This picture shows the nocturnal naval lights over the antennas of a telescope system in California, about 470 kilometers northeast of San Francisco. In this sparsely populated area there is around 1000 meters in height that has Creek Radio Observatory (HCRO), an observatory with several telescopic systems. Since there are hardly any disturbing light sources here, the colors of the Aurora are particularly easy to see.
Most of the Northern Lights appear as the green light in the sky. It is triggered by oxygen atoms in the air at a height of about 120 kilometers when invited particles from space meet the earth’s atmosphere in solar storms. The particles stimulate atoms that release the excess energy as light when they return to their basic state. Red and violet aurors like here in the picture are only created at around 200 to 250 kilometers by nitrogen atoms in the air, which are much more difficult to stimulate and are therefore much less likely to be observed.
The 42 antennas visible here in the contrast to the illuminated sky as black silhouettes have a relatively small diameter of only around six meters and belong to all telescope array (ATA). This radio interferometer, composed of many such antenna bowls, measures radio waves in the centimeter area with frequencies from 0.5 to 11.2 gigahertz – a unique bandwidth in radio astronomy. In doing so, the astronomers of the SETI research institute “eavesdrop on” and look for signals from extraterrestrial life and extraterrestrial intelligence every night. The US Air Force also monitors satellites and space scrap with the system.
The construction 308 of other such antennas is planned to cover an even larger area of the night sky and to be able to examine several stars at the same time. Currently, the telescopes can monitor around 1200 square meters of sky at the same time-already 17 times more than the significantly larger antennas of the very Large Array (VLA) Telescope system in the US state of New Mexico.