All of us have used Navigation Satellites, whether you realise it or not. Our modern western world can no longer function well without them. But it is a challenge to actually see them in the sky. In Medium Earth Orbit (MEO) at altitudes of ~20 000 km, they stay faint.
Four large constellations of Navigation satellites currently exist. The best known is the US GPS system (aka NAVSTAR). But there is also the European GALILEO system; the Chinese BEIDOU system; and the Russian GLONASS system. Together, they are often referred to as the Global Navigation Satellite System (GNSS).
In the evening of 6 November 2023, when the sky over Leiden was very clear, I by chance imaged examples of all four systems, largely within the same small part of the sky, while surveying for HEO objects. Here are some images, one each for each GNSS system (the images were made with a ZWO ASI 6200MM PRO camera and 1.2/85 mm lens, 10-second exposures):
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| NAVSTAR 73 (GPS) |
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| GALILEO 21 |
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| BEIDOU 3M7 |
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| KOSMOS 2501 (GLONASS) |
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