During 2021, my #allsky camera took an photo of the sky from the Netherlands every 15 seconds. This image combines the 2.1 million images into a year-long keogram, showing the length of the night change during the year, the motion of the Sun and Moon, and lots and lots of clouds.
In a keogram the pixels along the local meridian, the line along the sky from South to North, are plotted against time, as shown in this video. Keograms were developed for the study of Northern Lights, see blog.aurorasaurus.org/?p=1229 for more information.
During a clear night and day, a keogram will show the stars move through the meridian, with the constellations mirrored left to right. Here is the keogram for February 2nd, 2021, with the constellations of Orion, Ursa Major (Big Dipper), Leo, Bootes, Auriga and Taurus labelled.
Unfortunately, weather in the Netherlands means that the sky will be cloudy, giving keograms like this. This was for June 5th, starting at 16:00 local time. Notice how the night is a lot shorter now compared to February.
For each day, the keogram combines some 5760 individual images, and combining all daily keograms for 2021, gives the final year-long keogram.
The diagonal bands that occur roughly every month is the Moon moving through the sky, going from first quarter in the evening sky to last quarter in the morning sky. Note how the Moon is brighter during winter because it is higher in the sky.
Zooming in on the full keograms from January 19th (top) to February 2nd (bottom) shows the motion of the Moon a bit better. Occasional lunar halos are also visible, as are the clouds moving through the sky and raindrops on the camera dome (the horizontal lines).
The #allsky camera consists of an @zwoasi ASI178MC camera with a fisheye lens and a @Raspberry_Pi computer powered over power-over-ethernet, all in a weather proof enclosure. The hardware and software design is based on that of Thomas Jacquin. thomasjacquin.com/make-your-own-…
The camera takes an image every 15 seconds, using automatic exposure and gain control to control the camera sensitivity. The @Raspberry_Pi also controls a dome heater and a fan through a relais to manage dew on the dome and heat in the enclosure (max temp measured was 72 deg C).
It's also interesting to compare the keogram to the @SkyandTelescope's Skygazer's Almanac for 2021. The Almanac is for 50 deg North, whereas I observed from 53 deg North. shopatsky.com/products/2021-…
The raw keogram with full vertical resolution is now on @ZENODO_ORG. It covers 366 days (January 1, 2021 upto January 2, 2022) and starts at 00:00UTC. It's 1440 by 329400 pixels (378MB), so your browser may not be able to show it. zenodo.org/record/5828349
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