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“The Sky in 2021”

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“What if you could see the entire sky -- all at once -- for an entire year? That, very nearly, is what is pictured here. Every 15 minutes during 2021, an all-sky camera took an image of the sky over the Netherlands. Central columns from these images were then aligned and combined to create the featured keogram, with January at the top, December at the bottom, and the middle of the night running vertically just left of center. What do we see? Most obviously, the daytime sky is mostly blue, while the nighttime sky is mostly black. The twelve light bands crossing the night sky are caused by the glow of the Moon. The thinnest part of the black hourglass shape occurs during the summer solstice when days are the longest, while the thickest part occurs at the winter solstice. Yesterday was an equinox -- when night and day were equal -- and the northern-spring equinox from one year ago can actually be located in the keogram -- about three-quarters of the way up.”

Visit the image copyright and hover your pointer over the image to see the annotations for this image.

Courtesy of Astronomy Picture of the Day
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I think you *are* getting it, Pat. Pat reach out to Jane English?

Really enjoyed this one, Bill! An interesting puzzle-solve, but also got a thrill of realizing that I "must" (ha! when it's me speculating...) be seeing the moonlit night bands across the dark cup shape...and then finding out I was right when I read the blurb. It also seemed it must be fairly far north, and then yes, Netherlands. Gratifying to think I may be starting to 'get' some limited bits of this!!



Thanks for the laugh !


Enjoyment is all that matters, Lowell. Understanding is optional. :-)

I understand the different measurement of day light and how it changes during the year but I will be damned if I get the other characteristics it shows. I'm just too dull to understand the implications of the study. I guess I need to move to a puzzle of Mikey Mouse and let my mind cool down. But I did enjoy the time I spent solving the puzzle. Thanks, Bill


I agree, it's great fun when someone has such a creative idea. And someone else has the sense to post it as a puzzle! :-o)

Great post, love it when someone has the genius to explain things so simply like Neil Degrasse Tyson.


Amazing what photography can show us !! Great puzzle, thank you, Bill. I hope you have a great day, you have made my day with this puzzle !!


This could be a chalice




You're amazing, Bill. I admire you and I hope that finding such puzzles brings you pleasure. I wish you the best for you right now.


Thanks Bill for another APOTD and information.


Sands through an hourglass...


What an evening gown this would make make in a softly shimmery fabric draped in a Grecian style!

Makes me think of Yeats: “Had I the heavens’ embroidered cloths / enwrought with golden and silver light / The blue and the dim and the dark cloths / of night and light and the half-light...”


Bill, this is remarkable!


Amazing graph of our solar nights and days with peeks of moonlight thrown in ;-) I looked at the link you provided, looks like there was a lot of moonlight the night of my birthday towards the end of January in 2021. Great celestial lesson, thank you Bill, great to be seeing you back here with your universal knowledge. Keep at rest my friend and regain your strength. Peace and health walk along with you my friend.

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