Telescopes: The Keck Telescopes

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Out of shape

The Keck telescopes face the same problem that all telescopes with large glass mirrors encounter. Glass expands as it heats and shrinks as it cools. When the telescope dome’s shutters are opened, the mirror goes through a process of cooling until it reaches the temperature of the night air. Until then, it’s constantly changing shape — which means the focus is always shifting and the telescope is unusable.

To minimize the effect of the temperature changes, the buildings around the Keck telescopes were built with giant air conditioners to keep the mirrors the same temperature as the night air. Even during the day, the domes are at or below freezing. When the domes open for the night, the telescopes are already at the right temperature and can be used immediately.

Get to the root of it

Flex time

The Keck telescopes use a technology that helps reduce the blurriness caused by atmospheric distortion, a constant problem for astronomers. A computer making hundreds of decisions per second controls pistons attached to a thin, flexible mirror inside the telescope. The pistons cause this special additional mirror to slightly change its shape within milliseconds to cancel out the blurriness caused by the Earth’s atmosphere.

This inventive technique, called adaptive optics, provides a clearer view of the sky. It is being built into current and future telescopes, and added into older telescopes.

Double vision

But why build two identical telescopes? In addition to creating more viewing time for the astronomer, the two telescopes can be linked together to allow them to observe the same object at the same time. Like joining the segments of glass to form an even bigger mirror, this innovation allows the telescopes to form the equivalent of one huge telescope with a mirror the size of a football field. This technique of combining the signals from several telescopes to create images is called interferometry. Together, the two telescopes perform such tasks as searching for planets around other stars, which are very dim and hard to see.

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