From what I've read he gave a lot of money to help people get into science.
I'm not that keen on the idea of Brian May presenting the Sky at Night unless he's really committed to doing it as a serious venture.
The last thing the show would need is a series of transient celebs coming through. It may also be an issue if someone like Brian May wanted to be paid for doing it. The BBC may well use that as an excuse to kill it. I'd love to know outside of travelling costs what Chris, Pete and Paul were paid for doing the show, not a lot I'd bet.
I wouldn't consider Brian May to be a 'transcient celeb'. He did co-author 'BANG' with Sir P and Chris, he did return to complete his Phd, he was a long-time friend of Sir P, has been actively involved in promoting astronomy, and is worth about £90 million so I don't think payment would be much of an issue (!). He is alspo very committed and active in several 'causes'