The Universe

• In main sequence stars, hydrogen fuses to form helium. This creates enough radiation and gas pressure to balance the gravitational forces.
• Stars are large balls of gas. They are formed as gravity pulls large clouds of dust and gas (nebula) together. Protostars form as this dust and gas is compressed together further by gravity. Eventually, the pressure inside the core rises as particles begin to move faster, enough for the temperature to exceed 15 million.
• At a high enough temperature, nuclear fusion reactions of hydrogen start (forming helium).
• The hydrogen fuel begins to run out and the star will begin to fuse helium into larger elements (e.g. carbon). This increases the gas and radiation pressure. The star will expand and become a Red giant. Stars larger than the sun will become red super giants.
• Our solar system was created from the supernova death of a large star. It left behind a large cloud of dust called a nebula. Gravitational forces caused this cloud to collapse and the particles to collect together. As the cloud collapsed it began to spin, this made it turn into a disk. The centre of the disk became the Sun and the rest collected together to form the planets.
• The inner planets are rocky because it was too close to the Sun for the light gaseous elements to condense and so these elements were pushed further away from the Sun.
• The helium fuel begins to run out and the reaction will slow. The gas and radiation pressure will decrease. The star will shrink and become a White dwarf.
• The helium fuel begins to run out and the reaction will slow. The star becomes very unstable and will explode in a supernova, throwing gases and dust out into space. The high pressure and temperature in a supernova will cause the fusion of elements heavier than iron.
• The remaining matter will collapse due to the gravitational force as the gas and radiation pressure will be small and shrink to form a Neutron star or a Black hole. A neutron star is a core densely packed with neutrons.
• The asteroid belt is a region between the orbits of Mars and Jupiter where there are thousands of rocky asteroids and dwarf planets.
• Comets are formed from ice and dust beyond the orbit of Neptune and have highly elliptical orbits.
• High energy Gamma radiation released at the Big Bang has travelled through the universe over billions of years, because the universe is expanding the wavelength of these waves has been stretched (red-shifted) to become microwave radiation.
• As microwave radiation can be measured throughout the universe it is evidence that the universe started from a hot Big Bang which released a lot of energy. It fills all space of the observable universe.
• Absorption Line- These lines represent wavelengths of light that have been absorbed by elements in the gases in a star’s atmosphere. As every element will absorb different wavelengths, each element has a unique pattern of lines.
• The Big Bang theory states that the universe started from a single point, and has expanded over time slowly cooling and forming the universe we see today.
• As the distance from the Sun increases the temperature decreases; except for Venus which has a thick atmosphere that keeps more heat in
• Astronomical unit = the mean distance from the Sun to the Earth (approximately 150 000 000km) Light year = the distance light travels in one year.
• The speed of light is 3.0 x 10 to the 8
• Distance in metres= speed x time