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Observation by Martin Lewis: Mars 5th Dec 2020

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Martin Lewis


Martin Lewis


2020 Dec 05 - 17:50


2020 Dec 07 - 21:14



Planetarium overlay



Field centre

RA: 04h37m
Dec: -62°02'
Position angle: +0°56'

Field size

0°06' × 0°06'

  • 444mm Dobsonian
  • ASI174MM for IR & B
  • 642nm filter for IR
  • Astronomik Blue filter

St Albans, UK

Target name



Mars 5th Dec 2020

About this image

IR(sG)B in poorish seeing early on Saturday evening,

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Davide Pistritto
Davide Pistritto, 2020 Dec 07 - 23:36 UTC

Phase has now pretty advanced. Bad conditions but good result. Good job, Fossil dob and super job Martin!

Why did you choose 174MM with filters instead of OSC 224MC?

Martin Lewis
Martin Lewis, 2020 Dec 08 - 00:09 UTC

Hi David,
For a bigger scope, less affected by diffraction the IR + synthetic green + Blue method with a mono camera works well on Mars to pull out detail when the seeing is sub-optimal. 

When the seeing is good the straight colour wins out as the wavelength of the green, which dominates the resolution, is effectively much shorter than the synthetic green. For the sG, which comes from a 50:50 mix of IR and Blue images, the detail comes from the IR which obviously has a significantly longer wavelength and larger Airy disc. 

You can see comparisons of one shot colour and IR(sG)B in good and poor seeing on my webpage here;

Michael E. Marotta
Michael E. Marotta, 2020 Dec 09 - 16:02 UTC

Frankly, I am amazed. Your note of "poor seeing" may be false modesty. My primary interests in astronomy include history. (I edit for the AAS History division.) Your 444 mm dobsonian would have been the envy of a state observatory 100 years ago, not the UK or USA, France, Germany, and a few others, but just about everyone else of the time. More than that -- because we had the 100-inch mirror -- your photographic equipment would have been science fiction. 

Our progress in citizen science has been unprecedented. Some previous times and places enjoyed their moments, of course. This is ours.

Thanks for the picture of Mars. I archived for myself (full credits, of course), because it speaks to a broad and deep narrative.