Longest and shortest solar day?

Factual Questions
21

In case anyone’s wondering about all this talk of “analemmas”: At any given moment, there’s some point on the Earth where the Sun is directly overhead. If you start at some moment, and mark that point on a globe, and then wait exactly 24 hours, it’ll now be a slightly different spot where it’s directly overhead. Continue that way, marking the location every 24 hours, and over the course of the year, those sun-points will trace out a figure 8 shape. That’s what that shape on the globe is. You could put it at any longitude, depending on what moment you chose as your starting point, but globe-makers usually put it somewhere in the Pacific Ocean (along with the manufacturer’s logo, and a legend of symbols, and so on), because there’s a whole lot of nothing there.

I wrote a program years back to generate analemmas, given axial tilt, eccentricity of orbit, and so on. I ought to dig that up, and see if I can get it to work again.

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23

You would have had an even smaller and skinnier northern loop and a fatter and taller southern loop.

Two symmetric loops, intermediate in width between the present-day loops.

24

I remember reading about a guy who took a photo of the sun every clear day for a year, exactly at noon (ignoring DST), not changing the film (in the days when photos were on film). Even though there were gaps from cloudy days, the images traced an analemma.

25

Dennis di Cicco, Exposing the Analemma, Sky & Telescope, June 1979, p.536–540.