Astronomy 102 Problem Set #3

due 24 February 2000, 5:00 pm

 In order to solve problem #1 you may need some help, because we didn't cover the material in class yet. We will cover the material on Wednesday. (Its the easiest problem, once we cover the material on Wednesday, or once you read Ch 24 section 2 in FETU. Come to my office early if you need help.

Problem #1:
a) Calculate the distance to a star whose parallax is 0.012 arcseconds (NOTE: 1 arcsecond = 1/3600th of a degree).
b) If this star has the same luminosity as the Sun, what is its intensity (in W/m2) when viewed from the Earth?

Problem #2:

You observe that a K star in a star cluster has a intensity of 6.23 x 10-14 W/m2.

a) Assuming that this K star is a Main Sequence star and that Main Sequence K stars have a luminosity of 0.4 Lo, calculate the
distance to the star cluster.
b) Further observations shows that this particular K star is actually a red giant star (i.e., it's not on the Main Sequence). Since
the luminosity of K giants is more like 100 Lo, what is the true distance to this cluster?
 

Problem #3:

Assume for a moment that all of the hydrogen in the Sun is converted into helium via nuclear fusion (this doesn't
really happen).

a) How much energy would be produced in the sun?

Remember that a fusion process some of the mass of  hydrogen is converted into helim, and some is converted into energy.
Assume that the Sun is 80% hydrogen by mass.

c) How long would it take for the Sun to radiate this much energy at its current luminosity?