Resource: Above the Clouds: Telescopes on Mauna Kea

To study the universe, astronomers rely on light that is gathered by telescopes — instruments and computers that are able to capture the electromagnetic radiation emitted from distant objects and process it for astronomers to study. Unfortunately, views from Earth's surface are restricted by Earth's atmosphere, so there are limitations to the light that ground-based telescopes can see.

Optical and radio wavelengths penetrate Earth's atmosphere with the least difficulty — the atmosphere is said to be transparent at these wavelengths. The upper atmosphere absorbs short-wavelength light, such as ultraviolet. Water vapor, found mainly in the lower part of the atmosphere, absorbs microwave and infrared light. However, the water vapor content quickly decreases with height, so if observatories are located at high elevations, the transparency for microwave and infrared light is greatly improved.

The atmosphere has other negative effects on light. Turbulence — the movement of air due to pressure and temperature variations — bends incoming light and causes fluctuations, a phenomenon that can be seen in the twinkling of stars. Dust and aerosols can also cause light to scatter. As a result, satellites located above the atmosphere are generally able to provide clearer and more detailed views of the universe than ground telescopes because they are free from both the distortion and the absorption effects of looking at the universe through air.

However, there are some ground locations that support high-quality observations. Mauna Kea in Hawaiʻi is an ideal site for astronomical telescopes. At 4,250 m (13,796 ft) above sea level, the telescopes on Mauna Kea are placed above much of the atmosphere, thereby minimizing the atmospheric effects. In addition, Mauna Kea is in the middle of an ocean, which results in very stable air over the mountain. The air is also very dry and typically free of clouds — providing an exceptionally high number of clear nights. The site is also far from heavily populated areas and the light pollution of city lights.

With over a dozen of the world's best telescopes situated on Mauna Kea — the largest infrared and optical telescopes and one radio telescope are located there — it is one of the world's leading astronomical observatories. Astronomers use the telescopes to research many different areas of astronomy — including the existence of new planets, the expansion of the universe, and black holes. Given the advancement of new technologies — such as adaptive optics — ground-based telescopes in optimal locations such as Mauna Kea may be able to rival space telescopes.

To learn more about astronomical observations, check out Astronomical Images in Different Wavelengths.

To learn more about observations from Mauna Kea, check out Eclipse of the Century.

To learn more about early telescopes, check out The Beginnings of the Telescope.

• Why do astronomers continually build bigger and better telescopes?
• How have new technologies helped build better telescopes?
• What is meant by the phrase "technology drives the science of astronomy"?
• What does the narrator mean when he says that telescopes help us look backward in time?
• What are four factors that make Mauna Kea an excellent site for a telescope?