Stellarium describes itself as a “free open source planetarium for your computer.” That’s right, folks. This isn’t just software. When you install Stellarium you get instant guided access to the heavens above. There is a choc-a-bloc library of stars, constellations, nebula, planets and their satellites – and you can see them all in ravishing, 3D detail. It’s like having your very own observatory, In fact, it’s the software of choice in many real planetariums. Just download and off you go, explorer. Did I mention it’s free?