Astrophysics

Galaxy

is a large group of stars held together by gravity

Star

is a body which emits energy powered by nuclear fusion

Planet

is a large body which orbits the star

Dwarf planet

is a larger enough planet for its own gravity to have shaped it as roughly spherical

Moon

is a natural satellite in orbit around a planet

What does force of atttaction depend on

masses of two objects, distance between masses

Features of comets

dirty snowball, long narrow epileptical orbit, forms far from sun, fiery tail

Features of asteroids

lifeless rock, round orbit, forms closer to the sun, no fiery tail

Formula for gravity

W= mg

order stars from hottest to coldest

blue/white, white, yellow, orange, red

How was do stars form

Dust and gas are drawn together by gravity into a ball. This causes fusions. Hydrogen and nuclei fuse together to form helium. Energy is emitted as heat and light

Nebula

contains hydrogen and dust

Fusions

nuclear reactions

What is the cycle of stars similar to the sun

nebula, protostar, main sequence star, red giant, white dwarf, blue dwarf

What is the cycle of stars bigger than the sun

nebula, protostar, main sequence star, red super giant, supernova, neutron star OR black hole

What forces do fusions create

pushing outwards against gravity. When they are balanced the star is in the main sequence

What happens when hydrogen runs out

The large gravitational forces compress the star. the star shrinks and gets very hot. The reactions form helium making the star expand and turns into a red giant

What happens when all the helium is fused

The gravitational forces again compress the star. It shrinks and get very hot becoming a white dwarf with no more fusion, just heat.

What happens when the star loses all its heat

it turns into a black dwarf which is no longer visible

What happens when all nuclear fusion stops in red super giants

They explode into supernovas

What happens after the supernova if the star was big

it compresses into a neutron star

what happens after the supernova if the star was massive

it will collapse into itself becoming a black hole

Formulas for orbital speed

2πr / T