Home page shows exact Lat/Lon
The app is very easy to use. Basically, it uses location services to identify your location on Earth, and then draws from www.heavens-above.com (with permission) in order to create list of overhead passes during which the ISS will be visible. The author, Simon Vrdoljak, told TMO:
Even the charts that I use come from this website. The only calculations I do is to convert dates and times to the local time zone, calculate the pass length, and calculate the time left until the pass. I also display everything in dark colour scheme to help with night vision.
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Future list
After you select one of the passes, more data is shown for that pass. The duration of the pass is shown in the initial list to help you select a good viewing opportunity. Passes of less than a minute are likely to be low on the horizon, possibly behind houses or trees. Passes closer to six minutes will be almost overhead.
ISS photo: courtesy NASA taken from Space Shuttle (STS-114)
After you select a pass of interest, more details are shown. The local time and azimuth when the ISS is first visible is displayed along with the same data for both the highest elevation and the end of the pass.
The ISS is visible because it’s reflecting sunlight, and it looks like a very bright star, but moving fast. Sometimes it gets as bright as a planet like Jupiter or Venus — and that could be confusing for those not in the know. However, the ISS is, generally, not bright enough to see with the naked eye in the day time, so all of the visible passes will be at night or during twilight.* The astronomical magnitude is also computed and shown.
Pass data
Finally, you’ll have the option to see two kinds of sky charts to see what constellations the ISS will be passing through. Also, the ground track is displayed, and you can two-finger pinch to blow up the image. By imagining a perpendicular line from your location to the to closest approach of the ground track, you’ll have an estimate of the time when the ISS reaches the highest elevation. A circle in red shows when the ISS falls below the horizon.
Ground track
I found the app easy to use, so easy that there’s really no need for additional explanation or info panels. (However, it wasn’t apparent whether the bar graph on the pass list referred to the duration of the pass or the brightness.) Also, in the current version (1.3), there’s no way to get back to the home page without restarting. It really doesn’t matter because after you set your location, there’s really no need to go back. Mr. Vrdoljak told TMO that the next version will allow multiple locations.
If you’ve ever wanted to take a look at the ISS as it passes overhead, here’s a neat app that’ll help you identify good viewing opportunities. Note, you won’t see a whole lot more with binoculars, even 12x image stabilized binoculars. That’s because the ISS orbits at an altitude of about 215 miles (350 km), and much more magnification (and image stabilization) is required. However, one amateur astronomer I know has reported seeing the solar panels in an 8-inch (20 cm) astronomical telescope that was programmed to track the ISS.
ISS Visibility version 1.3 requires iPhone OS 2.0 or later and is priced at US$1.99.
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Here’s a NASA site you can use to view ISS status in a Web browser, but it’s not nearly as detailed with pass data. (Note, however, the zoom buttons at the bottom right.)
* Another handy iPhone app that shows the times of civil, nautical and astronomical twilight — in addition to sunrise/sunset — is Magic Hour by Vela Design Group.