Streaking through space at 5 miles per second, the International Space Station is the largest satellite ever built, massing 670,000 pounds and stretching 357 feet--longer than a football field--from one end of its main solar power truss to the other.
An hour or two before sunrise and after sunset, when you are in Earth's shadow and the space station--orbiting 220 miles up--is still illuminated by the sun, the ISS outshines Jupiter and rivals Venus as it sails across the sky.
The space station is by far the easiest satellite to see--it's impossible to miss if you're looking up when it's passing over--and occasionally, a truly jaw-dropping sight.
If the solar arrays catch the sun just right, it can flare and outshine anything in the sky but the moon. And if you're really lucky, you can watch a space shuttle approach or depart, a second, slightly dimmer "star" moving in lockstep with the station.
In years past, amateur satellite trackers relied on desktop software to predict when a satellite might be visible from a given location, manually plugging in or downloading NASA two-line elements--a string of numbers that defines a spacecraft's orbit--to generate sighting opportunities.
Later, NASA and other services automated that process and put it on the Internet. Chris Peat's Heavens-Above is the most sophisticated and widely used satellite tracking resource, allowing enthusiasts anywhere in the world to find passes for virtually any satellite in orbit.
With the introduction of Apple's iPhone and iPod Touch, satellite tracking entered a new era of convenience and ease of use. Now, you can check on the space station, the Hubble Space Telescope or any other satellite while watching a football game, camping out or doing just about anything at all.
At $9.99 it costs more than the typical app, but as my father used to say, "you get what you pay for." This powerful, beautifully rendered program has become my satellite tracking software of choice. Compared to .99 apps, it's relatively expensive but believe me, it's a genuine bargain.
GoSatWatch allows you to manually load multiple viewing sites--my home, my parent's house, towns I frequently visit--or you can rely on the iPhone's GPS.
Once the program knows where you are, you tell it which satellites you're interested in and make sure you've got the latest two-line elements. You do that by touching the update button (a circular arrow) on the Satellites page.
I reload elements every three or four days to ensure accuracy. An Internet connection is required for updating, but not for in-between use.
GoSatWatch comes pre-loaded with the space station and about 150 other satellites. The station and the shuttle are listed separately to make them easier to find and update. When new spacecraft are launched, they show up in the "visible satellites" tab on the Satellites page.
The program remembers your selections and will auto-load them the next time it's launched.
With your targets selected, program operation is virtually automatic. On the main Map page, the selected satellites are shown in their actual locations on a live map of the world. Touch one, and its next three obits are shown. Turn the iPhone or Touch sideways and the view rotates into landscape mode.
The map normally runs in real time, but you can speed it up or slow it down if wanted. A red view circle around a satellite indicates when it is above the horizon. If you're location is inside the circle, the satellite is visible in your sky.
The Passes screen lets you see if your selected satellites will be visible that night or any upcoming night. As with all satellite tracking applications, GoSatWatch gives you the time the satellite rises (or leaves Earth's shadow), when it reaches maximum elevation and when it sets (or moves into shadow), along with compass headings for each.
When a pass is found, just touch it and GoSatWatch will draw the satellite's path across your sky, showing the moon and stars in their actual positions. If you check the Sky page in the daytime, it shows the current position of the sun and moon.
The portability of GoSatWatch really shines when you go outside for an upcoming pass. When the satellite climbs above your horizon, a small image of the spacecraft appears on the Sky track that moves in concert with the real thing. A quick glance at the screen shows you exactly where to look.
GoSatWatch is on the home screen of my Touch and it's one of my most frequently used apps. I can't find any significant flaws in the program or its execution. It will occasionally warn of a "low memory" condition and ask for the Touch to be restarted, but I just dismiss the warning and press on. All in all, this is a near-perfect app.
If you've never seen the space station or used a tracking program, you'll enjoy GoSatWatch's ease of use. If you're a veteran satellite watcher, you'll love the portability. On top of all that, it's a great way to impress the neighbors.
But the real payoff is watching the space station fly over. If GoSatWatch does nothing else, it will encourage you to get off the couch, go outside and take in one of the modern wonders of the world.