[meteorite-list] The Greatest Comets of All Time

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 19 Jan 2007 16:19:26 -0800 (PST)
Message-ID: <200701200019.QAA09034_at_zagami.jpl.nasa.gov>

http://space.com/spacewatch/070119_ns_great_comets.html

The Greatest Comets of All Time
By Joe Rao
SPACE.com
19 January 2007

Last week favorably placed observers viewed a comet so brilliant that it
could be seen with the naked eye in broad daylight, if the Sun was hidden
behind the side of a house or even an outstretched hand.

Comet McNaught, which was discovered last August by astronomer Robert
McNaught at Australia's Siding Spring Observatory, was one of the
greatest comets in recent times. It evolved into a brilliant object
as it swept past the Sun on Jan. 12, at a distance of just 15.9 million
miles.

The comet's show is mostly over for those North of the equator.

Yet even as the comet puts on a fantastic show now in the evening sky
for viewer's in the Southern Hemisphere (McNaught himself produced a
fantastic photograph
<http://www.space.com/php/multimedia/imagedisplay/img_display.php?pic=070119_mcnaughts_pic_02.jpg&cap=Robert+McNaught,+the+Australian+who+discovered+this+comet+that+bears+his+name,+finally+got+to+photograph+it+this+week+when+it+became+visible+from+the+Southern+Hemisphere.+Image+used+with+permission>),
an incredible sight is still visible to seasoned observers in the
Northern Hemisphere. From Colorado, Mary Laszlo of used a 20-second
exposure to capture the outer extremities of Comet McNaught's tail
<http://www.space.com/php/multimedia/imagedisplay/img_display.php?pic=070119_mcnaught_lazlo_02.jpg&cap=From+Colorado%2C+Mary+Laszlo+of+used+a+20-second+exposure+to+capture+the+outer+extremities+of+Comet+McNaught%27s+tail+on+Jan.+17%2C+2007.+Paul+Robinson+of+Boulder+was+credited+as+having+realized+such+an+image+might+be+possible.+Credit%3A+Mary+Laszlo>
on Jan. 17. Paul Robinson of Boulder was credited as having realized
such an image might be possible.

Brighter than Venus

According to reports received from a worldwide audience at the
International Comet Quarterly (ICQ) it appears that the comet
reached peak brightness on Sunday, Jan. 14 at around 12 hours UT (7:00
a.m. EST). At that time, the comet was shining at magnitude -5.1. On
this scale, larger numbers represent dimmer objects; the brightest stars
are generally zero to first magnitude, while superbright objects such as
Venus - and Comet McNaught - achieve negative magnitudes.

I determined the comet's peak magnitude by averaging out more than a
dozen observations that were reported to the ICQ on Jan. 14. Some
observers, such as Steve O'Meara, located at Volcano, Hawaii, observed
McNaught in daylight and estimated a magnitude as high as -6, noting.
"The comet appeared much brighter than Venus!"

>From Jan. 12-16, Comet McNaught ranked as the third brightest object in
the sky behind only the Sun and the Moon!

Was Comet McNaught the best or brightest comet ever seen? While it's
true that comets that are visible with the naked eye during the daytime
are rare, the case of McNaught is not unique. In the last 263 years, it
has happened seven other times:

GREAT COMET OF 1744: First sighted on Nov. 29, 1743 as a dim fourth
magnitude object, this comet brightened rapidly as it approached the
Sun. Many textbooks often cite Philippe Loys de Cheseaux, of Lausanne,
Switzerland as the discoverer, although his first sighting did not come
until two weeks later. By mid-January 1744, the comet was described as
1st-magnitude with a 7-degree tail. By Feb. 1 it rivaled Sirius and
displayed a curved tail, 15-degrees in length. By Feb. 18 the comet was
equal to Venus and now displayed two tails. On Feb. 27, it peaked at
magnitude -7 and was reported visible in the daytime, 12-degrees from
the Sun. Perihelion came on March 1st, at a distance of 20.5 million
miles from the Sun. On March 6, the comet appeared in the morning sky,
accompanied by six brilliant tails which resembled a Japanese
hand fan.

GREAT COMET OF 1843: This comet was a member of the Kruetz Sungrazing
Comet Group, which has produced some of the most brilliant comets in
recorded history. It passed only 126,000 miles from the Sun's
photosphere on Feb. 27, 1843. Although a few observations suggest that
it was seen for a few weeks prior to this date, on the day when it made
it closest approach to the Sun it was widely observed in full daylight.
Positioned only 1-degree from the Sun, this comet appeared as "an
elongated white cloud" possessing a brilliant nucleus and a tail about
1-degree in length. Passengers on board the ship Owen Glendower, off
the Cape of Good Hope described it as a "short, dagger-like object" that
closely followed the Sun toward the western horizon. In the days that
followed, as the comet moved away from the Sun, it diminished in
brightness but the tail grew enormously,
eventually attaining a length of 200 million miles. If you were able to
place the head of this comet at the Sun's position, the tail would have
extended beyond the orbit of the planet Mars!

GREAT SEPTEMBER COMET OF 1882: This comet is perhaps the brightest comet
that has ever been seen; a gigantic member of the Kreutz Sungrazing
Group. First spotted as a bright zero-magnitude object by a group of
Italian sailors in the Southern Hemisphere on Sept. 1, this comet
brightened dramatically as it approached its rendezvous with the Sun.
By the 14th, it became visible in broad daylight and when it arrived at
perihelion on the 17th it passed at a distance of only 264,000-miles
from the Sun's surface. On that day, some observers described the
comet's silvery radiance as scarcely fainter than the limb of the Sun,
suggesting a magnitude somewhere between -15 and -20! The following
day, observers in Cordoba described the comet as a "blazing star" near
the Sun. The nucleus also broke into at least four separate parts. In
the days and weeks that followed, the comet became visible in the
morning sky as an immense object sporting a brilliant tail. Today, some
comet historians consider it as a "Super Comet," far above the run of
even Great Comets.

GREAT JANUARY COMET OF 1910: The first people to see this comet - then
already of first magnitude - were workmen at the Transvaal Premier Diamond
Mine in South Africa on Jan. 13. Two days later, three men at a railway
station in nearby Kopjes casually watched the object for 20-minutes
before sunrise, assuming that it was Halley's Comet. Later that
morning, the editor of the local (Johannesburg) newspaper telephoned the
Transvaal Observatory for a comment. The observatory's Director, Robert
Innes, must have initially thought this sighting was a mistake, since
Halley's Comet was not in that part of the sky and nowhere near as
conspicuous. Innes looked for the comet the following morning, but
clouds thwarted his view. But on the morning of the 17th, he and an
assistant saw the comet, shining sedately on the horizon just above
where the Sun was about to rise. Later, at midday, Innes viewed it as a
snowy-white object, brighter than Venus, several degrees from the Sun.
He sent out a telegram alerting the world to expect "Drake's Comet" - for
so "Great Comet" sounded to the telegraph operator. It was visible
during the daytime for a couple of more days, then moved northward and
away from the Sun, becoming a stupendous object in the evening sky for
the rest of January for the Northern Hemisphere. Ironically, many people
in 1910 who thought they had seen Halley's Comet, instead likely saw the
Great January Comet that appeared about three months before Halley.

COMET SKJELLERUP-MARISTANY, 1927: Another brilliant comet, first seen as
a third magnitude object in early December, had the unfortunate
distinction of being situated under the poorest observing circumstances
possible. The orbital geometry was such, that the approaching comet
could not be seen in a dark sky at any time from either the Northern or
the Southern Hemisphere. But it reached tremendous magnitude at
perihelion on Dec. 18. Located at a distance of 16.7 million miles from
the Sun, it was visible in daylight about 5-degrees from the Sun at a
magnitude of -6. As the comet moved out
of the twilight and headed south into darker skies, it faded rapidly,
but still threw off an impressively long tail that reached up to
40-degrees in length by the end of the month.

COMET IKEYA-SEKI, 1965: This was the brightest comet of the 20th
century, and was found just over a month before perihelion passage in
the morning sky moving rapidly toward the Sun. Like the Great Comets of
1843 and 1882, Ikeya-Seki was a
Kreutz Sungrazer and on Oct. 21 swept to within 744,000 miles of the
center of the Sun. The comet was then visible
as a brilliant object within a degree or two of the Sun, and wherever
the sky was clear, the comet could be seen by observers merely by
blocking out the Sun with their hands. From Japan, the homeland of the
observers who discovered it, Ikeya-Seki was described as appearing "ten
times brighter than the Full Moon" corresponding to a magnitude of -15.
Also at that time, the nucleus was observed to break into two or three
pieces. Thereafter, the comet moved away in full retreat from the Sun,
the head fading very rapidly but its slender, twisted tail,
reaching out into space for up to 75 million miles, and dominating the
eastern morning sky right on through the month of November.

COMET WEST, 1976: This comet developed into a beautiful object in the
morning sky of early March 1976 for Northern Hemisphere observers. It
was discovered in November 1975 by Danish astronomer, Richard West on
photographs taken at the European Southern Observatory in Chile.
Seventeen hours after passing within 18.3 million miles of the Sun on
Feb. 25, it was glimpsed with the naked eye 10 minutes before sunset by
John Bortle - the last daylight comet sighting until McNaught in 2007.
In the days that followed, Comet West displayed a brilliant head and a
long, strongly structured tail that resembled "a fantastic fountain of
light." Sadly, having been "burned" by the poor performance of Comet
Kohoutek two years earlier, the mainstream media all but ignored Comet
West, so most people unfortunately failed to see its dazzling performance!

What's next for Comet McNaught?

Viewers in the Southern Hemisphere will now have Comet McNaught pretty
much all to themselves in the days ahead. It should continue to be a
striking object in the west-southwest sky as darkness falls.

If a parallel can drawn between Comet McNaught and any of the
above-mentioned comets, it's that it should gradually fade as it moves
away from both the Earth and Sun. As we have previously noted, new
comets can be notoriously unpredictable to forecast, but it appears now
that McNaught should be shining somewhere between magnitude 0 and 2 on
Jan. 21, then fade to perhaps magnitude 5 by the end of January or early
February.

Although the comet is fading as it moves higher into the sky and sets
progressively later, its tail should appear to impressively lengthen.

Amazingly, the end of the tail (called the "terminus") has been glimpsed
as far north as Colorado; the multiple streamers protruding above the
southwest horizon resemble faint auroral rays in binoculars.

It should, in fact, appear at its longest this upcoming week - before the
increasing brightness of the waxing Moon begins to compromise the view.
Skywatchers should look for two tails. The one appearing slender and
straight and pointing nearly directly upward from the horizon, will be
due to gas, while the other, appearing as broad and gentle curving fan
is composed of dust expelled from the comet's head and made visible by
reflected sunlight.

Without doubt, however, Comet McNaught's performance will stand as one
of the most spectacular in recent years. For those fortunate enough to
have seen it, it will always be a comet to remember.
Received on Fri 19 Jan 2007 07:19:26 PM PST