[AZ-Observing] Comet C/2007 N3 (Lulin)

  • From: <jeremy@xxxxxxxxxxxxxx>
  • To: az-observing@xxxxxxxxxxxxx
  • Date: Sat, 10 Jan 2009 00:41:08 +0000

What does it take to get me out of bed at the abominable hour of 4 AM? Comet 
Lulin, I guess! I've been hearing some interesting reports about it, and saw a 
fantastic photo by Karzaman Ahmad at Spaceweather.com. So I was motivated 
enough to overcome the horrors of such an early morning.

I was hoping to make my first observation of C/2007 N3 (Lulin) before the 
full/waning-gibbous moon overpowers it for the next couple weeks. I drove out 
to Sunset Crater National Monument and arrived there shortly after 5 am with 
the moon blazing away and lighting up the snow-covered landscape. The head of 
Scorpius was rising, and Antares was flickering with a rusty light just over 
the tops of the cinder cones. While the sky was still bright with moonlight, I 
shot a few photos of the landscape, and then set up my 8 inch Dobsonian.

The comet was a snap to find at low power (37.5X) and readily pierced the 
moon-washed star field as a round glow with a nicely condensed core. I'd 
estimate the degree of condensation as 6. Initially, I saw probably about 2 arc 
minutes of the core region. The bright 6th magnitude star, 47 Librae anchored 
the east side of the field.

As the moonlight began to dwindle and the comet rose higher in the sky, more 
structure began to appear. Compared to the neutral gray background, the comet 
emitted a very slight aqua tint. A definite brightening proceeded eastward away 
from it at a PA of about 100 degrees. This extension (likely the dust tail?) 
was visible out to about 9 arc minutes from the core.

As conditions improved, the coma also appeared to blossom a bit more to a 
diameter of about 6 arc minutes. At this point, the brighter core took on a 
more elliptical shape that preferred to drag off to the east. On the west side 
of the comet, a much fainter extension (the ion tail?) emerged from the coma at 
a PA of about 290 degrees. A quick look at 240X showed the coma to be brighter 
along its southern half, perhaps due to the dust tail fanning widely behind and 
to the south of the comet. I didn't spend time trying to compare the comet's 
brightness to nearby stars, but it was definitely brighter than 8th magnitude 
M107--I'd estimate by at least 1.5 if not 2 magnitudes. That's a very rough 
estimate, so don't rely on it for anything. But if correct, that would put it 
around 6th magnitude, at the threshold of naked-eye visibility under a dark, 
transparent sky. I did not actually try to spot it naked eye, however (it would 
have been tough with 47 Librae right next door anyway).

The extended details I observed were very subtle and required much time spent 
observing with averted vision. Scope tapping, sweeping, and moving the core 
outside of the field of view on different sides, all helped to bring these 
structures into view. With strong moonlight, light pollution, or murky skies, 
they are likely to be invisible while the comet is so low. The central core 
however is quite bright and should be visible telescopically and with 
binoculars to some degree under poorer conditions.

The time between moonset and the beginning of morning twilight was fleeting, 
and the gradually improving view halted, and began to quickly deteriorate. I 
spent probably 15 minutes plotting the star field, then a half hour sketching 
and examining the comet for structure, and a final 15 minutes trying to eke out 
the last, faintest bits of detail. It was an hour very well spent. I attempted 
to track down the pairing of the nearby comet C/2008 X4 (Christensen) with 
globular cluster M107, but was only successful in spotting M107. I wasn't able 
to spend much time on that side trip, since I needed every bit of attention for 
Lulin, and I'm glad I made that choice. Hopefully, Lulin will be quite a bit 
brighter in two weeks when the new moon cycle returns and this comet's 
beautiful features will be easier to detect, and rich with developing structure.

The full report and a larger sketch can be found here: 

Clear skies,
Jeremy Perez
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