Star Walk is a pocket planetarium for your iPhone or iPod touch. Serious astronomers may need a more sophisticated tool, but I find myself burning through countless hours exploring the cosmos now. Shoot, I might go buy a darn telescope, and finally embrace my uber-geekiness!
You can install Star Walk through the App store (do a search for "star walk") as with any iPhone or touch application. It'll set you back a measly $4.99US. Once installed, it will detect the default location and calibrate the sky view to your locale and time zone. You can also set or change the location manually. So, in essence you could tweak your locale and use Star Walk to simulate the next solar ecclipse, and watch on your iPod sort of. Yeah, I know...not as cool as getting in your lear jet and flying there to see it (was that in a song?), but hey, whattya want for 5 bucks!?
Star Walk nicely breaks the aerodrome over and under your feet into 2 halves. Think of standing in the cente of a sphere. Below the horizon line (a red dashed line), celestial objects are still visible but more darkly shaded than the sky view above. Direction markers for N, S, E, W are displayed in a semi-transparent gray arrow as you turn your body through the directions (by dragging/flicking the display with your finger). The solar elliptic is indicated by a continuous yellow line circling the aerodrome. You navigate in all 4 directions using finger gestures, and can select celestial objects (stars, planets, nebulae, galaxies, etc). A green target-like indicator is then displayed around the object and a more zoomed view will appear if double-tapped (this can be used anywhere on the display). The typical 2-finger zooming in/out is also available. Icons quite similar to those in Google Earth (one for each corner) are indicated in a glowing, green, vector-like manner--think of targeting on the Death Star. Selecting objects (the "i" or information icon, for example) will also produce retro sounding beeps, animations and sound effects that are quite engaging (much like a video game). As you browse the universe, Star Walk points out major constellations to you by briefly flashing a semi-transparent shape (see first screen shot) over the normal dot-connected pattern indicated.
Star Walk Search..
As mentioned before, you can navigate around using your fingers, or select the search icon in the lower-left corner to query your favorite star, constellation, or planet. As you navigate across the sky, especially at lower zoom levels, the celestial objects even appear to move in a 3-D perspective that is quite realistic. The only complaint I have is there is no option to try to properly scale any of the planets, stars, moon or Sun. Diurnal light is applied appropriately during day/night periods to the sky (the Sun lights up as it passes over the horizon), and proper moon phase is also indicated.
Star Walk's coolest feature in my book is the ability to fast forward or reverse the cosmos by various time/date increments. When you select an object (like a planet) for instance while doing this, it is very easy to visually find a time that the object will be sufficiently high enough in viewing angle to see well (see screenshot above). It would appear that Jupiter and Venus should be just above the horizon on Dec 6, 2008 (at least at my location) will mean they should be relatively bright in the early evening sky. With just a flick of the scrolling time interface, I can send the sky wheeling around back/forward in time. By selecting a particular object, the display will stay focused there while the rest of the background changes instead. This is also useful for quickly determining what the level of lunar illumination might be during that time. As you see above, there appears to be no moon in the vicinity, but the moon is actually higher overhead and at half-moon phase, so probably in the early evening would be the best viewing time possible if at all. Or perhaps you might use this method to determine the next solar ecclipse near you, as suggested before.
The Information display appears when you have selected an object and then tap the "i" icon in the upper-left. It animates to a zoomed up view of the object, and then presents a list of factoids or details inside a left-side column. Most of the planets, the moon, and the Sun will produce factoids, whereby stars and such will produce more mundane specs. I would like an option here to switch the mode to display the actual declination, and elevation, for planetary objects as well as stars.
Conclusion: If you want a REALLY AWESOME experience exploring the solar system in a 3-D space simulator, try the completely gratis PC/MAC/LINUX program called Celestia. If you want a very good, uh shall we say, more earth-bound but similar experience on your iPhone, or iPod touch, go buy Star Walk from VITO at the iTunes app store. Whether you are a novice or expert astronomer, I believe you will find it entertaining and useful. At the very least, it'll be a cool ice-breaker at parties!