Advanced Introduction to Astronomy
Astronomy 51, Spring 2014
Pomona College
Problem Set 1 (due Monday, Jan. 27, 2014)
Reading: Text Chapter 1 – “Seeing the Sun”, and article by Gott, et al available at:
http://www.astro.princeton.edu/universe/
http://www.astro.princeton.edu/universe/ms.pdf
Look over our local web sites at:
http://www.astronomy.pomona.edu/
http://physastro.pomona.edu/facilities/brackett-observatory/
http://physastro.pomona.edu/facilities/table-mountain-observatory/
http://www.astronomy.pomona.edu/penprase/BEPresearch.website/Default.html
1). Please consider a couple of “Fermi Problems.”
a). How many oil changing vendors are there in Los Angeles? Provide an order of
magnitude estimate? (this is the modern equivalent of Fermi’s “piano tuner” problem).
b). Likewise, how many fully employed tattoo artists would you estimate are needed in
Los Angeles?
Now let’s try some astrophysical Fermi problems:
a). Assuming that our galaxy has 2x1011 stars, and that an “average” star like the sun lasts
for 1010 years, what is the order of magnitude of sun-like stars that are forming each year?
b). If we observe that in addition to stars like our sun a galaxy has about 109 high mass
stars which have lifespans less than 100 million years (these would be bluer stars like
those in the Orion constellation), how much star formation is needed to maintain a steady
state of these high-mass stars?
c). Some have said that the number of stars in the galaxy is comparable to the number of
grains of sand on a beach. Using an average grain size of about 1.0 mm, how many cubic
meters of sand would be needed to make the Milky Way?
e). If these grains were spread out to the same relative separation as stars, what would be
dhe mean separation between our sand grains?
2). Now let’s consider the scale of the universe. A few useful resources can be found by
reading both the Gott article above and Nick Strobel’s astronomy notes at the site:
http://www.astronomynotes.com/chapter1/s2.htm
Then answer the following questions:
a). We notice a gap in the distribution of objects at the edge of the solar system. This, as I
mentioned in class is a huge unexplored area of astronomy and astrophysics. Using the
figure from Gott, approximately what volume of space appears to be empty? How far is
the “Kuiper Belt” and “Oort Cloud” in units of AU, and light minutes?
b). Likewise a large amount of information exists for stars and nearby galaxies, but drops
off at the “edge of the universe” at redshifts of z > 4. (note: redshift is given by z =
(Observed wavelength - Rest wavelength)/(Rest wavelength); high values of z have huge
distances and are being observed in the early universe). Consider a few reasons why
sources are harder to detect at these redshifts, and what new telescopes might be useful
for exploring the “high redshift galaxies”. Give some specific characteristics (aperture,
wavelength range, and type of observations) that would help open up this region of the
universe to study.
c). Of the many projects ongoing in astronomy (OWL, TMT, GMT, Fermi Gamma Ray
telescope, Herschel, Hubble Space Telescope, JWST, JDEM), which seems most
intriguing to you and why? Choose one of these new missions and be prepared to present
a short overview of the mission in class next week. Also provide a page of notes about
what you have learned about the mission. Some links below may be helpful for this part
of the assignment.
FERMI telescope: http://www.nasa.gov/mission_pages/GLAST/main/index.html
OWL telescope: http://www.eso.org/sci/facilities/eelt/owl/index_3.html
TMT telescope: http://www.tmt.org/
GMT telescope: http://www.gmto.org/
Keck telescope: http://keckobservatory.org/about/the_observatory
Herschel telescope: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=16
JWST: http://www.jwst.nasa.gov/
Hubble Telescope: http://hubblesite.org/the_telescope/hubble_essentials/
Euclid Telescope: http://sci.esa.int/euclid/
WFIRST Telescope: http://wfirst.gsfc.nasa.gov
LSST Telescope: http://www.lsst.org/lsst/
Space Weather (good for the latest on sunspots, eclipses, and solar flares):
http://www.spaceweather.com/
Spaceref – a good general purpose space news site:
http://www.spaceref.com/