It's not surprising that Google has done such a good job with this software, after all, Android is their phone platform, and they should now it (and the reference hardware inside out). The folk in Mountain View also have a huge database of data they can take advantage of - in the shape of Google Earth and all its varied information layers.
So what is Google Sky Map?
It's pretty much what it says on the tin - a piece of software that shows you the sky above you, just like one of those star wheels that give you an idea of the swirl of constellations as they rotate around the night and the seasons. Where it differs from most computer based star maps is that it's live. It's an annotated window into the heavens, using the device's built-in GPS, compass, and G-sensor. The combination of the three lets the software know where the phone is, and where it is pointing - and at what angle. It then calculates the current view, and displays it. Google is augmenting reality, making it part of its world of search.
On a deeper level it's actually a specialised version of what marypcb calls a "What's-That", a device that when pointed at something, well, just does that. It annotates the world with an overlay of information to give us the information we want and need. Phones don't have the power needed to deliver that level of image recognition, but they do know where you are. Constrain the problem to maps of the heavens, and you've got a winner on your hands.
The sky at night can be confusing - with light pollution and high cloud making identification hard. Just being able to point a phone in the right direction to get the names of the objects you can see is an excellent solution to the problem. After all, it's the most personal of devices and one that's going to be with us when we most need it.
Then there's Wikitude, which is a step even further in the direction of the What's-That, using the device camera and the device sensors to overlay points of interest from geo-coded data in Wikipedia and Qype on the phone screen.
Here it is, letting me know what's in the world outside my hotel room. We used it today to identify mountains as we drove up the Cascades.There's still not enough data in the world of public geo-coded information - but what there is is enough to make you want more.
You know, I really like living in the future.