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Observation by Chris Hooker: Mercury in IR, 29th July 2021

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Chris Hooker


Chris Hooker


2021 Jul 29 - 08:00


2021 Jul 30 - 15:54



  • 254mm Newtonian
  • 5x IR Barlow lens
  • 685nm long-pass and 850nm short-pass filters
  • ZWO ASI174MM mono camera

0.35 msec @ F/31


Didcot, Oxfordshire

Target name



Mercury in IR, 29th July 2021

About this image

An unexpectedly clear morning allowed Mercury to be captured a few days before superior conjunction, at an elongation of just over 4 degrees. The local seeing was poor, and there was a very strong jet stream directly overhead, so I was not optimistic about recording any detail on the planet. A total of 44 videos each of 10,000 frames was captured. Initial processing in PIPP and Registax reduced the total to about 16,000 but further automated processing yielded only a disk, with barely a hint of detail. The tedious process of frame selection by eye was required to leave 840 frames with a circularly-shaped planet having an acceptably sharp limb, and this was further reduced to 700 to yield the image presented above. There was insufficient data to generate the usual verification images from separately-processed stacks.

The image suffers from a significant edge-rind due to diffraction and the poor seeing, but there is some correspondence between the image and the blurred reference, especially in the darker regions. Considering the small angular size of Mercury and the poor conditions, this is as good a result as could be expected.

NOTE: Observing Mercury close to the Sun requires great care and the use of specific techniques to ensure safety. These are described in the Mercury Observing Guide, available to members from the Mercury & Venus Section web page, and also in my observation of 3rd June 2018 in this gallery. 

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Martin Lewis
Martin Lewis, 2021 Jul 31 - 07:45 UTC

Great work Chris, and great to read your detailed comments about the nuts and bolts of taking such a difficult shot. Inspiring work. 

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