Date: May 4, 2012 4:10 AM
Author: Guy Brandenburg
Subject: Re: [MathTalk] transit of venus

Sometimes they really are amazingly detailed. At times, when you look at the sun and conditions are right and the scope has been properly tuned and focused, you can see detail on there as fine as on a sunflower under a microscope. And you can watch it change. Of course, when I saw it as detailed as that, I was in northern Vermont at an astronomical event known as Stellafane, looking through a privately-owned telescope belonging to Al Nagler, definitely one of the best-known and best-regarded eyepiece maker of this century, and he had one of the very best amateur hydrogen-alpha telescopes int he world at the time.

When I try it with my own, or even my club's, equipment, it's never as good, but sometimes we get close. 

I just did a sort of back-of-the-envelope calculation that the parallax you would see, if the AU is about 93 million miles as I was taught and if they weren't lying, and you had two earthside observers with a baseline of 4000 miles (any direction will do) then the parallax would be about 0.7% of the way across the sun. 

Could I see that sort of a shift on a number of photos taken by two experts (say, Greg Piepol number 1 and Greg Piepol number 2, on opposite sides of the Pacific)? I am positive, unless the atmosphere of Venus is so huge that it spreads the light out all over the place. Which I don't recall seeing back in 2004. 
Guy Brandenburg, Washington, DC

From: Louis Talman <>
To: "" <>
Cc: NCA Listserve <>; northern virginia astronomy club <>; mathedcc list <>; DC Council of Teachers of Math <>
Sent: Friday, May 4, 2012 3:04 AM
Subject: Re: [MathTalk] transit of venus

I have to wonder if the phenomena on the solar face are sufficiently well defined to enable measurements that are any more accurate than those of first, etc., contact---which are spoiled by the black-drop effect. (The aureole effect, though less important, is also a spoiler.)

--Louis A. Talman
Department of Mathematical and Computer Sciences
Metropolitan State College of Denver

On May 3, 2012, at 11:25 PM, Guy Brandenburg wrote:

> It occurs to me that one can today probably achieve impressive accuracy on measuring the distance to Vanus, and hence, of the length of 1 AU, by having two widely separated observers each make a single, simultaneous, hydrogen-alpha image of the sun and the dot of venus on its face. One doesn't have to wait to time first, second, third, and fourth contacts.
> My reason for saying this is that an Ha filter allows anyone to see all sorts of sunmarks; some careful scruitiny of where venus is in relation to those sunmarks will allow us to get the angular parallax fairly easily. Then a little bit of geometry will allow us to figure out how far the observers are from each other with respect to Venus (i.e., what's the length of the baseline). And then the rest of the calculations are pretty straightforward, at least in principle.

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