Using a Planetarium Program

Back in the "old days", planning an observing run took a lot of work. One needed an atlas of the sky, a set of catalogs of astronomical sources, and several tables made specially for each observatory which would convert one set of quantities (such as Right Ascension, Declination and time) into another set (such as airmass, altitude and azimuth). It was a pain.

But in the last fifteen years, cheap computers have made this all very easy. One can purchase for under $100 a program which will show the positions of millions of objects in the sky as seen from any location, and at any time. If you have a list of targets, you can figure out which ones to observe on any given night, and when, in just minutes.

Here at RIT, we have a choice of platforms and programs. Under Windows, we can use a program called Sky Map Pro. It is installed on the computers in the first-floor computer labs in the College of Science, on the computers in the Physics labs, and on the computer in the dome at the RIT Observatory. Our copies are version 5, which is far behind the current version. Visit the Sky Map Software home page for more information on their products and pricing. Note that this program can not only display a map of the sky, but also control common telescope mounts so that they point at objects of interest.

On the Mac computers (and on my own Linux machines), one can use a program called XEphem. You can purchase versions of this program which run under Windows, MacOS X, and Unix operating systems. I use it because I can download for free the source code for my Linux system. Free is good.

A brief introduction to xephem

Below are a set of possible targets for your observing projects this quarter. They fall into several categories:

variable stars: AM CVn, GO Com, 44 Boo
extragalactic objects: M81 and M82, 3C 273
clusters of stars: M44, M5, M13
stars with high proper motion: BD+59 1915
asteroids: 60 Echo, 756 Lilliana and 4029 Bridges
planets: Saturn, Jupiter

For THREE of these targets -- plus an additional target of your own choice -- please use the XEphem software (perhaps with help from SIMBAD and NED ) to do the following:

Look up the RA and Dec
Determine the times at which the object "rises" and "sets" on the night of April 25. Use the definition "rises" means "rises high enough that the airmass is less than 2.0", and "sets" means "sets low enough that the airmass is greater than 2.0". (At what elevation will an object's airmass be 2.0?) If the object never reaches an airmass 2.0, find the time when it culminates (i.e. reaches its highest point in the sky). Write all times in both local and Universal Time. Make sure you get Daylight Savings Time correct!
Make a finding chart for each object. Your finding chart should show the area of the sky around the target, with a field of view which is twice as big as our camera's field of view. We will use a Meade 12-inch LX-200 at focal ratio f/10 and an SBIG ST-8 CCD camera. Check to see if Sky Map Pro knows the field of view of this combination; if not, ask the instructor.
On each finding chart, mark the magnitudes of three or four of the brightest stars. If there are any stars roughly as bright as the target, mark those, too.
Check to see how close each object is to the Moon. Find all days between April 15-30 when the Moon is within 30 degrees of the object, and write them down. One should avoid trying to observe objects which are close to the Moon, especially when it is nearly full.
Imagine that you are going to the RIT Observatory on the night of April 25, 2006. Your task that night is to take pictures of each of the targets above. You will start when the sky becomes completely dark -- which is approximately when the Sun is 18 degrees below the horizon. Give yourself 20 minutes of time for finding and photographing each target. Make an ordered list, showing which object you will observe and when.