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--Apple-Mail-2--290917196 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed I've just come in from having a quick look at Comet Holmes this evening; the sky is clearing out. This may be the last opportunity for a while to have a look before moonlight begins to wash out the sky contrast again (more c;oudy weather in the forecast coming later through the night). Theere was a thin crescent of the New Moon visible, earlier this evening. Its location has not changed much....just a little nearer Mirfak. I am copying my message sent to the RASC list earlier today, reporting on an observation I made this morning. The comet diameter, in real size, has now expanded to about 1.5 million km. What I think is most neat about the comet is the binocular star field it is combined with. I'll also include Roy's response. Note also, his closing report on the crescent moon this evening. All the best, Sherman ***************** COMET HOLMES early this morning (Monday) ************************* > Finally, early this morning, I got in a nice observation session > of Comet Holmes after a few days of limited or no views due to > cloud and bad weather. > > I had the comet in my binoculars by 05:20 AST, high in the WNW. > Using the out-of-focus mode (in 10x50s and my nearsighted eyes), > it seems to be dimmer than delta Persei(3.0), so I'm putting it at > about Mag 3.2. > > It is at the NE fringe of the rich open cluster of stars associated > with Mirfak (alpha Persei). > The combination of this star field and Comet Holmes' wide, fuzzy > diameter make a magnificent sight in 10X50 binoculars. My book on > viewing the sky in binoculars (P.S.Harrington) refers to this group > as Melotte 20, off about 550 ly from us. > > The view in my 255 mm at 48X and 94X, was quite interesting too. > The coma was decorated with > several fine points of 10th, 11th, and 12th magnitude stars in the > background. Of these, > one mag 7.3 star was brightly shining just beyond the western > fringe of the coma. > This was also quite noticable in my binoculars. > > Another star, about mag 10.8(Starry Night), was easily seen within > the nuclear region, quite near to where we have been seeing the > bright nuclear spot. I thought the star-like part of the nucleus > was just barely visible, but now I'm not sure if I was seeing it, > because my Starry Night star field shows that there was an 11th mag > star in just about the same position. Perhaps someone else can > enlighten further on the detail in the nuclear region. Certainly it > is not as obvious as it once was. > > The bright zone in the central region seems narrower and > concentrated, especially as it elongates to the SW, centrally > aligned with what becomes the tail zone (my Starry Night gives it a > pa in the vicinity of 200 degrees). > I did not detect any definite tail structure beyond the coma, other > than an elevated glow in the SW direction, extending just beyond > the coma. On that same side of the coma the edge is noticeably > closer to a fuzzy "flat line" boundry rather than a curved, > distinct line like the rest of the coma edge (like someone chopped > off the curved edge on the SW side). In some of the recent shared, > technical, digitally processed photos, this is where we are seeing > tail structure leaving the comet. Such structure, however, was not > visible in either my telescope nor binoculars, only an indistinct > glow was noticed. Last week, using my binoculars, I could detect > some tail structure that had a definite boundary to it and > extending off to the NE about 1.3 degrees. > > I did a couple of timings to get a number on the actual increase in > diameter since last Wednesday. > My times (taken between 05:35 and 05:43 averaged out to 157.7 seconds. > Using the calculation Roy (Bishop) introduced to our discussion, I > get 25.1 min of arc. > Using the star field Starry Night shows (and that I recognized in > the eyepiece at the fringe of the coma ) plus the little angle > measure mode SN provides, it gives a diameter of about 27.2 min of > arc. > > From 05:50 to 06:00 AST I turned my attention to Mars, Saturn, > Venus and Mercury, in that order. The first three planets were seen > well, Mercury I did not see (it is still very low and clouds were > in that part of the horizon). Saturn is beginning to look like it > has a peg stuck through the disk. The rings are really closing up. > > Long winded as usual, > Sherman > Sherman, > > I was asleep at 5:40 this morning, and I am glad you were not! > Your measured diameter for the main disk of Holmes (25.1' timed, > 27.2' based on the star field) agrees with my time measurements > during the period October 26 to November 2. The latter measurements > fit a linear equation: > > Diameter in arc minutes = 1.444 x (6.51 + (November AST decimal > day)) > > which for 05:40 AST November 12 gives: 1.444 x (6.51 + 12.236) > = 27.1' > > in good agreement with your estimates. Thus the linear expansion > continues! > It will be interesting to see how long this behavior lasts (and can > be observed). > > The time of the "explosion" can be calculated from the equation: > Set Diameter = 0 and solve for the date. This gives November -6.51 > or October 24.49 AST = October 24.66 UT. The first observation > that reported Holmes to be acting up was from the Canary Islands on > October 24.07 UT, so the explosion occurred more than 0.59 day > before October 24.66 UT which indicates that during the first > several hours the ejected material was being accelerated outward > (that is, the expansion was not yet a linear function of time). > > Note that the above equation is preliminary in that it does not > include all my data and it does not take account of the varying > distance of Holmes from Earth. However that distance has been > remarkably almost constant (less than a 1% change over the past two > weeks). > > Incidentally, I just watched the crescent Moon set (at 17:55 AST). > It was remarkably far south of west, a vertical, orange scimitar > slicing along behind trees on the South Mountain. The Observer's > Handbook puts the Moon at maximum southern declination tonight, -28 > degrees, almost as low as it can get in our sky (due to the 18.6- > year wobble of its orbital plane, as mentioned on p. 79 of the > current Handbook). To see the Moon so low in that part of the sky > indicates that the evening may be clear later on, a chance for > another measurement of Holmes! Sherman Williams shermw@xcountry.tv --Apple-Mail-2--290917196 Content-Transfer-Encoding: quoted-