1/2.1107 19.30-20.00 / 22.00-23.30 BST
The night began very cloudy and hopeless for astronomy until I got a phone call from John Mc Connell informing me that he just caught the comet in forming gaps between the clouds and he was very impressed by its appearance. He was just off the phone to Dr. Andy Mc Crea in Belfast who was imaging the comet through those same gaps using his 14" S.Cass in his back garden observatory. Shortly after this clear sky began to open up over Maghera until the sky was incredible with a very dark sky background, Trans 8/10, Seeing = 6-7/10. It was a glorious clear night and I had all my gear set up in the back garden and let my eyes adjust to the darkness. This would be my first serious session with Holmes without the Moon in the sky. It was so warm I was wearing a T-shirt which I think is the first time ever during night time in November in this country!.
With the naked eye 17P/ Holmes was a stunning sight as a large slightly bronze coloured haze of large size with bright core boldly breaking up Perseus. With averted vision I could see sections of the fainter outer coma on its E and N sides. Estimating the comet's magnitude was more problematic. Telescopes and binoculars could not be used due to aperture effect so the naked eye was the best and most logical tool. With the finger technique I got a value of Mag +2.5 however I feel I have been very conservative with this estimate as it could be much brighter because the comet is of such large angular extent. In this situation estimates will vary greatly depending on sky conditions, eye sensitivity and on how much of the outer coma is seen.
In the 32mm eyepiece within the 8.5" F/7 dobsonian reflector Holmes was incredible!!. In fact, I would go so far to say that this is the best telescopic comet I have observed since Hale-Bopp in 1997. The complexity of the comet was difficult to take in and record. Its subtle secrets required solid dark adaption, a calm mind and hard work at the eyepiece. I seen 3 main components.
1) Main very bright coma, gorgeous bright yellow-green colour and almost circular measuring +12' in dia with the W, N and E sides brighter than the S. This bright ring was segmented with bright enhancements and gave the impression of a horse shoe profile. The S side of this coma was faint, soft and 'broken'. This inner coma was + 12' in dia.
2) At the centre of the coma was a faint, soft, orange false nucleus embedded within a circular misty cocoon. Sweeping back from this was a south pointing yelow-gold dust fan which was elongated in the direction away from the Sun. The Sun ward side was smooth and streamlined. Between the 'horse shoe' and FN was a dark void with subtle pools. patches and bubbles.
3) In such superb sky conditions I was able to see the much fainter dark green outer coma which was like a transparent disk with very sharpe edges like a CD ROM. It was filled with faint background stars and almost filled the entire low power FOV. I measured it at a minimum size of 40' (much bigger than the full Moon). I was able to confirm this in 10x50 binoculars. In the 12mm orthoscopic the view was absolutely outstanding with Holmes looking like a monster comet creeping across the field as the Earth rotated on its axis. However the best was yet to comes..
With relative ease I could see a bright colourless elongation extending from the fan region through the inner coma into the mists of the outer region. This was a dust tail pointing South. During moments of top class seeing I could see countless fine and very thin rays issuing out from the inner coma to the outer like a garden sprinkler only in linear fashion. The detail and complexity here was beyond description and reminded me of the mysterious synchrones I had seen on images showing great comet Mc Naught. I believe that the dust and Ion tails are superimposed on one another and extended for a minimum length of 12' however on several occasions I was confident they protruded beyond the other disk which would place them between 45' - 50' in length!.
To finish the session I relaxed into my observing chair, stretched out and took in the starry scene. With the naked eye I could see comet Holmes, Double cluster, M34, M31, M33, Gegenschein and Zodiacal light all in the same field!!!!. This was my best view of Holmes to date. Telescopic sketch below.
Mag: 2.5? Dia: > 40' D.C: 7 Tails: Types 1 & 2 between 12'-50'.