I am Dave Wallace and I like to do visual astronomy and night sky photography while traveling.
For this purpose, a full-blown planetarium program with its ability to show telescopic views, invisibly-dim objects and control telescopes was overkill. What I wanted was simply a program for the XO laptop that could answer the question:
"What's overhead next week and 5000 miles from here?"So my StarChart Activity was designed with those requirements in mind.
The program's catalog is small on purpose: If you're limited to the Mark One Human Eyeball, keeping track of all the stars in the Tycho catalog is way overkill. So my catalog only contains data for the 1800 brightest stars, the moon, the sun and six of the planets.
Setting the time for some other location or for some future or past instant requires that the user enter the time and zone offset -- this avoids having the program try to predict the correct time zone. "Right now" is easier, so I have the option of plotting the sky as of "now" (and updating the plot once a minute).
Setting location can be very approximate for a whole-sky chart. Knowing your location to within a couple of degrees of latitude and longitude is more than sufficient. I allow several options with respect to display color, provide the ability to show the chart in "star chart traditional" (east on the left) or "map" (east on the right) orientation, show or hide the constellation stick-figures and let the user choose how many stars to plot by their brightness.
The ability to share the activity data is not currently implemented. And I want to re-format the toolbars so all controls are still visible when the screen is rotated. Those two additions will complete "version one".
For version two, I'm tempted to extend the program to make it useful for an observer with binoculars. This means the observer has both magnification and greater light-gathering capability than the program is currently set up for. So I'd need to add the ability to show just a selected, small patch of the sky on demand and I'd have to show dimmer objects.
The catalog would therefore have to include about 10,000 more stars and represent the brighter Deep Sky Objects. I'd also like to be able to show the name of a selected star and of its constellation. This would be a teaching aid.
Besides being an aid for viewing the night sky, the star chart can show how the sky looks from somewhere else and/or at some other time. You can demonstrate what it means to live on a round, rotating planet.
You can show that the sky moves one way as the year progresses while the moon moves the other at about 13 times the rate. You can show how the planets seem to move roughly in the same path. You can even show that the moon will occult the planets and eclipse the sun. Even if your inside
I suppose it even could be used to teach Python programming for the XO. At least it helped me learn to do it! You can read about my adventures in programming the StarChart Activity on the OLPC News Forum.