Astrophysics

gravity

Large objects (astronomical bodies) that orbit a star

Planet-like objects that are not big enough to be planets but still orbit stars

Natural satellites (moons) orbit planets with almost circular orbits
Artificial satellites usually orbit Earth in fairly circular orbits

Lumps of rock and metal that orbit stars
Usually found in asteroid belts

Lumps of ice and dust that orbit stars
Orbits are usually elliptical
Comet tails point away from the star they orbit (due to solar wind)

The larger the mass of the body (planet, star etc), the stronger its gravitational field
The closer you get to a star or planet, the stronger the gravitational force is
The stronger the gravitational force, the larger the instantaneous velocity needed to balance it so the closer to a planet/star an object is, the faster it needs to travel to remain in orbit

A cloud of dust and gas where stars initially form

The force of gravity pulls the dust and gas together to form a protostar
The temperature rises as the star gets denser and more particles collide with each other and when the conditions are right, nuclear fusion occurs, giving out huge amounts of energy which keeps the core of the star hot, forming a main sequence star

The star enters a long stable period
During this, the star is stable because outward pressure from nuclear fusion is equal to inward pressure from gravity
The heavier the star, the shorter its time in this period

Eventually the hydrogen in the core begins to run out and the force due to gravity is larger than the pressure of thermal expansion and the star is compressed until the energy created makes the outer layers of the star expand
If it is a large star, it becomes a red supergiant which eventually explodes in a supernova
This supernova will lead to the formation of a neutron star or a black hole (if it is extremely large)

If it is a small star, it becomes a red giant
This will then become a white dwarf

Blue (hottest)
White
Yellow
Orange
Red (coolest)

A measurement of the brightness of a star at a standard distance