Why Are Observatories Built On Mountain Tops

This site contains affiliate links to products. I may receive a commission for purchases made through these links.

You may be asking why astronomers build large observatories on the mountain tops. Why not build it lower on the ground near the sea level where it won’t require so much work for transporting the telescopes high on the top of the mountain? There are a couple of reasons why the best and largest telescopes in the world are built on the peak of the mountains.

The observatories are built on mountain tops because there is less atmosphere at a higher elevation. The air is dry which means there is less water vapor that refracts light and less light distortion. Also, the air is cleaner so there is smaller atmospheric turbulence which is causing image distortion too.

But let me explain the pros and cons for building the observatory on the peak of the mountain in depth. 

The Advantage Of High Altitude Observatory

The big advantage of having a telescope on top of the mountain is to be above the clouds. Most of the observatories are build high enough to be above the middle cloud layer so they have clean nights to observe the universe even if it’s cloudy in the area below the mountain top. As an amateur astronomer, I know the struggle with cloudy nights. Sometimes, you have weeks of nothing else but clouds that are preventing you to use your telescope. Of course, it depends on the area and the place in the world where you live, but generally, you will get clouds if you are not high enough. 

Observatories are expensive facilities with telescopes worth millions of dollars so the astronomers have to be able to use them as often as possible. They can not wait for weeks for clear nights.

Atmospheric Turbulence

Another big factor in this topic is atmospheric turbulence. You may know it as star twinkling. When you look up to the sky at night you will notice that the stars are twinkling. In fact, they are not. The twinkling is caused by atmospheric turbulence that is distorting the light coming from the stars through the atmosphere. This is not good for observing the universe with the telescope. In higher elevations, the air is cleaner and with less water vapor. And because of the less atmosphere, there is less turbulence. The result is the image much clearer compared to the image seen by telescope near the sea level.

However, there is always some atmospheric turbulence present even at the highest observatories. To overcome this problem, we also have telescopes in space where is no atmosphere and the image is perfect. To overcome this problem on the ground, scientists developed a new technology for telescopes to fight the atmospheric turbulence called adaptive optics.

Why Do Observatories Use Lasers – Adaptive Optics

When I was starting with astronomy, I was wondering why are observatories shooting orange lasers into the universe. You have seen these images of telescopes with powerful lasers pointing to the sky. Some small telescopes are using lasers as guiding scopes to point the telescope to the right place in the sky but this is not the case with big telescopes in observatories.

I mentioned adaptive optics that are helping astronomers fight the atmospheric turbulence and these lasers are part of the adaptive optics technology. 

Telescopes with adaptive optics are using sophisticated mirrors controlled by a computer that can correct the turbulence of the earth’s atmosphere in real-time. The adaptive optics requires very bright reference star on the sky that is close to the object of interest. This bright reference star is produced by shooting orange sodium laser to the top layer of the atmosphere where it glows as an artificial reference star.

Because of atmospheric turbulence, the reference artificial star twinkles same as other stars on the sky. These distortions of the reference star are measured by a computer that creates a negative pattern in real-time and distorting the mirror by hundreds of electric magnets situated at the back of the mirror. They are bending parts of the mirror and canceling out the atmospheric turbulence. All this is happening in real-time and it eliminates most of the distortion caused by earth atmosphere.

The recent telescopes with adaptive optics are 10 times sharper than the Hubble space telescope not only because of the adaptive optics but also because of the size. Hubble’s telescope mirror is only 2 meters in diameter. The planed TMT(Thirty Meter Telescope) on the Manua Kea in Hawaii will have the mirror with a diameter of 30 meters.

What Factors Must Be Considered When Choosing a Sight To Build an Observatory

Finding the best location for the new observatory have a lot of factors to consider. Observatories can have optical telescopes but also radiotelescopes and there are different requirements. But because we are talking about observatories with optical telescopes, here are some factors to consider for the location.

  • Altitude – of course, the higher is better. As I said before, less atmosphere is the goal, so the higher we go the better conditions we can experience.
  • Dry Climate – dry climate provides good air clarity and no light distortion caused by water vapor. One of the best locations is in the Atacama desert in Chile because it is high enough and there is almost no rain during the year.
  • Ligh Pollution – a very important factor because even if you have high altitude and dry climate but there is a big city nearby, it is not going to work out. In general, observing with the telescope even on the amateur level requires a dark sky away from the light pollution. Remote locations are the best.
  • Politics – this may sound weird but you need full access to the site. Also, you don’t want to build an observatory near the war zone. The country where the observatory will be situated also donates a lot of money to have the telescope and the prestige.
  • Latitude – this is also a very important factor because southern and northern hemisphere are different skies and you want to build an observatory to see the particular part of the sky.
  • Access – you need to consider the access to the site. Transporting big telescope to the top of the mountain is a tricky task.

These are only a few requirements that astronomers have to consider before picking the right location. It is a long and expensive process.

Altitude Hazards for Astronomers

Having the observatory in the high altitude is perfect for astronomy but on the other hand, there are risks for astronomers and other workers that have to spend a long period of time there. I will use the observatory on Manua Kea in Hawai as an example to explain some of the hazards connected to working in the high altitude.

Altitude Sickness

The observatory elevation is 13,796 feet (4,200 m). In general, the risk of altitude sickness is starting above 3000m. There is 40% less atmospheric pressure compared to the sea level. So, less oxygen is available which can cause drowsiness, headaches, shortness of breath, nausea, and poor judgment. 

High altitude sickness is hazardous for people in a poor physical condition so every employee is medically examined before entering the site. For visitors, children under 16 years of age, pregnant women or people with respiratory or heart problems are advised not to travel beyond the Visitor Information Station which is in elevation of 3000m.

High altitudes can also cause pulmonary edema (fluid in the lungs).

Eye Damage and Sunburns

Because the site is in high altitude with less atmosphere blocking the ultraviolet radiation, the sun is very dangerous especially when there is snow on the ground. It can cause sunburns and eye damage so people are advised to wear sunglasses, use protective clothing and sunscreen.

Weather Hazards

The weather can change very quickly and cause winds over 100 miles per hour, freezing temperatures, and snowstorms.

Remote Location

Working in a remote location in high altitude is not easy. The emergency services can be two hours away. And during the bad weather, it is even worse.


It is important to build more and bigger observatories on the mountain tops so we can learn more about the universe. It is still cheaper than sending telescopes to space where is no atmosphere but the technology is moving forward allowing even ground-based telescopes to reach results close and sometimes above the quality level of the space telescopes.

Related Posts

Begin typing your search term above and press enter to search. Press ESC to cancel.

Back To Top