As I was walking home from work the other week, I looked up at the sky and saw the crescent moon shining beautifully, and then I noticed a particularly bright object in the sky just below and to the right of the moon. I immediately recalled from earlier in the day a few tweets from various people I follow on Twitter mentioning that Jupiter would be visible to the unaided eye that evening. And as coincidence would have it, I happened to have downloaded the free Planets app from the App Store just that afternoon. I took out my iPod touch, clicked on the app, and because it knew my current location, the app could immediately tell me which objects in the night sky were visible from where I was standing. And there they were--the Moon and Jupiter. Pretty rad.
Planets--not to be confused with The Planets--is a pretty nifty utility from Q Continuum that does just a few things, and it does them well. Not nearly as full featured as John Kennedy's affordable Pocket Universe, Planets delivers nonetheless; best of all, it's free.
The app's main screen is the Sky screen. On it is a compass-like image that shows you which objects are currently visible to you in the sky. For example, during the daytime, the most common visible object would be the Sun. Sometimes, you're also able to see the Moon during daylight hours. At night, you should usually be able to see the Moon and maybe even some planets. The Sky screen also maps the constellations that are visible in the night sky, though it doesn't identify the names of the constellations on that screen. For that, you need to tap the Sky 3D icon, a newer addition to the app.
The compass-like image of the Sky screen is also a real compass. Tap once on the North/South button in the upper left, and the image flips to show South on top and North on the bottom. Tap it again, and you have yourself an actual compass that moves to show you your orientation just as the iPhone's own Compass app does. To flip the East/West orientation, tap on the East/West button in the upper right.
The Sky 3D screen is a supercool addition to this free app. As its name indicates, this screen shows the heavens in 3D. There are north, south, east, and west compass indicators in this view. Slide your finger up, down, left, or right to view the constellations and planets as seen from your current location (or any location you set in the Options screen) on Earth. This view shows the constellations and their names. It also shows the planets in our solar system on the ecliptic path of the celestial sphere--so you can see exactly where each planet is on its orbital path and when planets are in alignment with each other. I easily got lost in constellation bliss for a while just looking around the Sky 3D screen.
On the Visibility screen, the app gives you information about when you can expect to see a given planet or the Sun or Moon on that day in the sky. If you tap one of the selections, you are taken to a summary about the particular object you chose. The Sun screen tells you when twilight begins and ends; the various screens for the planets give you stats, such as type of planet, radius, mass, the number of named moons for the planet, rotation period, and so forth; the Moon screen tells you which phase the moon is in.
Tap the Globe icon from the app's menu at the bottom of the screen to get a 3D globe view of any planet or the Moon. Swipe the globe, and it moves to show you the entirety of the object. The one for Earth, at least, is in real time, so you can see which areas of the globe are experiencing night, and which parts are in the middle of their day.
There is also an Options screen, but the options are few--you can toggle the automatic time, date, and location settings on or off. If you choose to not have your location detected automatically, you can set it manually. And you can toggle the Unaided Eye option on and off. If you turn it off, the Sky 2D screen will show you all of the celestial bodies that can currently be seen with the use of a telescope from your current location or a location of your choosing.
Planets is a very cool quick pocket reference for anyone who is curious about the celestial objects they see in the sky.
[Sue Voelkel is Macworld's managing editor.]
This story, "Planets for IPhone" was originally published by Macworld.