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Indeed, the keogram is the observed version of the S&T almanac. In the high resolution zoomable version at astron.nl/~dijkema/keo... you can even see the motion of the stars and planets. This part of the keogram shows Mars (left) and Jupiter (center) moving earlier in the sky.

A zoom of the 2025 keogram on the end of January, beginning of February, showing the motion of stars and planets.

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Well spotted! That is because the Earth's orbit around the Sun is elliptical and the inclination of the Earth with respect to its orbit, resulting in the Sun passing through the Southern meridian early/late depending on the time of year (see the yellow line at 12h). en.wikipedia.org/wiki/Equatio...

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This plot shows the exposure time and gain (camera sensitivity) used by the camera for one night, when compared to the keogram for that night. Sunset and sunrise are at the red lines. The camera remains sensitive to colors during evening and morning twilight.

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For the 2024 keogram I compared the observed keogram with predictions, where the yellow lines show sunset (dash-dotted), sunrise (dotted) and when the Sun is in the South (solid line), while the red lines show the same for the Moon. They match though the camera is sensitive to color into twilight.

A comparison of the 2024 keogram with predictions for set (dash-dotted line) and set (dotted line) of the Sun (in yellow) and the Moon (in red). The solid yellow line is when the Sun culminates in the South.

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This is the 5th year that the all sky camera has been running 24/7/365, and hence the 5th year-long keogram I've been able to make. These are the keograms from 2021, 2022, 2023 and 2024. The hourglass shape is the same, but the diagonal bands of the Moon shift from year to year.

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In the year-long keogram, 365 of these daily keograms are concatenated vertically to make up the full keogram. This image shows the 2021 keogram and daily keograms and separate all sky images for 3 separate days spread throughout the year.

The year long keogram on the right hand side is made up of 365 daily keograms, of which three on the right show differences throughout the year.

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In a keogram, the pixel values along a line running (approximately) from South to North are extracted from each image and concatenated in time. This video shows 24 hours of images, and the resulting keogram. It shows the colors of the night and day and the passage of the Sun, Moon and stars.

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Sometimes can camera captures rare events, such as Aurora borealis (Northern lights), an Earth grazing meteor, or even the atmospheric re-entry of a Space X rocket.

Northern lights showing a red to green curtain high in the sky.

The long luminous trail of an Earth grazing meteor. These only graze the atmosphere and don't completely burn up, resulting in these long trails.

The atmospheric re-entry and breakup of a Space X Falcon 9 rocket.

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Every 15 seconds, the camera takes a picture of the entire sky such as these, showing the Sun, Moon, stars and their constellations, but being in the Netherlands, lots of clouds. The exposure & gain of the camera are automatically adjusted, to 15 seconds at night, and 32 microseconds during daytime.

A daytime view from the camera, showing the Sun, blue sky and clouds.

A night time image showing thin clouds, the Moon with a halo around it, and a satellite passing to the right of the Moon.

On clear moonless nights, many stars are visible. You can make out the constellation Orion in the bottom right, and Ursa Major (the big dipper) in just left and above the center. The Milky way is faintly visible on the right hand side of the image.

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The all sky camera consists of a 6 mega pixel astronomical color camera from ZWO with a fish-eye lens that is controled by a Raspberry Pi mini computer and housed in a weather proof enclosure with an acrylic dome. The computer also controls a relay to enable a fan and a dew-heater against moisture.

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Cees Bassa @cbassa.bsky.social · 01/01/2026

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.

The image shows the hourglass shape of the length of the day and night over the 365 days in 2025. Diagonal bands indicate when the Moon was up in the night sky.

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Happy new year! My all sky camera imaged the sky every 15 seconds and this picture shows what happened in the sky in 2025. It shows the length of the night and day with the hourglass shape, the monthly lunar cycle with the diagonal bands, the elevation of the Sun at local noon, and lots of clouds.

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Cees Bassa @cbassa.bsky.social · 09/05/2025

Two days too late and perhaps only funny for those speaking Dutch. (H/T Gemma Janssen.)

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Cees Bassa @cbassa.bsky.social · 20/04/2025

Original paper is at ui.adsabs.harvard.edu/abs/1967AJ..... and our simulations could reproduce the observed curves for all their observing dates. The backscatter power relation we used is from Evans & Hagfors (Radar Astronomy, p306).

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Cees Bassa @cbassa.bsky.social · 20/04/2025

Thanks for the independent analysis! The doppler spread curve is one that we had looked at to estimate the loss in the link budget, which was about 3dB in 1Hz. Using Arecibo radar measurements of Venus from 1964 we could reproduce the delay-doppler curve from Dyce et al. 1967 (red points).

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Cees Bassa @cbassa.bsky.social · 10/04/2025

A bit late, but here is some additional analysis of the Earth-Venus-Earth radar experiments with @radiotelescoop.bsky.social from March 22nd, 2025. It takes the 4 recordings at the Dwingeloo and Stockert telescopes and searches in Doppler frequency and Doppler rates for the radar reflections.

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Cees Bassa @cbassa.bsky.social · 01/04/2025

This video shows the Moon occulting several stars from the Pleiades star cluster (M45) earlier this evening. The 40 minute observing run is condensed into 40 seconds. The brightest star is Merope (23 Tau) at magnitude 4.2. Now to work through 20GB of timestamped images to extract occultation times.

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Cees Bassa @cbassa.bsky.social · 01/04/2025

Some how I completely missed the fact that the Moon was going to occult several of the stars in the Pleiades. I managed to quickly put together a CMOS camera and a 300mm lens to capture the motion of the Moon across these stars at 10fps. Here's the occultation of the 8th magnitude star HD23361.

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Cees Bassa @cbassa.bsky.social · 06/03/2025

Zooming in on the final minutes of the descent burn, we can see the braking burn transitioning into a hover around 17:28UTC and then a slower descent. At 17:28:45UTC there's a jump in frequency and then a slower leveling off to the Doppler frequency of the Moon. Congratulations on the landing!

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Cees Bassa @cbassa.bsky.social · 06/03/2025

This spectrogram shows the signal from when #IM-2 emerged from behind the Moon around 16:30UTC, and then started its descent burn at 17:16UTC. The signals faded a bit during powered descent, but around 17:28:55UTC the frequency drift stopped, indicated it had successfully landed!

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Cees Bassa @cbassa.bsky.social · 06/03/2025

For the second time this week, the @radiotelescoop.bsky.social had a front row seat on a lunar landing attempt. This time by @intuitivemachines.bsky.social #IM-2 lunar lander. We listed to Doppler effect on the S-band signals at 2210.6MHz during its successful descent to the lunar surface.

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As we've seen with other spacecraft near the Moon, we also see reflected radio signals from the lunar surface as the fuzzy signals above the carrier signal from 08:26 to 08:33UTC. When the velocity of the spacecraft decreases, these signals merge with the carrier as they have the same Doppler shift.

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The zoomed in plot shows the observed line-of-sight Doppler shift during the landing burn, until terminal guidance around 08:32UTC, and the wobble during landing guidance around 08:33UTC. Landing is at 08:34UTC and the Doppler shift then stabilizes as it follows that of the Moon.

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While the signal is broadband as it carries data (left plot), squaring the recorded voltages successively reveals carriers (middle and right plots). This is because the data is phase modulated, masking the carrier frequency. Squaring the data removes this and shows the carrier signal.

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With the #BGM-1 lander from @firefly-aerospace.bsky.social now safely on the surface of the Moon, we've had some time to take a closer look at the @radiotelescoop.bsky.social's observation of the #BGM-1 signal during the landing, which shows several events during the landing sequence.

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The radio signals show a brief dip in signal strength around the space craft pitch over just before landing around 08:35UTC and then remaining constant after the successful landing. Lunar surface operations appear to have started with a change in the signal modulation at 08:47UTC.

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Cees Bassa @cbassa.bsky.social · 28/02/2025

Tracking the @firefly-aerospace.bsky.social Blue Ghost MIssion 1 #BGM1 lunar landing with @radiotelescoop.bsky.social. The effects of the descent burn are becoming visible in the Doppler data.

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For those in Western Europe, check out the Western sky right now! There's some green cloud display happening. This is a video of the last 30 mins (19:30 to 20:00UTC). It's unclear to me if these are Northern Lights or some freak Noctilucent Clouds.

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Cees Bassa @cbassa.bsky.social · 19/02/2025

Last night at 03:45UTC a Falcon 9 rocket body re-entered the Earth's atmosphere over Europe. My all sky camera caught it breaking up into several pieces and leaving luminous trails. This Falcon 9 launched Starlinks on February 1st, and apparently the upper stage did not de-orbit after launch.

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To clarify what is exactly happening, this figure compares the keogram with predictions for rise and set times of the Sun and the Moon.

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Combining the 8.4 million individual exposures (2TB of data) into a single keogram covering the 4 years from 2021 upto 2025 shows the repeated change in length of the night, and also highlights the small differences in sunset and sunrise times due to the eccentric orbit of the Earth around the Sun.

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It is interesting to compare the shape of the 4 separate year-long keograms. The shape of the hourglass stays the same, but the diagonal bands of the Moon moving over the sky change from year to year.

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The all-sky camera consists of a ZWO ASI178MC color camera with a 2.5mm F/1.2 fish-eye lens. A small Raspberry Pi computer operates the camera and sets the exposure time and camera gain based on the sky brightness. It also controls a dew heater and a fan to prevent condensation on the acrylic dome.

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During 2024 there were two nights with Northern Lights that were relatively clear. The keograms of those nights captured the colors and motion of the Aurora Borealis. Keograms were specifically designed to study the Aurora: victoriaweather.ca/keogram.php.

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Similarly, the stars move across the sky. During June, when the nights on the Northern hemisphere are short and the sky does not fully darken, the bright star Vega is high in the sky. Over these 12 daily keograms, we see Vega moving slowly left by 4 minutes every day.

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Zooming in on the daily keograms, the motion of celestial objects becomes clear. These daily keograms from January 16th to February 2nd 2024 show the Moon moving across the sky. It starts at sunset near first quarter, culminates around full moon, and ends at sunrise near last quarter.

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The year-long keogram is constructed from daily keograms, where each daily keogram takes the central pixel column of the all-sky images of each successive image to show motion in the sky. This video shows the all-sky images for a 24h time span and the resulting keogram shown below.

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