Posted on 06/03/2012 6:34:00 PM PDT by SunkenCiv
Explanation: The rare transit of Venus across the face of the Sun in 2004 was one of the better-photographed events in sky history. Both scientific and artistic images flooded in from the areas that could see the transit: Europe and much of Asia, Africa, and North America. Scientifically, solar photographers confirmed that the black drop effect is really better related to the viewing clarity of the camera or telescope than the atmosphere of Venus. Artistically, images might be divided into several categories. One type captures the transit in front of a highly detailed Sun. Another category captures a double coincidence such as both Venus and an airplane simultaneously silhouetted, or Venus and the International Space Station in low Earth orbit. A third image type involves a fortuitous arrangement of interesting looking clouds, as shown by example in the above image taken from North Carolina, USA. Sky enthusiasts worldwide are abuzz about the coming transit of Venus on Tuesday. It is perhaps interesting to wonder whether any person will live to see -- and remember seeing -- both Tuesday's Venus transit and the next one in 2117.
(Excerpt) Read more at 129.164.179.22 ...
The transit commences just after 5PM, CDT, so that's 3PM PDT, right? ... but this is on Tuesday June 5! so hold on.
Heh - I thought it was Monday today! Still a 70% chance of rain on Tuesday. I sure as h&*% hope those 8 days of nice weather in mid-May wasn’t our “summer” for the year!
Wow! That is so dang cool!!!!
I was going to say this "won't work", but it could be made to work. However, the requirements are severe. I should say requirement, I guess, because it is this, that the apparent size of the "tiny bit" at the distance of the projection, be much less than the apparent size of Venus. This is very nearly 1 minute of arc, or about 1/3500 radians. This means that with a 1 mm "bit" you would need a >> 3.5 meter projection distance to resolve Venus. You would need an elaborate "camera obscura" setup to have any hope of success.
Why not just use eyepiece projection with a small binocular?
To address the substance of your question, I would say that the brightness of the sun presents the same problem regardless of the size of the object eclipsing it, or even if the there is no eclipse at all! If you observe the sun for sunspots, for example, the brightness must be reduced so that it is presentable to the eye. If this is done, then you will be able to see sunspots, and in addition the silhouette of any object which crosses the face of the sun, whatever its size.
“...so that it is presentable to the eye.”
Thanks. I figured it must have been a limitation because of our eyes. So the pinhole in the cardboard trick is really just reducing the amount of total light I guess. But to see Venus one would need a bit of magnification as well.
Well, Venus is about 1 minute of arc, and the sun is about 30 times that, in diameter. So by usual telescopic standards, it's pretty easy to see as a disc. If we think of eyepiece projection, a solar image of 6 cm will show the silhouette of Venus as a 2 mm disc, which should be plainly discernible. If you're using a binocular, it doesn't take anything special to display this. The only thing I would rule out is plastic body toy or giveaway items. Anything substantial should fill the bill, even those small "spotting scope" type things, which are useful at the beach ;-)
Having said this much, I should point out that it takes a little bit of practice to project a solar image with hand held binoculars ( I’ve been practicing. ) Of course, you have to point the large objective lens toward the sun, while you look at the ground or a wall for the image. The trick is the alignment. If you look at the shadow of the rim of the objective end on the casing of the binocular itself, you can quickly learn how it must appear to give an image. Just remember that the lens must be centered in its own shadow, so you’ll want to see one edge of this circular shadow positioned this way. It makes sense when you’re doing it.
It does take a steady hand, but then by slight movements you can position the projected image, for example into the shadow of your own body. So then if you have a flat screen somewhere, you can position yourself by your own shadow so that you can, by learned habit, put the image onto the screen based on this.
If you see a circle of light, this is the image of the sun, not the field of view of the binocular, which is larger. If you get enough control to move the circle around, you can find the edge of this field of view, where it disappears. To focus, just make the edge of this circle sharp. You will find it challenging to hold the circle in position while you do this, so you can try repeated adjustments with “reacquisition”. Be assured that the required adjustment is small, if you start with the binoculars focused at distance. If some wispy clouds should happen to pass over the sun, you will see that you are indeed in focus, if you have made the edge of the disc sharp. Of course this can all be done beforehand, and you will be ready to go.
Lest anyone plan based on my posting: the transit occurs Tuesday the 5th in North America.
It will be the 6th over the IDL.
Thanks cicero2k. I plan to wait for the 2117 transit, I’ll be better prepared by then. ;’)
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