Comet 17P/Holmes


October 28th

A very rare event has just occurred in the night sky which is visible to all with the naked eye.

Comet 17P/Holmes is normally a faint periodic comet, orbiting the Sun once every 6.9 years. It was discovered in 1892 by English amateur Edwin  Holmes just at a time as it was undergoing an outburst or sudden brightening. It has been observed regularly on many of its other passes into the inner solar system but apart from one further outburst has always remained an inconspicuous object. However, on October 24th Juan Santana a Spanish astronomer noticed it had brightened by 7 magnitudes. This was surprising as it lies currently between the orbit of Mars and Jupiter and making its outbound journey so solar heating is decreasing.

During the course of the last week we have seen the comet brighten a million times, and the gas and debris cloud around it grow in size to be as large as the planet Jupiter. In the history of comet observing no one has ever seen such a rapid brightening occur. What has caused this, we do not know. It may have been an impact by a small asteroid, but as this is its second outburst we think it more likely to result from a substantial collapse of part of its surface. Comets have been described as dirty snowballs and Comet Holmes may well have a weak chambered honeycomb structure which may well have just caved in to release a cloud of dust and ice around it. My first image (10x10 sec fixed camera) of the comet taken October 28th shows the comet as the brightest "star" in the field. (Click on all small images to enlarge).



These images show the turquoise gas shell (left) taken with 300mm lens, and inner coma as imaged through the
C 9.25".

October 30th

This is an R:G:B image 10 minute exposure in each colour using a Megrez 110mm and SXVF-M9 CCD showing  the turquoise
outer gas coma. The central bright dusty coma appears colourless, and also overexposed  in this image.


October 31st

Not much sleep tonight! Now imaging through the longer focal length of the C 9.25". A stack of short exposures shows that
the central coma is not quite so uniform in brightness.

Using an unsharp mask reveals a little more structure in the coma. The bright "blob" to the south west now seems to be striated in that direction. The two images below have been further processed with rotational gradient filter or Larson - Sekanina. There seems to be a main bright projection of material with less prominent ones lying parallel and to either side. Are we seeing a line up of small fragments each displaying a mini-comet tail?




November 4th
A blue ion tail  is now appearing to the south west of the comet.
It will appear fore shortened as the comet is moving away from us tail first. Note that the colour of the ion tail  differs slightly in hue from the turquoise of the circular outer coma.



An unsharp masked image tonight shows more detail in the inner coma as the ejecta drifts further away from the nucleus. The comet is currently showing a coma of 60,000 miles in diameter  (80 x the diameter of Earth).


November 5th
Images aligned on comet nucleus showing stars as trails. This is a total exposure time of 40 minutes subsequently unsharp masked.

November 7th
Animation of two images
taken November 5th and 7th, showing the expansion of the
coma in 48 hrs.

November 9th
An unsharp mask reveals
more structure surrounding the nuclear region.

November 11th
Intermittent cloud and rain, only managed a few frames, but it looks as though we are now beginning to lose the fine nuclear detail.



A rotational gradient filter on the above image shows a curious kink in the main plume as it leaves the comet nucleus. I am not sure yet whether this is an image processing artifact or a real feature. Time will tell.

Skies now clear after brief rain shower. This 20 min  total exposure unsharp masked image shows the striated dust trail clouds of  several fragments still persists.

November 12th

Skies remain clear  for this image taken a few hours later. Confirms detail seen  in previous image.

Image taken with Celestron 9.25"  for increased resolution and image scale.
This is a series of short exposures aligned on comet nucleus.
In set image with a Larson Sekanina filter applied.

November 14th

Here is a short article about Historical Observations of this comet made 115 years ago -  almost to the day! Tonight the enlarged coma now  fills the CCD chip. Nuclear detail still visible and further elongated.

This is an R:G:B image 20:20:20 minutes total exposure. It has not been unsharp masked and although the nuclear detail is not so clear, this equates to what is seen visually at this time through small telescopes.

November 15th



Comet now approaching Mirphak. This is probably my last chance of imaging the comet in a dark moon less sky for a while.

November 26th

Coma now noticeably larger than the full moon.The comet no longer fits inside the CCD frame which is 46' x 34' arc.The dust stripes in the coma are now fading.
November 28th

Comet  now too large for CCD now using Canon 300D  at  prime focus of  Megrez 110mm..
Seeing conditions poor, moonlight still present and a few images grabbed through clear patches in clouds..
December 1st

Comet now larger and more prominent than  M31 with the naked eye.

Widefield view with 28mm lens.
December 11th

Now imaging through a small 70mm Televue Ranger f/6.8 focal length 480mm. This gives a field of view of 60'x47'. The comet now barely fits so its angular diameter must exceed one degree or two moon widths.
 January 7th 2008

Comet Holmes now appears fainter as it enlarges. It  is now over one degree in angular size.
This 5 minute exposure with 200mm lens shows the comet in the field of view of Algol and  star cluster M34.