astrophysics Flashcards
how many galaxies in the universe and what is ours called
billions; milky way
what is our solar system
all the stuff that orbits our sun
what is a moon
orbits a planet with an almost circular orbit
what is an asteroid
a lump of metal and rock which orbits the sun
what is a comet
lumps of ice and dust that orbit the sun with elliptical orbits
describe how the planets stay in orbit
the planets move in circular orbits so they are constantly changing direction so there must be a force acting on them.
the force causing this is a centripetal force. it acts towards the centre of a circle
the instantaneous velocity is at right angles to the centripetal force making it travel in a circle.
the force which makes this happen is provided by gravitational force
why do comets travel faster near to the sun
the closer the comet gets to the sun, the stronger the gravitational force is
the stronger the force, the larger the instantaneous velocity needed to balance it
so the closer the comet gets to the sun, the faster it has to go to stay in orbit
describe the stellar evolution of a main sequence star like our sun
1) nebula : cloud of dust and gas
2) protostar: gravity pulls gas and dust together to form a protostar; temp rises and hydrogen nuclei fuse releasing lots of energy
3) main sequence star: outward pressure caused by fusion balances inward pressure of gravity.
4) red giant: hydrogen runs out so the force of gravity is larger than the outward pressure; the star is compressed until it is dense and hot enough so that the outer layers expand
5) white dwarf: star becomes unstable and ejects outer layers of dust and gas, leaving a hot, dense, solid core
describe the stellar evolution of a star bigger than our sun after being a red giant
they start to glow brightly again as they undergo fusion to make heavier elements
eventually, they explode in a supernova
this leaves a neutron star and if it is massive enough it collapses into a black hole
which colour star is the hottest
blue
