Telescopes

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Telescopes

For all the colors of light

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Similar to the telescope Galileo used to see the moons of Jupiter, the moon, and Venus

Uses Lenses!

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Galileo’s telescopes

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150 foot long refracting telescope!!

Built by Johannes Hevelius

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An old Refractor with guide scope

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But lenses absorbed some of the faint light, caused the colors to focus at different points, and could only be made to a certain size.

The largest is the 40 inch refracting telescope at Yerkes observatory. Glass bigger than that would not be able to hold itself up!

SO…

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Designed by Isaac Newton – originally designed with no secondary mirror or eyepiece. You just put your eye near the top and looked in!

Eyepieces and cameras made it all easier to use.

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Early Newtonian telescope

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You could make a glass mirror a LOT bigger than 40 inches – and it didn’t distort the light.

A 5 meter mirror (the Hale telescope at Mt. Palomar) was the largest for a long time.

Currently, the largest Single Piece of glass telescope is 8 meters (Subaru and others)

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People were still unsatisfied – and came up with the idea of putting together a number of carefully made mirror segments, controlled by computer to stay extremely accurate.

Keck I was a 10 meter segmented telescope – and the current largest.

The addition of Keck II (another 10 meter telescope) makes a very large telescope array.

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The deeper the curve, the closer in the focal point.

Optical telescopes have farther focal points, Radio telescopes have shorter ones.

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To make a shorter telescope, they put a secondary mirror in front to reflect it back through the main mirror.

Most large telescopes use this design.

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