Telescope Reviews: ALERT - Comet 17/P Holmes in mega outburst

I went out again last night and spent a good deal of time observing, mostly with 16x70s but also with a WO80SDII at low powers. I made some sketches and took some measurements with detailed back and forth from binocs to scope to note-table (but paid a very uncomfortable price for the time spent and the up/down positions I needed to get into. Aching and some (little) common sense ended my observing. Afterward my night's sleep was disrupted several times by significant leg and hip pain. Rest this morning seems to be helping provide welcome relief).

Anyway, I made some comparisons of the star field around the comet to some known and measurable star fields. I took these measures in my scope at 40x, as the binocular fov was just too wide. Take note of the photo provided above by Olivier. Comet Holmes photo by Olivier Biot It represents the closest to what I saw in the 16x70s. Take particular note of the string of three stars pointing to the north (to the left towards 9:30-10:00). From the third star out, the faintest one, to the center of the comet measures almost identical as from Alcyone to star A10 on my M45 charts. That distance measures 43 arcminutes. As a verification that covered almost exactly one half the fov of my 12.5Ult in my WO80, approx 40 arcmin. From that, there is enough information to use as an estimating scale for size estimates. End result is that my estimate of the outer diameter of the coma is 11 arcminutes and the inner bright core is 3 arcmin.

The bright central 3 arcmin core is offcenter in the coma with more of the outer coma (4-5 arcmin) visible towards the north, the side near the bright nucleus. Also, the bright central core appeared not exactly round, but maybe more egg-shaped, with the narrow tip of the egg at the location of the bright nucleus. The south side of the outer coma ring is not rounded to a complete outer circular edge, unlike the north side. I see about 3 arcmin of coma to the south of the bright core. It's almost like the outer edges of a circular coma were unevenly blotted out slightly over a thin 1-2 arcmin wide cresent, almost as if the cresent were fully and evenly lit, the bright core would be centered in the coma.

Intersting was that several times I went back and forth from the 16x70s to my scope at 23x (21.5RKE) and 28x(18TakLE) and I could not easily notice any difference in the size of the object. Seemed the same to me until I bumped the scope up to 40x. The bright nucleus did indeed have a non-stellar appearance at 40x. Also several times I compared overall brightness to out of focus stars and still find a close resemblence to Gamma Per (mag2.6), but perhaps midway between Gamma (2.6) and Delta Per (2.9).

I had my 80mm scope mouted to a Microstar Atl/Az, so needed periodic adjustment. At 28x(18TakLE) and 40x(12.5xUltima), I "thought" more than once, as I moved the scope to recenter my view, that I saw an extended glow completely around the coma. The glow "seemed" more readily apparent and somewhat broader off the south (the dark cresent) side. I did not see this in the Fujinons.

I made several observations also with a pair of 10x50 Leupold Wind River Mesas (on loan from the most generous Walter Locke) and a pair of Captain's Helmsnman 7x50s. I used the smaller 10x and 7x binoculars both mounted and handheld. In the 7x50 is was difficult if at all to see the differentiation of the bright central core and the wider coma. It simply appeared as a bright diffuse extended object. In the 10x50s, for moments I could hold them still enough to at least notice a distinction between the brighter center and the fainter outer coma. The nucleus was not seen in either 50mm binocular.

The 7x50s provided a very nice widefield view that included the entire Alpha Perseus Association in the same view with comet Holmes, a pleasant escape from the views I made for detailed measurements. The 10x50s just barely covered this area, but the 7x50s did so with room to spare.

At one point I popped my new Agena 38mm/70° eyepiece into the scope for a 13x80 view. Even at that view I could make out the bright pinpoint nucleus.

edz

Edited by EdZ (10/31/07 03:39 PM)