1. Galaxy Notes

2. Star System
Star System: a star and all objects orbiting it (planets, dwarf planets, SSSBs)
Some star systems have two or more stars orbiting each other!
The words “sun” and “star” mean the same thing
“sun” is used to refer to “our” star
“Solar system” and “star system” also mean the same thing
“solar system” is used to refer to “our” star system

3. Exoplanets
Exoplanet: (extrasolar planet), a planet orbiting a star other than our own Sun
Long theorized, first discovered in 1992
Over 1,000 discovered so far
Can be rocky planets, gas giants, or dwarf planets
Some might be habitable, but no evidence of life yet
Super-Earth: a rocky planet larger than Earth
Hot-Jupiter: a gas giant that orbits close to its star
Rogue Planet: a planet floating through space that doesn’t orbit any star at all!
Also interstellar planet, nomad planet, free-floating planet, or orphan planet
Might have been ejected from a star system or formed like a star, but no fusion!

4. Galaxies
Star Clusters: large groups of stars that formed in the same nebula
Galaxy: a huge group of stars, star systems, star clusters, and nebulas that are bound together by gravity
Spiral Galaxy: large bulge in the middle, arms that sprial outward (our galaxy, Milky Way)
Elliptical Galaxy: like round or flattened balls
Irregular Galaxy: no regular shape

5. Universe Universe: contains all known galaxies
Big Bang Theory: 14 million years
ago, our universe formed.
All matter condensed into a single point, that suddenly exploded outwards into a constantly expanding universe
Evidence: all galaxies are moving away from each other
Evidence: cosmic background radiation, energy distributed in every direction in the universe, leftover thermal energy from big bang

6. Will the universe expand forever?
Will the universe end?
Are there other universes?

7. Dark Matter
Dark Matter: matter that does not give off electromagnetic radiation, and cannot be seen directly
23% of universe’s mass
Can be observed by the effect of gravity
Very mysterious, don’t know much about it
Dark Energy: hypothetical form of energy that helps accelerate the expansion of the universe

8. Scale Multiverse? Universe Galaxy Nebula Star Cluster Star System
Stars, planets, moons, comets, asteroids