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    Re: Indian Astronomical Ephemeris as a "Retro Almanac"
    From: Frank Reed
    Date: 2019 Jun 28, 20:20 -0700

    Brad, you wrote:
    "That's going to make it difficult to pick it out with your sextant, even under the best of circumstances. Does a sextant have sufficient light gathering characteristics to observe Pluto? I will go out on a tiny limb and say no, but will also readily admit I don't know the true answer"

    Sure. You just need a larger than average star scope. Something with an aperture of 8 inches should be sufficient with correspondingly large index and horizon mirrors. Then you can shoot Pluto altitudes. :) But can you see the horizon when it's dark enough to see Pluto?! Ha ha ha. Yeah, it's all crazy.

    The problem here, of course, is that an "astronomical ephemeris" is a cousin of the standard "Astronomical Almanac" and not the navigators' "Nautical Almanac". But it's made much more confusing because of the old naming scheme. The astronomers' "astronomical ephemeris" was formerly known as the Nautical Almanac! The naming system had become flipped around by the end of the 19th century. Back in, let's say, 1939, no navigator would have used the volume titled (on the spine) as "The Nautical Almanac". Instead navigators used "The American Nautical Almanac" or "The Abridged Nautical Almanac" (British) or one of various commercial equivalents, which later merged to become our "Nautical Almanac". So while this "Indian Astronomical Ephemeris" is no doubt an interesting curio, I really don't think it has much relevance to celestial navigation.

    By the way, for Tony, while I was on Neil deGrasse Tyson's "StarTalk" we spoke at length about Moana (and some other movies --very little about actual navigation), and coincidentally Tyson is often counted as the "man who killed Pluto" (well before the IAU decision). And also coincidentally, my first "publication" in the world of science (when I was a teenager) was about demoting Pluto. That was back in 1980, and my point at that time was that other minor planets, formerly counted among the "principal planets", had already been demoted. Astronomy and celestial navigation books published c.1825 listed "eleven planets" in the Solar System. Four of those were demoted (informally but decisively) in later decades. The logic for demoting Pluto was reasonable in 1980 and remains reasonable today. At the same time, Pluto is indeed a "planet". It's a dwarf planet. It's a minor planet. Pluto is the "King of the Kuiper Belt". It is, so far, the brightest and largest of the Trans-Neptunian Objects, though Eris is the most massive by a significant margin. Pluto is one among many... If contingent history had gone just a little differently and Pluto had been discovered in the year 1995 instead of, by amazing luck, in 1930, the mistake would never have been made. Pluto would never have been counted as a major planet. Is it an extraordinary, even amazing, minor planet? Yes. But it's not a major planet.

    Frank Reed

       
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