From Wikipedia, the free encyclopedia:

A keogram
("keo" from "Keoeeit" – Inuit word for "Aurora Borealis") is a way of displaying the intensity of an auroral display, taken from a narrow part of a round screen recorded by a camera, more specifically and ideally in practice a "whole sky camera". These images from the narrow band, which usually face up in the north-south orientation in the Northern Hemisphere and the south-north orientation in the Southern Hemisphere, are collected and form a time-dependent graph of the aurora from that part of the sky. This allows one to easily realize the general activity of the display that night, whether it had been interrupted by weather conditions or not, and allows the determination of the regions in which the aurora was seen in terms of latitude and longitude of the area.

The use of keograms started in the 1970s by Eather et al. to allow a more practical and efficient way of determining the activity of the aurora throughout the recorded night and provide a view of the detailed movements of it, the light of which is also recorded in wavelengths outside of the human visible spectrum. Thus, keograms are also used to analyse the conditions of the equatorial plasma bubbles (EPB) in the ionosphere of the Earth, to estimate its zonal drift at lower latitudes.

This animation illustrates the construction of a keogram. Keogram image generated from the center column of pixels of 997 sequential RGB images using author's software. Each image was a 2 second exposure. Captured at Midnight Dome, Dawson City (Lat 64.067, Long -139.396), on the night of September 6/7, 2021 using an AurorEye portable all-sky imaging camera. Compressed vertically from a 4000px to 240px height.

Date: 7 September 2021
Source: Jeremy Kuzub at Wikimedia

https://en.wikipedia.org/wiki/Keogram

FYI: TOPIC> Auroras
https://defcon.social/@grobi/114646611195811889

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2022 March 21

The Sky in 2021
* Image Credit & Copyright: Cees Bassa (Netherlands Institute for Radio Astronomy)
https://www.planetary.org/profiles/cees-bassa
https://www.astron.nl/about/

Explanation:
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.
https://www.nesdis.noaa.gov/about/k-12-education/optical-phenomena/what-solstice
https://apod.nasa.gov/apod/ap220320.html
https://skyandtelescope.org/astronomy-news/how-bright-moon-exactly/
https://apod.nasa.gov/apod/ap220301.html
https://spaceplace.nasa.gov/blue-sky/en/
https://commons.wikimedia.org/wiki/File:Keogram_explainer.gif
https://victoriaweather.ca/keogram.php#:~:text=What%20is%20a%20keogram
https://apod.nasa.gov/apod/ap011119.html

https://apod.nasa.gov/apod/ap220321.html

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2025 December 21

Solstice on a Spinning Earth
* Image Credit: Meteosat 9, NASA, Earth Observatory, Robert Simmon
https://www.eumetsat.int/our-satellites/meteosat-series
https://www.nasa.gov/
https://earthobservatory.nasa.gov/
https://www.nasa.gov/centers/goddard/about/people/RSimmon.html

Explanation:
Can you tell that today is a solstice by the tilt of the Earth? Yes. At a solstice, the Earth's terminator -- the dividing line between night and day -- is tilted the most. The featured time-lapse video demonstrates this by displaying an entire year on planet Earth in twelve seconds. From geosynchronous orbit, the Meteosat 9 satellite recorded infrared images of the Earth every day at the same local time. The video started at the September 2010 equinox with the terminator line being vertical: an equinox. As the Earth revolved around the Sun, the terminator was seen to tilt in a way that provides less daily sunlight to the northern hemisphere, causing winter in the north. At the most tilt, winter solstice occurred in the north, and summer solstice in the south. As the year progressed, the March 2011 equinox arrived halfway through the video, followed by the terminator tilting the other way, causing winter in the southern hemisphere -- and summer in the north. The captured year ends again with the September equinox, concluding another of the billions of trips the Earth has taken -- and will take
-- around the Sun.
https://en.wikipedia.org/wiki/Terminator_(solar)
https://www.youtube.com/watch?v=LUW51lvIFjg
https://spaceplace.nasa.gov/all-about-earth/en/
https://en.wikipedia.org/wiki/Geosynchronous_orbit
https://en.wikipedia.org/wiki/Meteosat
https://science.nasa.gov/ems/07_infraredwaves/
https://time.gov/
https://apod.nasa.gov/apod/calendar/ca1009.https://apod.nasa.gov/apod/ap220321.htmlhtml
https://science.nasa.gov/earth/
https://spaceplace.nasa.gov/seasons/en/
https://science.nasa.gov/kids/earth/which-pole-is-colder/
https://en.wikipedia.org/wiki/Solstice
https://defcon.social/@grobi/115754395753301984
https://www.universetoday.com/articles/why-are-there-seasons
https://apod.nasa.gov/apod/ap220321.html

https://apod.nasa.gov/apod/ap251221.html

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19.12.14 at 02.00 PM Peaio’s Bicycle Path (Belluno, Italy).
The Sun was already behind the mountain.
Close to the winter solstice.
They looks like the lines of a car park. They actually are composed of the ice on the road after a short passing of the Sun (less than a hour), leaving the fence’s shadows printed on the ground.
Surprising natural geometries!

On February 2015 we found the opposite situation, white and black: the shadow and the snow.

Music: "Peppino Impastato" composed and performed by Paolo Battaglia.
Maker: Marcella Giulia Pace

https://greenflash.photo/portfolio/tatoo-solar/

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2025 December 20

A Solstice Sun Tattoo
* Image Credit & Copyright: Marcella Pace
https://twanight.org/profile/marcella-giulia-pace/confirmed-photos/page/2/
https://greenflash.photo/
https://www.ragusah24.it/2025/09/12/un-altro-prestigioso-premio-per-la-fotografa-marcella-pace/

Explanation:
The word solstice is from the Latin for Sun and to pause or stand still. And in the days surrounding a solstice the Sun's annual north-south drift in planet Earth's sky does slow down, pause, and then reverse direction. So near the solstice the daily path of the Sun through the sky really doesn't change much. In fact, near the December solstice, the Sun's consistent, low arc through northern hemisphere skies, along with low surface temperatures, has left a noticeable imprint on this road to the mountain town of Peaio in northern Italy. The morning frost on the road has melted away only where the sunlight was able to reach the ground. But it remains in the areas persistently shadowed by the fence, tattooing in frost an image of the fence on the asphalt surface.
https://apod.nasa.gov/apod/fap/ap251220.html
https://apod.nasa.gov/apod/ap250102.html
https://earthsky.org/astronomy-essentials/everything-you-need-to-know-december-solstice/
https://apod.nasa.gov/apod/ap110423.html
https://greenflash.photo/portfolio/tatoo-solar/

https://apod.nasa.gov/apod/fap/ap251220.html

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