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 Earth ’s 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 umbra’s and penumbra’s, 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 Earth ’s 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 the electromagnetic 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.  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 Earth ’s 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 Earth ’s atmosphere doesn’t 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 moon’s surface, where as the highlands are very rugged and heavily cratered- 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 srcin 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  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 as wrinkle 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 moon’s magnetic field, and the ASE, to measure any seismic activity on the moon. l Describe the likely srcin 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 Earth ’s 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 in this 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  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 Sun ’s 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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