Transit of Venus

In article ,
(Steve Willner) writes:
The bottom line is that a black drop effect should be seen in any
solar transit, and the magnitude of the effect should depend on the
PSF of the observation.

It occurred to me later that this shouldn't be hard to model. It
might make a fun little project for someone. I wouldn't be surprised
if it has already been done in the literature, but that shouldn't
stop anyone who wants to play with the idea.

You might start by modelling the Sun's disk with a surface brightness
that goes as cos(pi/2*r/R), where R is the solar radius (about 15
arcmin) and r is the projected distance from the center of the Sun.
Anybody want to suggest a more accurate formula? I would suggest a
grid of 0.01 arcsec pixels. That would be a pretty big grid for the
whole Sun, but you only have to model a small area near the limb.

Choose a distance between the center of Mercury and the Sun's limb,
and set all the pixels that Mercury covers to zero. Mercury has a
diameter of about 11 arcsec, so that's a circle of diameter about
1100 pixels. (You might want to check my numbers!) Now you have an
image of what a transit would look like if observed with near-perfect
optics and seeing.

To model the optics and seeing, convolve your "perfect" image with
Gaussians of various diameters. Or you could try other functional
forms such as Airy disks. I'd suggest using 0.1 arcsec pixels at
this stage, but you might want to use larger ones. Convert your
"observed" images into a form that can be displayed (gif or tiff or
fits, perhaps), and see what parameters lead to a black drop.

If anyone tries this, please let us know your results.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)

Steve Willner wrote:

To model the optics and seeing, convolve your "perfect" image with
Gaussians of various diameters. Or you could try other functional
forms such as Airy disks. I'd suggest using 0.1 arcsec pixels at
this stage, but you might want to use larger ones. Convert your
"observed" images into a form that can be displayed (gif or tiff or
fits, perhaps), and see what parameters lead to a black drop.

If anyone tries this, please let us know your results.

It's even easier than this sounds. As a first pass, it isn't necessary
to model limb darkening or worry about image scale. Just draw a circle
in Photoshop and try a few different radii for the Gaussian blur filter.
See

http://home.comcast.net/~erniew/astro/bd.html

In addition to the PSF, there appear to be sensor properties that can
contribute to the effect. Simulating non-linear response and limited
dynamic range enhanced the effect substantially.

- Ernie http://home.comcast.net/~erniew

Ernie Wright wrote:
It's even easier than this sounds. As a first pass, it isn't necessary
to model limb darkening or worry about image scale. Just draw a circle
in Photoshop and try a few different radii for the Gaussian blur filter.
See

http://home.comcast.net/~erniew/astro/bd.html

In addition to the PSF, there appear to be sensor properties that can
contribute to the effect. Simulating non-linear response and limited
dynamic range enhanced the effect substantially.

I tried it myself. The black drop effect even when the dark disc is quite
a ways away from third contact is startling.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

Brian Tung wrote:

I tried it myself. The black drop effect even when the dark disc is
quite a ways away from third contact is startling.

I made an animation this morning that shows this pretty well. I've
added it to

http://home.comcast.net/~erniew/astro/bd.html

along with some changes and corrections to the text.

- Ernie http://home.comcast.net/~erniew

In article , Steve Willner wrote:
In article ,
(Steve Willner) writes:
The bottom line is that a black drop effect should be seen in any
solar transit, and the magnitude of the effect should depend on the
PSF of the observation.

It occurred to me later that this shouldn't be hard to model. It
might make a fun little project for someone. I wouldn't be surprised
if it has already been done in the literature, but that shouldn't
stop anyone who wants to play with the idea.

Sure enough it has been done -- I stumbled across this
30-year-old paper on the morning of the transit, after someone
had asked how the Earth's atmosphere related to the black-drop
effect and I'd struggled to find a credible answer.

Unfortunately my stupid newsreader won't let me post 80-char lines
so you'll have to paste these two together with no space
after the question mark:

http://adsabs.harvard.edu/cgi-bin/nph-bib_query?
bibcode=1974A%26A....31..239W&db_key=AST

Its author simulates the black drop effect using atmospheric blurring
and solar limb-darkening, and includes illustrations which include
believable-looking black drops -- pretty much as you suggest below
though with a better limb-darkening model. Pretty cool. It makes a
lot more sense now.

Stuart Levy

Stuart Levy wrote:

Unfortunately my stupid newsreader won't let me post 80-char lines
so you'll have to paste these two together with no space
after the question mark:

http://adsabs.harvard.edu/cgi-bin/nph-bib_query?
bibcode=1974A%26A....31..239W&db_key=AST

Try this:

http://tinyurl.com/29sdj.

--
Odysseus

(mailto: ) wrote:

Risto Karttunen writes:

Then why did you bring up the alleged lack of visible effects,
Karttunen? Classic inconsistency.

Then please tell me, what were the *practical* visible effects, not
just visible effects.

It allows the determination of the distance between the Sun and Earth,
Karttunen, but what does that practical effect have to do with classical
music?


What does this have to do with classical music, hypocrit?

--
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(mailto: ) wrote:

Risto Karttunen writes:

Then why did you bring up the alleged lack of visible effects,
Karttunen? Classic inconsistency.

Then please tell me, what were the *practical* visible effects, not
just visible effects.

It allows the determination of the distance between the Sun and Earth,
Karttunen, but what does that practical effect have to do with classical
music?


What does this have to do with classical music, hypocrit?

--
Freddie D. 'fag' Shorts

I'm loud and I'm proud. I'm gay and I like it that way!
Another proud buttplug owner. Honk if yer horny!
I support Gay Pride! The Ramrod rocks! Kerry sux!

Wanna hire me for web site development? I'm way under-employed!
Contact me by email ) or mail me at
FS Newssite Inc.
101 West 23rd St. Suite 2237, New York, NY, 10011
On second thoughts, don't bother. Just sign me up for subscriptions.
I like to steal copyrighted material.

Check out my current web sites -
http://www.orwellian.org
http://www.miscstuff.org
http://home.nyc.rr.com/cypherpunk/

I'm really proud of this -
http://Frederick.Shorts.swellserver....orldrecord.php

http://www.plugger.info
http://www.pluggers.com/daily/

mailto: ) wrote:

Risto Karttunen writes:

You'll need to ask Karttunen; he's the one who thinks there are no
practical visible effects.

I haven't said that "there are no practical visible effects", nor do I
think that way.

"No visible effects, practically speaking."

Yes?

Aren't you sure what you said? First you said it, then you said that
you haven't said it.

I have said that there were no visible effects, practically speaking.

"I haven't said that 'there are no practical visible effects',
nor do I think that way."
--Risto Karttunen

I have not said that there are no practical visible effects. Can't you
understand the difference?

"No visible effects, practically speaking."
--Risto Karttunen

Obviously you don't get the difference.

Obviously you don't get that there are visible effects, practically
speaking, Karttunen.

I'll try once mo as I see
it, "practically speaking" means much the same as "generally
speaking", speaking about the "big picture", but "a practical visible
effect" - somewhat strange as it sounds - means an effect which has
certain practical importance or consequences.

Why try one once more to justify a statement that can't be justified,
Karttunen?

There was also a difference between tenses.

Irrelevant, given that you still can't justify a statement that can't
be justified.

And your response to the evidence that you did say it is a question?

Is *that* a question?

Classic evasion.

What did I evade?

My question, Karttunen.

I tried to find out, whether you had asked something.

You would already know the answer to that if you had better reading
comprehension skills, Karttunen.

The sun shone just as bright as always etc,

Incorrect, Karttunen.

Certainly not, in the context of composing classical music.

Non sequitur.

Why? Remember, we are in r.m.classical now.

Then why did you make an erroneous claim about the Sun shining just as
bright as always, Karttunen?

practically speaking.

How much range does your "practically speaking" allow, Karttunen?

As much as there is in the everyday context. It is no wonder to me
that composers have not considered this incident dramatic enough to
make music about it.

Sousa did.

I looked at

http://www.transitofvenus.org/sousa.htm

which says: "Sousa originally composed the march for the unveiling
ceremony of the statue of Joseph Henry, the first Secretary of the
Smithsonian Institution. The ceremony had been planned to occur
before the 1882 transit, but didn't actually happen until April 19,
1883. Henry, whose statue is now in front of the Smithsonian "Castle"
in Washington, D.C., was on the U.S. Transit of Venus Commission."

So, Sousa had certain reasons for composing his march, not just the
transit of Venus itself.

Doesn't change the fact that the incident was dramatic enough to make
music about it, Karttunen.

A tiny dot traversed across the solar disc - so what?

Consult the newspapers; it received wide coverage.

What does that have to do with classical music?

You should know, Karttunen, given that you asked the question in a
classical music newsgroup.

Many other topics
receive wide coverage as well, even wider. Nobody wonders, though, why
there is no connection with classical music around those topics.

How many of those "many other topics" have a march titled after them,
Karttunen?

How many people would have even noticed it without knowing
beforehand?

I won't attempt to speak for others, Karttunen.

That was a rhetorical question. I didn't expect an exact figure.

Rhetorical questions do not expect answers, Karttunen.

You can't even look straight at the sun.

Irrelevant, given that there are numerous safe ways to look at the
Sun.

What does that have to do with classical music?

You should know, Karttunen, given that you made the statement in a
classical music newsgroup.

Sousa composed the "Transit of Venus March", Karttunen. Of course, I
mentioned that in the very first posting of the thread, which you
would know by now if you had better reading comprehension skills.

Then why were you surprised, in the first place?

You're presupposing some "surprise" on my part, Karttunen.

perhaps we could say that the effects of traffic lights
are practical.

What does that have to do with the transit of Venus, or the Sousa
march by the same name, Karttunen?

I didn't say that it does.

Then why did you bring it up, Karttunen?

This is why:

I see -- no reason at all.

It is up to the composers to make or not to
make music about certain effects. I was just trying to figure out the
meaning of the phrase "practical visible effects", which you
introduced into this discussion about classical music.

You are the one who introduced the matter, Karttunen:

No, you introduced *that* phrase.

Liar:

"No visible effects, practically speaking."
--Risto Karttunen

"No, they were not - *practically speaking*."
--Risto Karttunen

Anyway I haven't said that there are no practical visible effects.

Liar:

"No visible effects, practically speaking."
--Risto Karttunen

"No, they were not - *practically speaking*."
--Risto Karttunen

*Liar*?

Still suffering from reading comprehension problems, Karttunen?

Again you do not understand the rhetorical style.

What does your unsubstantiated and erroneous claim have to do with
classical music, Karttunen?

That was very rude and strange indeed.

What is allegedly strange about the truth, Karttunen?

Ah...you admit the rude part?

Still suffering from reading comprehension problems, Karttunen?

Please try to get some good manners.

Practice what you preach, Karttunen, and quit lying.

About what?

Still suffering from reading comprehension problems, Karttunen?


What does any of this bull**** of yerz have to do with classical music, hypocrit?

--
Freddie D. 'fag' Shorts

I'm loud and I'm proud. I'm gay and I like it that way!
Another proud buttplug owner. Honk if yer horny!
I support Gay Pride! The Ramrod rocks! Kerry sux!

Wanna hire me for web site development? I'm way under-employed!
Contact me by email ) or mail me at
FS Newssite Inc.
101 West 23rd St. Suite 2237, New York, NY, 10011
On second thoughts, don't bother. Just sign me up for subscriptions.
I like to steal copyrighted material.

Check out my current web sites -
http://www.orwellian.org
http://www.miscstuff.org
http://home.nyc.rr.com/cypherpunk/

I'm really proud of this -
http://Frederick.Shorts.swellserver....orldrecord.php

http://www.plugger.info
http://www.pluggers.com/daily/

mailto: ) wrote:

Risto Karttunen writes:

You'll need to ask Karttunen; he's the one who thinks there are no
practical visible effects.

I haven't said that "there are no practical visible effects", nor do I
think that way.

"No visible effects, practically speaking."

Yes?

Aren't you sure what you said? First you said it, then you said that
you haven't said it.

I have said that there were no visible effects, practically speaking.

"I haven't said that 'there are no practical visible effects',
nor do I think that way."
--Risto Karttunen

I have not said that there are no practical visible effects. Can't you
understand the difference?

"No visible effects, practically speaking."
--Risto Karttunen

Obviously you don't get the difference.

Obviously you don't get that there are visible effects, practically
speaking, Karttunen.

I'll try once mo as I see
it, "practically speaking" means much the same as "generally
speaking", speaking about the "big picture", but "a practical visible
effect" - somewhat strange as it sounds - means an effect which has
certain practical importance or consequences.

Why try one once more to justify a statement that can't be justified,
Karttunen?

There was also a difference between tenses.

Irrelevant, given that you still can't justify a statement that can't
be justified.

And your response to the evidence that you did say it is a question?

Is *that* a question?

Classic evasion.

What did I evade?

My question, Karttunen.

I tried to find out, whether you had asked something.

You would already know the answer to that if you had better reading
comprehension skills, Karttunen.

The sun shone just as bright as always etc,

Incorrect, Karttunen.

Certainly not, in the context of composing classical music.

Non sequitur.

Why? Remember, we are in r.m.classical now.

Then why did you make an erroneous claim about the Sun shining just as
bright as always, Karttunen?

practically speaking.

How much range does your "practically speaking" allow, Karttunen?

As much as there is in the everyday context. It is no wonder to me
that composers have not considered this incident dramatic enough to
make music about it.

Sousa did.

I looked at

http://www.transitofvenus.org/sousa.htm

which says: "Sousa originally composed the march for the unveiling
ceremony of the statue of Joseph Henry, the first Secretary of the
Smithsonian Institution. The ceremony had been planned to occur
before the 1882 transit, but didn't actually happen until April 19,
1883. Henry, whose statue is now in front of the Smithsonian "Castle"
in Washington, D.C., was on the U.S. Transit of Venus Commission."

So, Sousa had certain reasons for composing his march, not just the
transit of Venus itself.

Doesn't change the fact that the incident was dramatic enough to make
music about it, Karttunen.

A tiny dot traversed across the solar disc - so what?

Consult the newspapers; it received wide coverage.

What does that have to do with classical music?

You should know, Karttunen, given that you asked the question in a
classical music newsgroup.

Many other topics
receive wide coverage as well, even wider. Nobody wonders, though, why
there is no connection with classical music around those topics.

How many of those "many other topics" have a march titled after them,
Karttunen?

How many people would have even noticed it without knowing
beforehand?

I won't attempt to speak for others, Karttunen.

That was a rhetorical question. I didn't expect an exact figure.

Rhetorical questions do not expect answers, Karttunen.

You can't even look straight at the sun.

Irrelevant, given that there are numerous safe ways to look at the
Sun.

What does that have to do with classical music?

You should know, Karttunen, given that you made the statement in a
classical music newsgroup.

Sousa composed the "Transit of Venus March", Karttunen. Of course, I
mentioned that in the very first posting of the thread, which you
would know by now if you had better reading comprehension skills.

Then why were you surprised, in the first place?

You're presupposing some "surprise" on my part, Karttunen.

perhaps we could say that the effects of traffic lights
are practical.

What does that have to do with the transit of Venus, or the Sousa
march by the same name, Karttunen?

I didn't say that it does.

Then why did you bring it up, Karttunen?

This is why:

I see -- no reason at all.

It is up to the composers to make or not to
make music about certain effects. I was just trying to figure out the
meaning of the phrase "practical visible effects", which you
introduced into this discussion about classical music.

You are the one who introduced the matter, Karttunen:

No, you introduced *that* phrase.

Liar:

"No visible effects, practically speaking."
--Risto Karttunen

"No, they were not - *practically speaking*."
--Risto Karttunen

Anyway I haven't said that there are no practical visible effects.

Liar:

"No visible effects, practically speaking."
--Risto Karttunen

"No, they were not - *practically speaking*."
--Risto Karttunen

*Liar*?

Still suffering from reading comprehension problems, Karttunen?

Again you do not understand the rhetorical style.

What does your unsubstantiated and erroneous claim have to do with
classical music, Karttunen?

That was very rude and strange indeed.

What is allegedly strange about the truth, Karttunen?

Ah...you admit the rude part?

Still suffering from reading comprehension problems, Karttunen?

Please try to get some good manners.

Practice what you preach, Karttunen, and quit lying.

About what?

Still suffering from reading comprehension problems, Karttunen?


What does any of this bull**** of yerz have to do with classical music, hypocrit?

--
Freddie D. 'fag' Shorts

I'm loud and I'm proud. I'm gay and I like it that way!
Another proud buttplug owner. Honk if yer horny!
I support Gay Pride! The Ramrod rocks! Kerry sux!

Wanna hire me for web site development? I'm way under-employed!
Contact me by email ) or mail me at
FS Newssite Inc.
101 West 23rd St. Suite 2237, New York, NY, 10011
On second thoughts, don't bother. Just sign me up for subscriptions.
I like to steal copyrighted material.

Check out my current web sites -
http://www.orwellian.org
http://www.miscstuff.org
http://home.nyc.rr.com/cypherpunk/

I'm really proud of this -
http://Frederick.Shorts.swellserver....orldrecord.php

http://www.plugger.info
http://www.pluggers.com/daily/