Use
The telescope was located on the grounds of Observatory House, Herschel's house in Slough, between 1789 and 1840. The first observation with the telescope was on 19 February 1787, when Herschel pointed the then-incomplete telescope towards the Orion nebula, which he observed by crawling into the telescope and using a hand-held eyepiece:
| “ | The apparatus for the 40-foot telescope was by this time so far completed that I could put the mirror into the tube and direct it to a celestial object; but having no eye-glass fixed, not being acquainted with the focal length which was to be tried, I went into the tube, and laying down near the mouth of it I held the eye-glass in my hand, and soon found the place of the focus. The object I viewed was the nebula in the belt of Orion, and I found the figure of the mirror, though far from perfect, better than I had expected. It showed four small stars in the nebula and many more. The nebula was extremely bright. | ” |
The one achievement of the telescope was to discover Enceladus and Mimas, the 6th and 7th moons of Saturn, although this is not certain, as Herschel used other telescopes at the same time. Herschel described the view of Sirius through the telescope:
| “ | . . . the appearance of Sirius announced itself, . . . and came on by degrees, increasing in brightness, till this brilliant star at last entered the field of view of the telescope, with all the splendour of the rising sun, and forced me to take the eye from that beautiful sight. | ” |
As part of the funding deal with the telescope, Caroline Herschel was granted a pension of £50 per year to be William's assistant. As a result, she was the first woman in England to be paid to carry out astronomy.
The telescope was a local tourist attraction, visited by rich and famous people on their way to the nearby Windsor Castle to visit the King, and was featured on Ordnance Survey maps. It was the largest telescope in the world for 50 years. It was called the "40-foot telescope" as at the time telescopes were referred to by the length of their tube rather than the diameter of the mirror.
Due to problems with the mirrors and because the telescope was unwieldy, the telescope did not prove to be a substantial improvement over smaller telescopes. The weather was rarely suitable for the telescope, and most objects observed by Herschel were also visible in his smaller telescopes. The final observation made by the telescope was in 1815.
The telescope was featured in Herschel's coat of arms:
| “ | Argent on a mount vert a representation of the forty-feet reflecting telescope with its apparatus proper; a chief azure thereon the astronomical symbol of Uranus or Georgium Sidus irradiated Or. | ” |
Read more about this topic: 40-foot Telescope
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