Basic version astronomy app goes free for now.
The basic version of SkySafari 4 shows you 119,000 stars, plus 220 of the best-known star clusters, nebulae, and galaxies in the sky. It displays the Solar System's major planets and moons using NASA spacecraft imagery, and includes the best-known 500 (or so) asteroids, comets, and satellites. It accurately shows you the sky from anywhere on Earth, at any time up to 100 years in the past or future, and lets you identify stars, planets, and constellations with your iDevice's GPS, compass and/or gyroscope.
Sorry, no deal on Android just now.