Re: Black-drop - is it real?

From: Sam Wormley (swormley1_at_mchsi.com)
Date: 06/09/04 

Date: Wed, 09 Jun 2004 14:35:13 GMT

Pete Lawrence wrote:
>
> 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>

I didn't see a hint of it in the first hour of the transit--looking via
web cams and nasa tv. Got clouded out for the direct observation. :-(