Today’s cool bit of software is Stellarium: a realistic sky simulator available for both Windows and Linux and Mac OS X (thanks mneptok!). While it is unlikely to fufill the needs of a serious observer of the heavens, it is a dead simple application which provides beautiful views of both the day and night skies. It is supposed to have over 120,000 stars in its database, but the catalog itself seems fairly weak to me: it didn’t seem to have appropriate double star data. But if you are just a skygazer or you frequently scan the sky with small telescopes or binoculars, this program might be just what you are looking for.