17P / Holmes – OCT 26, 2007

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Observation Notes:

Over the course of the last 24 hours, the size of this comet has increased greatly. Using my astrometric eyepiece, I measured the central condensation at about 35 arc seconds, the bright coma at 150 arc seconds, and the faint outer halo at 400 arc seconds. The color was more subtle than yesterday and had an ivory appearance. I’ve heard some other observers liken it to a softly lit pearl, and I think that description fits perfectly. The central condensation flows off center at a PA of about 220 degrees and has a much softer transition than it appeared to have yesterday. The northeastern tip of this condensation surrounds a stellar pseudo-nucleus. The bright coma appears to have developed an annular structure. The southwest half is brighter and the ring-like edge is more apparent along the northeast side. While looking for any consistent irregularity in the faint outer halo, I thought I still detected a subtly brighter area along the southwest portion that corresponded to the position of the central condensation. The full moon really makes it tough to analyze this faint detail though.

To the naked eye, the comet is brighter than Delta Persei, but not as bright as Alpha Persei, so somewhere around mag 2.5 still I’d roughly guess. With the aid of my stargazing glasses, I think that it appears just the tiniest bit softer than a proper star of similar magnitude. I’d like to say I’m going to give it another extended look tomorrow night, but I think I may succumb to an involuntary sleep-deprivation coma. We’ll see…

Subject 17P / Holmes
Classification Comet
Position* 8:15 UT – Perseus: [RA: 03:51:46.7 / Dec: +50:14:02]
Size Central condensation: 35 arc seconds
Coma: 150 arc seconds / 2.5 arc minutes
Outer halo: 400 arc seconds / 6.7 arc minutes
Brightness* ~ 2.5 vMag
Date/Time October 26, 2007, 1:15 AM
(October 26, 2007, 08:15 UT)
Observing Loc. Flagstaff, AZ – Home
Instrument Orion XT8 (203 mm dia./1200 mm F/L)
Eyepieces/Mag. 25 mm Sirius Plössl (48X)
10 mm Sirius Plössl + 2X Barlow (240X)
12 mm Meade Astrometric + 2X Barlow (~200X)
Conditions Clear, calm, full moon
Seeing 3/10 Pickering
Transparency ~ Mag 4.0 NELM
*Sources Aerith.net; Starry Night Pro Plus 5

*Based on published data.

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