Telescopes from the Ground Up

Era of Early Refractors

Hevelius’ Refractors

An astronomer gets creative, and telescopes get longer

In the early 1600s, Galileo had built telescopes that were no more than 4 feet long. By 1647, Johannes Hevelius, a Polish brewer and councilor, had built a 12-foot-long telescope in an attempt to improve his view of the sky. That was just the beginning.

Hevelius used the new understanding of how lenses worked to improve his refracting telescopes. The flatter the telescope’s primary lens, the longer it took the light rays to meet and focus. This produced a clearer image but meant that the two lenses in a telescope had to be placed further apart.

As long as it takes

Not satisfied by the 12-foot-long telescope, which magnified 50 times, Hevelius created more powerful ones that were 60 and 70 feet long. Then, for his crowning achievement, he built a 150-foot telescope on the shore of the Baltic Sea.

The 150-foot telescope was too long to be encased in an expensive and heavy iron tube, and a paper tube would have fallen apart. So Hevelius arranged the lenses in a wooden trough, suspended the whole thing from a 90-foot pole, and used ropes, pulleys, and a team of workmen to operate it from the ground.

The telescope would shake in the smallest breeze, the wooden planks warped, and the ropes had to be constantly adjusted because of stretching and shrinking in the humidity. The unsteadiness also made it difficult to line up the lenses for observations. Due to all these difficulties, this huge telescope was rarely used.

• Hevelius’ Refractors1673
• Huygens’ Refractors1686

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