I can try to work through the math later, but I viewed the 2012 transit on the east coast of the USA where it ended at sunset. We were using images projected through binoculars or small telescopes onto the side of the building. As sunset approached, you could see the Sun get dimmer, AND see the side closer to the ground be dimmer than the side farther from the ground*. Near the end (like the last minute) the Sun's image was stretched out
( ... )
I'll try to project an image through binoculars on the next sunny day, to see how it works (taking very great care!) If - and only if - you have time to do the calculations for the exit time, that would be brilliant. I can approximate it if necessary from Cape Town and St Helena but it'd be awesome to have the correct times.
"I'll try to project an image through binoculars on the next sunny day, to see how it works (taking very great care!)"
Something to know about that: you don't want to project a little image of the sun, like burning something with a magnifying glass. You want to pull the binoculars farther back from the wall (with one lens covered) so you're projecting a much larger image. The image of Venus in my projection was about the diameter of a BB.
Yay! Wish I'd known all this three years ago. I drove through floods (admittedly just a few inches deep) to get to a big telescope, which isn't inappropriate given what the 18th century astronomers did - but if I'd had the brains to set up my binoculars to see the exit..!
(Apologies; I see you already have Andrea Wulf's book - this article has an illustration of the viewing apparatus used.)
I watched the transit of 2012 by projecting it on to my living-room wall with a spyglass, and could see it perfectly well that way.
According to the U.S. Naval Observatory Data Services, on June 6, 2015 at W19° S30°, civil twilight began at 07:40, sunrise was at 08:06, sunset 18:23, end civil twilight 18:49. That wouldn't be precise to the minute for the year 1761, but then they weren't able to calculate it precisely to the minute back then anyway.
That article is useful - thanks! there are pictures there which make things clear, like what the parasol thingy is around the eyepiece of the telescope. Literally a sunshade.
It's good to know that my observers don't have to get up at a ghastly hour to start watching, too. Mid-winter in the South Atlantic, even at that latitude, would not, I imagine, be too much fun. *goes off to look up climate figures*
Comments 6
Reply
Reply
Something to know about that: you don't want to project a little image of the sun, like burning something with a magnifying glass. You want to pull the binoculars farther back from the wall (with one lens covered) so you're projecting a much larger image. The image of Venus in my projection was about the diameter of a BB.
Reply
Reply
I watched the transit of 2012 by projecting it on to my living-room wall with a spyglass, and could see it perfectly well that way.
According to the U.S. Naval Observatory Data Services, on June 6, 2015 at W19° S30°, civil twilight began at 07:40, sunrise was at 08:06, sunset 18:23, end civil twilight 18:49. That wouldn't be precise to the minute for the year 1761, but then they weren't able to calculate it precisely to the minute back then anyway.
Reply
It's good to know that my observers don't have to get up at a ghastly hour to start watching, too. Mid-winter in the South Atlantic, even at that latitude, would not, I imagine, be too much fun. *goes off to look up climate figures*
Reply
Leave a comment