29:62 General Astronomy
First Homework Set...Due Feb 3, 1999

Show calculations and give reasons for your answers. Don't go around confused and despondent; if you do not know how to get started, ask us for help. The purpose of problem sets is to promote thinking and lead to understanding, not produce a confiteor of revealed truth.

1. In class I will distribute a figure showing the spectrum of the star Herculis. What is your estimate for the surface temperature of this star?
2. A star lke the Sun is 30 parsecs away. It is orbited by a planet identical to the Earth. What would be the angular separation between the star and the ``other Earth''?
3. A star is 25 parsecs away. It has a proper motion of 0.5 arcseconds/year. In its spectrum is a spectral line of oxygen which has a rest wavelength of 500.700 nanometers. In the stellar spectrum it is observed at 500.733 nanometers. Is it approaching or receding from the Earth? How fast? What is its velocity perpendicular to the line of sight? What is its total speed with respect to the Earth?
4. Here's a fun one. Take your SC1 chart and Xerox the part which contains the bright star Sirius (believed by the ancient Egyptians to be the celestial incarnation of the goddess Isis). The celestial coordinates of Sirius are RA=6h45m, Dec=-16degrees. Plot the position of Sirius relative to the other stars 20,000 years from now! Assume (incorrectly) that the proper motions of the other stars are negligible.
   Hint: there is a URL link in the 29:62 page to the Hipparcos homepage.
5. In class I talked (at length) about the Planck function, from which we obtain Wien's Law. Assume that, instead of the complicated form with exponential functions it has the following form:

   

   where T is the temperature in K, and is the Planck function with units described in class. Assume is the ``right'' value given by Wien's Law. For a blackbody with the temperature of the Sun, give the radiated power in Watts/m given off by this blackbody.

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