University of Hawaii 2.2-meter telescope Public information

Short history

In 1964, an extensive program was undertaken to evaluate Mauna Kea as a site for astronomy. The results suggested that the air was exceptionally stable, and that Mauna Kea was among the best sites in the world for astronomy. The University of Hawaii 2.2-meter (88-inch) telescope was the first large telescope constructed on Mauna Kea. It commenced operation in 1970.

The early results from the UH 2.2-meter telescope demonstrated to the world how good Mauna Kea is for astronomy. The smooth shape of the mountain, and isolated location of Hawaii, means that the air flows very smoothly over the mountain. Degradation of images from atmospheric tubulence is low. The high altitude places the summit above much of the Earth's water vapor.

The excellent conditions atop Mauna Kea have enabled the University of Hawaii 2.2-meter telescope to become one of the most productive telescopes of its size in the world.

Major discoveries

The most important discovery made with the University of Hawaii 2.2-meter telescope is the existence of the Kuiper Belt in the outer part of the Solar System. Prior to 1990, the only known object (other than comets) beyond the orbit of Neptune was Pluto.

We now know that the outer Solar System is populated by countless asteroid-size bodies, some almost as large as Pluto. These are commonly referred to as Kuiper Belt Objects, and Pluto is now usually regarded as the largest known Kuiper Belt Object, not as the ninth planet.

The first Kuiper Belt object was discovered in 1990 by Dave Jewitt and Jane Luu using the University of Hawaii 2.2-meter telescope. During the early 1990s, much of the groundbreaking research on the Kuiper Belt was done using the 2.2-meter telescope.

Instrumentation

The University of Hawaii 2.2-meter telescope has a long legacy of forefront astronomical instrument development. Many of the key achievements are related to large-format imaging arrays:

• The first efficient 256x256 infrared array camera in the world
• The first efficient 1024x1024 infrared array camera in the world
• The first 4096x4096 infrared array camera in the world
• The first 8192x8192 CCD camera in the world

How a telescope collects light

Most modern telescopes use mirrors to collect light rather than lenses. The reason for this is that a lens can only be supported around its edges, whereas a mirror can be supported over its entire rear surface. The largest telescope that uses a lens (refracting telescope) has a 1-meter diameter lens. The largest telescopes that use mirrors (reflecting telescopes) are the Keck Telescopes, each with a 10-meter diameter. Light first hits the concave primary mirror, is reflected to the convex secondary mirror, and is usually directed through a hole in the primary mirror to a focus behind the primary mirror (see picture at left).

The University of Hawaii 2.2-meter telescope is like a giant telephoto lens. It has a focal length of 22.6 meters, or 22,600 millimeters, and a focal ratio of f/10.

The photograph above shows that the UH 2.2-meter telescope has a tube joining the primary to the secondary mirrors. More modern telescopes utilize an open structure to allow air to flow freely over the primary mirror. Differences in air temperature are a major nuisance to astronomers, because they cause turbulence that degrades image quality. The temperature differences cause shimmering of images much like you see above a road on a hot day.

Copyright 2005, Richard J. Wainscoat