NavList:

I wrote previously:
"If the goal is to preserve as much as possible of the simplicity and familiarity in the clearing process that comes from this longitude by lunar altitudes system, and I think we all agree that this is appealing to navigators raised on standard late-20th-century LOP navigation..."

George H, you wrote:
"Why on Earth would we all agree about that? I, for one, disagree strongly."

Yeah, but George, if I said the sky is blue, you would "disagree strongly". That's normal for you. :-)

But let's dissect things word-by-word, just for fun. I said that "this is APPEALING to navigators..." I have found that this is the case by experience talking with navigators (and navigation enthusiasts), not by declaring it to be so. And it's hardly surprising that people "raised" on LOP navigation would find it easier to understand and easier to relate to the concept of getting longitude by observations of the Moon when they can fit it into the LOP navigation scheme that they already understand. And for that matter, most of the people who have brought this idea up over the decades, Letcher, Chichester, etc. --even that guy back in the 1840s (have to look him up again)-- has said pretty much the same thing. If we're using tools from the same toolbox, then the work is easier. That's why it's "appealing" to navigators.

You asked rhetorically:
"Why is longitude-by-lunars being taught, I ask? Not, these days, to obtain a qualification."

Of course. That ended over a century ago and even then it was long over-due --an echo of a navigational method which had fallen out of use (at sea) 50 to 75 years earlier than that.

And you wrote:
"Nor, presumably, as an emergency backup, nowadays, when everyone in a lifeboat is likely to have a sufficiently precise timepiece strapped to his wrist."

And they don't even need those since people unfortunate enough to end up in a lifeboat "nowadays" aren't expected to navigate at all. They're expected to sit tight and wait for rescue. But I agree with your general comment that everybody has a watch, and we really don't have to worry too much about time anymore. I've often said --and said so very plainly!-- on NavList that I don't believe anyone is ever going to lose GMT again, in any meaningful navigational sense.

And you wrote:
"Nor for those who just want to measure lunar distance to test-out their prowess with a sextant, but live too far inland from a sea horizon; for them, Frank's lunar distance website will suffice."

In a number of posts over the past several years, you've appeared to suggest that the lunars calculator on my web site is not relevant to someone "really" interested in lunars. I think that you've fundamentally missed the point. The lunars calculator on my site is simply a tool to make the work easier. If you're analyzing historical lunars, you certainly wouldn't want to work them out long-hand, except maybe one or two to find out how it works on paper. If you're learning about lunars, for historical interest or for modern interest, you wouldn't want to waste hours on paper calculations until and unless that becomes your specific focus. For those unfamiliar who may be following along, this is software which I wrote that clears lunars, quickly and as exactly as possible, for any date from the late 18th century through the near future. You can get to it here: http://www.historicalatlas.com/lunars/

And George, you wrote:
"The only reason for learning, and for teaching, the lunar-distance technique is because of its historical significance."

I wholeheartedly agree that this is ONE excellent reason for learning about lunars, and it's the one that appeals to me, but it's not the only reason. Some people enjoy being prepared even for extremely unlikely events like losing GMT. They're a rather small group. In my experience, I think the largest fraction of people who take up an interest in lunars are just interested in learning a new and challenging way of using their sextants and their skills to do something different and interesting in navigation. In other words, they do it out of general enthusiasm for the subject, a desire to become a real expert, or even simpler, but I don't want to trivialize this too much, they do it for fun. And there's nothing wrong with any of these motivations. They're just different "market segments", just different types of students with their own interests. I'm willing and happy to talk with anyone and anybody about this topic, and I'm always open to consider their reasons for taking an interest in lunars or any aspect of celestial navigation. Naturally, at the same time, if I think they have mistaken expectations, like imagining that they really need lunars in order to do practical celestial navigation (whatever that is in the GPS era), then I will advise them to re-think the matter. But it's up to them to decide, not me.

You added:
"It's a historical subject, and a fascinating one, but it belongs entirely to the past. If anyone wishes to repeat such observations today, it's entirely because in doing so, he is following the path of his forebears, who had no alternative, until they were rich enough to possess a chronometer (or three)."

I agree with you that this is the most logical reason to explore lunar distance sights, and it's the one that I emphasize when I teach or demo lunars. But as I have said above, people take up an interest in lunars mostly out of general enthusiasm for celestial navigation. That general enthusiasm opens the door to all sorts of variations. For example, some people enjoy working lunars using Bruce Stark's tables. Those tables are based on an entirely novel method for clearing lunars, quite unhistorical. I can't recall --did you ever complain that people were engaging in something unhistorical by using Bruce Stark's tables?? Then there are people who enjoy working lunars using software tools for the calculations. Those folks are interested in the manipulation of the sextant, the sight-taking process itself, but not so interested in the paper calculations (at least not yet). Others are interested in the general process of finding GMT from celestial observations. It gets them thinking.

You wrote:
"So why, if a student is to learn about measuring lunar distance, should he be taught a method that, because of its inferior performance, no mariner ever used?

First, longitude by lunar altitude's performance is not always significantly inferior. But the basic answer to this question is that it provides an example of the general principle: you can determine longitude by using the rapidly-changing position of the Moon. And if it's done under the right circumstances, it works great. For some people interested in navigation, that's all they want or need.

You also wrote:
"If he leaves the class, having learned that lunar distances were measured by observing altitudes above the horizon, and not angles across the sky, he will have learned an untruth."

Well, what you have right there, George, sounds like a complete FANTASY. No one I know of is teaching anything of that sort. Do YOU know someone who is teaching lunars this way?? Or were you just engaging in a little innuendo?

I am running out of time for this evening, so I am going to stop here. I will reply to the rest of your message tomorrow.

-FER
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