Markus Pössel
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mpoessel.de
Markus Pössel
@mpoessel.de
13K followers 820 following 19K posts
Astronomy and relativity outreach (Tweets in German & English) | personal account | he/his | managing scientist @hausderastronomie.bsky.social | director @astro4edu.bsky.social |outreach @mpi-astro.bsky.social | Seestar enthusiast
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mpoessel.de
I've produced a lot of b/w figures for a book (general physics knowledge for Dummies, in German) with tikz recently; here are some random examples. :-)
Object rotating around an axis, with two orthogonal forces. Sketch of ballistic conduction Sketch of the Stern-Gerlach setup, with silver atoms flying in from the right, passing through a magnet, and the beam being split into spin +1/2 and -1/2 before landing on a screen Kepler's first and second law
January 7, 2026 at 12:32 PM
mpoessel.de
Die moderne theoretische Beschreibung von Elementarteilchen baut auf solchen Spin-Eigenschaften von Teilchen auf ("irreduzible Darstellungen der Rotationsgruppe"). Nachzulesen hoffentlich irgendwann im Laufe des Jahre in "Allgemeinwissen Physik für Dummies" :-) 3/3
Screenshot einer Buchseite, oben ist als Kapitel "Kapitel 22 Quantenfeldtheorie" angegeben, mit Standbildern des gedrehten Wanderschuhs und des Herumführens der Schnürsenkel.
January 4, 2026 at 2:42 PM
mpoessel.de
Heute habe ich ein Video von einem der für mich beeindruckendsten Physik-Miniversuche gemacht. Dazu habe ich einen Wanderstiefel an seinen beiden Schnürsenkeln aufgehängt. Eine doppelte Drehung des Stiefels lässt sich rückgängig machen, ohne die Orientierung des Stiefels zu verändern! 1/
January 4, 2026 at 2:42 PM
mpoessel.de
Ich mache hier mal eine Version des Posts von @masz.bsky.social mit ALT-Text.
Wir dürfen bei aller Aufmerksamkeit für Venezuela den Iran nicht aus dem Blick verlieren. Auch hier ist Europa bislang viel zu still geblieben, hat zu wenige klare Signale gesendet und zu wenig politische Unterstützung gezeigt. Europa muss den Menschen durch konkretes Handeln deutlich machen, dass es ein echtes Interesse an einem Wandel im Iran hat. Dort herrscht weiterhin ein brutales, illegitimes Unterdrückungsregime. Diese Zurückhaltung gegenüber Teheran muss ein Ende haben. Statt Schweigen und diplomatischer Illusionen braucht es eine klare politische Haltung: unmissverständliche Solidarität mit den mutigen Menschen im Iran, konsequente und wirksame Sanktionen gegen die Machtstrukturen des Regimes sowie eine substanzielle Unterstützung der iranischen Zivilgesellschaft und der Exilopposition. Ein Regime, das systematisch Menschenrechte verletzt, ist nicht reformierbar. Europa darf seine Werte nicht länger relativieren, sondern muss geschlossen, sichtbar und glaubwürdig handeln.
January 4, 2026 at 1:11 PM
mpoessel.de
I would argue those look like rather shallow craters :-)

Small asteroids are weird, and fascinating.

[Image credit: ISAS/JAXA, JAXA Hayabusa 2 ONC-T v-filter, Government of Japan Standard Terms of Use (Ver.2.0)]
December 30, 2025 at 12:07 AM
mpoessel.de
Here's today's version of my work-in-progress Orion mosaic. Cloudy skies tonight, so no upcoming additions. Keeping my fingers crossed for tomorrow night. And as you can see, I produced another gap, darn :-/ 🧪🔭⚛️
Mosaic consisting of image tiles. The constellation of Orion is visible, with its main stars (shoulder stars, feet, belt stars, sword with Orion nebula). There is a small gap to the left of the belt stars, where the images do not suitably overlap.
December 29, 2025 at 9:41 PM
mpoessel.de
And yes, I'm a bit annoyed I left that little gap under Beteigeuze. I will have to fix this today. :-(
Upper part of the left mosaic. The belt stars can be seen near the bottom of the picture, Betelgeuze as a bright red star on the upper left. Below left of Betelgeuze there is a thin horizontal gap where the images do not quite overlap.
December 28, 2025 at 5:29 PM
mpoessel.de
Another clear night ahead (although the Moon is getting more and more annoying), so I'll try to extend my #Seestar S30 Orion mosaic again. Shown is the version so far (left) and the version one day before. The difference is last night's haul :-) 🧪🔭⚛️
Two mosaics of sky photographs. The left is more complete than the right. The main stars of the constellation Orion are visible in both (shoulder stars, feet, belt, sword with the reddish Orion nebula).
December 28, 2025 at 5:29 PM
mpoessel.de
Conditions are not as good as yesterday, but I’ll try to grab some new tiles for my #Seestar S30 Orion mosaic. The image shows the mosaic’s current state (left), and the state before yesterday’s additions. 🧪🔭⚛️
Two still rather sketchy mosaics of the constellation Orion, but the one on the right has a few more holes than the one on the left.
December 27, 2025 at 5:02 PM
mpoessel.de
In parallel to the #Seestar S30 Orion mosaic work, the @hausderastronomie.bsky.social #Origin took a nice image of the Pacman nebula :-) 🧪🔭⚛️
A reddish nebula in the sky whose shape is similar to that of Pacman-in-profile: circular, with a wedge-shaped part missing.
December 26, 2025 at 11:17 PM
mpoessel.de
Catching some Pleiades while waiting for Orion to come into view. (There is an inconvenient building in the way, so I can only catch Orion between S and about SWW.) 🧪🔭⚛️
A cluster of bright stars. Around some of the stars, greyish-blueish wisps of starlight-reflecting dust are becoming visible.
December 26, 2025 at 8:26 PM
mpoessel.de
As things are looking right now, the sky will be clear enough for me to grab a few more images for my #Seestar S30 mosaic of the Orion constellation. It's a slow process (see image), but I'm making progress :-) 🧪🔭⚛️
Patchwork mosaic of astronomical images that trace about half of the main part of the constellation of Orion. Visible are the three starrs of Orion's belt, the "sword" stars including the Orion nebula, the right foot and the right shoulder (from the point-of-view of an observer looking up at the sky). There are some conspicuous holes.
December 26, 2025 at 7:48 PM
mpoessel.de
The "Big Dipper in 3D" installation in our "Astronomy for Everybody" exhibition started out as a toothpick-and-plasticine mock-up on a cardboard. :-) 🔭🎢
Yellow plasticine "stars" on toothpicks and plasticine bases on a cardboard. From the perspective of the photograph, they form the "Big Dipper".
December 21, 2025 at 3:01 PM
mpoessel.de
Genau um den Lesezugang geht es aber in der BOAI dort, wo der Begiff "open access" definiert und beschrieben wird. Siehe angehängter Screenshot. Den Effekt von Publikationsgebühren kann man ja durchaus darüber hinausgehend kritisch besprechen. Und dass open access geringere Gesamtkosten für 1/
Open access meint, dass diese Literatur kostenfrei und öffentlich im Internet zugänglich sein sollte, so dass Interessierte die Volltexte lesen, herunterladen, kopieren, verteilen, drucken, in ihnen suchen, auf sie verweisen und sie auch sonst auf jede denkbare legale Weise benutzen können, ohne finanzielle, gesetzliche oder technische Barrieren jenseits von denen, die mit dem Internet-Zugang selbst verbunden sind.
December 18, 2025 at 8:38 PM
mpoessel.de
There is no such thing as having too much spectral colors in your life :-) 🧪🔭⚛️
Setup with a prism producing ax spread of spectral colors Details of the spread of spectral colors produced by the prism
December 15, 2025 at 12:31 PM
mpoessel.de
This is nice. Reposting with ALT text.
Tense Christmas 1 The Ghost of Christmas Past Perfect Progressive Midnight. Awoken by a ghost. I thought I must be raving. He'd come to me so I could see how badly I'd been behaving. 2 The Ghost of Christmas Present Perfect Simple Later still, a ghost again with a much more recent scene. More evidence piling up of how unpleasant I have been. 3 The Ghost of Christmas Future Unreal Conditional Then, a final ghostly vision - but this one lacked the pain and strife. I saw if I could be a kinder man I would create a better life. Brian Bilston
December 14, 2025 at 10:01 PM
mpoessel.de
I think my intuition was wonky at that point. My starting point was the image I‘m attaching here, which I use to show the transition from terrestrial (cannon ball) to celestial physics, abd how for Newton it‘s all the same. I hadn‘t much thought about the other direction, namely speeds 1/
Idealized cannon on a sphere, firing horizontally at different speeds. At first, the results are eccentric ellipses, but for the fastest case shown, a circular orbit.
December 11, 2025 at 8:43 AM
mpoessel.de
Einige Strukturen seit deutlich mehr als 20 Jahren nicht!

(Aus https://heiup.uni-heidelberg.de/catalog/view/441/653/113243 S. 99.)
Schwarzweißbild der vorderen Partien desselben Hörsaals. Galerie und Pult/Tisch sind offenbar unverändert geblieben.
December 10, 2025 at 5:56 PM
mpoessel.de
Last lecture of 2025 done: check!
View from the back towards the blackboards in front in a slanted lecture theatre
December 10, 2025 at 4:48 PM
mpoessel.de
I've got my Pallas movie ready for tomorrow's lecture. Seestar S50 on 22 November, 2h 20m of (2) Pallas serenely moving through the outskirts of Aquarius. 🧪🔭⚛️
December 9, 2025 at 10:56 PM
mpoessel.de
Did I hear someone mention massive #earlymodern telescopes? de.wikipedia.org/wiki/Datei:T...
Contemporary image of Hevelius's 140 foot telescope, from "Machina Coelestis" (1673)
December 8, 2025 at 3:09 PM
mpoessel.de
Mir war nicht klar dass “Eulen nach Athen tragen” andockt an ein historisch belegtes “Athena trägt Eule [bzw. Käuzchen] herum”.
Ausschnitt aus einem griechischen Vasenbild. Athena trägt mit der rechten Hand einen Weinkrug und hält mit der linken ein Käuzchen als Körper, dem das Ganze dem Gesichtsausdruck nach zu urteilen nicht recht geheuer ist.
December 7, 2025 at 9:16 AM
mpoessel.de
No, the ISS looks completely different, and also moves a *lot* faster. This is a blob with a halo - a comet. But a special one: 3I/ATLAS which came to us from another star. :-)

I did capture the ISS in front of the Moon last March, though, with the same instrument, cf. below
November 23, 2025 at 3:55 PM
mpoessel.de
Astro peeps: Would you say that this here was probably a meteor? Given the greenish glow associated with it? Single Seestar S30 frame yesterday around 1:20 am. 🧪🔭🎢
Stars (the Pleiades) with a yellowish streak through them. The yellowish streak has a green nebulous feature along one side of it.
November 22, 2025 at 8:55 PM
mpoessel.de
Yesterday, there was a completely clear night here in Heidelberg, and between 5am and 6am, my trusty little #SeestarS50, patiently waiting on the balcony, managed to catch 3I/Atlas - so here's a little animation of an extrasolar object in motion :-) 🧪🔭🎢
November 22, 2025 at 7:15 PM