Geo-stats are geostationary communication satellites in nearly circular orbits, in the equatorial plane of the Earth, and with an orbital period of one sidereal day. If these three conditions are met, an artificial satellite will be stationary above the Earth. They are usually invisible to the unaided eye (limit of magnitude 6), since the geo-stat’s average brightness is magnitude 12. At night, stars will trail through a fixed camera time exposure of this scene. We have learned how to photograph them using a fixed simple camera from Kitt Peak Mountain in Arizona. We give examples from 30 years of annual observations with identifications from the European Space Agency. One example is over East Africa—yes, seen from Arizona.
As a solar observer on Kitt Peak in Arizona one has evenings free, and I have amused myself with photography of twilight phenomena. One such exposure near the McMath–Pierce Telescope in the early evening sky revealed, in addition to the expected star streaks, a curious line of three fixed “stars” (Fig. 1). These proved to be geostationary satellites, or geo-stats. That we were aimed at the equator of the sky may be judged by the red streak due to the equatorial Orion nebula and the three bright stars of Orion’s Belt. Since the latitude of Kitt Peak is 31°N, the sky equator is that distance south from directly overhead.
Geo-stats are relay communication and environmental satellites with nearly circular orbits, in the equatorial plane of the Earth, and with an orbital period of one sidereal day—the time it takes the Earth to fully rotate measured relative to the fixed stars rather than the sun. If these three conditions are met, an artificial satellite will be stationary in space about 35,786 km (approximately 22,276 mi) above the Earth, and subject only to minor gravitational effects of the moon, the sun, and an imperfectly circular Earth. At night, stars will trail through a fixed camera time exposure of this scene (Figs. 2a,b). Identification of satellites was done using the European Space Agency’s (Flohrer and Fray 2016) “List of satellites in geosynchronous orbit.” This list includes geostationary objects, presumably because many satellite orbits are close but imperfectly circular.
Satellite structures cannot be resolved because such details subtend less than 0.01 arc s (Hindsley et al. 2011). At the end of 2015, according to ESA publications dated 3 June 2016, there were more than 400 objects within the geostationary band worldwide whose longitude and latitude were fixed and under intermittent control. Such control is maintained by periodic small gas discharges from the satellite—this is called “station keeping.” According to an international agreement, before the gas supply is exhausted the satellite is supposed to be boosted into a 300–400 km higher supersynchronous, or “graveyard,” orbit. This operation requires the equivalent of about 3 months of station keeping, depending on the satellite. It will then no longer be geostationary, and lunar and solar gravitation will cause it to move farther away from Earth over subsequent years (air drag is negligible). Station keeping is expensive in terms of total satellite lifetime, and it is not always done.
If you watch TV or use the Internet, geo-stats may be the relayed source of your signals. These satellites have expected lifetimes of 12–15 years. Their brightness in the sky is from reflected sunlight and has a stellar magnitude of 10–14 (recall the naked eye limit is around magnitude 6). Exceptions (called “glints”) occur when chance solar reflections arise—for example, off solar cell arrays. In a glint, a geo-stat may be visible to the naked eye for around one minute.
At present, a single 8-h fixed Hasselblad camera exposure on Fujichrome 100 film, with its 80-mm lens set at f/6.3 and its 40° field centered east–west on the cloudless sky equator, reveals about 38 geo-stat objects. Figures 2a and 2b are dual pictures taken 2 years apart on 29 March 2014 (top half) and 3 March 2016 (bottom half). The fixed dots across the frames are geo-stats transmitting to both North and South America. The camera position is near the McMath–Pierce Telescope on 2,120-m-high Kitt Peak. Both exposures were from approximately 1930 to 0330 MST. In this picture, most satellites are unchanged in position over the 2-year span and only slightly changed in intensity.
An enlargement is seen in Fig. 3. Occasionally, two satellite images will overlap because of a lack of camera resolution. In this case, AnikF1R, a later observation of the same area, overlaps AnikG1 (by 0.01° latitude) and the latter is not listed.
At about $500 million each, including launch costs, the display in Figs. 2a and 2b thus represents $20 billion (U.S. dollars). Most geo-stats that we record can be identified and are largely commercial. Only one geo-stat here is labeled with a question mark. The lack of an ID could be because it was launched after the ESA credits closed. There are no “spy satellites,” since they are against the law over the United States—but not so over the non-U.S. sky. I am told “secret” objects are not allowed over the United States, but this term has not been explained to me.
An example from our data of how the number of geo-stats has changed over the years is shown in Fig. 4.
Expanding our 40° field of view to the full span of the sky over Kitt Peak is a horizon-to-horizon composite assembled by Anna Malanushenka (Figs. 5a,b). A detail of the east limb for 9 February 1999 is also shown in Fig. 5b. The satellites Intelsat 706 and Intelsat 709 were in fact over the Middle East (recall its elevation is approximately 35,786 km above the Earth’s equator).
We have taken a few recordings on our travels using the same photographic method. One (Fig. 6) at Teide, in the Canaries, has good identifications, and the ownership is indicated. These observations proved helpful for identifications elsewhere near the horizon.
Arthur C. Clarke (1945) proposed the practical use of the geostationary orbit for communication. Eventually this activity evolved into the TV and Internet, among other uses. Another example of Clarke’s imagination is seen in the movie 2001: A Space Odyssey, which he coauthored. It is now somewhat ironic that the pictures in the present article were a product of such old-fashioned techniques: long time exposures on film; pointing of the camera in the sky over Kitt Peak by visually sighting due south toward the summit of Baboquivari, our reference point, on the O’odham reservation in Arizona (Fig. 7), and the equator—over which sit stationary “stars”: geo-stats.
We acknowledge help from Roger Lynds, National Optical Astronomy Observatory, and Anna Malanushenko and Jack Harvey, both then at the National Solar Observatory.