In a matter of days, Comet
ISON will make its perihelion approach, coming within 750,000 miles
(a very close shave in astronomical terms) from the Sun. Both
astronomers and the general public have gone abuzz over Comet
ISON thanks
to a prediction released a year ago by NASA's
Jet Propulsion Laboratory (JPL) that stated that the comet could
reach magnitude -11.6,
or about as bright as the Full Moon. Additionally, besides being
shadow-casting bright at night, the comet would be bright enough to
easily be spotted during broad daylight.
If
this were to happen, it would not be a first, but it would allow
Comet ISON to join a very exclusive list of the brightest comets ever
seen. To days, only 9 comets in recorded history have been bright
enough to be seen in daylight. Now, in chronological order, here they
are . . .
Great
Comet of 1106.
The
Belgian historian Sigebertus Gemblacensis completed his Chronica
in 1111. In it, he wrote that on 1106 February 2 a star appeared
during the daytime, between the third and ninth hours, about a cubit
from the sun. The probable universal time of this observation was
February 2-3. A cubit is roughly equal to one degree, meaning that
the comet was in Aquarius. The comet was observed in other European
countries as well as in the Orient. Some estimates credit the comet
as having a tail spanning 100 degrees at peak.
Great
Comet of 1680.
Even if it weren't for its amazing show, the Great
Comet of 1680 had another distinction: it was the first comet
discovered by telescope. First seen on November 14, 1680, the comet
rapidly brightened as it approached perihelion, which took place on
December 18, 1680, at which time the comet, which passed within
600,000 miles of the Sun, was reportedly bright enough to be seen
in broad daylight. Coincidentally, the Great Comet of 1680 has an
almost identical orbit to that of Comet ISON.
Great
Comet of 1743-4.
This comet was discovered simultaneously be
several astronomers in November, 1743. At the time, it was
reported as appearing as a nebulous star without a tail. By February,
1744 it was as bright as Venus and, after perihelion approach in
March, 1744, it developed a spectacular, fan-like tail with 6
prominent streaks. This 6-tailed comet was even observed before
it rose, its tail was that bright. The comet then moved into the
Southern hemisphere, where some observers credited it with a tail
spanning 90 degrees. After 2006-7's McNaught, some came to believe
that the Comet of 1743-4 was the first recorded appearance of a comet
featuring prominent dust striae.
Great
Comet of 1843.
First observed in February of 1843, the comet
rapidly brightened to the point it was seen in broad daylight at
perihelion, which brought it to about 1 angular degree (or about
830,000 miles) of the Sun. This comet was known for its extremely
long tail. At over 2 astronomical units (over 180 million miles), the
Comet of 1843 would have the longest measured tail until Comet
Hyakutake of 1996 was found to have a tail of over twice that length.
Great
Comet of September 1882 (the Super Comet).
Perhaps the brightest
comet ever seen, at peak, some estimate the Great Comet of September
1882 of having had a peak brightness of magnitude -20, rivaling that
of the Sun. Initially spotted in either late August or early
September 1882, the comet brightened rapidly as it approached
perihelion, which took place on September 17. At this time, the comet
was reported as being scarcely dimmer than the limb of the Sun,
suggesting a magnitude as bright as -20. After perihelion, the comet
quickly moved into dark skies, making it perhaps the most spectacular
comet ever seen in all of recorded history. The comet remained
visible to the naked eye for a long time, until February, 1883, with
the last confirmed sighting coming in June, 1883. This comet was also
notable in being the first great comet to have been photographed.
The
Daylight Comet of January 1910.
In 1910, comet mania was in high
gear with the anticipated return of Halley's Comet set for April.
However, in January, a surprise came about in the form of a comet
that literally burst into naked eye visibility virtually overnight.
Initially observed in the Southern Hemisphere, the comet reached
perihelion on January 17 and moved into the Northern Hemisphere
thereafter, easily out-shining Venus and having a tail possibly 50
degrees long. Thanks to appearances of Halley's Comet later that year
and the passage of decades, many recollections of the two comets were
confused when Halley's Comet reappeared in 1986, with the Daylight
Comet being falsely remembered as Halley's Comet.
Comet
Skjellerup Maristany (1927).
This comet became very bright in
late, 1927, being naked-eye visible for about a month. In mid
December, the comet, already notable for its yellow appearance thanks
to a shedding of sodium atoms, shot into daylight visibility thanks
to a forward scattering of light, provided one blocked the Sun with
one's hand. The Comet reached perihelion on December 15 passing
within 1.5 angular degrees of the Sun.
Comet
Ikeya Seki (1965).
Initially discovered in December, 1965, initial
predictions projected a perihelion approach to within 500,000 miles
of the Sun coming in mid October and the comet reaching incredible
brightness. In this case, the comet lived up to the hype, reaching an
apparent magnitude of -10 in October, 1965, becoming visible next to
the Sun in daylight near perihelion. After the comet reappeared on
the other side of the Sun following perihelion, it sported an
extremely bright, long tail.
Comet
West (1976)
Discovered photographically in September, 1975, Comet
West was predicted to reach perihelion on February 25 of the
following year. At perihelion, observers reported the comet as being
bright enough to be seen in broad daylight. Unfortunately, despite
its spectacular appearance, comet West was largely ignored by the
non-astronomical media thanks to another comet, Kohoutek, which
failed to live up to its initial billing as 'comet of the century' in
1973.
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