There used to be a time when you could easily impress a date by pointing to the night sky and dreamily rattling off names of major stars, constellations, and the like. Now, instead of cramming your head full of names or making up stuff as you go along, you can use your trusty iPhone to guide you through your stargazing. There are a bunch of apps that you can download, depending on your interest level and degree of expertise. Most of the apps are based on augmented reality--so all you have to do is point your phone towards the sky and the app does the rest. If you're a beginner, Pocket Universe ($3) and Star Walk ($3) are recommended by The New York Times for iPhone users; while Google Sky Map is great for Android users. With Pocket Universe, you can use the camera view to look at the evening or morning sky, and the app will overlay the labeled view over the real sky. (The iPhone's camera isn't good enough yet to pull off this feat with a dark night's sky.) The app also plots the position of the sun, moon, and planets, displays 10,000 stars, and traces the shapes of the ...