Our solar system consists of the Sun, eight planets and their natural satellites (such as our Moon), dwarf planets, asteroids and comets. The order of the planets is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The planets move around the sun in elliptical orbits while satellites orbit the planets. Rocky bodies named asteroids exist between Mars and Jupiter and comets have been found
Early civilisations believed that the Earth was the centre of everything with planets and the Sun orbiting it – the geocentric model. Copernicus thought that the Sun was the centre of the universe and Galilei discovered four of Jupiter’s four moons, further supporting Copernicus’ belief that the Sun was the centre of the solar system – the heliocentric model. As telescopes improved, Uranus, Neptune and the dwarf planet Pluto were discovered
The invention of photography allowed astronomers to make detailed observations and computers have increased the speed of data analysis. Telescopes in orbit around the Earth give clearer images than ground-bases telescopes which are interfered with by clouds and dust. The Solar System is investigated using space probes. Many objects in space emit radio waves and infrared radiation. Different telescope types are used to detect different EM waves. Some telescopes must be placed in orbit at the atmosphere absorbs some other radiation they should detect
Weight is the force of gravity acting on an object, depending on mass and the gravitational field strength. The GFS on the surface of a planet or satellite depends on the mass of the body and the distance from its centre to its surface. The greater the mass and the smaller the radius, the stronger the GFS
Artificial satellites are used for communication and to observe Earth and space. There are three types of orbit:
- Highly elliptical orbits for communication in areas near the poles
- A satellite in polar orbit will pass over all parts of the Earth
- Satellites in circular geostationary orbit remain over one point and are used for broadcasting
- Low Earth orbits need the least fuel for launch
A satellite in a circular orbit has a constant speed, however as direction is changing and velocity is a vector quantity, the orbiting body is changing velocity and is accelerating. A moving object will continue in a straight line unless there is a force that makes it change direction or speed. The gravitational force between the Earth and a satellite is at right angles to the direction of movement so the force changes its direction. The gravitational force on a satellite in low orbit is greater than that on a satellite in high orbit. If it slows it will fall to Earth, gaining speed until it is moving fast enough to stay in a new, lower orbit. If it goes low enough to reach the atmosphere it will slow from contact with the air and fall to Earth
Life Cycle of Stars
- A nebula is a cloud of dust and gases. The materials are pulled together by their own gravity. As the cloud contracts it becomes denser. The hydrogen becomes hotter and may start to glow
- As more mass is attracted, the cloud’s pull gets stronger and heats the material, forming a protostar
- Eventually the temperatures and pressures in the protostar become high enough to force hydrogen nuclei to fuse and form helium, releasing energy as EM radiation
- The outward pressure from the hot gases balances the compression due to gravity. The star is now in the main sequence part of its life-cycle, where our Sun is
- Stability for stars the size of the sun can last for 10 billion years
- When most of the hydrogen is fused, the core is not hot enough to withstand gravity and collapses
- The outer layers expand to form a red giant, much larger than the original star
- Other fusion reactions occur to form heavier elements over a billion year period
- A shell of gas is thrown off
- The rest of the star is pulled together to form a white dwarf
- No fusion happens and it gradually cools to form a black dwarf over a billion years
- Stars larger than our sun are hotter and brighter. They fuse hydrogen faster and become red supergiants
- The supergiant collapses and exploded in a supernova
- The outer layers are cast off and expand outwards
- What is left is pulled back together by gravity to form a black hole. The gravitational pull is so strong that even light cannot escape
- If the remains are not larger enough to form a black hole, gravity pulls them together to form a small, very dense star called a neutron star
Red-Shift
The Doppler Effect is the change in the observed frequency and wavelength to an observer if a wave source is moving relative to an observer. The wavelength is longer behind the source and shorter in front of it. A similar thing happens with light waves. The visible spectrum of light from stars contains patterns of dark lines. If these are red-shifted (moved towards the red end of the spectrum) the star is moving away from us. The further the lines are shifted, the faster the star is moving relative to is. Hubble discovered that the further away a galaxy is, the greater the red shift so that faster it is moving away from us. This is key evidence to support the Big Bang Theory
Origins of the Universe
The Big Bang Theory suggests that 13.5 billion years ago, the universe began expanding from a single point of concentrated energy and is still expanding to this day. The evidence for this theory comes from red-shift, and also from cosmic microwave background radiation. The Big Bang Theory says that huge amounts of radiation were released at the beginning of the Universe. Because the universe is expanding, the wavelength of this radiation has increased and so now it is only detectable as microwave radiation. It was found from a radio telescope which detected microwave signals from all over the sky
The Steady State theory says that the Universe has always existed and is expanding, supported by redshift. This theory cannot explain CMB radiation and since there is more evidence for it, the Big Bang Theory is the accepted theory for the origin of the Universe