My new answer to Why does Venus flicker? addresses something that I find particularly interesting; Venus can be an incredibly thin crescent at times, and even a 1 arcminute large thin ring with an edge width of only one or two arcseconds (see below).

This suggests to me that Venus can twinkle much more like a star than a filled-disk planet at certain times. So for example in a comment there I wrote:

I have a strong hunch that if Jupiter were sitting right next to Venus on 12 April 2015 it would not have twinkled to the same extent.

@ProfRob notes that it turns out that Venus was a large-ish 15 arcecond disk 75% illuminated on 12 April 2015 so "crescent-twinkling" wasn't the reason that Venus twinkled for the OP on that day.

But I'm still convinced that it's gotta be a real, measurable phenomenon if there is such a thing as a planet "twinkleometer" and it's been applied systematically to Venus.

So I'd like to ask:

Question: Has "crescent-twinkling" even been demonstrated or at least calculated/predicted? Any "twinkleometer" data out there?

For more on how Venus's dance changes distance from Earth and illuminated fraction in such a way that it's almost always between -3.8 and -4.8 magnitude, see answers to

From the linked answer:

Phases of Venus, from https://commons.wikimedia.org/wiki/File:Phases_Venus.jpg

above: Phases of Venus, originally from Wikimedia but annotated.

For three times in 2004 (Feb 27, May 7, and June 8) I've taken the angular diameters of Venus from JPL's Horizons and using the largest (June 8) as a calibration for the image shown the full diameter of Venus.

Then I've drawn a thin rectangle to eyeball the width of the bright part of the limb that would contribute most of the light. The annotated numbers (15/5, 40/3, 58/1) are the apparent diameters of the full disk and the width of the bright limb in arcseconds.

  • $\begingroup$ Note: as I've commented elsewhere: "The same localized random phenomenon in the upper atmosphere that makes an object of ~arcsec extent in 2 dimensions twinkle must also make an object of ~arcsec extent in 1 dimension twinkle, though by a somewhat lesser amount. This is inescapable physics and is not open to debate. What I've asked is if anyone has measured it and/or formally predicted it in a rigorous and peer-reviewed way. I've added the [resource-request] tag to the question to make that clearer." $\endgroup$
    – uhoh
    Nov 7, 2022 at 21:56


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