Mercury, Black Drop Effect, and Sunspotter scope
On Oct 15, 2006, at 8:54 PM, Chuck Hards <chuckhards@yahoo.com> wrote:
I haven't read anything on the black drop in years-obviously it's an optical illusion, but I had thought it was more related to telescope optics or earth's atmosphere. I've seen it with Mercury, but I've never seen a Venus transit to compare it to.
How big is the image with your sunspotter? Mercury may be hard to spot if the projected solar disk is under about four inches in diameter.
Good point, Chuck. The solar image is about four inches with the scope. With Mercury's apparent diameter of 10 arcseconds, that works out to be .02 inches. Pretty small,but I think visible. I would not expect to be able to see any black drop effect at such a size. Venus' disk during transit is considerably larger (58 arcseconds during the 2004 transit) because it is a larger planet, and because it is so much closer to earth at transit. It is visible naked eye (with proper protection). I happened to be in Boston on that date and saw it using eclipse glasses. Jim Cobb james@cobbzilla.net
That's almost a full minute of arc- and larger than Jupiter usually appears, if that helps folks visualize. Another way of looking at it is that Venus can appear about 1/30 the diameter of the sun during a transit- no wonder you saw it visually. With this in mind, one can see why certain sharp-eyed individuals can see the crescent phase of Venus visually. When at crescent phase, Venus is very close to superior conjunction, and thus almost as large diametrically as possible. Superior conjunction is also when transits can take place. Neat! --- Jim Cobb <james@cobbzilla.net> wrote:
Venus' disk during transit is considerably larger (58 arcseconds during the 2004 transit) because it is a larger planet, and because it is so much closer to earth at transit. It is visible naked eye (with proper protection). I happened to be in Boston on that date and saw it using eclipse glasses.
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Chuck Hards wrote:
With this in mind, one can see why certain sharp-eyed individuals can see the crescent phase of Venus visually. When at crescent phase, Venus is very close to superior conjunction, and thus almost as large diametrically as possible. Superior conjunction is also when transits can take place. Neat!
Ummm, isn't superior conjunction when Venus is on the other side of the Sun and inferior conjunction when it's between us and the Sun (and when transits take place)? pw
Yep, according to Sam Brown, you are correct sir! Now I wonder why I transposed them? Early onset of dementia, I suppose. Thanks! --- Patrick Wiggins <paw@wirelessbeehive.com> wrote:
isn't superior conjunction when Venus is on the other side of the Sun and inferior conjunction when it's between us and the Sun (and when transits take place)?
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participants (3)
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Chuck Hards -
Jim Cobb -
Patrick Wiggins