Under Hossi's influence

 tl;dr - On the nights of December 10th, 13th, and 14th, 2025 we decided to target the small asteroid "Hossi", named after the German physicist and influencer Dr. Sabine Hossenfelder. Altogether, we collected 81 light frames with an exposure time of three minutes each along with the corresponding calibration frames. This allowed us to follow the asteroid's path over half a degree in the sky in the constellation Cetus.

If you read the "Discovery Circumstances" section for the asteroid Hossi on the JPL Small Body Database browser you'll find: 

"Sabine Karin Doris Hossenfelder (b. 1976), nicknamed “Hossi” in school, is a German physicist, philosopher of science, author, science communicator, musician, and singer. She has authored several books about fundamental physics, cosmology, and philosophy."

Dr. Hossenfelder conducts her work as a science communicator mainly through her YouTube channel and thus some of the members of astrocusanus were familiar with her. This inspired me to suggest searching for the asteroid Hossi that was named in her honor. 

Image 1: Our 16-inch telescope pointing at the sky in search for Hossi.

Image 2: Miriam, Tommy and Katharina opening the roll-off roof at the beginning of the night.

Hossi isn't a bright object. If it were at a distance of one astronomical unit (1 AU) both from Earth and from the Sun, it would shine at a (so called absolute) magnitude of ~15. However, in December 2025 the celestial geometry was far less favorable and thus its brightness was just slightly above 19 mag. This is 150,000 times dimmer than the faintest stars visible to the naked eye. From our previous experience with the search for asteroids we knew that hunting down such an faint asteroid was a feasible task for our telescope, however, the initial idea to obtain a rotational light curve and thereby determining the asteroid's rotational period had no realistic chance of success. That job would require a significantly bigger telescope aperture. 🔭💰💰💰

The procedure was straightforward: We extracted the coordinates from the JPL website, entered them into the interactive sky map Wikisky and looked for cataloged stars near the asteroid's position. We picked HD16313, a 8.5 mag star in Cetus (the whale), and slewed the telescope to its position. Because of the star's brightness it immediately stood out on the looping short exposure sequence. From this starting point we slowly slewed eastward, swinging along some more or less remarkable star groups, chains or doubles, we could recognize on both Wikisky and our live view from the camera.

Once arrived at the presumably correct sky region, the asteroid remained invisible as expected. We knew in order to discern such a dim object we would need to collect more light. So we started a sequence of three-minute exposures, but even on these images it was a tough quest identifying the right tiny dot among all the other stars, the one that had no corresponding match on Wikisky.

While the holy trinity of mount, telescope and camera was doing its job, we started investigating Dr. Hossenfelders life. We checked her entry on Wikipedia, looked at two of her videos, and finally, I gave a quick overview of the key concepts of quantum mechanics and gravity, the main research fields of "Dr. Hossi". 

About 1.5 hours later we ended the exposure sequence and checked if the tiny dot we alleged to be Hossi had moved. It had, so it was indeed our object of interest! Mutual pats on the back were appropriate and extensively exchanged. ✌️😎

Image 3: The track of asteroid Hossi wandering through the constellation Cetus.
From left: 10.12., 13.12. and 14.12.2025

Image 5: The beautiful spiral galaxy IC1825 at a distance of approximately 230 million
light-years was a nice bycatch to our hunt, as well as the asteroid on the left side of the image.
The streak of light on the right originates from a bright star just outside of the field of view.

Image 5: Talking about quantum physics and gravity at our school's observatory under the watchful eyes  of Dr. Sabine Hossenfelder on the display.

Image 6: Working on our data back at the school.

Video 1: Timelapse video of Hossi on the night of the 13.12.25.

At the time of writing of this blog article Hossi has fled any further scientific advances from our side. It is now in the constellation Aries and its brightness has faded by another magnitude. However, it certainly  can't flee the solar system and thus cannot elude us forever. According to the JPL ephemeris, in March 2027 the asteroid will shine at around 17.4 mag at opposition. In September 2028 it will be at 17.3 mag, and in May 2031 it will even reach 17.0 mag. Then, at the latest, we will give that idea of the rotational light curve another shot! 💪📈

Christof Wiedemair