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William
Herschel's 20-Foot Telescope
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In the
hands of William Herschel, the telescope became a powerful
scientific tool. Herschel had a talent for telescope making
that matched his passion for studying the heavens. He began
building them in the 1770s. Soon he was creating the most
powerful telescopes in the world and looking deeper into the
Universe than ever before. The telescope displayed here was
Herschel's favorite: his 20-foot reflector.
Woodcut image courtesy Royal Astronomical Society, Burlington House, Picadilly, London
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The
Telescope Tube
This
long wooden tube is from William Herschel's 20-foot telescope.
He began observing with the telescope in 1783, and though
he went on to build even larger ones, his 20-foot remained
his favorite. In 1820 Herschel and his son John rebuilt the
telescope, which had deteriorated after decades of use, salvaging
what they could from the original. The tube displayed here
is a product of that reconstruction.
Herschel constantly worked at improving the telescope, modifying
its optics, framework, and controls many times. With it, he
and his son discovered thousands of nebulae and star clusters
and mapped the entire sky.
Lent by the National Maritime Museum, London
Image Courtesy of the Royal Astronomical Society |
View inside 20-foot telescope tube
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What
Was It Like to Use the Telescope?
The telescope's eyepiece was mounted at the top of the tube, so
Herschel observed from a platform that could be raised or lowered
as needed. Caroline sat inside the house nearby at an open window,
recording her brother's observations as he called them down to
her. Of his nights at the telescope, Herschel wrote,
"Here
an observer may sit for many hours, with constant entertainment,
continually expecting new objects to present themselves, which
he never could have perceived in common telescopes."
The work wasn't
always so pleasant. Herschel observed whenever possible, sometimes
even in bitter cold. One night, while using an earlier telescope,
the temperature dropped to -12 ºC (11 ºF). His ink froze
in its bottle and his best mirror "crack'd into two piece."
| The
Telescope Mirror |
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This
mirror was one of several crafted for the 20-foot telescope.
Like other early telescope mirrors, it was made of metal (mostly
copper and tin) and tarnished quickly, so it had to be repolished
often. The base of the telescope could be opened and the mirror
easily removed. Another mirror was always on hand to use while
the first was being polished.
Lent by the National Maritime Museum, London |
Return
to: Looking
Further: Exploring The Universe with Telescopes
Next: Looking Further: Exploring
The Universe with Photography
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