SOUTHERN ASTRONOMERS and AUSTRALIAN ASTRONOMY
JOHN TEBBUTT (1834-1916) : Part 2
Discoveries of John Tebbutt
By Andrew James
Recent Update : 16th August 2008
COMETS
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
Brisbane’s 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, Tebbutt’s Comet had
grabbed the public’s 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!
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.
Tebbutt’s Comet and is expected to
return again sometime in 2269 A.D. Certainly after this spectacular
event, Tebbutt’s 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)
VARIABLE STAR OBSERVATIONS and Eta Argûs
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 1820’s 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.
OTHER ASTRONOMICAL OBSERVATIONS
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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