(Inside Science) -- If you look at the night sky, you’ll see stars, planets and vast empty spaces in between. But within that darkness are thousands of satellites revolving around the Earth. They are invisible to the naked eye most of the time, but not to the camera of a curious astronomer with free time.
Astronomer Bill Livingston’s research involved observing the Sun from the National Solar Observatory, at the top of Kitt Peak in Arizona. “That means I'm busy during the day,” he said, “but at the end of the day I don't have anything to do.”
Thirty years ago, before mainstream digital cameras were around, Livingston started photographing the night sky with his Hasselblad camera, looking for twilight phenomena for a book he was working on.
One evening near the McMath-Pierce Telescope, he pointed his camera south and took an 8-hour exposure photo of the cosmos. Because of the Earth’s rotation, the stars looked like bright streaks across a dark sky, as expected. But Livingston also noticed something odd in the photo.
The photo that gave away the geo-stats (left image). The structure on the lower left of the image is part of the McMath-Pierce Telescope. Right image: Some of the geo-stats can be identified thanks to their position on the sky. Intelsat 709 in this photo is over Somalia. Taken in February of 1999.
Both images © American Meteorological Society. Used with permission.
“Then I discovered these little ‘stars’ that were stationary in the sky,” he said. Intrigued, he figured out that they were right on the equator because of the equatorial Orion nebula’s red streak in the photo. With that clue, “I worked out that they were geostationary satellites,” he said.
Geostationary satellites -- or “geo-stats,” as Livingston called them in a paper about the photos published this spring in the Bulletin of the American Meteorological Society -- are satellites with nearly circular orbits directly above the Earth's equator.
At about 35,786 kilometers (approximately 22,236 miles) above the Earth, the artificial satellites stay in a fixed place relative to the Earth and that’s why they appear as dots and not as trails in Livingston’s photos. The satellites are not visible to the naked eye, but the long exposure enhances the little light they reflect. Later, he would identify some of the satellites thanks to a list put together by the European Space Agency.
As of 2015, there were more than 400 objects in geostationary orbits. Most of these satellites are used by communications companies for internet and TV services, but others are used for research purposes. The satellites stay fixed by firing small jets of gas to keep them in the right orbit.
Although geo-stats can now be imaged using telescopes and fancy digital cameras, Livingston only needed an old-fashioned camera, some film, and a special location.
Bill Livingston with his Hasselblad camera on Kitt Peak, Arizona (right). Livingston used Baboquivari Mountain, in the top left corner of the picture, as reference to the south (see the map on the far left).
© American Meteorological Society. Used with permission. Map created by Abigail Malate, staff illustrator.
Livingston has tried to replicate his photos elsewhere -- in California, in Tenerife in the Canary Islands and in Nepal -- but Kitt Peak, at nearly 7,000 feet high, remains the best place to take the stellar photos. “It’s a very good place to do this job,” he said. The mountain -- and observatory -- is far away from artificial city lights, he said. “Kitt Peak was good in that regard.”