated gravitationally.Constellations are areas of the sky, and are usually recognisable by a particular pattern or shape that the stars

appear to form. However, they are not linked in any other way, and could be light years apart physically, only

appearing together when viewed from Earth. On the other hand, stars in a cluster were formed together, are very

near to each other and orbit a common centre of mass.

b Distinguish between optical double stars and binary stars.


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Optical double star- two stars that are close together when seen projected on the sky, but which are not

gravitationally linked.

Binary star- two stars that are (physically) so close together that they orbit a common centre of mass, i.e. are

gravitationally linked.

c Demonstrate an understanding of the apparent magnitude scale and how it relates to observed brightness of

stars.

This is the brightness that a star or object appears to be to an Earth-based observer. Depends on things such as

distance, luminosity, dust between us and the star and the amount of light absorbed by our atmosphere. A

magnitude one star is a hundred times brighter than a magnitude six star, and this means that an decrease of onemagnitude means that it becomes 2.152 times brighter (or 2.5 in exams).

d Use the scale of apparent magnitude.

e Describe the method of heliocentric parallax to determine distances to nearby stars.

Parallax is the method by which we observe stars from two different positions; we then take the angle that it

appears to have moved relative to very distant objects to find the distance, using trigonometry.

f Recall the definition of one parsec (pc).

Parsec- the distance at which a star has parallax of 1. Equal to 3.26 light years.

g Recall the definition of absolute magnitude.

The magnitude of an object as it would be seen at a standard distance of 10 parsecs.

h Demonstrate an understanding of the Universe square law nature of the intensity of light.

As with gravity, the inverse square law applies to light intensity, or brightness. For example, if we double thedistance between us and a star, the star will appear to be a quarter of its original brightness.

i Demonstrate an understanding of, and perform simple calculations involving, apparent magnitude (m), absolute

magnitude (M) and distance (d in parsecs) using this formula:

M=m + 5 - 5log d

involving powers of 10 parsecs only (students are not required to calculate d using this equation only M and m ).

j Identify a Cepheid variable star from its light curve and deduce its period.

Cepheid variables are very unstable; the star is small with concentrated

light mass in the middle, until pressure forces it out again at very high

speeds. Gravity and pressure balance out eventually, but the star keeps

going, until gravity becomes larger than pressure and it contracts again.

This continues until energy runs out, meanwhile the star gets brighter and

dimmer as it pulsates, due to luminosity being based on both radius and

temperature.

k Explain how Cepheid variables can be used to determine distance.

Henrietta Leavitt found a relationship between pulsation period and mean absolute magnitude in 1912, now known

as the period-luminosity law. This allows astronomers to work out absolute magnitude from a star period, and

combined with apparent magnitude distances can be calculated.

l Identify a binary star from the light curve and deduce its period.

Binary stars are two stars which orbit a common centre of mass, so aregravitationally related. If they are on our plane, this means that they

appear to eclipse each other, as shown in the diagram.

m Explain the causes of variability in the light curve of a binary star.

Binary stars are two stars which orbit a common centre of mass, so are gravitationally related. If they are on ourplane, this means that they appear to eclipse each other, as shown in the diagram.

n Demonstrate an understanding of what information can be obtained from a spectrum, including chemical

composition, temperature and radial velocity.

Stars can be classified according to their spectrum shape, and are given letters from the following sequence: O B A

F G A K M (Oh Be A Fine Guy And Kiss Me). O is the hottest with M the coolest, and this is also linked to the size of


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the star. Within these categories there are smaller ones, for example with numbers and roman numerals.

o Demonstrate an understanding of how stars can be classified according to their spectral type.

See above.

p Demonstrate an understanding that a star's colour is related to its temperature.

As can be seen in the diagram, the stars heat relates to wavelength, meaning that the colour appears to change

according to temperature and light intensity. This is also shown on Hertzsprung-Russell diagrams.

q Sketch and recognise the main components of the

Hertzsprung-Russell diagram (HR diagram).

(See left).

3.4 Evolution of Stars

a Associate the stages of evolution of a star:

i) with a solar mass

ii) with a much greater mass

with the components of the HR diagram.Stars evolve like anything else, but it depends on their original

mass as to what they evolve to (see diagram). Our Sun is

following the top cycle, whereas something like Sirius would

be the bottom one, to become a black hole or neutron star.

b Demonstrate an understanding that emission nebulae, absorption nebulae and open clusters are associated with

the birth of stars.

An emission nebula is an ionised gas cloud (mostly hydrogen, helium and dust) which has been excited by a nearby

star, causing it to emit a wide range of visible and ultraviolet radiation. These collapse until the core begins to heat,

converting PE into KE; when nuclear fusion begins it becomes a star. Alternatively, an absorption nebula is the

opposite, absorbing all other radiation. Open clusters usually come from emission nebulae, and are areas of stars

formed from the same cloud, so which are roughly the same age.

c Demonstrate an understanding that planetary nebulae and supernovae are associated with the death of stars.

Planetary nebulae form when a red giant or supergiant run out of helium to convert to carbon, having been doing

this to replace hydrogen. These become expanding clouds of gas, which either cool to white dwarfs or begin to

form a new star. If the original star was more than 1.5 times as massive as the Sun a supernova is formed, followed

by a neutron star or black hole.

d Describe the nature of neutron stars and black holes.

Neutron stars (or pulsars, due to the bursts of intense radio waves which they emit) are very rapidly rotating

objects with huge magnetic fields, formed when a supergiant had mass of over 1.5 times that of the Sun- they still

have this, but contained in an area with only a 20km diameter. If they had three or four times solar mass a black

hole is formed- these absorb everything, and not even light has speed enough to get out of it, meaning that they

cannot be seen. However, the high mass causes disturbance in the surrounding area, so they can be detected.

e Describe how astronomers obtain evidence for the existence of neutron stars and black holes.

These can be detected due to the high masses, and also the intense bursts of radio waves which pulsars emit.

4.1 Our Galaxy - the Milky Way


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a Describe the appearance of the Milky Way as seen with the naked eye and binoculars or a small telescope.

From Earth, the Milky Way looks like a cloudy band across the sky, from which light is being

emitted. It is widest and brightest in the middle, appearing to run through constellations such as

Cassiopeia, Cygnus and the edge of Orion. With the aid of a small telescope or binoculars we

can see the thousands of individual stars in there.

b Demonstrate an understanding that the observed Milky Way forms the plane of our own Galaxy.

We are on the edge of a spiral or spiral bar galaxy, looking into the centre- this is why it appears brightest here

when viewed from Earth. We are unable to see the other side of the galaxy, so can only guess what it looks like.

c Demonstrate an understanding of the size and shape of our Galaxy and the location of the Sun, dust, sites of starformation and globular clusters.

d Demonstrate an understanding of how astronomers use 21 cm radio waves rather than visible light to determine

the rotation of our Galaxy.

The nature of dust in our spiral arms means that we are unable to actually see them. However, radio waves can

penetrate them, so we can detect them using these; the waves become Doppler shifted, and the changes in length

can help us to determine radio velocities, to attain how different parts of the galaxy rotate.

4.2 Galaxiesa Demonstrate an understanding of the appearance of spiral, barred spiral, elliptical and irregular galaxies.

Spiral Galaxy Barred Spiral Galaxy Elliptical Galaxy Irregular Galaxy The Milky Way!

b Draw Hubble's tuning fork diagram.

c Recall that the Milky Way is an Sb type galaxy.

d Use images of galaxies in order to classify them.

(See 4.2a).

e Demonstrate an understanding that some galaxies emit large quantities of radiation in addition to visible light

(for example, radio waves, x-rays).

See below as to which AGNs emit which radiation types, but most things emit most of them, in varying quantities.

f Demonstrate an understanding that an Active Galactic Nucleus (AGN) is powered by matter falling into a super

massive black hole.

AGNs emit huge amounts of all kinds of radiation, and they split up into four kinds of galaxy; Radio, Seyfert,

Quasar and Blazer. In order to power this, we think that they have huge black holes at the centre; things are

sucked in at incredible speed, and a trillion times as much energy is generated than our Sun emits. Some gas

escapes, causing jets of gas to shoot out of the disc-shaped centre- these are detectable in x-ray and radio forms.


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g Recall the types of active galaxies, including Seyfert galaxies, blazers, and quasars.

Seyfert Galaxies- Discovered in 1963 by Carl Seyfert, these are mainly spiral, and both types (Seyfert 1 and 2) are

radio quiet. 1 is similar to quasars but less bright, and 2 have a lot of emission all around the spectrum.

Radio Galaxies- Discovered in the 1950s, are mainly elliptical and are intense sources of radio waves.

Quasar Galaxies- Again in two parts, about 10% are radio loud and the rest very quiet. Like stars with huge red-

shifts, they are the most distant known objects, so extraordinarily bright (10000x Milky Way). Discovered in 1963.

Blazer Galaxies- These look like quasars, but much closer, but range hugely in brightness. Discovered in the 1970s.

h Demonstrate an understanding that astronomers use many regions of the electromagnetic spectrum to obtain

evidence for the existence and properties of AGNs.We are now able to detect all EM radiation in some way, so can tell which types different objects emit. Not only

can we then say what they are, we can make generalisations about each category, and research in this way.

i Describe the Local Group of galaxies.

A local group is a collection of galaxies (between 50 and 100) which are gravitationally bound, and orbit a

common centre of mass. Ours is about 10 million light years in diameter. Each local cluster belongs to a

supercluster, ours being about 130 million light years in diameter.

j Recall the names of some galaxies in the Local Group, including the Large and Small Magellanic Clouds,

Andromeda Galaxy (M31) and the Triangulum Galaxy (M33).

k Demonstrate an understanding that galaxies are grouped in large clusters and superclusters.

Galaxies are in local groups, several of which make a cluster or supercluster- ours is 130m light years wide.

4.3 Cosmology

a Recall the Doppler principle for radial velocities.

As things move towards us, wavelengths are pushed together, causing them to become shorter, or blue tinted; in

the same way when they are moving away from us waves get longer, so red tinted. In the same way, frequencies

become higher when things come towards us and lower as they move away again- these are Doppler shifts, and

account for things like ambulance siren pitches changing when going past and stars having different colours.

b Demonstrate an understanding that light from distant galaxies is shifted to longer wavelengths (redshift).

(See above).

c Use the Doppler equation to determine the radial velocity of a galaxy.

d Demonstrate an understanding that for galaxies in the Local Group blueshift is possible.

Since the Universe is expanding, everything moves away from us, meaning that they are red shifted. However, as

the Local Group is orbiting a common centre of mass, galaxies also within it can be moving towards us sometimes.

e Recall that quasars are distant galaxies with high redshifts.

f Describe the discovery of quasars by astronomers.

In the 1950s, hundreds unidentifiable source of radio waves were being recorded, and eventually astronomers

found one with a corresponding light source. They were officially discovered when they were found to have a

huge redshift, and are now believed to be a form of AGN- they are potentially very useful due to being so far

away, as being up to 12 billion light years away we are seeing a very early Universe when we see quasars.

g Demonstrate an understanding of the relationship between distance and redshift of galaxies (Hubble's Law)and use the formula: v = Hd

h Describe how astronomers use the value of the Hubble Constant to determine the age of the Universe.

The Hubble Constant, in addition to Doppler shifts, can be used by taking what we think are the oldest objects (eg

quasars), finding their velocity and using this to estimate distance. From this we can calculate time, which means

we have a rough, but better estimate, than ever before as to how old the Universe may be.

i Demonstrate an understanding of the existence and significance of Cosmic Background (CMB) radiation.

Cosmic Microwave Background is a powerful point evidencing the Big Bang, as it matches radiation emitted by a

standard black body (nothing); it is merely detected as a small background glow from every direction in space.

j Describe how CMB radiation was discovered.

CMB was discovered by Penzias and Wilson in 1965, who were testing new radio telescopes in New Jersey when

they found an interference, despite all equipment being turned off. They realised by coincidence that it was what

other radio scientists had been searching for; each received the Nobel Prize for Physics in 1978 for their discovery.

k Describe recent observations of CMB radiation, including the Wilkinson Microwave Anisotropy Probe (WMAP),

and their significance to cosmologists.

In 1989 the COBE was launched to confirm the existence of CMB, which it did. More recently, in 2001 WMAP was

launched to help cosmologists give more accurate estimates of composition, age and evolution of the Universe.


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l Demonstrate an understanding of the possible nature and significance of dark matter.

Dark matter is given to things which we cannot see and which do not emit or reflect radiation, but which have

gravitational effects on the Universe; this includes black holes, neutrinos and WIMPs (Weakly Interacting Massive

Particles). It was first proposed by Fritz Zwicky in 1933, and is used to explain the odd rotation of spiral galaxies.

m Demonstrate an understanding of the significance of dark energy.

Dark energy could explain a range of things, for example the huge difference between how rotation curves for

spiral galaxies were predicted and how they are observed. Most cosmologists think that it makes up over 90% of

the Universe, a huge amount, and it could even be responsible for Universal Expansion itself.

n Demonstrate an understanding of the observational evidence for an expanding Universe.Observational evidence for Universal Expansion includes Doppler shifts, CMB radiation, evolution and quasars,

although there are no real limitations regarding it.

o Demonstrate an understanding of the past evolution of the Universe and the main arguments in favour of the

Big Bang.

The Big Bang currently the most common idea of the Universe, stating that it started as a very dense, hot lump

which has been expanding and cooling ever since. There is a whole range of evidence for it, listed above.

p Demonstrate an awareness of the different evolutionary models of the Universe (past and

future) and why cosmologists are unable to agree on a model.

The Universe as a whole has been changing constantly throughout history, as have our ideas

of it. We have gone from Ptolemy (model shown to left), to Copernicus with his heliocentric

model, to Galileo proving this, to Kepler and Newton and the Collapsing Universes, all theway to the Big Bang theory that we use today. Now, there are even more ideas coming

through about big crunches and rips, but we may ultimately never know the full truth.

Documents

Astronomy GCSE Syllabus Explanations_opt