APOD: 2026 June 21 – Keogram: The Sky in 2025
Astronomy Picture of the Day
Discover the cosmos!<br>Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2026 June 21
Keogram: The Sky in 2025
Image Credit &<br>License:<br>Cees Bassa<br>(Netherlands Institute for Radio Astronomy)
Explanation:<br>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 seconds during 2025, an<br>all-sky camera took an image of the sky over the<br>Netherlands.
Central<br>columns from these images were then aligned<br>and combined to create the featured<br>keogram, with January at the top,<br>December at the bottom,<br>and the middle of the night<br>running vertically just left of center.
What do we see?
Most obviously, the daytime<br>sky is mostly blue, while the nighttime sky is mostly black.
The twelve<br>light bands<br>crossing the night sky are caused by the<br>glow of the<br>Moon.
The thinnest<br>part<br>of the black hourglass shape occurs during the summer<br>solstice, like<br>today,<br>when days are the longest, while the thickest part occurs at the winter<br>solstice.
Equinoxes can also be located in the keogram, for example<br>the northern-spring<br>equinox from one year ago is about<br>three-quarters of the way up.
Tomorrow's picture: Sun's future
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