No, GPS is transmitted directly from the satellites at ~1.5GHz to your GPS receiver. It has nothing to do with phone data. (If it did, Magellan, TomTom and Garmin GPS receivers would need phone connections.)
But some GPS apps need a data (2G, 3G or 4G) connection. Imagine a GPS tracker that lets your boss know where you are all day - in real time. The GPS knows where you are, but the device needs a phone connection so it can transmit that data to some server that shows you on a map.
I don't know what kind of app you're talking about to scan the night sky, but if the app needs Kepps (lists of where things like the ISS are at the moment) it's going to need a data connection. If it's showing where Mars is tonight? That's math and, given a few starting numbers, you can calculate exactly where Mars will appear to be at any moment from any spot on Earth for the next - is it 8 billion years of so before Mars becomes a cinder? No data connection needed for that.
Without A-GPS (getting the current satellite positions from a ground station), it might take the GPS a lot longer to lock up. (Remember, each channel has to get the entire word from the satellite to be able to read its location. One little noise burst and it has to wait for the start of the next word, then start all over.) That's why some cheapie GPS receivers can take 10 minutes for a cold start, while your cell phone should have a fix from at least 4 or 5 sats in a minute or less.
So I guess the answer is "it depends". Which apps are we talking about?
