Transit of Venus

In article ,
Henry Spencer wrote:

In article ,
Robert Casey wrote:

In particular, check the iamge taken at 11:07 UT --- no black drop
visible there.

I don't see any teardrops either. Must be an artifact of the human eye.

No, it has been photographed during transits of Mercury (which also proves
that it is not a result of Venus's atmosphere).

The Black Drop is an effect of how our eyes perceive when two unsharp
edges between bright and dark approach one another. It can be readily
simulated by keeping two of your fingers as close to your eye as you can
and then let the fingers approach one another: they seem to touch before
they actually touch.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

"Paul Schlyter" wrote in message
...

The Black Drop is an effect of how our eyes perceive when two unsharp
edges between bright and dark approach one another. It can be readily
simulated by keeping two of your fingers as close to your eye as you can
and then let the fingers approach one another: they seem to touch before
they actually touch.

is that the same thing as seeing the drop effect in front of the sun?
somebody else explained on here, i think it was at metaresearch.org
or something, that it is due to moving cells of air in the atmosphere.

rj

randyj wrote:
"Paul Schlyter" wrote in message
...

The Black Drop is an effect of how our eyes perceive when two unsharp
edges between bright and dark approach one another. It can be
readily simulated by keeping two of your fingers as close to your
eye as you can and then let the fingers approach one another: they
seem to touch before they actually touch.

is that the same thing as seeing the drop effect in front of the sun?
somebody else explained on here, i think it was at metaresearch.org
or something, that it is due to moving cells of air in the atmosphere.

rj

I haven't read that particular explanation, but if you check what else is on
the site, it's probably a load of *****.


DaveL

In article ,
randyj wrote:

"Paul Schlyter" wrote in message
...

The Black Drop is an effect of how our eyes perceive when two unsharp
edges between bright and dark approach one another. It can be readily
simulated by keeping two of your fingers as close to your eye as you can
and then let the fingers approach one another: they seem to touch before
they actually touch.

is that the same thing as seeing the drop effect in front of the sun?
somebody else explained on here, i think it was at metaresearch.org
or something, that it is due to moving cells of air in the atmosphere.

Well, these moving cells do increase the fuzziness of the limbs of the
Sun and of Venus...



--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

In article ,
randyj wrote:
is that the same thing as seeing the drop effect in front of the sun?
somebody else explained on here, i think it was at metaresearch.org
or something, that it is due to moving cells of air in the atmosphere.

I'm not sure what it says at metaresearch.org, but since the black
drop effect was seen when Mercury transited the sun as observed by a
spacecraft, the black drop effect cannot be due to either the earths
atmosphere or the atmosphere of the planet in transit.

"Greg Hennessy" writes:

I'm not sure what it says at metaresearch.org, but since the black
drop effect was seen when Mercury transited the sun as observed by a
spacecraft, the black drop effect cannot be due to either the earth's
atmosphere or the atmosphere of the planet in transit.

I saw my first transit of Mercury and first black drop
effect in 1960. It has always been obvious that the atmosphere of the
transiting planet has nothing to do with the black drop effect because
Mercury has no atmosphere.

But think about what you are saying. Earth does have an
atmosphere, and the light from the transit must pass through it. Our
atmosphere slightly distorts all light passing through it. Why should
transits be an exception?

Lunar occultations prove that the apparent enlargement of
the Sun's and Moon's disks caused by irradiation does not occur in
space. So it must happen in Earth's atmosphere. And stellar "seeing"
disks show that it does happen here, caused by variable refraction in
moving air cells.

At the Meta Research site you will find the evidence and
details. See
http://metaresearch.org/home/viewpoint/blackdrop.asp.
Be sure not to be one of those people who can't unlearn things once
learned wrongly. Look at the evidence and draw your own conclusions
anew, without the influence of the bias of having previously held a
contrary position. -|Tom|-


Tom Van Flandern - Washington, DC - see our web site on replacement
astronomy research at http://metaresearch.org

"Tom Van Flandern" wrote in message
...
"Greg Hennessy" writes:

I'm not sure what it says at metaresearch.org, but since the black
drop effect was seen when Mercury transited the sun as observed by a
spacecraft, the black drop effect cannot be due to either the earth's
atmosphere or the atmosphere of the planet in transit.

I saw my first transit of Mercury and first black drop
effect in 1960. It has always been obvious that the atmosphere of the
transiting planet has nothing to do with the black drop effect because
Mercury has no atmosphere.

But think about what you are saying. Earth does have an
atmosphere, and the light from the transit must pass through it. Our
atmosphere slightly distorts all light passing through it. Why should
transits be an exception?

Lunar occultations prove that the apparent enlargement of
the Sun's and Moon's disks caused by irradiation does not occur in
space. So it must happen in Earth's atmosphere. And stellar "seeing"
disks show that it does happen here, caused by variable refraction in
moving air cells.

What about the spacecraft in orbit outside earth's atmosphere that
someone mentioned? It too saw the black drop effect in a Mercury
transit from outside
the atmosphere, according to whoever posted that.

rj

In article ,
Tom Van Flandern wrote:
But think about what you are saying. Earth does have an
atmosphere, and the light from the transit must pass through it. Our
atmosphere slightly distorts all light passing through it. Why should
transits be an exception?

You are proposing a logical fallacy.

Earth's atmosphere distorts light.
The black drop effect is a light distortion.
The earth's atmosphere causes the black drop effect.

The logical fallacy is because other effects besides the earths
atmosphere distort light.

If the black drop effect is from the earths atmosphere, how come the
TRACE sattelite saw the effect?

This replies to Greg Hennessy and Dave Tholen.


"Greg Hennessy" writes:

[tvf]: Earth does have an atmosphere, and the light from the transit
must pass through it. Our atmosphere slightly distorts all light passing
through it. Why should transits be an exception?

[Hennessy]: You are proposing a logical fallacy.
-- Earth's atmosphere distorts light.
-- The black drop effect is a light distortion.
-- The earth's atmosphere causes the black drop effect.
The logical fallacy is because other effects besides the earths
atmosphere distort light.

Earth's atmosphere produces an effect on starlight,
moonlight, and sunlight entering it that enlarges those visible disks.

The known effect produced by Earth's atmosphere is
qualitatively necessary and quantitatively sufficient to produce the
observed black drop effect.

Therefore, no other causes are needed in the case of
transits.

[Hennessy]: If the black drop effect is from the earths atmosphere,
how come the TRACE satellite saw the effect?

Thanks very much for mentioning the article you cited at
http://nicmosis.as.arizona.edu:8000/POSTERS/TOM1999.jpg, which I will
add to the bibliography for my article with an acknowledgement to you.
It is about space-based observations of transits of Mercury that
reported seeing the black drop effect. However, what the article says is
consistent with my own article and many others before it. The
investigators agree that the image spreading (their "point-spread
function" of PSF) is essential to the black drop effect, and that the
primary cause of the black drop for ground-based observers is
atmospheric "seeing" because that is the main cause of image spreading
(PSF) on the ground. Their point was that diffraction is also present
and, although much smaller than "seeing" effects, becomes the dominant
cause of image spreading (PSF) in space where there is no atmospheric
effect. (I had already mentioned diffraction as a secondary cause in my
section on image spreading for lunar occultations.) Therefore, a small
black drop effect is still seen by spacecraft unless one corrects for
limb darkening, in which case the black drop effect can be effectively
removed from the data.

Here are three paragraphs with the actual words of these authors:

[from abstract]: ". we examined the images in and around the point of
internal tangency for evidence of the historical 'Black Drop' effect.
After calibration (including careful removal of image/instrumental
artifacts and flat-fielding) the only radially directed brightness
anisotropies found were due to the interacting effects of diffracted
limb-darkened photospheric light around the Mercurian disk and the
instrument's Point Spread Function (PSF). We discuss, and model, these
effects as they would have applied to earlier ground-based observations
of Mercurian transits (also including the effects of atmospheric
"seeing") to explain the historical basis for the Black Drop effect."

[from text]: "Shortly after the 1769 transit of Venus [i], De la Lande
identified the origin of this effect in blurring due to atmospheric
turbidity (i.e., 'seeing'). Today, space-based transit observations are,
of course, devoid of, (time variable) atmospheric seeing effects,
previously modeled [3]. Nonetheless, the Black Drop effect arises due to
the finite instrumental resolution (blurring by the instrumental PSF)
convolved with the solar limb-darkening profile."

[from conclusion]: "The principal cause of the Black Drop effect, which
has historically impeded ground-based planetary transit measurements, is
optical broadening due to the convolution of the systemic PSF with the
planetary and limb-darkened solar disks. TRACE [satellite] observations
are free from PSF instabilities due to 'seeing' in the terrestrial
atmosphere and allow mitigation of the Black Drop effect from the
intrinsic disk images."

"Mitigation" means "lessening". The ground-based black drop
effect caused by "seeing" is not present in space, but a lesser effect
from a different cause (diffraction) is still present there. Unlike
rapidly time-variable "seeing" effects, diffraction and limb-darkening
effects can be easily modeled and corrected for. The ground observers
have no such luxury.


and writes:

[Tholen]: Why don't you practice what you preach and think about what
you are saying. Greg said the effect was observed by a spacecraft,
therefore your entire reference to the Earth's atmosphere is irrelevant.

Tholen, you are a professional, and are supposed to be
helping matters, not spreading disinformation. In this case, I'm taking
about information that has been known for over 200 years, not some
theory of mine. See for example the references in Peter Abraham's first
message in the current thread "black drop, longer explanation" in
newsgroup sci.astro.amateur.

You could have read my article, the other references, or the
spacecraft article, and set matters straight yourself, even if you have
never personally seen the black drop effect. Instead, you opted for the
chance to take another shot at me, rather than helping to get the
science right. Pathetic. When will you get that this isn't about you or
me, but about advancing science? -|Tom|-


Tom Van Flandern - Washington, DC - see our web site on replacement
astronomy research at http://metaresearch.org

Tom Van Flandern writes:

Why don't you practice what you preach and think about what
you are saying. Greg said the effect was observed by a spacecraft,
therefore your entire reference to the Earth's atmosphere is irrelevant.

Tholen, you are a professional, and are supposed to be
helping matters, not spreading disinformation.

I did help matters by noting that the effect was observed by a spacecraft,
therefore your entire reference to the Earth's atmosphere is irrelevant.

In this case, I'm taking
about information that has been known for over 200 years, not some
theory of mine.

You're talking about some explanation that involves the Earth's
atmosphere, which cannot explain the effect seen by a spacecraft.

See for example the references in Peter Abraham's first
message in the current thread "black drop, longer explanation" in
newsgroup sci.astro.amateur.

Unnecessary. In a nutshell, we have the following:

Q: What causes the black drop effect?
A: The Earth's atmosphere.
Q: But a spacecraft observed the black drop effect, so doesn't
that invalidate the claim that it's caused by the Earth's
atmosphere?
A: Think about what you are saying. Earth does have an atmosphere,
and the light from the transit MUST [emphasis added] pass
through it.

Sorry, but from the spacecraft's perspective, the light does not
have to pass through the Earth's atmosphere, which means that you
didn't think about what you said.

You could have read my article, the other references, or the
spacecraft article, and set matters straight yourself,

The matter had already been set straight. I was merely recommending
that you practice what you preach and think about what you are saying.

even if you have
never personally seen the black drop effect. Instead, you opted for the
chance to take another shot at me,

That's rather ironic, coming from someone who has taken shots at me.

rather than helping to get the science right.

That's rather ironic, coming from someone saying that the light from
the transit must pass through the Earth's atmosphere, even for a
spacecraft.

Pathetic.

My sentiments exactly.

When will you get that this isn't about you or
me, but about advancing science? -|Tom|-

The science had already been advanced, Tom. It's about you telling
someone to think about what they're saying while not doing so yourself.