|
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
black drop effect
Has the black drop phenomenon for transits of Venus been explained to
the satisfaction of the majority of the scientific commumity? |
#2
|
|||
|
|||
black drop effect
|
#3
|
|||
|
|||
black drop effect
alistair (or somebody else of the same name) wrote in message
thusly: Has the black drop phenomenon for transits of Venus been explained to the satisfaction of the majority of the scientific commumity? Sorry, could you tell us what this effect is supposed to be please? -- Paul Townsend I put it down there, and when I went back to it, there it was GONE! Interchange the alphabetic elements to reply |
#4
|
|||
|
|||
black drop effect
In article , pvstownsend@zyx-
abc.fsnet.co.uk says... alistair (or somebody else of the same name) wrote in message thusly: Has the black drop phenomenon for transits of Venus been explained to the satisfaction of the majority of the scientific commumity? Sorry, could you tell us what this effect is supposed to be please? I was wondering that too, but a quick google gives satisfying results. http://www.exploratorium.edu/venus/question3b.html Nice picture of it there. Also, although it's mainly talking about Mercury, this one gives what sounds to me like a *good* explanation: http://www.aas.org/publications/baas.../aas203/26.htm "...black-drop effect comes from a convolution of the instrument's point-spread function and the solar limb darkening..." It's a bit mathematical for man-in-street, but I'd say a good bottom line is that it shows limitations of, and is a function of, the fact that we're using instruments with limitations to observe the event, rather than the divine perfect perception that we too often take for granted when we look at something. Most interesting. Whatever, I'm looking forward to it. |
#5
|
|||
|
|||
black drop effect
Peter Harding wrote in message ...
In article , pvstownsend@zyx- abc.fsnet.co.uk says... alistair (or somebody else of the same name) wrote in message thusly: Has the black drop phenomenon for transits of Venus been explained to the satisfaction of the majority of the scientific commumity? Sorry, could you tell us what this effect is supposed to be please? I was wondering that too, but a quick google gives satisfying results. http://www.exploratorium.edu/venus/question3b.html Nice picture of it there. Also, although it's mainly talking about Mercury, this one gives what sounds to me like a *good* explanation: Maybe transits should be looked at MUCH closer. Atmospheric refraction might do it, but might not just a "teensy" part of the effect be due to the gravitational deflection of light from the sun's edge taking it away from our "line of sight"? Jim G |
#6
|
|||
|
|||
black drop effect
In article ,
says... Maybe transits should be looked at MUCH closer. Atmospheric refraction might do it, but might not just a "teensy" part of the effect be due to the gravitational deflection of light from the sun's edge taking it away from our "line of sight"? ?? Wouldn't this apply to looking at something on the other side of the sun? Venus is on our side of it during a transit. Or are you suggestion that the relatively minor gravitational influence of Venus is responsible? I think if you want to look at transits MUCH more closely, a good first step would be to show that the mechanism given in http://www.aas.org/publications/baas.../aas203/26.htm doesn't fully account for the effect. Then you'll have a reason to look for e.g. gravitational effects. |
#7
|
|||
|
|||
black drop effect
"Peter Harding" wrote in message ... In article , says... Maybe transits should be looked at MUCH closer. Atmospheric refraction might do it, but might not just a "teensy" part of the effect be due to the gravitational deflection of light from the sun's edge taking it away from our "line of sight"? ?? Wouldn't this apply to looking at something on the other side of the sun? Venus is on our side of it during a transit. Or are you suggestion that the relatively minor gravitational influence of Venus is responsible? I think if you want to look at transits MUCH more closely, a good first step would be to show that the mechanism given in http://www.aas.org/publications/baas.../aas203/26.htm doesn't fully account for the effect. Then you'll have a reason to look for e.g. gravitational effects. The point-spread function also has to include terrestrial atmospheric seeing effects. But the problems encountered in the 18th century were with small telescopes (early achromatic refractors of 2-4 inches), so the effect was largely instrumental (Airy disks of a couple of arcsec). In the 19th century, observers used bigger telescopes where seeing was more of an issue. The original supposition that the effect was caused by the atmosphere of Venus has been pretty well discounted now--its "edge" is far too sharp (observed by Mariner and other probes). -- Mike Dworetsky (Remove "pants" spamblock to send e-mail) |
#8
|
|||
|
|||
black drop effect
To the Group:
"Mike Dworetsky" wrote in message ... "Peter Harding" wrote in message ... In article , says... Maybe transits should be looked at MUCH closer. Atmospheric refraction might do it, but might not just a "teensy" part of the effect be due to the gravitational deflection of light from the sun's edge taking it away from our "line of sight"? ?? Wouldn't this apply to looking at something on the other side of the sun? Venus is on our side of it during a transit. Or are you suggestion that the relatively minor gravitational influence of Venus is responsible? I think if you want to look at transits MUCH more closely, a good first step would be to show that the mechanism given in http://www.aas.org/publications/baas.../aas203/26.htm doesn't fully account for the effect. Then you'll have a reason to look for e.g. gravitational effects. The point-spread function also has to include terrestrial atmospheric seeing effects. But the problems encountered in the 18th century were with small telescopes (early achromatic refractors of 2-4 inches), so the effect was largely instrumental (Airy disks of a couple of arcsec). In the 19th century, observers used bigger telescopes where seeing was more of an issue. The original supposition that the effect was caused by the atmosphere of Venus has been pretty well discounted now--its "edge" is far too sharp (observed by Mariner and other probes). Couldn't the effect be simply edge diffraction? I realize the Sun's light isn't a point souce... David A. Smith |
#9
|
|||
|
|||
black drop effect
In article Xz6mc.69592$Jy3.57171@fed1read03, "N:dlzc D:aol T:com
\(dlzc\)" N: dlzc1 D:cox says... Couldn't the effect be simply edge diffraction? Does it look like it? http://www.exploratorium.edu/venus/question3b.html What would "simply edge diffraction" look like? What makes you suggest this? Some people who actualy do maths have accounted for it as described. No, it's not simply edge diffraction. |
#10
|
|||
|
|||
black drop effect
Dear Peter Harding:
"Peter Harding" wrote in message ... In article Xz6mc.69592$Jy3.57171@fed1read03, "N:dlzc D:aol T:com \(dlzc\)" N: dlzc1 D:cox says... Couldn't the effect be simply edge diffraction? Does it look like it? http://www.exploratorium.edu/venus/question3b.html Yes, it does. Single slit diffraction, with a = planet radius, and theta a function of planet radius and the distance from the Earth observer to (basically) the planet's center. What would "simply edge diffraction" look like? What makes you suggest this? Just curious. Of course, multiple wavelengths at the source would make hash of this idea pretty quick. I'd wonder if the "black-drop" had any spectral anomalies at the periphery. Some people who actualy do maths have accounted for it as described. No, it's not simply edge diffraction. OK. Thanks. David A. Smith |
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Jets Spout Far Closer to Black Hole Than Thought, Scientists Say(Forwarded) | Andrew Yee | Astronomy Misc | 6 | January 7th 04 11:49 PM |
The last cry of matter (Forwarded) | Andrew Yee | Astronomy Misc | 0 | November 27th 03 02:42 PM |
VLT Observes Infrared Flares from Black Hole at Galactic Centre (Forwarded) | Andrew Yee | Astronomy Misc | 0 | October 29th 03 09:05 PM |
Black Hole Q: | Greg Neill | Astronomy Misc | 2 | July 24th 03 12:09 PM |
Link between Black Holes and Galaxies Discovered in Our Own Backyard(Forwarded) | Andrew Yee | Astronomy Misc | 0 | July 17th 03 07:36 PM |