Sample Problems for Midterm #1

Astronomy 1 / Section 3 (S. Myers)

These are problems that you should be able to do. Similar problems to these will appear on the midterm. I do not guarantee all of these will be on it, nor that all that are on the test are like these. However, if you can do these you will be in good shape for the test!

Note that some of these questions use the results of previous questions. Be sure to show your work so that if you make a mistake in one question, we can see that you knew how to do the next one and not penalize you twice for one error! If you can't get one at all, pick a plausible number and then follow through on the calculation (be sure you write down that you are doing this!).

I may not give as many hints on the midterm as I give here after the question.

You will need a calculator for this and for the midterm!

  1. The Synodic period of Saturn is 1.03513 years. What is the Sidereal period of its orbit? (Use the formula relating sidereal to synodic periods. Be sure to choose the correct version - is Saturn an inferior or superior planet?)
  2. Using the sidereal period of Saturn just derived, calculate the semi-major axis of its orbit in AU. (Use Kepler's 3rd law)
  3. Assuming the orbit is close to circular, what is the average orbital velocity of Saturn in km/s? Compare this value to the velocity of the Earth in its orbit at 1 AU. Note 1 AU = 1.496 x 10^8 km. (Find circumference of orbit compared to its sidereal period)
  4. From the Earth at Saturn's closest approach (distance is approximately the difference between Saturn's orbital radius and the Earths = 1 AU) the disk of Saturn is observed to have an angular diameter of 19.5 arcseconds. What is its physical diameter in kilometers? (use small angle formula)
  5. The apparent visual magnitude of the brightest star in the sky, Sirius, is -1.47. The 20th brightest star, Beta Crucis, has a magnitude of 1.28. How many times brighter is Sirius than Beta Crucis? (find intensity ratio)
  6. The greatest elongation of the planet Mercury is observed to be about 22 degrees, 30 minutes. What is the semi-major axis of its orbit in AU, assuming a nearly circular orbit? (use the triginometric relation to find the ratio of orbital radius to that of Earth)

I will work through these problems on Monday. Remember, the midterm is Wednesday Feb 14 in class.


Go to the Lecture Notes Index
Back to the ASTR001/Sec3 Page


Steven T. Myers - Last revised 12Feb96