[sac-forum] FW: [ASKC] holmes size & data article
- From: "Richard Harshaw" <rharshaw2@xxxxxxx>
- To: <sac-forum@xxxxxxxxxxxxx>, <az-observing@xxxxxxxxxxxxx>
- Date: Tue, 20 Nov 2007 08:23:30 -0700
Good article and link on Holmes, “The Biggest Thing in the Solar System” (right
now, anyway).
Dick H
From: ASKC@xxxxxxxxxxxxxxx [mailto:ASKC@xxxxxxxxxxxxxxx]
Sent: Tuesday, November 20, 2007 8:05 AM
Subject: [ASKC] holmes size & data article
article, links, and pics at:
_http://www.space.com/spacewatch/071115-comet-holmes-size.html_
(http://www.space.com/spacewatch/071115-comet-holmes-size.html)
Incredible Comet Bigger than the Sun
By Robert Roy Britt
Senior Science Writer
posted: 15 November 2007
10:38 am ET
A comet that has delighted backyard astronomers in recent weeks after an
unexpected eruption has now grown larger than the sun.
The sun remains by far the most massive object in the solar system, with an
extended influence of particles that reaches all the planets. But the
comparatively tiny Comet Holmes has released so much gas and dust that its
extended
atmosphere, or coma, is larger than the diameter of the sun. The comparison
is clear in a new image.
"It continues to expand and is now the largest single object in the solar
system," according to astronomers at the University of Hawaii.
The coma's diameter on Nov. 9 was 869,900 miles (1.4 million kilometers),
based on measurements by Rachel Stevenson, Jan Kleyna and Pedro Lacerda of the
University of Hawaii Institute for Astronomy. They used observations from the
Canada-France-Hawaii Telescope. The sun's diameter, stated differently by
various sources and usually rounded to the nearest 100, is about 864,900 miles
(1.392 million kilometers).
Separately, a new Hubble Space Telescope photo of the comet reveals an
intriguing bow-tie structure around its nucleus.
The comet's coma—mostly microscopic particles—shines by reflecting sunlight.
See for yourself
Holmes is still visible to the naked eye as a fuzzy star anytime after dark,
high in the northeast sky. You can find it by using this sky map. It is
faintly visible from cities, and from dark country locations is truly
remarkable.
"Right now, in a dark sky it appears as a very noticeable circular cloud,"
said Joe Rao, SPACE.com's Skywatching Columnist. Rao advises looking for the
comet this weekend, before the moon becomes more of a factor. The comet will
likely diminish in brightness yet remain visible for the next two to three
weeks, he said.
"Over the next few weeks and months, the coma and tail are expected to
expand even more while the comet will fade as the dust disperses," Stevenson
and
her colleagues write.
On Monday, Nov. 19, the comet will create a unique skywatching event with
its see-through coma, according to the Web site Spaceweather.com: "The comet
will glide by the star Mirfak [also called Alpha Persei] and appear to swallow
it—a sight not to be missed."
A small telescope will reveal the fuzzy coma. Lacking a long tail
characteristic of some great comets, however, Holmes is not the most dramatic
object in
the sky for casual observers.
Mystery outburst
Nobody knows why Holmes erupted, but it underwent a similar explosive
brightening in 1892. The recent display, which began Oct. 24, brought the comet
from visual obscurity to being one of the brighter objects in the night sky. It
has since dimmed somewhat as the material races outward from the nucleus at
roughly 1,100 mph (0.5 km/sec).
The Hawaiian astronomy team writes in a press statement: "This amazing
eruption of the comet is produced by dust ejected from a tiny solid nucleus
made
of ice and rock, only 3.6 kilometers (roughly 2.2 miles) in diameter."
The new image from the Hawaiian observatory also shows a modest tail forming
to one side, now just a fuzzy region to the lower-right. That's caused by
the pressure of sunlight pushing on the gas and dust of the coma.
But the comet is so far away—149 million miles (240 million kilometers), or
about 1.6 times the distance from Earth to the sun—that even Hubble can't
resolve its nucleus.
The offset nature of the coma, seen in ground-based images, suggests "a
large fragment broke off and subsequently disintegrated into tiny dust
particles
after moving away from the main nucleus," Hubble astronomers said in a
statement today. The comet's distance, plus all the dust, prevent Hubble from
seeing any fragments, however.
...click the following for more ...
The Greatest Comets of All Time
Video: Comets Through Time ... Myths and Mystery
Comet Image Gallery
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