Black-drop - is it real?

Interesting reports on the black-drop from yesterday's transit. Some
saw it while other's didn't. So is it real?

Well, nothing happens to create this effect (the atmosphere of Venus
doesn't know when it's in line with the edge of the Sun and doesn't
have a requirement to suddenly jump out!) but there could be something
that happens when the thin layer of atmosphere surrounding our sister
planet gets very close to the Sun's limb. Or so I was hoping.

I deliberately kept my exposures dark at 2nd and 3rd contact and I did
not, categorically, see the black drop visually or photographically.

Now I could just be a bad photographer but to me if it wasn't visible
in a clear image then it was not occuring outside of the Earth's
atmosphere. If the effect is there, it's being caused somewhere
between the top of our atmosphere and our eyes/cameras.

While processing my dark images and increasing the brightness a tad,
it was clear that the 2nd contact images could be coaxed into a black
drop by boosting the contrast of the image.

http://www.pbl33.fast24.co.uk/black-drop.jpg

So what are the factors that cause it? Do you have an
observation/image that shows it? If so - let me have the
observation/equipment details and I'll try and collate them into some
sort of analysis of the effect.

I believe that the effect was quite well seen by solar projectionists
so these observations would be of interest too.

If you're interested in taking part, drop me an email letting me know
whether you saw it at 2nd or 3rd contacts, your observing method and
whether there is any physical record (image, drawing) of it. For
photos, exposure times and ISO settings will be required. Don't send
any images unless I ask for them yet. I'll put up a website for this
shortly.

Send your details to pete dot lawrence at pbl33 dot co dot uk and put
"black-drop" in the message subject.


--
Pete Lawrence
http://www.pbl33.co.uk
Most recent images http://www.pbl33.fast24.co.uk/recent_images.html