A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Date: 2014 Oct 24, 19:34 +0100
I will try that. I think the ancients had telescope objectives engraved with graticle lines that could give them a measure of distance between points to give minutes, calibrated from known moon and sun diameters I guess? Hopefully Frank or one of the astronomers could elucidate?
Anyways, totally good fun and I will carry on! Thanks for the inspiration.
My plan is to get accurate longitudes from lunar eclipses and Jupiter moons with telescope and digital camera + 200-400mm lens. Also from telescope + graticle a la 1760s. Oh well dream on! By the way, I suspect lunar eclipses could have been done (occasionally) by eye (no telescope) even on ship. But this would have been so rare as to make it not viable as a marine system. (any way, still need a fairly accurate watch to get LAN time and time of lunar /Jupiter observation. When did they first appear? Before H4 I think.) The Jupiter moons and all the telescope dependant systems were impractical at sea. OK on terra firma.
Wonderful stuff. Carry on please. I will too.
The 400mm telescope should get it done for both eclipse and Jupiter's moons. You should use at least 10 mega pixel digital camera. For image processing I use Adobe Photoshop Lightroom 5.3 and then measure pixels with Windows 7 paint brush tool. Warning-there is a learning curve for getting the most out of Lightroom 5.3
If a zoom lens is used then it has to be calibrated for each image. Not convenient. For filtering I use linear polarizers with one of the polarizer filters flipped in the holder so that the pair acts as an adjustable neutral density filter. I'm sure solar film will work on your 400mm telescope objective lens. Start at f22, ISO 100, 1/4000 sec, infinite focus.
The classic astronomers must have measured realtime with something similar to a theodolite. I'm not sure when photo astronomy first started ..1850s?
From: Francis Upchurch
Date: 2014 Oct 24, 17:53 +0100