astrophysics
units
kilogram
mass
metre
distance
metre/second
orbital speed
newton
weight
second
time
newton/kg
gravitational field strength
doppler effect
if there is a wave source moving relative to an observer, there will be a change in the observed frequency and wavelength.
doppler shift is responsible for the red-shift of light from galaxies which are moving away from Earth, which is when the wavelength of the light coming from them increases. The faster it is moving, the more its light is red-shifted
evolution of the universe
Cosmic microwave background radiation
this radiation is present everywhere in the universe
just after the big bang, lots of short wavelength radiation should have been released. This radiation, as the universe expanded over time, would have been stretched to become microwaves
red shift
the red shift of light from galaxies shows that they are all moving away from us and that those which are furthest away are moving the fastest, suggesting that the universe was formed from an explosion at a single point (the big bang)
A galaxy is a large collection of billions of stars
The Universe is a large collection of billions of galaxies
our solar system is in the Milky Way galaxy
the gravitational field strength is the force per unit mass on a body in a gravitational field
g varies with the mass and size of the body so is different on other planets and the moon
gravitational force causes
moons to orbit planets
slightly elliptical orbits with a constant orbital speed
planets and comets to orbit the sun
planets orbits are slightly elliptical with constant orbital speed
comets orbits are highly elliptical
artificial satellites to orbit the earth
comets have greater speed nearer to the star because the ice inside them melts as they get closer so their mass decreases
stars can be classified according to colour
a stars colour is related to its surface temperature
evolution of stars
nebula
main sequence star
red giant
white dwarf
a cloud of dust experiences weak interaction due to gravity and begins to clump together
this continues until the pressure and temperature is great enough for nuclear fusion
hydrogen nuclei fuse together to form helium nuclei, releasing energy causing outwards pressure
the outward pressure balances with the inwards pressure due to gravity and the star is now stable (main sequence)
eventually there is no more hydrogen so it collapses due to the unbalance from inwards and outwards pressure, becoming unstable
red supergiant
supernova
neutron star
black hole
if the star is a similar mass of the sun then it expands massively and becomes a red giant
it then becomes a white dwarf as it cools down
if the star has a mass greater than the sun, it expands and becomes a red supergiant
it then explodes to become a supernova
if it is exceptionally massive, it becomes a black hole
otherwise it forms a neutron star
brightness of a star
dependant on where it is measured
at a standard distance, it can be represented using apparent or absolute magnitude
absolute magnitude
the apparent magnitude if the star was viewed from exactly 10 parsecs away
the apparent magnitude if how bright it appears at a particular point in space
HR diagrams
HR diagram shows the relationship between the star's surface temperature and brightness
supergiants are top right
red giants are below supergiants
main sequence are a diagonal strip from top left to bottom right
white dwarfs are bottom left