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The Solar System

Planets reflect sunlight and orbit the sun in ellipses. There are 8 planets that orbit the sun in ellipses(circular paths). Stars are huge, very hot and very far away and give out lots of light where as planets are smaller and only reflect light. 

The solar System was formed from big clouds of dust and gas and once the particles moved closer gravity took over therefore it pulled things closer together until the whole cloud collapsed in on itself. At the centre of the collapse particles came together to form a protostar and when hot, fusion happened- hydrogen nuclei joined together to make helium. The heat and light gave out created the sun.

Asteroids and comets are smaller than most planets and are made of the leftover stuff from the solar system. Asteroids are small lumps of rubble and rock. Comets are balls of rock, dust and ice which orbit in different planes from the planets.

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Beyond the Solar System

The sun is one of thousands of millions of stars which form the Milky Way galaxy. Distances in space can be measured using light years (as the distances between galaxies are enormous). A light year is the distance that light travels through a vacuum in one year. Relative sizes and distances from smallest to largest:

Diameter of earth, diameter of the sun, diameter of the earth's orbit, diameter of the solar system, distance from the sun to nearest star, diameter of the milky way and the distance from the milky way to the nearest galaxy.

The sun's diameter is about 100 times bigger than the diameter of the earth. The earth is 5000 million years old. Sun= 5000 million years and the universe= 14,000 million years in age.

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Looking into space

Distance to a nearby stars can be done using parallax which is when something appears to move when you look at it from different places. Astronomers take pictures of the sky six months apart= the apparent movement of a star between two photos allows you to work out how far away it is. Stars further away appear to move less. Also the distance can be measured by it's brightness. However, when detecting light the earth's atmosphere absorbs light before it reaches us. Light pollution makes it hard to see dim objects.

We see stars and galaxies as they were in the past. Since the sun is about 150 million km away from earth, the radiation from the sun that reaches us left about 8 minutes before we see it meaning we see the sun as it was about 8 minutes ago. 

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Life of the Universe

Distant galaxies are moving away from us- the wavelength of the light from it changes, the light becomes redder (red shift). This is used to show how quickly it's moving away. The greater the red shift the faster it's moving away. This is evidence that the whole universe is expanding.

The Big Bang Theory is that all the matter and energy in the universe must have been compressed and then exploded and started expanding. If there's enough mass compared to how fast the galaxies are currently moving, the universe will stop expanding and contract. 

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Wegener's Theory- Continental Drift

Fossils of similar plants/animals had been found on opposite sides of the ocean, most people thought this was because the continents had been linked by 'land bridges' . Wegener suggested that Africa and South America had previously been one continent which had split. Also, he said that about 300 million years ago there was only one 'supercontinent'.

The theory was not accepted at first as it was not convincing and because he was a meteorologist not a geologist. 

The mid-atlantic ridge was investigated and they found that magma rises up through the sea floor, solidifies and forms underwater mountains. Also, the magnetic field suggests movement as the erupting particles align themselves with the Earth's magnetic field. This is evidence the Sea floor is spreading suggesting continental drift. 

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Structure of the Earth

We live on the Earth's crust which is very thin. Below that is the mantle which has the properties of a solid but can flow very slowly. Heat from the core causes the mantle to flow in convection currents. At the centre of the earth is the core. 

The earth's surface is made up of tectonic plates. Convection currents in the mantle cause the plates to drift. Volcanoes form at the boundaries between two tectonic plates (as magma is produced which rises up). As plates crash into each other mountains are formed.

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Seismic Waves

Earthquakes cause different types of Seismic waves. As a result of an earthquake wave motions travel on the surface and inside the earth.These are measured using a seismograph. There are two types of seismic waves= P-waves and S-waves.

P-waves travel through solids and liquids and travel faster than S-waves. They're longitudial. Whereas, S-waves only travel through solids, are slower than P-waves and are transverse. 

When the waves reach different boundaries between different layers of the earth, some waves are reflected and change speed an=s the properties of the layers change. The change in speed causes the waves to change direction (refraction). A Seismograph tells us what is in earth e.g. the fact that S-waves are not detected in the core's shadow tells us that the outer core is liquid.

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Amplitude is the distance from the rest postition to the crest. The bigger the amplitude the more energy the wave has. The wavelength is the length of a full cycle of the wave. Frequency is the number of complete waves passing a certain point per second (measured in Hz) 

Distance(m) = speed (m/s) x time (s)

In Transverse waves the vibrations are at 90 degrees to the direction of the travel of the wave.

In Longitudinal waves the vibrations are along the same direction as the wave is travelling. 

wave speed= frequency x wavelength

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