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timwetherell

Venus; Ashen light

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Since venus is very well placed at the moment, thought I'd have a look for the Ashen light (a faint earthshine-like illumination that some observers see in the dark portion of venus) I've been using a 7" refractor and TMB monocentric eyepiece to try to eliminate as much scatter as possible. A couple of weeks ago when the phase was a little fuller, there did appear to be a faint glow within the crescent but it definitely didn't extent to the whole disc. More of an oval. However once the crescent is very slim (last night) there's no real sign of this glow at all. When I use wide angle eyepieces with more glass, there is a general faint blob of glow all around venus mimicking in shape the glow I noticed when the phase was larger. I tried with an old Erfle eyepiece that has no coatings and got two venus' which was very pretty but added little to my studies. So after all that, I'm still not much the wiser. I'd be interested to hear the experiences of other observers with this phenomena :)

Venus ashen light.jpg

A couple of weeks ago, there did appear to be a glow on the dark side but only over some of the disc and it's impossible to be certain if it's real or just light scatter

venus2.jpg

Last night there was really no convincing ashen light at all with the refractor and the lowest scatter eyepiece I have

venus lower contrast EP.jpg

Left: a modern wide angle eyepiece with more glass does introduce some darkside glow effect and interestingly it's oval again not circular. Right A 1950s uncoated erfle gives lots of ghosting but no darkside glow

I saw some nice drawings on the BAA pages of venus in the late 50s where the ashen light was far more prominent at 1/3 phase than when venus was a slim crescent which is interesting because that's pretty much what i saw :) 

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The Ashen light is still a controversial topic. There are many who say it does not exist but others who claim to have viewed it. Among those in favour of this effect was the late great Sir Patrick Moore. I have never seen any trace of it myself, but my trust is with Sir Patrick.

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Though I've often seen the dark globe of Venus held within the brilliant crescent, and set against a lighter twighlight sky, I've never yet seen the Ashen light. W F Denning on page 152 of his book "Telescopic Work for Starlight Evenings" calls it the "Ashy light" and states that it appears to involve some kind of phosphorescence. Its definitely something to pay attention to and would make the study of Venus a bit more interesting. Good seeing will doubtless be required to have success.

Mike 

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Thus far with Venus observing and sketching, I have not seen this.
But if such esteemed persons such as Sir Patrick Moore and W F Denning say they have seen it, then I trust that they have.
I have to agree with Mike about good seeing being required.

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