[meteorite-list] Bright New Comet Could Become Brilliant

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Fri, 5 Jan 2007 01:24:07 -0600
Message-ID: <00ed01c7309a$7ce815b0$b421e146_at_ATARIENGINE>

Hi, List,

Everybody loves a bright comet...

http://www.space.com/spacewatch/070104_comet_mcnaught.html

A newfound comet is about to loop around
the Sun and might offer skywatchers a rare
and fantastic view. But comets are unpredictable,
and this one has a wide range of possible
outcomes, experts say.

When Australian astronomer Robert McNaught
announced Aug. 7 that he had discovered a
faint comet on a photograph taken at the Siding
Spring Observatory in New South Wales, it was
a distant and inconspicuous object. But its
orbital motion at once made it clear that this
comet, officially catalogued as C/2006 P1,
might grow very bright right about now.

Comet McNaught's orbit [video] indicates
that it will sweep to within just 15.8 million
miles (25.4 million kilometers) of the Sun
on Jan. 12. This rather close approach-less
than half the average distance of Mercury,
the closest planet to the Sun-suggests the
comet has the potential to briefly evolve
into a bright object. The big question is,
just how bright?

Recent estimates have ranged widely from
magnitude +2.1 (about as bright as Polaris,
the North Star) to a dazzling -8.8 (about 40
times brighter than Venus)!

[The lower the magnitude number, the brighter
the object. The brightest stars in the sky are
categorized as zero or first magnitude. Negative
magnitudes are reserved for the most brilliant
objects: the brightest star is Sirius (-1.4);
the full Moon is -12.7; the Sun is -26.7.
The faintest stars visible under dark skies
are around +6.]

The reason for the great uncertainty stems
from the fact that for the past few weeks
the comet has been positioned at such a
relatively small angular distance from the
Sun in the sky that it has been extremely
difficult to get good measurements of its
brightness. Now, with a little over a week
to go before the comet makes its closest
approach to the Sun (called perihelion),
just how bright it may ultimately get and
how long a tail may develop remain to be seen.

Predicting a newly discovered comet's
brightness has proven historically to be
difficult, especially around the time of
perihelion. This is the 31st comet to bear
McNaught's name and at time of discovery,
it was no brighter than magnitude 17-far
too dim to see with the naked eye.
 
Observers have followed its gradual
brightening as its distances from Sun
and Earth decreased. It's currently
both a morning and evening object,
visible very low near the east-southeast
horizon about 30 to 40 minutes before
sunrise and very low near the west-southwest
horizon about 30 to 40 minutes after sunset.
 
During this upcoming week, prospective
observers should seek the most favorable
conditions possible. Even a bright comet
can be obliterated by thin horizon clouds,
haze, humid air, smoke, twilight glow, city
lights, or moonlight. Binoculars are strongly
recommended for locating it.

But the past few days, reports suggest that
Comet McNaught is becoming easier to sight
even through the bright twilight glow. David
Moore reported seeing the comet on New
Year's Day evening from Dublin, Ireland.
He writes: "After searching for over half
an hour in strong twilight I saw it easily in
20x80 binoculars from an upstairs window.
I could see a small fuzzy and surprisingly
bright head about as bright as the mag 3.5
star Lambda Aquilae 6 degrees above it.
That said, it was not an easy observation
given the strong twilight and the comet
was only 3.0 degrees above the horizon!"

Well-known comet observer, John Bortle
of Stormville, New York caught sight of
the comet just before sunrise with 15 x 80
binoculars on Jan. 2. "My eastern view was
largely obstructed by trees," Bortle said.
"Still it was somewhat amazing to see the
comet against such a bright sky and through
all those tree branches! From experience
in making similar observations, I'd judge that
it was not any fainter than 2nd magnitude."

Regardless of just how bright Comet
McNaught becomes, beginning on Friday,
Jan. 12 and continuing through Monday,
Jan. 15, it will be passing through the field
of view of the Solar and Heliospheric
Observatory ("SOHO"); a spacecraft
that was launched in 1995 to study the Sun.
Received on Fri 05 Jan 2007 02:24:07 AM PST