While astronomy apps tend to have a built-in nightmode, I was very pleased to come acrossChainFire3Dfor Android which, among other things, has a global night mode that works on all apps. The red is a bit too bright, I think (maybe someone should email the developer about it), but otherwise I think it's great. It needs a rooted device. p.s. I'm still working away on AstroObserver. It's going more slowly than I'm used to, partly because I've been sick. I'm basing it on AstroTools, but I'm redoing a lot.