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MARGINALIA

The Inimitable Caroline

The sister of British astronomer William Herschel was herself a capable and pioneering celestial observer

J.Donald Fernie

Music of the Spheres

It was precisely at this point that the genius of William Herschel was established. His eventual fame among astronomers came not from any great insights into astronomy itself—indeed it might be said that his fame was established despite some of his beliefs. For example, he long held that the Moon was almost certainly inhabited as very likely was the Sun. In the latter case, Herschel opined, the inhabitants lived well below its fiery cover, protected by very dense clouds through which tall mountains occasionally protruded, which appeared as dark sunspots to us. The establishment of the time, although it knew almost nothing of astronomical physics, had no doubt that Herschel must be wrong on such matters. (In his defense, other conclusions of William's, such as his claim that the Sun could not be at the center of the Milky Way, were correct; yet they met with the same disbelief.) What his contemporaries soon came to realize, however, was that Herschel built better telescopes than any the world had ever seen.

And so life for the Herschel siblings became more hectic. It was still music that formed the basis of their livelihood: endless rounds of concerts and student lessons, responsibility for all Sunday morning musical matters at Octagon Chapel, and composition. (William wrote some of the most charming music of the time, and a number of his symphonies remain popular to this day, selling well in CD recordings.) But in the midst of all this, the building of telescopes grew steadily more important. At critical stages during production of a new telescope, all else was put aside. Caroline writes of her "attendance on my Brother when polishing [a new mirror], that by way of keeping him alife I was obliged to feed him by putting Vitals by bitts into his mouth—this was once the case when at the finishing of a 7 feet mirror he had not left his hands from it for 16 hours together."

William's reputation as a telescope maker began to be noticed, even by such notables as the Astronomer Royal, and it eventually led to an invitation to take one of his telescopes to the Royal Observatory at Greenwich. There it was set alongside the best of the Observatory telescopes for comparison. William later reported that "These two last nights I have been star-gazing at Greenwich with Dr Maskelyne [the Astronomer Royal]. . . . We have compared our telescopes together, and mine was found very superior to any of the Royal Observatory. Double stars which they could not see with their instruments I had the pleasure to show them very plainly. . . ."

The superiority of William Herschel's instrumentation became incontestable in March 1781. On the 13th of that month William happened to have his telescope turned to the region of sky near the star Zeta Tauri. He immediately noticed that one star in the field of view appeared different than the others. Although all stars viewed telescopically show some kind of surrounding disk (for purely optical reasons), this one had a significantly larger disk than its neighbors. William concluded, reasonably enough, that it was likely a comet, tail-less because of its distance from the sun. He carefully noted its position in the sky relative to the surrounding stars, and on returning to it a few nights later found to his satisfaction that it had indeed changed position. It must surely be a comet! He sent a report to the Astronomer Royal, hoping for quick verification, only to hear that the telescopes at the Royal Observatory were so inferior that all the stars in the area showed significant disks. The Greenwich observers would have to measure and re-measure the positions of all objects in the area to find which one was moving. When that was done, however, the result was startling. Unlike the elongated, tilted orbit of a typical comet, this object had an orbit typical of a major planet! In fact, there was no alternative. This was a major planet—the first ever discovered in modern times.




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