Account of a Comet. By Mr. Herschel, F. R. S.; communicated by Dr. Watson, Jun. of Bath, F. R. S.—OR—Understatement.

“On Tuesday the 13^th of March, between ten and eleven in the evening, while I was examining the small stars in the neighborhood of H Geminorum, I perceived one that appeared visibly larger than the rest: being struck with its uncommon magnitude, I compared it to H Geminorum and the small star in the quartile between Auriga and Gemini, and finding it so much larger than either of them, suspected it to be a comet.” 

Position of Herschel's comet (starbust with white center)

Herschel hadn’t found a comet, and he knew it.  Comets and planets have a few characteristics in common, including their movement compared to the “fixed stars”, their changing diameter as they approach the earth, and the proportional increase in their diameter as magnification increases.   Herschel painstakingly shows that this new object meets all of these criteria, showing off for the first time the unprecedented magnification of his homemade telescope. 

Herschel never refers to his discovery as a planet; he simply notes that he has been unable to observe the “least appearance of any beard or tail”, the defining characteristic of a comet.  In fact, Herschel had discovered the first new planet in 4000 years – Uranus, or Georgium Sidus (George’s Star) as Herschel called it.     

Having stated these facts, Herschel “was happy to surrender” his comet “to the care of the Astronomer Royal”, who would quickly confirm Herschel’s discovery and announce the discovery of the new planet.

Herschel, W.  “Account of a Comet.”  Philosophical Transactions (1781) 71:492-501.

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