The Milky Way and planet Jupiter shine brilliantly in this photo from the top of Mauna Kea. The yellow glow are the lights from the city of Hilo, located about 25 miles (40 km) away from the mountaintop summit. (Credit: Jason K. Chu; NOIRLab/AURA/NSF)
There are a number of factors to consider when choosing where to build a telescope. These 3 locations, on their merits, surpass all others.
Astronomers observe the Universe by looking up.
This photo shows Gemini South’s laser guide star system in action. The telescope is located atop Cerro Pachón in the Chilean Andes. The laser interacts with particles in the Earth’s upper atmosphere and allows for real-time corrections of the telescope’s optics to compensate for atmospheric turbulence. The laser light from the sodium layer actually goes up ‘only’ about 60 miles before colliding with a thin layer of sodium in our own atmosphere, which absorbs and re-radiates that light, creating an artificial guide star. (Credit: International Gemini Observatory/NOIRLab/AURA/NSF/M. Paredes)
The best observations demand that many factors be overcome.
As light strikes the Earth from space, it must pass through the various layers of the atmosphere, where it’s distorted by turbulence, clouds, molecules, and can be absorbed and/or reflected as well. The atmosphere distorts incoming light, which is a huge obstacle for ground-based astronomers. (Credit: Fyodor Yurchikhin/Russian Space Agency)
For astronomy, gathering light undisturbed by the atmosphere is key.
Under a pristine night sky, the Milky Way’s center casts shadows. As light pollution worsens, nebulosity and stars disappear, until maybe a few dozen stars remain. The numbers 1 through 9 are the Bortle scale, which provides observers with a metric to measure the darkness and clarity of the sky overhead at their location. Only a few locations remain on Earth with pristine, dark skies. (Credit: ESO/P. Horálek; M. Wallner)
Dark skies, free from light pollution, are mandatory.
Although the Keck Observatories on the summit of Mauna Kea offer some of the best views of the universe from Earth as far as dark skies are concerned, like all sites near the equator, they must now reckon with satellite pollution due to megaconstellations of communications satellites: largely from one company, Starlink. The effects of satellites on astronomy are severe, and are only worsening with more and more unregulated launches. (Credit: Andrew Richard Hara)
High altitudes are also ideal, located “above” the thickest part of the atmosphere.
