Astronomy 123: Third Homework Assignment

Suppose that I take a spectrum of two galaxies.
- Galaxy 1 I observe that the hydrogen line has a wavelength of 8204 angstroms.
- In Galaxy 2 I observe the hydrogen line has a wavelength of 6549 angstroms.
I know from laboratory measurements that the rest wavelength of this hydrogen line is 6563 angstroms. Given this data, compute radial velocity of galaxies 1 and 2.
Thus tutorial might help
A proton and a neutron differ from each other only by a change of one of its Quark constituents:
- Show that the total charge of a Proton is +1
- Show that the total charge of a neutron is 0
( P.S. this problem is simple - you can do it much faster by referring to the material in Module 3 Lecture A than by "googling" for the answer)
Give a brief explanation of why its not possible for galaxies to start forming in the Early Universe immediately after it begins to expand.
For particle reactions, the conservation rules of Charge (C), Lepton number (L), and Baryon number (B), all have to hold, otherwise the reaction can't occur. Show that the reactions below follow these rules (i.e. show that C, L and B are the same after the reaction as before the reaction)

anti-neutrino+proton neutron+anti-electron
neutrino + neutron proton + electron
Explain why its not possible to make elements heavier than Helium during the period of Big Bang Nucleosynthesis.
Explain why, in a uniformly expanding Universe, every observer would think they are in the center of that expansion.