# Edexcel Physics - Topic 10 Space

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• Created by: 13pattenp
• Created on: 21-01-20 12:24
• Topic 10 - Space
• Finding Distances
• One AU (astronomical unit) is the mean distance between the Earth and the Sun.
• Trigonometric Parallax - using the change in position of the Earth and the change in position of the object relative to distant, stationary objects, we can measure the distance to the object.
• 1 parsec is the distance from an object to the Earth if the angle of parallax = 1 arcsecond or 1/3600°
• Luminosity
• Luminosity is total energy per second.
• If luminosity of an object is constant, intensity experienced by another object and distance between the two objects obey the inverse square law.
• Standard Candles
• Standard candles are objects of known luminosity.
• By using the luminosity of a standard candle and the intensity experienced by Earth, we can calculate the distance between the standard candle and Earth using inverse square law.
• Standard candles are used to calculate the distance to far away objects as trigonometric parallax would not be suitable.
• By finding a standard candle in a galaxy, we can calculate how far away that galaxy is from us.
• eg: supernovae or Cephid variables.
• Life cycle of a star
• Main sequence - cloud of dust and gas contracts under gravity to form a protostar which heats up until hydrogen nuclei fuse to form helium, releasing energy and creating pressure to stop gravitational collapse.
• Red giants - when all hydrogen has fused to become helium, fusion stops and outward pressure decreases. The helium core contracts, heats up and fuses as the outer layers expand and cool.
• White dwarf - when all the helium has fused, the star begins to collapse. The core contracts and the outer layers become unstable so they are ejected as a planetary nebula, leaving behind the hot, dense, solid core.
• Supernovae - high mass stars (red supergiants) spend less time in main sequence because they use their large amount of fuel more quickly. When all helium is fused, the star explodes in a supernova leaving behind a neutron star or a black hole.
• Age and Fate of the Universe
• Age of the universe can be calculated using t=1/H
• The Hot Big Bang Theory states that the universe began very hot and dense and has been expanding and cooling down ever since.
• we cant know the age of the universe until we know its density.
• If the density of the universe is more than the critical density, a 'big crunch' will occur.
• If the density of the universe is equal to the critical density, the rate of expansion will slow down.
• If the density of the universe is less than the critical density, the universe will continue to expand.
• Doppler Effect
• Redshift - the increase in wavelength of a wave received by an observer due to the source and the object moving away from each other.
• Blueshift - the decrease in wavelength of a wave received my an observer due to the source and the object moving towards each other.
• The Doppler Effect shows that the universe is expanding because Hubble observed that further away galaxies had more galactic redshift, meaning that the further away they were, the faster they were travelling away.
• Cosmological distances can be measured using v=Hd where v is recessional velocity in kms-1, H is Hubble's constant in kms-1Mpc-1 and d is distance in Mpc.