Many readers probably have already, without knowing it, seen an artificial satellite moving across the sky. At first glance, there is nothing spectacular about watching "slowly moving stars", since that is what artificial satellites look like. Yet, since the launch of Sputnik 1 in 1957, thousands of amateur astronomers have become fascinated by these artificial objects. The reasons are manyfold, but the at times unpredictable behavior and the scientific usefulness of observations certainly play an important role in this fascination.
There had been about 4900 successful satellite launches by the end of 2015. Each of these launches not only delivers one or more payloads into Earth orbit, but also leaves garbage in space. This garbage may include the third or fourth stage of the launcher, nose cones, apogee or perigee kick motors, etc. A number of satellites and rocket bodies have exploded, polluting the near Earth environment with small fragments. Technically, this garbage is known as orbital debris.
All these objects are regularly tracked by means of the sensitive radar equipment of US Space Command (USSPACECOM). USSPACECOM is a US military organization (formerly NORAD) which assigns a catalog number to each object in orbit. By the end of 2015, 41189 objects had been catalogued of which more than 17446 remained in Earth orbit. The others have burned up in the Earth's atmosphere, landed on Earth or another celestial body or continued into the solar system and beyond. There is still an unknown number of very small fragments which are too small to be discovered by radar.
Hundreds of satellites and rocket stages can be observed with the naked eye, thousands using regular binoculars. The requirements and conditions are covered in the observing introductory guide.
The International Space Station ISS can become as bright as magnitude -4.
Telescopes and sophisticated tracking methods enable observation of structural details of large and low orbiting satellites, or to see small fragments.
The observer can make observations of both a positional and rotational nature.