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

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. :-(

On Wed, 09 Jun 2004 14:35:13 GMT, Sam Wormley
wrote:

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. :-(

Bad news Sam - I'm sorry you missed it

A lot of solar projection observations mention the black-drop effect.
Was there anyone out there that saw the transit with a projection
arrangement but didn't see the black-drop?

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

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

What is "is?" and What is "real?" It was "real" for those who saw it,
and it did not exist for those who didn't. There is no conflict there,
since it is a phenomenon involving the behaviour of light, and not a
concrete object.

Davoud

--
usenet *at* davidillig dawt com

On Wed, 09 Jun 2004 11:06:25 -0400, Davoud wrote:

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

What is "is?" and What is "real?" It was "real" for those who saw it,
and it did not exist for those who didn't. There is no conflict there,
since it is a phenomenon involving the behaviour of light, and not a
concrete object.

I'm not questioning it's reality as such - there are quality images
that show it and quality images that don't. What I'm questioning is
why some see it and why some don't. It's not possible to answer that
unless the circumstances for each observation are known (hence the
request for equipment details).

It's a fascinating dichotomy (well it is for me anyway!) that this
variation exists. I'd like to know more...

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

On Wed, 09 Jun 2004 15:54:05 +0100, Pete Lawrence wrote:

On Wed, 09 Jun 2004 14:35:13 GMT, Sam Wormley
wrote:

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. :-(

Bad news Sam - I'm sorry you missed it

A lot of solar projection observations mention the black-drop effect.
Was there anyone out there that saw the transit with a projection
arrangement but didn't see the black-drop?


I saw a photo of it yesterday somewhere on the web. I'll wager it's an
atmosphere effect of seeing conditions and what the seeing is like over an
observer's area will determine if they'll see the drop effect.

Tom

I saw a photo of it yesterday somewhere on the web. I'll wager it's an
atmosphere effect of seeing conditions and what the seeing is like over an
observer's area will determine if they'll see the drop effect.

Tom


I think that this may be the cause. However,

I just did a quick experiment using Photoshop. However, you can do the
same with any image or painting program.

I made a large, high resolution white circle on a black background, and
pasted upon it a black circle roughly in scale with Venus on the Sun's
disk. Photoshop allowes layering, and I slowly slid the artificial Venus
along until it touched the edge and I played with it to see if I had a
"black drop" or bridging effect. To my eye, it is plainly visible just
after the planet crosses the edge. And by "just after", I'm talking 1 or
2 pixels. To simulate 'Seeing' issues and Venus' atmosphere, I allowed
Anti-Alias edge smoothing. The white "Sun" was about 254 mm and the
black "Venus" about 4.75 mm. I'm not sure how well that fits the actual
scale, and I would be interested to know if anyone else can duplicate
this little test and if they get the same results.

For my money, the black drop appears to be substantially caused by the
eye's own optical illusion, and is dependant upon the image scale of the
eyepiece (the effect was more pronounced at what experience tells me is
medium magnification and wasn't noticable when the Venus image was very
small (zooming out the Photoshop image greatly) or very large (highly
zoomed in.)

Thus, in addition to the eye playing tricks, the magnification, quality
of the optics and the seeing most likely contribute to the effect,
positively or negatively.

Bart Fried


Pete Lawrence wrote:

On Wed, 09 Jun 2004 11:06:25 -0400, Davoud wrote:


Pete Lawrence:

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

What is "is?" and What is "real?" It was "real" for those who saw it,
and it did not exist for those who didn't. There is no conflict there,
since it is a phenomenon involving the behaviour of light, and not a
concrete object.


I'm not questioning it's reality as such - there are quality images
that show it and quality images that don't. What I'm questioning is
why some see it and why some don't. It's not possible to answer that
unless the circumstances for each observation are known (hence the
request for equipment details).

It's a fascinating dichotomy (well it is for me anyway!) that this
variation exists. I'd like to know more...

On Wed, 09 Jun 2004 14:35:13 +0000, Sam Wormley wrote:

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. :-(

My damn mouse wheel broke. Please trim quotes for context.

Tom Randy wrote:

I saw a photo of it yesterday somewhere on the web. I'll wager it's an
atmosphere effect of seeing conditions and what the seeing is like over an
observer's area will determine if they'll see the drop effect.

Tom

That's what I'm beginning to think too. It may be a very localized
event.


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