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Inspired by @cbassa.bsky.social, I simulated a 2025 keogram for the Netherlands using skymodelr in #RStats. Each strip spans a day, showing seasons and lunar cycles. The package models sunlight, moonlight and atmospheric scattering, with adaptive exposure here to show day and night together.

Tyler Morgan-Wall

@tylermw.com

Here the simulation alternates with Cees’s observations. The red line is just a guide to the Prague model’s twilight limitation: solar sky radiance stops at -4.2 degrees, leaving a gap to the red line at -10 degrees, which overlaps just about perfectly with the original.

27/10/26, 4:55 pm1 repost3 likes

Tyler Morgan-Wall

@tylermw.com

20h

Cees Bassa’s thread explaining how he made the original keogram and how to interpret it: mastodon.social/@cgbassa/115...

mastodon.socialCees Bassa (@cgbassa@mastodon.social)Attached: 1 image Since posting this 2025 year-long keogram, there have been quite a few questions asking how it was created and what is visible. In this thread I'll try to explain how it all works.