General Astronomy -
Spring
2013
Homework #4 - due February 18
1. (1 pt) How does the spectrum from an emission nebula differ from
that
of a reflection nebula?
2. (1 pt) When does a protostar become a star?
3. (3 pt) A gas cloud with a mass of 5 solar masses collapses
from a
radius of 1000 solar radii to 10 solar radii (phase A) and then from
10
solar radii to 1 solar radius (phase B). What is the ratio of
the
energy released in phase A to the energy released in phase B?
4. (2 pt) A gas cloud has a temperature of 10 K and a density
of
1000 cm-3.
How large are the pieces that the cloud fragments into?
5. (3 pt) Our Milky Way galaxy contains about 200 billion
solar
masses
of material. If the Milky Way formed from a cloud of
intergalactic gas with a density of 10-3 cm-3,
what was the temperature of the cloud?