[meteorite-list] Bright New Comet Could Become Brilliant

[Sterling K. Webb]

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.