Friday, June 8th, 2012...9:00 am
You’ve Got Mail: Some Beautiful Observations of the Georgium Sidus
The excitement of this week’s transit of Venus was somewhat dampened in Boston by cloudy skies and rain. To make up for this, we offer a bit of astronomical history from the time of the first widely viewed transits of Venus in the 18th century. Though we’ll never see it transiting the sun, William Herschel’s (1738-1822) Georgium Sidus was arguably the most important single discovery in the heavens since the time of the ancients.
A musician by trade and training, as was his father, Herschel’s love for amateur astronomy blossomed after he settled in England from his native Hannover. His successful musical career led him to be organist of the Octagon Chapel in Bath. It was there that he found time to begin serious astronomical observations. These observations would have been impossible without the his younger sister, Caroline, who served as his assistant.
In a letter to Edward Pigott (1753–1825), a British astronomer, he writes some thoughts about the movement of the fixed stars being possibly caused by the movement of the solar system through space, and about a specific observing session where
I have very lately (by the severe cold) had my best 20 feet Speculum destroyed. It cracked at 15 o’Clock the 1st of January when the thermometer was at 11° of Farenheit’s measure. Dr. Lind, and some other company were with me in the evening, when we had some beautiful observations of the Georgium Sidus, The Nebula of Orion, &c: the latter was so bright that in coming into the field of view its splendour was strikingly beautiful, and the four stars in the Corner so strong & well defined that it occasion the greatest surprise to Dr Lind who had never seen it with that Instrument.
Who knew there could be such dangers in astronomical research? The reflector telescopes which Herschel constructed far out-shined contemporary telescopes in terms of light-gathering and magnification. This greater power required greater size. To observe with his 20 foot instrument he needed to be quite far off the ground on a viewing platform. Herschel states without emotion and detail, other than temperature measurements, about the collapse of his instrument that could have been disastrous for his health and safety, and which certainly was a financial loss.
Houghton’s collection of Herschel material includes not only this letter to Pigott, but also an autograph account of observations from the evenings in March, 1781, when he first sighted the “Georgium Sidus.” At the time, he thought it only an unknown comet, exciting enough for an astronomer to discover. Through many observations and calculations it became clear to Herschel and other astronomers that this was something more than a mere comet. The name Herschel had wanted for it, The Georgian Star, to honor his patron and fellow Hanoverian King George III of England, was not accepted by other astronomers, particularly those outside of that country. They preferred a more traditional Greek name. It instead came to be known as Uranus, after the god of the heavens and astronomy, an acknowledgment of the science that led to its unveiling.
Some called Herschel’s discovery of Uranus accidental. It was certainly not planned or calculated, but Herschel’s unique combination of long and methodical observation sessions, meticulous note-keeping, and telescope craftsmanship made it less surprising. He himself answered this criticism in an undated (though likely written in 1809) autograph manuscript titled “In a letter to Dr. Hutton”:
It has generally been supposed that it was a lucky accident that brought this star to my view. This is an evident mistake. In the regular manner I examined every star of the heavens not only of that magnitude but many far inferior. It was that night its turn to be discovered. I had gradually perused the great Volume of the Author of Nature & was now come to the Page which contained a seventh Planet. Had business prevented me that evening, I must have found it the next, and the goodness of my telescopes was such that I perceived its visible planetary disk as soon as I looked at it.
And perhaps we can leave it to Keats to describe what it must have been like for Herschel. In “On First Looking into Chapman’s Homer”—an early draft of which is in Houghton’s Keats collection— he used Herschel’s discovery to mirror his own,
Then felt I like some watcher of the skies
When a new planet swims into his ken.
Below you may view the letter in full.
This post is part of a weekly feature on the Houghton Library blog, “You’ve Got Mail,” based on letters in Houghton Library. Every Friday this year a Houghton staff member will select a letter from the diverse collections in the Library and put that letter into context. All posts associated with this series may be viewed by clicking on the You’veGotMail tag.
[This post was contributed by James Capobianco, Reference Librarian.]