• Hydrogen and helium formed shortly after the Big Bang. Heavier elements were created after a few hundred thousand years.

• Stars contain heavy elements such as iron.

• The "Inside-out" theory states that the center of the galaxy formed first, followed by the outer parts.

• The "Outside-in" theory state that the outer parts of the galaxy formed first, with the center created at another time.

• Stars contain mostly hyrogen and helium, but also have iron, carbon and oxygen.

• There are four stages of stars: Protostar, main sequence, red giant/supergiant and white dwarf/black hole.

• The Earth formed with heavy elements inside of it.

• Heavy elements are found within stars today

• Recent evidence shows that there is a lot of matter in the universe that we cannot directly detect. This matter is called dark matter

• The rate of expansion of the universe is increasing. The cause of this increase is unknown; one possible explanation involves a new form of energy called dark energy.