I think that's a very good idea. I myself do not do celestial navigation - I put that code in at the request of a user. So I do not have a good idea about what features would actually be useful for celestial navigators. But I'm very happy to put stuff like this in the code, because it is functionality that I don't think exists in Stellarium et al., and more importantly it's exactly the type of code you want to have in an app that has been optimized for use without a cellular data connection. When writing an app like this you must ask yourself if you're really adding any value to the phone above what the user can get merely by using their web browser and Google search. Clearly things like offline celestial navigation will be of use to some people. Furthermore, the number of people who actually do celestial navigation is probably too small to grab the attention of commercial app writers (although no doubt someone has written such apps for iOS and Android by now).

I'll think about how to do this, and I may try to get comments from you about it before I implement the code. As I said, I don't do this myself, so I need some help to figure out what the user really needs. Also, the Hildon widget set doesn't really contain a good widget for entering floating point numbers, so details about data entry have to be thought about with some care.