NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: UNK
Date: 2014 Oct 24, 19:34 +0100
Brilliant.
Thanks Greg.
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.
Francis
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Greg Rudzinski
Sent: 24 October 2014 19:06
To: francisupchurch@gmail.com
Subject: [NavList] Re: Big fat sunspot and a solar eclipse
Francis,
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?
Greg Rudzinski
From: Francis Upchurch
Date: 2014 Oct 24, 17:53 +0100
Thanks Greg,
It gets better. I already have a good digital SLR and 200mm lens (zoom though ,not prime, does that alter things?) Maybe this ok for lunar eclipses but will probably need telescope for Jupiter moons. My 4 inch refractor also works as a 400mm prime lens, so I guess that would do for both.
What filters did you use for the 200m? Polariser +/- solar filter, not sure?
What software to work out the number of pixels?
How do you think the old guys (eg Cook et al) did it in the 1770s without photography and computers? Did they measure the thing real time with lens objective graticles or whatever they are called? Any information on those? I’ll probably try to do it the old way if I could find out how.
Anyway, very good fun. Just need the clear weather at the right time.(not easy in wintery, wet and windy UK. I suspect that is why we sent hundreds of ships south to find clear skies and warm weather.)
Thanks a lot, I’ll get to work asap on this.
Francis
