[AZ-Observing] 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
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Good article and link on Holmes, =E2=80=9CThe Biggest Thing in the Solar =
System=E2=80=9D (right now, anyway).
=20
Dick H
=20
=20
From: ASKC@xxxxxxxxxxxxxxx [mailto:ASKC@xxxxxxxxxxxxxxx]=20
Sent: Tuesday, November 20, 2007 8:05 AM
Subject: [ASKC] holmes size & data article
=20
article, links, and pics at:
_http://www.space.com/spacewatch/071115-comet-holmes-size.html_=20
(http://www.space.com/spacewatch/071115-comet-holmes-size.html)=20
Incredible Comet Bigger than the Sun=20
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=20
extended influence of particles that reaches all the planets. But the=20
comparatively tiny Comet Holmes has released so much gas and dust that =
its extended=20
atmosphere, or coma, is larger than the diameter of the sun. The =
comparison=20
is clear in a new image.=20
"It continues to expand and is now the largest single object in the =
solar=20
system," according to astronomers at the University of Hawaii.=20
The coma's diameter on Nov. 9 was 869,900 miles (1.4 million =
kilometers),=20
based on measurements by Rachel Stevenson, Jan Kleyna and Pedro Lacerda =
of the=20
University of Hawaii Institute for Astronomy. They used observations =
from the=20
Canada-France-Hawaii Telescope. The sun's diameter, stated differently =
by=20
various sources and usually rounded to the nearest 100, is about 864,900 =
miles=20
(1.392 million kilometers).
Separately, a new Hubble Space Telescope photo of the comet reveals an=20
intriguing bow-tie structure around its nucleus.
The comet's coma=E2=80=94mostly microscopic particles=E2=80=94shines by =
reflecting sunlight.
See for yourself=20
Holmes is still visible to the naked eye as a fuzzy star anytime after =
dark,=20
high in the northeast sky. You can find it by using this sky map. It is=20
faintly visible from cities, and from dark country locations is truly =
remarkable.=20
"Right now, in a dark sky it appears as a very noticeable circular =
cloud,"=20
said Joe Rao, SPACE.com's Skywatching Columnist. Rao advises looking for =
the=20
comet this weekend, before the moon becomes more of a factor. The comet =
will=20
likely diminish in brightness yet remain visible for the next two to =
three=20
weeks, he said.=20
"Over the next few weeks and months, the coma and tail are expected to=20
expand even more while the comet will fade as the dust disperses," =
Stevenson and=20
her colleagues write.=20
On Monday, Nov. 19, the comet will create a unique skywatching event =
with=20
its see-through coma, according to the Web site Spaceweather.com: "The =
comet=20
will glide by the star Mirfak [also called Alpha Persei] and appear to =
swallow=20
it=E2=80=94a sight not to be missed."
A small telescope will reveal the fuzzy coma. Lacking a long tail=20
characteristic of some great comets, however, Holmes is not the most =
dramatic object in=20
the sky for casual observers.
Mystery outburst=20
Nobody knows why Holmes erupted, but it underwent a similar explosive=20
brightening in 1892. The recent display, which began Oct. 24, brought =
the comet=20
from visual obscurity to being one of the brighter objects in the night =
sky. It=20
has since dimmed somewhat as the material races outward from the nucleus =
at=20
roughly 1,100 mph (0.5 km/sec).=20
The Hawaiian astronomy team writes in a press statement: "This amazing=20
eruption of the comet is produced by dust ejected from a tiny solid =
nucleus made=20
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=20
to one side, now just a fuzzy region to the lower-right. That's caused =
by=20
the pressure of sunlight pushing on the gas and dust of the coma.=20
But the comet is so far away=E2=80=94149 million miles (240 million =
kilometers), or=20
about 1.6 times the distance from Earth to the sun=E2=80=94that even =
Hubble can't=20
resolve its nucleus.
The offset nature of the coma, seen in ground-based images, suggests "a=20
large fragment broke off and subsequently disintegrated into tiny dust =
particles=20
after moving away from the main nucleus," Hubble astronomers said in a=20
statement today. The comet's distance, plus all the dust, prevent Hubble =
from=20
seeing any fragments, however.=20
...click the following for more ...
The Greatest Comets of All Time=20
Video: Comets Through Time ... Myths and Mystery=20
Comet Image Gallery=20
************************************** See what's new at =
http://www.aol.com
__._,_.___=20
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