Arecibo Observatory

Celestial coordinates, time and using Arecibo for ALFALFA

The Arecibo Observatory is located at (long, lat) = (66d45m09s W, +18d20m39s N). The ALFALFA observing strategy is simple: We fix the telescope's azimuth arm along the meridian with the dome set to the proper zenith angle corresponding to the declination of the drift we want to observe in a particular observing session, start the data taking and let the sky drift by. This is called "fixed azimuth drift scanning".

In reality, we move the telescope by a small amount so that the drifts along which we acquire data in a given observing session follow tracks in constant J2000 declination. Otherwise, over the 6-7 year period of the survey, the Earth's precession would cause tracks at different declinations to wind up not being parallel in J2000 declination; the amount of deviation would depend on the right ascension. A minor effect, but why not avoid it to start with?

Work the answers out so that you understand where you got them. In some cases you can find the answers by searching on the web. That's not a healthy way to learn - so don't do it!

Things to do:
Of course, the purpose of these exercises is to get you to understand how to work through all the answers without the need for a lot of calculation. If you can't figure out how to answer these questions simply, then you're probably on the wrong track. So, ask! Questions we can answer are free.

Last modified: Sat Oct 6 10:52:47 EST 2007 by martha