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Biarmicus
2017-Jan-30, 10:57 PM
Having seen the 2012 transit, I now want to put a transit observation into a historical novel I'm trying to write. My astronomer is on Ascension Island, 7.56 S, 14.25 W.

I'm having trouble working out when the third and fourth contacts would occur. Ferguson's maps give me a broad idea, but ideally I would like to know to the second. Is there a formula I can slot lat and long into or if not, does anyone here feel like tackling the maths?

I would be very grateful for any help! Writing the novel is hard enough but the maths is way beyond me.:confused:

antoniseb
2017-Jan-31, 02:09 PM
There are historical accounts of that even. I've seen narrative versions in old Sky and Telescope magazines from before the recent Venus Transit. My recollection is that Venus looked fairly blob-like on entry and exit, so the duration between contacts may be imprecise.

tony873004
2017-Jan-31, 04:44 PM
Here's a simulation of that date from that location:
http://orbitsimulator.com/gravitySimulatorCloud/simulations/1485877980155_venus1761.html
Press "P" on your keyboard or [>] on the Time Step interface to begin.

Although the timing should be pretty good, I would not trust it "down to the second".
Testing the simulator against known eclipse data from NASA's page, it gets the Oct 17 1762 eclipse down to the minute, with a small location error because the real Earth precessed a little, but my simulated Earth did not.

Hornblower
2017-Jan-31, 06:21 PM
I would take Tony's figures and write your story without being concerned with accuracy to the second.

Biarmicus
2017-Jan-31, 11:39 PM
Yes, that's true - it would give me a bit of wriggle-room, should anyone challenge me! (Which I don't think they will, but I do like to get things right.)

Biarmicus
2017-Jan-31, 11:43 PM
This is perfect - thank-you so much! And for checking it against the eclipse too. I now know I've got plenty of time for the conversations I wanted to have going on during the transit, which is great. Watching the simulation brought back memories of seeing the real thing, too: just brilliant.

Biarmicus
2017-Jan-31, 11:48 PM
The figures are pretty much what I was hoping for, so I'm going to take them with gratitude! But I'll admit to being fascinated by the work that those instrument-makers did; they didn't mess about where precision was concerned, and I'd like to reflect that. (Also, your username made me smile, since it's in part a sea-story, though a few decades earlier, of course.)