One of the first things you will need to learn as a new stargazer, is how to locate planets, stars and constellations in the night sky. However, what you see in books, charts and planetariums doesn't always translate to what you actually see. Part of the problem is due to light pollution. .Thus, when you look for the constellation Leo, you can not always find it because some of the stars that form it are not very visible so it is hard to "connect the dots." With a PDA, you can use the Alt-Az coordinate system to help you locate it.

To use a PDA to find your celestial object of choice:

ONE - Install a planetarium software program onto your PDA and set it for your location and time. It will have a data base of cities you can choose with associated longitude and latitude. Some will also permit you to enter the coordinates yourself. Be sure to adjust for daylight savings time if it is in effect. (Chabot Space & Science Center's location is about 37 degrees 49 :minutes North latitude, and -122 degrees 11 minutes West longitude.)

TWO - Face North. If you are unable to see Polaris, the North Star, use a compass. Be sure to adjust for the magnetic declination for your locality as Magnetic North is different from true North. Not all compasses will permit you to do this. Brunton has a model that allows you to adjust the declination. It is the Brunton 9020G Classic that sells for $11 at REI. The declination for Oakland is about 12 degrees East.

THREE -. Once you face North, enter the celestial object of choice on your PDA and request the Altitude-Azimuth (Alt-Az) coordinates. You will get the azimuth coordinate first, then the altitude coordinate. The azimuth is the compass position and the altitude is the angle position.

North is Az 0 degrees, East is 90 degrees, South, 180 degrees and of course West, 270 degrees. The imaginary horizon is Alt 0 degrees and the zenith (directly over head) is 90 degrees. So, for my current location and time, the Alt-Az coordinates for Jupiter is Az: 344:51; Alt -32:41. Thus, it is in the Northwestern (almost North) skies but below the horizon. The Alt-AZ coordinates for the constellation Andromeda is Az: 070:24; Alt 43:53. Thus, it is roughtly in the East-Northeastern skies.

Remember that the earth is rotating so the objects will move as time passes. When the PDA gives you the Alt-Az coordinates for Jupiter, it will only be for that period of time. Tap the software program's current time panel an hour later and you will see the coordinates for it will have changed.

FOUR - PDAs run under either the Palm or Windows CE operating system. There are planetariums for both OSs and are downloaded from commercial web sites. For the Palm OS, two popular programs are "Planetarium for Palm Pilot" and "2Sky." For the Win CE OS, two programs you can try are "The Sky Pocket Edition" and "Pocket Deepsky 2003." All four have the ability to add extensive data bases to them. "Pocket Deepsky 2003" is a mini-program within "Deepsky 2003." (An attractive scaled-down program for the Win CE OS PDA is "Pocket Universe." It is visually attractive and intuitive to use and learn. The developer provides a demo for you to download.) Go to any of the developers' web site to look at a program's screen shots and learn more about it's features.

To get to their web site, go to: http://www.seds.org/billa/astrosoftware.html

Scroll down half way until you see a hand holding a PDA. You will see there are other PDA planetariums. Click on one of them and you'll be taken to the developer's website. Be sure to check the minimum systems requirements to determine if the program will run on your PDA.

OK, so go out, have fun and be amazed at the wonder of our beautiful skies.

Darlene Fung