Physics HL – Astrophysics definitions
Star
A planetary object bound by “self-gravity” and that “radiates energy” that is primarily created by “nuclear fusion within the core”
Binary Star
“two stars” orbiting a “common” center of mass
Planet
A object that (1) is in “orbit around the sun”, (2) has “sufficient mass” to “assume a round shape”, (3) has “cleared the neighbourhood” around its orbit
Moon
An object that “naturally orbits a planet”
Shape of planetary orbits
All orbits are “elliptical”, although comets’ orbits are more “stretched out”
Comets
(1) made of “ice and dust”, (2) are in an “elliptical orbit around the sun”
Asteroids
They are made up of the same things as planets are, and they are found along the asteroid belt between Mars and Jupiter
Stellar cluster
A group of stars that are held together by “mutual gravitation”
Globular cluster
A group stars that are “closely packed”
Constellation
A group of stars that from Earth, form a pattern
Nebulae
A cloud of interstellar gas and dust visible in the night sky
Light year
The distance travelled by light in a year
Distance to Proxima Centauri
4 light years
Distance to galactic center
25,000 light years
Distance to Andromeda galaxy
2.5 million light years