When artificial satellites became a fact of life some 40 years ago, someone - reputedly the author Arthur C. Clarke - had the bright idea that if its speed in orbit over the equator were synchronised with the rate of the planet's rotation on its axis, a spacecraft would appear fixed in space; it would look down all the time, like a fixed eye in the sky, on the same segment of the globe. This can be achieved by placing the satellite in what is called a geostationary orbit, where the spacecraft is positioned at about 23,000 miles above the Earth.
It takes about five weather satellites positioned around the Earth in this way to provide pictorial coverage of the entire globe. The "who'll-do-what?" arrangements are arrived at by a combination of voluntary effort and international agreement, the objective being to ensure the whole world is captured, but also, because of the expense involved, to try to keep overlap to a minimum. Let's look at "who's who" in geostationary orbit.
In this part of the world, weather images from geostationary orbit are provided by the Meteosat series of satellites operated by EUMETSAT, the European Meteorological Satellite Organisation. Its main mission is to provide a weather satellite over the intersection of the equator and the Greenwich meridian, which turns out to be a spot to the west of Africa in the Gulf of Guinea.
Meteosat-7 is in that position and has a bird's-eye view of Africa and Europe. Satellites have a limited lifetime, and replacements must be launched at regular intervals; the 7 indicates this is the seventh spacecraft of the Meteosat family.
Further west are two satellites operated by NAOA, the National Atmospheric and Oceanic Administration of the USA. These are called GOES satellites, for Geostationary Operational Environmental Satellites; GOES-8, commonly called
GOES-East, looks down in Quito in Ecuador where the 75th meridian intersects the equator, and GOES-West is over the Pacific at 135 degrees west longitude.
The equatorial skies are a little crowded over Asia. EUMETSAT has a spare satellite, Meteosat-5, at 63 degrees east over the centre of the Indian Ocean. India operates two geostationary satellites, one at 74 degrees east, to the west of the southern tip of the Indian subcontinent, and another a little further east at 83 degrees.
Russia plans to launch one at 76 degrees east in two years, and China already has one in position at 105 degrees east, looking down on Indonesia.
A Japanese geostationary meteorological satellite is stationed at 140 degrees east, looking down on Papua New Guinea.