The Great Comet of 1861

May 19, 2022 0 comments

The 19th century was a great time for sky watchers. Between 1811 and 1882 as many as eight great comets became visible from earth dazzling scientists and common man alike, and inspiring artists and composers. Probably the most beautiful one was Donati's Comet of 1858, which became the first to be successfully photographed. Three years later, another dramatic comet appeared in the sky. The Great Comet of 1861 was exceptional because it passed right across Earth’s orbit, and for two days the Earth itself was within the comet's tail. As the Earth ploughed through the comet's gas and dust, viewers had a giddy view of streams of cometary material converging towards the distant nucleus. The tail also obscured the Sun’s rays during the day.

Great Comet of 1861, also known as C/1861 J1 or comet Tebbutt. Drawing by E. Weiss

The Discovery

The Great Comet of 1861 was first spotted by a sheep farmer and amateur astronomer John Tebbutt. On 13 May 1861, the young farmer, using an ordinary marine telescope, saw a fuzzy star in the constellation Eridanus. Tebbutt checked his celestial charts but found no nebula listed in the position. He guessed it must be a comet but he could see no tail. Tebbutt watched the object for the next several days but could find no visible change in its position, until a week later when he saw the object move by about half a degree confirming his initial conjecture.

Tebbutt sent off a letter to the Rev. William Scott, the Government Astronomer at Sydney Observatory, declaring his discovery as well as a letter to the Sydney Morning Herald. This letter was published in the paper on 25 May 1861, the young farmer’s 27th birthday.

In those days, communication between Australia and the rest of world was slow. Before news of the discovery could reach the northern hemisphere, the comet itself appeared in northern skies. The first person in England to see it may have been William C. Burder, of Clifton, Bristol, who dashed off a letter to the Times on Sunday, June 30th:

Sir - At 2.40 a.m. today I detected a brilliant comet near the north-west horizon. It was visible till 3.20 a.m….it appeared as bright as Capella and was favourably situated for the comparison. It was surrounded by a nebulous haze, but I saw no tail…The daylight put out the both the comet and Capella nearly at the same time; your readers will therefore consider this a proof that it is a brilliant object.

The same day, Samuel Elliott Hoskins, a doctor from Guernsey, observed:

At 9.p.m. a large luminous disc surrounded by a nebulous haze became visible in the N.W. horizon. At 9.40 it unmistakably assumed the character, to the naked eye, of a comet, having a large nucleus & a fan-like tail projecting vertically towards the zenith. It was permanently brilliant until sunrise the next morning − travelling with apparent rapidity, but slight declination, from N.W. to N.E.

As summer approached and the days lengthened, there was noticed a strange appearance in the sky. E. J. Lowe, at Beaston, said, "The sky had a yellow, auroral, glare-like look, and the sun, though shining, gave but a feeble light…in our parish church the vicar had the pulpit candles lighted at seven o'clock, a proof that a sensation of darkness was felt even with the sun shining." J. R. Hind, in London, told the Times; "there was a peculiar phosphorescence or illumination of the sky, which I attributed at the time to an auroral glare; it was remarked by other persons as something unusual".

The change in the sky was due to the Earth passing through the tail of the comet, as  J. R. Hind explained to the Times: "Allow me to draw attention to a circumstance relating to the present comet…It appears not only possible, but even probable, that in the course of Sunday last, the earth passed through the tail at a distance of perhaps two-thirds of its length from the nucleus". writes:

On June 28, at 6 pm, the nucleus of the comet was in the ecliptic, about 13 million miles from the Earth. Had the tail streamed directly behind the comet, the Earth would have encountered it soon after 10 p.m. on June 30th. But tails always lag behind the nucleus, and Hind, judging by the amount of tail curvature and the comet's direction of motion, estimated that the Earth would have entered the tail in the early morning of June 30; "or, at any rate, it was certainly in a region which had been swept over by cometary matter a short time previously."

The tail of the comet assumed a large nebulous disc-like appearance about a quarter of a circle wide. On July 1 and 2, the tail was measured 118° wide. As the comet moved away from the earth, the tail became long covering nearly half the sky.

By midsummer the comet was bright enough to cast a shadows, despite the fact that the nucleus was only a few degrees above the horizon. During the night of June 30 – July 1, 1861, the famed comet observer J. F. Julius Schmidt watched in awe as the great comet cast shadows on the walls of the Athens Observatory.

By the middle of August the comet was no longer visible to the naked eye, but it was visible in telescopes until May 1862. An elliptical orbit with a period of about 400 years was calculated, which would indicate a previous appearance about the middle of the 15th century, and a return in the 23rd century.

John Tebbutt’s Later Life

John Tebbutt in his great grandfather's observatory at Windsor, New South Wales on April 14, 2004. Photo: Carlo Thomas

The discovery of this comet launched young John Tebbutt as an astronomical hero and introduced him to astronomers the world over. In 1864, Tebbutt built a small observatory and installed a couple of instruments including a 3¼-inch telescope, a two-inch transit instrument, and an eight-day half-seconds box-chronometer. Over the next forty years, Tebbutt published numerous high quality observations of comets, minor planets, variable stars, eclipses and transits and his reputation continually increased. In 1881, Tebbutt discovered yet another comet. Although not quite as spectacular as the Great Comet of 1861, it showed his dedication and persistence as a serious amateur astronomer. John Tebbutt was elected first president of a branch of the British Astronomical Association which was established at Sydney. He retired from systematic astronomical work at the age of seventy in 1904. John Tebbutt died in 1916. He was commemorated on the reverse side of the Australian one hundred-dollar note.

# The Gallery of Natural Phenomena
# Nick Lomb, The discovery of the Great Comet of 1861 by John Tebbutt, Museum of Applied Arts and Sciences
# Tabea Tietz, John Tebbutt and the Great Comet of 1861, SciHi Blog


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