Planetarium on your computer

One of the hardest parts of the Astronomy Merit Badge is identifying at least ten constellations (requirement 4), four of them in the zodiac, and eight conspicuous stars. Here is a list of most prominent constellations and stars, which are visible in the night sky now. This is the list you should try to learn to identify for the test.


  • Ursa Major
  • Ursa Minor
  • Cassiopia
  • Cephus
  • Draco
  • Orion
  • Taurus
  • Auriga
  • Gemini
  • Canus Major
  • Canus Minor
  • Cancer
  • Leo


  • Dubhe
  • Merak
  • Polaris
  • Sirius
  • Betelgeuse
  • Bellatrix
  • Rigel
  • Saiph
  • Aldeberan
  • Capella
  • Castor
  • Pollux
  • Procyon
  • Regulus
  • Arcturus
  • Spica

You don’t have to learn all of them (see the book), but if you know all of them it will make it easier to take the test. One way to learn them is by using a computer planetarium program. One of my favorite free programs is Stellarium. It’s available in Windows, Mac and Linux versions so download it (with your parents permission of course) and play around with it for a while, to get a hang of how it works.

Stellarium a desktop planetarium

If you’re using another program adjust what you do to the program you’re using.

First thing is to set your location. If you’re using Stellarium there will be a little tool bar on the lower left side of your screen and one of the tools is a little wrench. Click on it to open the set up box. Click on the location tab and you will find several options, but the ones we’re interested in are latitude and longitude.

Do you know yours? If you don’t you can go here to find it: . To check latitude and longitude just enter your zip code. This will be your local post office as your observation point which is close enough for us. Enter your coordinates by using the little up and down arrows next to lat. and long. in Stellarium and click save, so you always start out looking at the sky the way it will in your back yard.

Now click on the Date & Time tab and check to make sure the current date and time are set. If they are incorrect, your computer may have the wrong date set so check your computer’s clock. If you want to play with the landscapes, go for it, but Guerens (the skyline you get when you first start the program) seems to be the best choice for keeping the screen fairly clean and still give us a reference for where the horizon is. Close the set up screen and now we can take a look at the sky.

If it is already night time you’re all set, if it’s day time you need to speed time up a little. Click the fast forward (>>) on the lower right of the screen two or three times. Don’t get carried away or time will really fly. When the sky gets dark hit the play (>) and time will slow down to real time. Now you should see a nice clear night sky and a few stars. If you have a scrolling mouse, try scrolling your view in and out. If you don’t have a scrolling mouse use the page up and page down keys. Too much ground, too few stars? Left click anywhere on the screen and drag your view up or down. You can also drag left and right to look to the East, West, North or South. Play around with this for a while until you get used to it.

If you can find Mars ( it will be low in the West at around 8:00 pm ), click on it and hit your space bar. What happens? Now try scrolling or using the page up and down keys. You can do this with any objects that could be seen with a telescope, I’ll give you some things to look for on another day.

Now to start learning the constellations and star names.  Try playing with the three controls on the left end of the control bar. By turning these on and off and learning the star patterns behind the graphics, you should be able to start learning the constellations.

If you are using another desktop planetarium and having trouble, you can email me with your questions as I have several other programs and I should be able to help out. When it’s clear at night go out right after sunset and see if you can apply what you’ve learned.

If you have any problems or questions, send them along.


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