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Venus atmospheric ring

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About this observation
Observer
Chris Hooker
Time of observation
02/06/2020 - 07:00
Object
Venus
Observing location
Didcot, Oxfordshire
Equipment
254 mm Newtonian
x2 Barlow
ZWO ASI174MM camera
Baader 685 nm IR-pass filter
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Venus imaged in the infra-red on successive days as it approached inferior conjunction. The elongation early in the morning of 2nd June, when the third observation was made, was just within acceptable limits for safe imaging.

These images will not win any prizes for aesthetics, because they have been subjected to extreme processing to look for the presence of the complete atmospheric ring formed by refraction and scattering in Venus’ atmosphere. This is not present in the first image, but can be seen in the third. There is a faint feature in the second but it is marginally visible at best, and what is there does not conform to the circular shape of the rest of the planet. The orientation of the terminator on June 2nd was about 3.5 degrees from the line of sight to Earth, and this corresponds to a propagation distance for sunlight of at least 360 km in the planet’s atmosphere on the side away from the illuminated crescent. Although strongly attenuated, enough light was transmitted to be detectable. On the earlier days, the corresponding distances were about 790 km and 580 km, and the attenuation would have been nine times greater on the 31st and about five times greater on the 1st. This explains why the complete atmospheric ring is clearly visible only on the third image.

The technique for imaging Venus under these conditions is the same as for Mercury near superior conjunction, and is described in the Mercury Observing Guide which can be found on the Mercury & Venus Section page. Anyone intending to make observations of this type is recommended to read this and the associated warnings before starting.

Comments

Fossil Light's picture

Great work Chris. Too scary for me on the 2nd.
Martin

Chris Hooker's picture

Thanks, Martin.

After slewing to the predicted position I was extremely careful to check that the sunlight was all exiting the tube, and I didn't look into the eyepiece, just attached the camera. Once I set the exposure correctly I saw Venus straight away, so the whole observation was actually pretty easy. The hard part was the processing, because PIPP didn't do a very good job of centring the frames on the very faint crescent, so I mostly had to select the frames for stacking by eye. I'm not sure there's any scientific value but it was an interesting challenge to get the image!

Chris

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