It's called a Helios Planetarium, and would normally cost £400 or so, which considering what's inside it (a motor, some gears, and a torch bulb) is a bit silly. What it does, of course, is show the movement of the planets out to Saturn with the gearing correct so that you get a couple of Earth years in one Mars year and so forth. It comes with a set of tables so that you can set the position of the planets for any date then set things in motion to see them change. No other electronics - it's purely a mechanical system.
They're obsolete, given the astronomical software that's available, but I've always wanted one - it's been on my geek toy list for many years, and I've had it as an eBay search for the past three years. This was the third I've bid on and the first I could afford, possibly because the vendor only has 2 feedback.
It's fairly obviously been in a cupboard for many years, you can tell by the state of the box and the corroded battery compartments (fortunately it has a mains power unit too, which looks like it was originally designed for a train set), and it's missing an extra globe that's used for demonstrating eclipses, but I can live with that - shouldn't be too hard to fake something up.
The only problem is the sheer size - somehow I had the idea it was about a foot wide, but it's a good deal bigger. One of my "tidying the flat real soon now" goals will now be finding room for it somehow.