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Thanks David, yes that is kind of helpful.
It’s still a pity they haven’t done one Mercator projection (or similar) map for the whole planet. I have now worked out that their global mosics go from 180 deg to 180 deg longitude, not from zero to zero, which was confusing me for some time. It’s still a lot of work to relate these images together, as Mercury’s suface, like that of the Moon, looks completely different under different illumibation angles. Also they’ve made a problem by reproducing all these image really dark. You have to import them ito Photoshop and turn up the levels to see much.
One of the things I’ve been trying to establish in my reasearch is if there is any valid relationship at all between telescopic maps and drawings and what is really there. Peter Grego in his 2008 Springer book on Mercury and Venus still holds that the traditional maps do represent things that can be seen repeatably by good observers. Patrick Moore, on the other hand, after Mariner 10 visited, always said that the visual maps had been ‘hopelssly wrong’. My examination of the Messenger data tends to side with him – there’s no relationship whatsoever.
To ‘third’ these comments, I would say that Jonathan’s greatest achivement over these years had been maintaining the BAA and SPA combined comet webpage in a way that has made it perhaps the most useful and practical port of first call for anyone looking for up to date information on what comets are actually visible with amateur equipment from their particular location. Comets are coming and going all the time, and the fact that this page always seemed to be maintained reliably and was up-to-date with basic information, that could then be followed-up elsewhere, is quite remarkable in view of Jonathan’s work schedule with extended visits to Antarctica. It has always been very useful to someone like me who is not sufficiently interested in comets to subscribe to the specialised newslists, but wants to dip in from time to time.
From Edgware the occultation lasted 14.7s from 04:28:09.5 to 04:28:24.2.
I’ve placed the time-stamped video on YouTube
David
Yes, this is a common experience that the callibration frames are not quite right and create problems rather than solve them.
If you have a light-polluted sky at all then flats are much more important than darks; also if there is any vignetting (uneven illmination) in the system at all.
I’ve never had success with artificial flats (using a light box for example) but find the best method is to take flats on a clear sky at sunset or slightly earlier. The optical system needs to be focused and ideally pointing in the same direction as for the light frames (in case there is any mechanical slop).
With a DSLR it’s fairly important that the dark frames are taken at the same temperature as the light frames (to within, say 3 degrees C). I always note the temperature, and have built up a library of darks taken at different exposures and different temperatures.
Anyway that’s a nice shot. I’ve got an ED 80 and it’s a good combination with a DSLR.
David
I managed to get a similar result from Edgware in a claggy sky early on Thursday evening before it clouded-up. The disconnection is just about shown despite the LP gradient. R Ligustri’s image on Spaceweather is pretty stunning.
Here is the result I was able to get from a light-polluted London suburb the first night it attained enough altitude, Dec. 28/29. A single 30s exposure shows it with M79 to upper right.
A stack of 17 exposures, with extensive processing, revealed the tail (this surprised me considering the conditions and the 14 degree altitude).
Inverting this image and making it mono shows the tail better.
I could not see the comet visually with 10×50 binoculars, but I expect I soon will be able to. As it gains altitude certainly UK imagers will be able to reveal far more detail than this.
David
One small point worth clarifying about the required file-naming format, because it isn’t stated anywhere, so I had to ask, is that the time in the file name should be the mid-time of the image. So if, as common, you stack a series of sub-exposures, you need to work out what the mid-time was for the sequence.
Maybe this was obvious to everone else, but not to me.
David
