JOHN TEBBUTT (1834-1916) : Part 2

Discoveries of John Tebbutt

By Andrew James

Recent Update : 16th August 2008


John Tebbutt made so many observations and discoveries during his long life. Perhaps among his most significant discoveries was the two comets of 1861 and 1881 —l the former leaving the greatest impression.

Comet Tebbutt 1861 II (C/1861 J1)

John Tebbutt found his first comet just before his twenty-seventh birthday, and was to prove to make him a local and international household name. This was the discovery of the Great Comet Tebbutt 1861 II (C/1861 J1) as a small inconspicuous haze in the southern constellation of Eridanus. Using the small 4.1cm. telescope on the evening of 13th May 1861, he found the nebulous object while sweeping the skies just after sunset for comets — much as amateur astronomers do today. At first, he was uncertain that it was really cometary because it showed no significant movement, and he first considered this as some uncatalogued 7th or 8th magnitude deep-sky object. By the 23rd, he was again able to observe the comet appearing as some nebulous object about 6′ or 7′ across.

Convinced this was really a comet from the 0.5° movement, he wrote of the discovery to both the Government Astronomer, Rev. William Scott (1825-1917) and the Sydney Morning Herald on the 22nd or 23rd, which the latter was belatedly published on the 25th May 1861. Announcement of the discovery of Comet Tebbutt 1861 II had arrived at Sydney Observatory at the right time, as Scott had just received the delivery from Europe of the new 7¼-inch Merz refractor, and became the first object seen with this telescope. He quick adapted the old ring micrometer once used at Thomas Brisbanes Parramatta Observatory to then measured cometary position. On 27th May, Scott then found the small tail, which started rapidly to grow in length. By 8th June 1861, the comet had become naked eye, reaching about 2nd magnitude on 11th. On the 14th, and unexpectedly, Comet 1861 II continued increased in brightness and brilliance as it approached the Earth, when suddenly and majestically brightened as it reached perihelion on the 12th, and became a morning object.

Tebbutt on 15th June published in the Sydney Morning Herald his improved preliminary ephemeris. He stated that he predicts on 29th June, the Earth would pass directly through the 180 million kilometres long comet tail! Scott was at first unable to conclude this himself, expressing that the reason for this was mainly concentrating getting use to using the new refractor and had other more pressing priorities. By the 20th, the comet tail split into two, now extending in length by some 42º.

By this time, Tebbutts Comet had grabbed the publics attention, and had now moved sufficiently further north for European and American observation. In the Sydney papers, came the first expressions of real fear of the consequences of the Earth passing through the comet tail. By the end of June, the cometary nucleus had reached first magnitude with the main tail now stretched up to 120º in length and 6º wide!

John Tebbutt 20cm.

The observed effects proved quite dramatic. On the 30th, the daytime sky adopted a peculiar yellow hue, though some in Sydney, including Tebbutt, reported this as more whitish, and some later compared it to the similar soft glow of aurorae. Worldwide, this produced various phenomena, and a few even reported of an apparent observable dimming of sunlight — to the extent that candles were required to indoors.

By early July, this great comet had been lost to the southern skies, and rapidly moved towards the north celestial pole. Here the great northern observatories continued observations. Some other remarkable events also occurred. This included changes is colour, which the Rev. T.W. Webb on the 15th described as a strong golden hue, while in the telescope, he describes the coma as being greenish yellow. Over the next several days, observations could only be made of the cometary nucleus during the daylight hours, when it was predicted to have reached about −3 magnitude — similar brightness to planet Venus, some have reduced this to closer to 0.0 magnitude.

By mid-July, the brightness had quickly dropped to 3rd magnitude, and by the end of July, this remarkable cometary apparition had all but ended. It proved to be one of the brightest comets of the 18th century, and certainly, remains in the top five comets throughout recorded history. It brightness was mainly because of the very close approach to the Earth, which produced this spectacular display.

By 2nd August, Tebbutt again had the opportunity to observe the now 4.5 magnitude comet, which he at first thought was another possible discovery. Although returning to be visible in the southern skies, however, it was certainly now much less impressive. By the 10th, the comet had become a telescopic object, which the last time he saw on 5th September 1861. It disappeared into the depths of the Solar System in May 1862

Analysis of the positions now shows that the highly inclined orbit of 85º has the long period of about 408 years. The comet can be as close as 0.82 A.U., and travelled more than 109 A.U. from the Sun. Tebbutts Comet and is expected to return again sometime in 2269 A.D. Certainly after this spectacular event, Tebbutts astronomical reputation, both in Australia and abroad remained permanently secure.

Comet Tebbutt 1881 : C/1881 K1

Tebbutt discovered this bright comet exactly twenty years to the day after Comet Tebbutt 1861 II. Also named as Comet Tebbutt 1881 III, (remainder to be completed)


Another important series of observations was on the spectacular rise of the variable star known as Eta Argûs, now called Eta Carinae. This star was seemingly a fairly unremarkable and unimportant 4th magnitude star, but this changed somewhere between 1603 and the early 1820s when η Car rose to 2nd magnitude. After seemingly inexplicable series of changes in brightness, it blazed into full glory in March 1843, by almost rivalling the brightest star Sirius. Tebbutt made regular observation of this remarkable variable between 1854 and 1868, and these have proved quite important in understanding the nature and history of this star.


At the time of his discovery of the 1861 Comet, he was a virtual unknown observer. Yet within ten to fifteen years, he began working on many different types of astronomical observations, with many being personal requests for particular observations of various phenomena invisible to the northern skies. For this, many of these results made John Tebbutt recognised by many foreign observatories in Europe, England and America. These included the predictions of;

• A Total Solar Eclipse on the 26th March 1857.
Comet positioning for the determination of their orbits (over 700 observations.)
Lunar Occultations used in the improved the ephemerides on lunar positions
    (some 435 events between 1896 and 1900)
Variable Star magnitude estimations of many southern variables.
    including R Carinae.
Double Star measures of the brighter doubles and binary stars.
Transit of Venus in December 1874
• Missed the December 1882 Venus transit due to heavy cloud.


Last Update : 13th November 2012

Southern Astronomical Delights © (2012)

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