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

Another good, free planetarium program -- though it requires quite a bit of CPU and graphics power -- is Stellarium. It runs under most major operating systems. If you happen to be using Mac OS X, then you might find it quick and easy to run Stellarium by copying this .dmg file to your desktop and then clicking on the "Stellarium" icon.

In order to enable a tool which measures angular separations between objects, follow these instructions -- thanks to Mr. Acresti:

Go to the Configure menu (on the right slide-out menu) or just hit F2 (Mac users: fn-F2)

Select the "Plugins" tab.

Select the "Angle Measure" plugin from the plugins list.

Check the "Load at startup" checkbox.

Restart Stellarium

To use the tool, select the little angle-icon from the lower menu (it should be just to the right of the "Full screen" button) and click-drag anywhere in the sky.

It can produce very pretty and very realistic views of the night sky, like this:

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, Mars

For two of these targets -- plus an additional target of your own choice -- please use the XEphem and/or Stellarium 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, which has a field of view of about one-quarter of a degree by one-quarter of a degree. Therefore, your charts should be around one-half of a degree on a side.
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, 2010. 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.

For more information

Sky Map merges real photographs of the sky into a big, zoomable mosaic
Celestia lets you fly through the Solar System or the galaxy to take a look at planets from new directions.