iObserve is a great app for aiding planetary observations and for use in planning future observations. It includes a number of features that can quickly help you tell which planets are visible from anywhere on earth at any given point in time. The interactive displays are carefully thought-out and are not only fun to experiment with but provide a lot of data in an easy to understand format. Specifically there are three main interactive graphics: (1) a nighttime summary of planets above the horizon, (2) the positions of the four largest moons of Jupiter, and (3) the positions of five of the larger moons and ring orientation of Saturn. There is also a table with the complete list of rise, transit (highest point in the sky), and set times for the planets, Pluto, the Moon, and the Sun, along with specialized Sun timings for astronomical, nautical, and civil purposes. Finally there is an easy to use interface to set your current location (or any position on Earth you are interested in), which can also make use of the GPS or other location services on your device. iObserve has an overall dark interface theme to make it easier on the eyes when used at night.