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    Re: Quick Estimate of Sun Declination: analemmas?
    From: Frank Reed
    Date: 2018 Apr 5, 09:02 -0700

    Hello Max M.,

    You wrote: "Just use an analemma!"

    Yes, but can you draw one from scratch with minimal memorized data? The circle or quadrant diagram for declination requires only data that we all have already learned: dates of equinoxes and solstices and range of the Sun's declination. It's low accuracy -- good for planning and estimation.

    In all of my navigation classes, I talk about analemmas extensively and include one in every set of handouts. I also include a long-term sun almanac which gives the Sun's declination and equation of time (or GHA at midnight or noon GMT in some cases, which is equivalent to equation of time) for four years. That's the same data that's included in the analemma, and it fits on two sheets of paper, printed double-sided. For comparison a readable analemma requires one sheet of paper, double-sided. The analemma can be read to an accuracy of 0.1-0.2° while the long-term almanac can be read to its nominal printed accuracy which is on the order of 0.01°. Which option is better? I firmly believe that from a pedagogic point of view it's nice to have it both ways. In fact, it takes more training to use the analemma, but it's more "fun" in many ways. But this sort of data cannot be recreated reliably from scratch. You either have it printed out, or you don't.

    You wrote:
    "By the way has anyone noticed that  globe manufacturers no longer include the analemma on their globes? I was in a Globes and Maps shop in Tucson recently and none of the salesman knew what an analemma was."

    Yes. It seems that mostly American globe makers were still including analemmas on their products in the 20th century. They stopped post-war, so it's been something like fifty to seventy years since they were common on globes. Some also included "oval analemma" which displayed declination only. Why? Well, who knows... It was a marketing decision decades ago. Another question for you to ponder, Max: why were they printed on globes in the first place, and when did that practice start? I've got some preliminary data on that one. Also, who decided to refer to these graphics as "analemmas"? They weren't called that until globe manufacturers began adding them to globes, and the name "analemma" referred to something rather different. 

    I keep an eye out for analemmas in pop culture. There's an old globe in the TV comedy series "How I Met Your Mother" (2005-2014) as a background prop. It's frequently rotated so that the analemma in front and center. The survival show "Survivorman" (2004-?) featured an analemma in the opening credits.

    Frank Reed

       
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