Holmes(17P) - 2007
On October 24, 2007 this comet dramatically brightened from estimated
magnitudes of 17 to 2.5 making the comet very easily naked-eye visible even
in light polluted skies. This page is to be a series of
shoots documenting the changing appearance of this comet. Click the
date links below to view each entry.
Entry 1 - 10/27/2007
Entry 2 - 10/28/2007
Entry 3 - 11/10/2007
Entry 4 - 12/04/2007
Entry 1 - October 27, 2007
The comet is very high in Perseus on this night about 3 degrees north of
Delta Persei. It is very easily naked eye visible even under a full
moon and light pollution from Oklahoma City. The coma is easily
visible using 7x35 binoculars and is spectacular through a 10" Newtonian
Two series of images were shot on this night. Both series were shot
from my driveway between midnight and 1:45am.
The first series was shot using a Canon 20D DSLR with a Canon EF 200mm 2.8 L
telephoto lens and a 1.4X tele-extender. This resulted in a focal
length of 280mm and f/stop of f/4. 203, 8 second raw images were taken
at ISO 200 and then calibrated, average combined and digitally developed
using Images Plus. Additional enhancements were done using Photoshop
8 second exposures were done to avoid overexposing the very bright core of
this comet in any one frame. I shot 203 frames to average a smooth
background and coma and also to be able to attempt detection of any faint
tail evident through other combining methods. No tail was evident on
this night though the coma is slightly asymmetrical.
Image 1 - The full frame image at 280mm.
images for larger version.
Even at this relatively short focal length and exposure time the comet's
coma and brightness is impressive.
Image 2 - A crop of the full frame.
This version is a crop of the full frame and is also enhanced just a bit
more to better show the extent of the coma. Note the bright inner core
surrounded by a bright inner coma which in turn is surrounded by a much
dimmer and more extended coma.
Image 3 - Enhancements to better show the outer coma extent.
The background sky glow has been neutralized and the image has been
stretched much further to better show the outer coma and incidentally many
more background stars. This of course burns out the core detail of the
comet. Visually using a 10" Newtonian the outer extended coma was not
visible on this full moonlit night.
The second series of images on this night was an afocal series using a 10"
Orion XT Newtonian with a 26mm eyepiece. This yields a magnification
of 46X and circular field of view of about 1 degree. The camera crops
this field further. The 20D was mounted to the telescope using an
Orion afocal extension tube and standard t-ring adapter. 115, 2.5
second images were taken at ISO 800 for this series. The higher ISO
and shorter exposures were necessary to properly expose the comet's core
without introducing motion blur at the telescope's magnification. A
group of 10 images was shot between repositions of the Dobsonian mounted
scope. The images were calibrated, planetary aligned on the core and
digitally developed using Images Plus. Additional enhancements were done
using Photoshop CS2.
Image 1 - Full frame
Note the relative motion of the comet over the 10 minute duration of the
series as evidenced by the star trailing present.
This image offers the opportunity for some better analysis of the core of
Image 2 - Indications of multiple cores or concentrated gas clouds.
This image has been processed to better show the core detail of the comet.
Note the obvious multiple brighter areas. I at first felt the upper
bright region might be a motion blurred background star but the angle is
incorrect as shown by the full frame view above. Either the comet's
core has broken up or the larger lower bright lobe is an expanding eruption
from the main core.
Image 3 - Possibly another and more distant fragment of the core?
This image shows yet another possible fragment of the comet well outside of
the brighter coma region. Again the angle is wrong for this to be a
motion blurred background star. I also considered the possibility of
an in camera aberration but this is consistent relative to the comet center
from frame to frame so it's not in the camera. Since the bright region
is consistent from frame to frame over the series, this eliminates the
possibility of a satellite pass or other more local object.
Entry 2 - October 28, 2007
The shoot this evening was 24 hours after Entry 1 an afocal series using the
10" Newtonian with identical exposure parameters as in Entry 1 for
comparative purposes; ISO 800, 165 frames @ 2.5 seconds. Unfortunately
my focus was a bit soft on this series.
Image 1 - Full frame
Image 2 - 24 hour coma size comparison.
The comet's coma expanded considerably over this 24 hour period. I
estimate an overall increase in diameter of about 40%. The relative
brightness of the core is abut the same. This analysis was done by
equalizing the backgrounds of both images from the two nights to create a
similar exposure on the core. However some error is probably
introduced by the different position and slightly dimmer moon on this night.
This would have made the overall sky glow less bright.
Image 3 - Core detail
The comet's core retains a definite lobed structure and appears to be little
changed over the 24 hour period.
Image 4 - The mystery fragment
The possible fragment evident in Entry 1 is still visible but is no longer
in such close proximity to the comet's main body. It has also taken on
the appearance of possible multiple out gassing bodies. I at first
felt this was an aberration introduced in the alignment of the multiple
frames on the comet's core but if so this should also be evident in the
background stars. It is not. The "fragment" has also moved
relative to the background stars so this is definitely not a background deep
Entry 3 - November 10, 2007
Over that time Holmes has grown and dimmed and now requires longer and
tracked exposures to be able to image it well. This shoot was done
using an Orion 80ED at 600mm with a modified Hutech 350D and IDAS LPS filter
on a Losmandy GM8. 43, 90 second images were taken for a total
exposure time of 64.5 minutes.
Image 1 - Full Frame
There are certainly indications of a dim tail here but I was not able to
pull out additional detail from the light pollution from home and could not
capture more integrations due to a late fog.
Image 2 - The Core
Now that the coma has dissipated and spread it's much easier to see the
comet's core as a distinct and small object amid the coma as seen in the
Entry 4 - December 4, 2007
Comet Holmes has continued to expand and dim.
Image 1 - Full Frame
This shoot was done using a Canon 200mm f/2.8 L II telephoto lens with a
Hutech 350D mounted on a Losmandy GM8. 100, 45 second exposures were
made at f/2.8 for a total exposure of 75 minutes.
The inset in this image shows a scaled representation of the comet on
November 10th for size comparison. The comet's coma has more than
doubled in size visually while at the same time moving away from us from our
vantage point. The density and brightness of the coma has decreased
dramatically. Holmes is no longer visible through binoculars and is
difficult to see from urban skies even with a 10" Newtonian. Only the
brighter core region is evident. Though the comet appears to be of
similar brightness in these images and the overall exposure times are
similar, note the density and brightness of the background stars in the main
image as compared to the inset. This main image was shot at f/2.8
versus the inset image at f/7.5. This makes Holmes less than 1/4th as
bright overall as it was near the beginning of November.
Image 2 - The Core
As the coma continues to dissipate the comet's core becomes more and more
visible as a distinct point within the coma. The tail is still evident
sweeping off to the left and away from us as Holmes journeys outbound from