Herschel's 20-Foot Telescope
Herschel's Favorite Telescope
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 shown here is Herschel's 20-foot reflector. He began observing
with the telescope in 1783, and though he went on to build even larger ones, his
20-foot remained his favorite.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. Herschel's sister 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 -12ºC (11ºF). His ink froze in its bottle and his best mirror "crack'd into two piece."
The Milky Way Universe
In
Herschel's time, the Universe encompassed all that could be seen in the sky by
eye or telescope, including the faint and distant stars that formed the hazy band
of light called the Milky Way. Nothing was known for certain to exist beyond the
stars of the Milky Way. The patches of light known as nebulae were mysterious
in nature, but they were generally thought to be part of the Milky Way as well.
While most astronomers continued to plot the positions of stars and planets, Herschel began to ask new questions: How large is the Universe? What is its shape? What are the nebulae, those mysterious smudges of light that reside among the stars?
Herschel tried to determine the shape of the Milky Way by counting stars and created the first diagram of the Milky Way based on observational data. He also examined the entire sky visible from England, searching for and cataloging nebulae. He remained uncertain about their nature. Whether they resided within the Milky Way or lay beyond it would remain unresolved for more than a century.
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