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    Re: What time is it?
    From: Frank Reed
    Date: 2020 Aug 22, 22:45 -0700

    The reason you will find this analysis impossible, David, is because the Sun was not out! I have analyzed a great many photographs like this one, many for my own interest, and quite a few as a paid consultant, including as an "expert witness" in court.

    This image has extremely diffuse shadows on the ground and on other surfaces, and these shadows result when the Sun is hidden behind clouds. The clouds are not opaque, and if we could look to the left, out-of-frame in this image, we would almost certainly see a broad band of clouds brighter than the rest of the sky. That is what is producing the very diffuse shadows in the photo. The time cannot be determined to better than one or two hours, at best, from this photo. 

    As for almanac data for 1950, I have long maintained (for over 15 years!) an online Nautical Almanac that is designed both for modern sights and especially for the analysis of historical sights (and also photographs like this one). Go here: http://www.reednavigation.com/lunars/#NA. Note that you can display coordinates both for GMT and also GAT (Greenwich Apparent Time) which was the standard time variable in the early days of the almanacs (over a century before the photo in your post, so not relevant here but useful in other cases). Of course you're quite correct that you could use data for 1930 or even 2020, and it would make almost no difference for the analysis of common ground shadows, even if the shadows were sharp.

    I went looking for the location anyway. One can enter coordinates directly into most search engines (like Google!), so I typed in your coordinates and found myself "in the middle of nowhere". It appears that the longitude in the caption of your image is out by one degree, right? Here's the Woburn Station, looking pretty much the same as in 1950: https://goo.gl/maps/5jf8EmTWRevRhbLq8. And by the way, that little "wing" on the building, directly below the "Woburn" sign in your photo, should be casting a shadow on the rest of the building that would, on a sunny day, provide excellent evidence of the time. But as you can see, there is no actual shadow. The Sun is not out.

    Finally, and once more, the old British expression "long by chro" for a common "time sight" calculation was a colloquial euphemism. It was a poor choice back then, and it's a poor choice today. Have you noticed that the expression is in quotes in the Admiralty Manual of Navigation in the early 20th century? There is a reason for this. It's misleading slang. It doesn't describe what it is or what it does. By the way, there was an equally puzzling American slang for this sort of sight and its output, and I don't mean "time sight" which is the modern name. The process was known historically in American navigation culture as a sight to "regulate the watch". By that they meant taking a sight and analyzing it to produce local time which would then be compared against a common watch to "regulate" it --that is, to determine its error. Suppose your watch says 9:05:30 AM. It's close to local time, because you set it at the call of "noon" the previous day, but thanks to the uncertainty in the time of noon (plus or minus five minutes easily) and equally importantly, because you have been sailing for some 21 hours since that previous local noon, your watch time is not an accurate measure of local time. So you take a sight, the calculation yields the correct local time, may 9:02:20, and that accurate local time let's you correct or "regulate" your watch by assigning it an "error" of 3m10s fast. That "regulated" local time is then compared with some measure of Greenwich time, either immediately or after some elapsed time time to get the longitude. Today, the process and calculation of local time from a morning or afternoon Sun sight (and by extension, similar sights of other bodies) is known almost universally in navigation as a "time sight" for better or worse. I should add that I rarely use this name in my classes even when I am teaching it, even when it "says time sight right there on paper". I prefer to call these "sights for sundial time" or "sights that turn our sextants into sundials" since, with any luck, these expressions explain what's really going on. As with all things, it depends on the student.

    Frank Reed

       
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