That's a 20sec exposure at 12000ISO. I thought we were discussing shadows cast that are visible to the naked eye.
I have no doubt Venus casts a shadow. Photons will be stopped. I just can't ever imagine it would be visible to humans.
As for your quote.good find, I'm just not sure I believe it. Sorry.
I regularly see things that photographers spend tens of minutes or hours of exposure time on (mostly nebulae.) Others do the same, so that isn't anything unusual. The eye's effective integration time when fully dark adapted is a few tenths of a second at most. The difference is that visually the fine resolution is missing (and so is color except on the highest surface brightness objects).
There are many reports of Venus casting shadows if you search around. There are online article mentions of it as well. The surprising thing to me is that you had never heard of this.
Again, I'll take your word for it, but I remain skeptical.
I was in a B2 site this end of September when Mars was high and bright and Jupiter was also visible earlier . No moon. There was no way either of those were casting anything.
You saw it. Great. I'll have to see it myself to believe it.
There are various things I have not seen that are known to be visible, but because I have not seen them doesn't mean they aren't visible. It just means that I haven't gotten around to trying them yet, or have not had the right combination of conditions, or perhaps my eyes are not up to it. The green flash was like that for me until I finally caught the right conditions one sunset in Hawaii--and the one my wife and I caught was a weak one. The objects that folks have the most trouble with are low contrast/low surface brightness or just visually dim. In many cases, the difference is experience and whether or not people have actually tried.
A better question to ask yourself is: what is your experience level for noticing such phenomena in dark sky? If you didn't notice this sort of thing in September (before this thread was posted) then perhaps it was because you were simply unaware of it.
There are quite a few things that I see naked eye that few amateurs even try to locate that way or don't realize are visible. Some are relatively easy in rural sky, like Uranus which I find visually comparing my charts to the ecliptic in the general area, looking for an un-plotted ~6 mag star. I confirm by pointing my scope at the "star" to reveal it is actually a planet. I have seen Ceres and Vesta naked eye multiple times at favorable oppositions.
Those are point sources. Then there are targets more applicable to this subject: lower brightness, lower contrast objects like the gegenschein, zodiacal band, zodiacal light, Barnard's Loop, the Angelfish Nebula, various comets, etc. I see the first three in the list even at low altitude Bortle 3 sites if the conditions are good and each are well placed. I track the gegenschein throughout the year at various sites, except when it is lost lower in the sky or enmeshed in the Milky Way glow. I use it and the zodiacal band as ways to measure transparency since the band disappears first or is seen less completely in all but the best condtions.
Are you familiar with these features naked eye? There is no shame in not being familiar with them if you haven't. Most astronomers are not familiar with them. I finally learned to recognize them when I began observing regularly in Bortle 2 conditions. The better you become at recognizing such features, the more likely you are to be able to detect shadows from the brightest planets and stars.
As an example of something I have not seen that is associated with the above, there are Kordylewski's clouds. While they have been reported visually by a couple of astronomers who have studied and imaged them with special apparatus in published work, these are exceedingly faint and variable by nature, and only likely to be reasonably possible at my darker sites a few nights a year.