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This composite of 70 exposures shows the trail of the ISS passing through the night sky in Germany. (Till Credner via NASA)
Satellite spotting is great fun! With a little preparation you can hunt for satellites on your next camping trip. Whenever our Scouts are looking at constellations and finding the north star someone usually thinks they may have glimpsed a satellite passing overhead.
On a dark, clear night satellites reflect sunlight back to us and become visible. Prime time for satellite spotting is about an hour before sunrise or an hour after sunset. The earth’s shadow blocks sunlight from illuminating most satellites during most of the night. Larger satellites with bigger reflective surfaces reflect more light and are more likely to be visible.
Not all satellites are functioning communications or research satellites. The United States Space Space Command catalogs and monitors active/inactive satellites, spent rocket bodies, or fragmentation debris. The first object in the catalog, number 00001, is the final stage of the rocket which launched Sputnik 1. By 2001, the number of cataloged objects was nearly 20,000. Here’s a mind-blowing visualization of these objects in Google Earth.
The International Space Station (ISS) can be dramatically visible when there’s a minimum of light pollution, no moon, and clear skies. Chris Peat’s Heavens-Above Home Page provides excellent satellite tracking tools. Here’s an example of a chart for tracking a pass of the ISS;
| Date: | 14 April 2013 |
| Orbit: | 403 x 417 km, 51.6° (Epoch: 14 April) |
| Event | Time | Altitude | Azimuth | Distance (km) | Brightness | Sun altitude |
| Rises | [00:27:25] | 0° | 278° (W) | 2,333 | 2.4 | -9.6° |
| Reaches altitude 10° | [00:30:05] | 10° | 300° (WNW) | 1,470 | 1.1 | -10.1° |
| Maximum altitude | [00:32:15] | 16° | 342° (NNW) | 1,151 | -0.5 | -10.5° |
| Drops below altitude 10° | [00:34:25] | 10° | 23° (NNE) | 1,468 | -0.5 | -10.9° |
| Sets | [00:37:04] | 0° | 46° (NE) | 2,327 | 0.3 | -11.4° |
You can generate charts for your location using the tools at Heavens Above. The brightness of objects is rated numerically, negative numbers are brighter than positive – the full moon is rated -13 and objects up to +4 are generally visible to the naked eye.
I suggest using the “Daily predictions for brighter satellites” link you’ll find in the left hand column of the Heavens Above page to search for objects with a minimum brightness of 4.o. Using your tracking chart locate the predicted track of the object in the night sky several minutes before the first time on the chart and keep an eye out for these lights in the night sky.
