Lord Rosse and the Crab Nebula
William Parsons (1800–67), the 3rd Earl of Rosse, built two massive telescopes in the grounds of his ancestral seat at Birr Castle, Ireland: a 36-inch reflector in 1839, followed by a 72-inch popularly known as the Leviathan, at that time the largest telescope in the world, which began work in 1845. With these powerful telescopes he set out to crack what was then one of the greatest puzzles of astronomy: the nature of the diffuse objects termed nebulae. Were they all resolvable into stars given sufficient aperture or were some entirely gaseous?
One of the first objects he turned his attention to with the new 36-inch was the nebula Messier 1 (M1) in Taurus, which we now know to be the remains of a supernova seen from Earth in AD 1054. Oddly, Rosse described it not as a nebula but as a cluster, as had John Herschel before him. Perhaps this was because both observers were able to resolve faint stars which lay in the foreground but were not actually part of the nebula itself.
When did the name first appear?
Exactly when Rosse made the famous ‘crab’ drawing shown above (actually looking more like a tadpole) is uncertain as it is undated, but was probably around 1842 or 1843. It was published in 1844 by the Royal Society in a short paper reporting results with the 36-inch titled Observations on some of the nebulæ. However, Rosse did not call it the Crab in that paper. The first written record of him using the name is in his observing notes for 1848 November 29, which were not published for another 30 years (see illustration below). In fact Rosse himself never used the name in any of his published papers, which were mostly concerned either with telescope building or the shape of spiral nebulae. So when and where did the Crab Nebula get its name?
The first mention of it in print seems to have been by the Scottish astronomer and author John Pringle Nichol (1804–59), one of a number of visitors who observed with Rosse at Birr. In 1846 he reproduced Rosse’s drawing (with black and white reversed) in his book Thoughts on Some Important Points Relating to the System of the World, and captioned it as ‘Lord Rosse’s Crab Nebula’. This book, incidentally, also included the first reproduction of Rosse’s drawing of the Whirlpool, which Nichol referred to as the Scroll Nebula.
Nichol seems to have been the conduit through which the name Crab Nebula entered general circulation, for he used it again in his popular-level books The Stellar Universe (1848) and Architecture of the Heavens (1850), the latter of which he dedicated to Rosse’s wife Mary in recognition of ‘the labours of her illustrious husband’.[note] As well as being a great admirer of Rosse (and his wife), Nichol also enthusiastically publicized his observations, reproducing drawings made at Birr in his books before they were published by the Earl himself, as in the case of the Whirlpool mentioned above.
Who actually invented the term Crab Nebula remains unclear. Its origin may be due at least in part to Thomas Romney Robinson (1792–1882), director of Armagh Observatory and a frequent visitor to Birr. He observed M1 through the 36-inch with Rosse in October 1840 and described it as having ‘streams running out like claws in every direction’. Perhaps the name was jointly coined by Rosse and Robinson and was used informally at Birr before being popularized by Nichol.
Rosse realizes his error
Rosse’s drawing through the 36-inch has been much criticized for its lack of resemblance to the true nebula. Rosse himself recognized this when he reobserved M1 with the improved power of the 72-inch on 1848 November 29. Specifically calling it the “Crab nebula” (in quotation marks), he ruefully noted: ‘Would have figured it different from the drawing in Phil. Trans. 1844’, adding: ‘Great mass of neby. [nebulosity] to south side’. He had by now evidently realized that it was not a cluster after all.
Three years later Rosse observed the Crab again with the mighty 72-inch, describing ‘sev[eral] stars throughout the neb., which is quite patchy and very unlike h’s [John Herschel’s] figure.’ This last comment is a reference to John Herschel’s drawing in his paper Observations of Nebulæ and Clusters of Stars published in 1833 which had shown it as a featureless ellipse. In 1851 November Rosse (or his assistant at the time, Bindon Stoney) made micrometer measurements of several stars and added them to an outline sketch of the nebula for orientation purposes (see illustration above).
Rosse turned the 72-inch on the Crab again at the end of 1853, confirming that it ‘Appeared very different from the drawing in the Phil. Trans. [of 1844]’. His regret at having published that unrealistic sketch was now palpable.
An enigmatic note dated 1855 January 15 mentions ‘Drawing finished’, without naming an observer. This is very likely the drawing made by his assistant at the time, R. J. Mitchell, which remained unpublished until 1879 (see below). Rosse did not observe the Crab again after 1855, having turned his attention to the spiral nebulae following the discovery of the spiral structure of M51 (the Whirlpool) in 1845.
Belated publication
Rosse died in 1867 leaving many of his observations unpublished, including those of the Crab nebula with the 72-inch. Over a decade later Rosse’s eldest son Laurence Parsons (1840–1908), who had become the 4th Earl on his father’s death, assembled the Birr observations from 1848 to 1878 into a three-part memoir with the help of his distinguished assistant J. L. E. Dreyer; this was published in 1879 and 1880 in the Scientific Transactions of the Royal Dublin Society. It includes the drawing of the Crab made by R. J. Mitchell, Rosse’s assistant from 1853 to 1858 (Plate II, upper right).
This is apparently the drawing referred to in the observing notes for 1855 January 15 mentioned above and is the most realistic view of the Crab Nebula as seen at Birr. However, it has not often been reproduced and is less well-known than the earlier but fanciful ‘crab’ sketch by Rosse which gave rise to the now-universal name.
Rosse’s original drawing of Messier 1 (not yet known as the Crab Nebula) as seen through his 36-inch reflector, undated but around 1842–43. At that time he thought it was a cluster of stars and described it as having ‘resolvable filaments … springing principally from its southern extremity’. This drawing was published in 1844 in the Philosophical Transactions of the Royal Society and subsequently copied, with black and white reversed, for a book by John Pringle Nichol in 1846. (Royal Society)
Mary Parsons (née Field), Countess of Rosse (1813–85), was herself an astronomer and a pioneer of photography. The building of the Birr 72-inch was financed by her personal fortune.
Rosse’s observing notes of the Crab from 1848 and 1851 as viewed through the giant 72-inch reflector, published posthumously in 1879 in the Scientific Transactions of the Royal Dublin Society. The number 1157 in the outline sketch at right is its reference number in John Herschel’s General Catalogue of Nebulae and Clusters of Stars (GC) published in 1864.
