[jfindley]

I don't believe this is entirely correct. DSLR sensors get very hot during long exposures - to the point where excessively long exposures can introduce noise into the output from this heat. I don't see why this wouldn't apply even more so to phone sensors, with their incredibly high photosite density.

However really long exposures are going to suffer from star trail effects - the earth is rotating relative to the stars, so a long exposure changes stars from a point to a short line, which _usually_ isn't what you want. On a 35mm camera with a fairly wide lens you can get away with ~ 30s of exposure time.

On a pixel phone I think you'd be able to get away with ~ 3s exposure time, but as it's going to get pretty hot over this time I'm not sure how much extra image quality you'd actually end up with.