File:How the illumination of satellites is made visible from Earth.jpg

English: "Illumination of satellites. Satellites are only visible when the Sun illuminates them and the background sky is not too bright. The higher the altitude of the orbit, the longer the satellite is outside the shadow of the Earth. The view is from the South Pole."

"The subject of this section is how to recognise signs of artificial objects in the pre-satellite images. For low orbits the evidence could be satellite streaks. Fig. 1 shows how the illumination of satellites is made visible from Earth. Typical low-orbit satellites that can be seen by the naked-eye do not emit light themselves, and are visible through the reflection of sunlight. Obviously they cannot be observed during daytime because of the sky brightness, and at night they are in Earth’s shadow for most of the night. That means they are best observed either before sunrise or after sunset. They are seen as fast-moving point sources, giving rise to long, continuous streaks in photographic images of long exposure. A satellite whose reflective surface is spinning gives rise to dashed or broken lines. Continuous streaks may often be confused with natural objects e.g. meteors or asteroids. Closer inspection can be used to distinguish between meteors and satellites, for example fainting edges."

"Both targeted and untargeted searches for laser signatures have been reported. [7], [8], [9], [10]. Meanwhile, alternative new concepts for how to search for ET are emerging, [11], [12]. Many of these ideas propose searching for ET far away, in distant galaxies or around other star systems.
Of these different research topics within SETI, solar system SETI has received far less attention than others. This is paradoxical, as humans have demonstrated the motivation and the capacity to send exploratory probes to other stellar systems. For example, the Breakthrough Starshot program plans to launch a probe to Alpha Centauri within twenty years. If humans have these capacities it seems natural to search for extraterrestrial probes or other so-called “Non-Terrestrial Artifacts” [13], [14] inside our Solar System."