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I had previously asked about how useful everyday solar physics data is to other astronomers ... But about a year from now, we will have another Venus transit, where Venus will pass between the sun and the earth ...

I was just in a meeting with some EPO (education and public outreach) folks about trying to prepare something for the event, and we can do the basic 'make a pinhole camera' kids activities, and use it for awareness of our field ...

But is there any novel science that we could use the event for? We're especially interested in trying to find something 'Citizen Science', where we could try to organize people to contribute some data from across the world that might help advance our knowledge of something.

(it doesn't even have to be astronomy ... We had an idea of trying to get people to take pictures of the transit, and send the images, and we could try to use it to estimate how the quality of seeing varies, but we weren't sure if there were liability issues if someone managed to ruin a camera or their eyes in the process)

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closed as off topic by Waffle's Crazy Peanut, Manishearth Jan 15 '13 at 11:52

Questions on Physics Stack Exchange are expected to relate to physics within the scope defined by the community. Consider editing the question or leaving comments for improvement if you believe the question can be reworded to fit within the scope. Read more about reopening questions here.If this question can be reworded to fit the rules in the help center, please edit the question.

Is this question - and its 6 answers! - going to be deleted now that it is closed? How is it "off-topic"? Physics SE is supposed to include astronomy, since the Astronomy SE closed down. – Mitchell Porter Jan 15 '13 at 12:07
@MitchellPorter : I'm pretty sure that I asked it on Astronomy, and it was migrated here after that site was shut down. – Joe Jan 15 '13 at 14:03

What was discovered in earlier transits of Venus was that it's extremely hard to get accurate timings of the event, even with very good equipment, because of Venus' thick atmosphere, which makes timings literally very fuzzy. So there's very little scientific value in trying to make timings.

In the 2004 transit, the concentration was on observing the "black drop" effect and the "ashen light". Both of these require telescopes with solar filters. The "black drop" is the thin ligature of shadow that appears to join the disk of Venus to the sky background with Venus just inside the Sun's limb. The "ashen light" is the apparent illumination of the "dark side" of Venus, an appearance similar to earthlight on the Moon, visible when Venus is partially off, or just off, the disk of the Sun.

I observed the 2004 transit of Venus just after sunrise from Cathedral Bluff in Scarborough, Ontario, Canada, using a 127mm Maksutov-Cassegrain with a Kendrick/Baader solar filter. I think I saw hints of the ashen light. I also observed it with my naked eye (while still deep in morning fog), just to assure myself that prehistoric man could actually have observed it, if he were watching at exactly the right time. The disk of Venus was easily visible naked eye against the disk of the rising Sun.

I think in 2012 I will try observing with my Coronado Personal Solar Telescope, as it would be interesting to see Venus silhouetted against solar prominences.

None of these observations have much serious astronomical research value, but my 2004 observations were personally very satisfying to me, as a once (or twice) in a lifetime opportunity. I'm not really sure that there is much of scientific value in observing a transit of Venus, but it is still a remarkable event, and proved to be much more interesting to me in 2004 than I had anticipated.

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I observed the entire transit in 2004 using a 200 mm Cassegrain telescope with a mylar solar filter. I was lucky with the weather and was at the right latitude. The "black drop" effect was clearly visible both at ingress and egress. But it is a optical illusion (?). – Peter Mortensen Jun 16 '11 at 19:51

The transits of 1761 and 1769 were used to determine the size of the solar system through parallax and Kepler's third law. By the 17th century, astronomers could calculate planets' relative distance to the Sun through the Earth's distance (AU), but they had no accurate measure of the absolute distance.

Precise times of transit of Venus across the solar disk were measured from widely separated points on Earth. Then the precise distance to Venus and the Sun was measured via triangulation. This would be a fairly straightforward experiment, provided it can be done from relatively widely separated points on earth to obtain enough precision.

Now we use more modern techniques like space probe telemetry and radar to make more precise measurements of the Solar System's size. So in 2004 the transit was observed to detect the pattern of light dimming of the Sun to refine techniques used to detect extra-solar planets.

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One big discovery since the 2004 transit is all the transiting exoplanets seen with Kepler, including some the size of Venus. The great thing about transits is the potential for measuring the chemical abundances of the planet's atmosphere with spectroscopy. Of course, the sun give us a way of testing this in the extreme limit of nearly infinite signal-to-noise. Then we can test it with emission spectroscopy of venus when at quadrature phase.

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This amazing piece of research was performed during the last transit. The effect of the transit on the ionosphere was measured. The results are quite remarkable.

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This should certainly be repeated for the 2012 transit. I don't buy the authors' explanation of the effect, but one should always have an open mind. – Pete Jackson Aug 12 '11 at 17:38

This answer is a bit off topic since it doesn't mention a direct science knowledge gained from the transit of Venus. But I will say that if you are fortunate enough to view the 2012 transit, you will starkly remember it for the rest of your life.

I saw the 2004 transit of Venus over the sun rising over the Chesapeake Bay in June 2004, and it formed an image burned in my mind: this completely black circle in the Sun's larger bright circle, all surrounded by more blackness. Think of some of the monolith images from the movie "2001: A Space Odyssey". As many people as possible should be encouraged to see this remarkable apparition, not to be seen again until 2117.

And if some of those viewing it are enthralled enough to devote their lives to doing or teaching science, then that would be the science contribution of the 2012 transit!

Of course, viewing the transit of Venus should be done with all the precautions needed to view the Sun through a telescope, mainly by using special solar filters or by projection.

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I, too, felt a tremendous emotional impact from my observation of Venus in transit rising through the mists over Lake Ontario, far more than I had expected. It was awesome to realize that some prehistoric man might have also witnessed this. – Geoff Gaherty Jul 3 '11 at 21:00

Yes, there is a notion that could be scientifically explored and confirmed through a citizen science project. However, you gotta have some moxie because you'll ask the public to look at the sun without eye protection, with caveats, of course. Namely, survey observers near sunset or sunrise to discern whether an effect equivalent to the "moon illusion" occurs for Venus in transit. When the sun is nearly at the true horizon, does Venus appear larger and more readily than it did when the sun was higher and you when you observed it through solar shades? With the moon illusion, the moon "seems" bigger. With the transit, the illusion is affecting an object on the cusp of visibility. Venus is only about one arcminute in diameter, near the limit of the human eye. Does the Venus Illusion suddenly make the tiny dot easier to see, boosting it over the threshold of naked eye visibility? Perhaps you could view it at sunset (the only time during the transit to look without solar filters, in my opinion, and even then only briefly), when the horizon and surroundings are visible, and then put on solar shades and view it at sunset--same time, but the latter in the absence of horizon references.

Tony Flanders comments on the illusion in the September 2004 issue of Sky & Telescope magazine. Other than that, there is not much in print that I have seen. Please contact me through the Contact Us form at if you wish to pursue this experiment further. Among your considerations is not to plant the idea of an enlarged Venus in the minds of the observers--you need to eke that out of them unwittingly at first, if indeed it applies. The 2012 transit of Venus is a great opportunity to pursue this in North America, where the visual event will end at sunset.

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