This is a lecture from the course (Astro C10 / LS C70U Introduction to General Astronomy) was taught at Berkeley by Prof. Alex and here are some notes taken from that lecture
The whole universe is made of the same material as is present on earth mainly hydrogen and helium. How to do we know that?
Well....from the (pattern of lines/spectrum) which act as fingerprints from the
emission or absorption of photos by atoms
Electrons have discrete well defined energy levels.
When we shine a photon on an atom and if it happens be of the right
energy level the electron in that atom can go to a higher energy
level and absorbe this photon. Later it can give that photon back
and emit that same photon. If the electron escapes then the atom is ionized.
2 ways to ionize
- Absorption of a photon (students were throwing balls at the professor)
- Knocking it out by a collision (and how Christina kicked him)
