October 31, 2007


Stellarium is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope. It is being used in planetarium projectors. Just set your coordinates and go.

That is from the home page. The way I stumbled on this software is because of an Indian festival that requires wifey to fast until she has seen the moon. A quick Google search to find the trajectory of the moon led me to this blog entry, and eerily the author of this article had also found the software for the same reason.

Now you might think why I need a software to locate the rising of the moon. After all, the moon follows the sun in its rise and set pattern, so moon should just rise in the east right? Wrong! One of the tidbits I remember from my astronomy club at school is that the lunar orbit is elliptical, which causes a daily variation in the directional orbit of the moon for an observer in the earth. Here is what Wikipedia has to say…

The orbit of the Moon is distinctly elliptical with an average eccentricity of 0.0549. The non-circular form of the lunar orbit causes variations in the Moon’s angular speed and apparent size as it moves towards and away from an observer on Earth. The mean angular daily movement relative to an imaginary observer at the barycentre is 13.176358° to the east. The orientation of the orbit is not fixed in space, but precesses over time.

Anyways, I have used a few planetarium software in my school days from being in the astronomy club. And this tool has pretty much everything you need for an amateur astronomer. The user interface is also very slick.

You basically specify your location in terms of latitude and longtitude, and can look at the object in the sky. You can pan and zoom around. It also has a neat search feature, where you type in a celestial object, and it would pan, in a Google-earth-stlye, to that object. It also has quite a few interesting layers for constellations, azimuthal grids and so on.

The only problem I have had so far is the ability to retrieve a saved location. The software always seems to start up in the last location, and I cannot seem to find a way to list and use a previously saved location.


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