Galaxy Notes

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

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!

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

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

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

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

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