- The stars that create elements are off the main sequence (the ones on the main sequence are making helium).
- A galaxy with blue stars is actively forming new stars, because they’re hotter and newer.
- Oxygen is the most abundant element in the Earth.
- How planets form:
- A supernova forms lots of cloud and dust
- Planets pick up mass like a snowball
- Solar winds (of gasses) blow away other dust
- The solar system is 74% hydrogen, 24% helium, and 2% everything else.
- Densities of common objects:
- Iron: 7.9 g/cm^3
- Water: 1 g/cm^3
- Ice: 0.9 g/cm^3
- Rocks: ~3 g/cm^3
- Terrestrial worlds:worlds we can stand on (like the 4 inner planets).
- Frost line: 3 AU
- Inside the frost line, planets form out of only rock and iron (water vaporizes)
- Outside the frost line, planets form out of rock, iron, and ice
- Denser things vaporize and condense at higher temperatures