Fig. 1: The most prominent lunar swirl with its proposed new name Galilaei Impulsus (currently named Reiner Gamma). Crater Galilaei lies to the northwest, crater Reiner to the east. Lunar Reconnaissance Orbiter Camera photographic map, 2011
Since 12 June 2024, I have proposed to return the original name to the most prominent lunar surface swirl and magnetic anomaly, Reiner Gamma, at 7.5°N 59°W, by renaming it to Galilaei Impulsus.
This page provides a detailed background on the history of the original name 1651, the renaming in 1834, the adoption of the new name in 1935, and why I consider the change in 1834 a scientific mistake that needs to be corrected.
In addition, I give a secondary reason for giving the swirl a dedicated name: its specific importance for human lunar surface exploration.
I propose to revert the informal name change of this feature done in 1834. Because originally in 1651 Giovanni Battista Riccioli named it Galilaei to honor Galileo Galilei, who died nine years earlier. In 1834 the name was moved to a nearby crater due to some formalism as only craters are named and not other visible features, which may have been outside of the contemporary scientific worldview: en.wikipedia.org/wiki/Galilaei_(lunar_crater)
In case a name addition is preferred instead of a plain revert to the old name: Galilaei Impulsus may be something to consider if Latin is the preferred language for surface features and would even fit its electric origin, because without electricity the magnetic field could never have been created. I am not a Latin expert. Suggestions for improvements are welcome!
Fig. 3: Giovanni Battista Riccioli: Almagestum Novum, 1651 e-Rara Swiss digitized rare books platform
With the publication of his Almagestum Novum in 1651, Giovanni Battista Riccioli, a contemporary of Galileo Galilei, honored him by naming a bright oval he saw on the Moon, Galilæus. The location was well chosen, near the Moon's western limb, surrounded by names of revolutionary discoverers like Copernicus and Keplerius in the larger area known as Sea of the Storms (Oceanus Procellarum). For his own crater Ricciolus, he selected a place at this sector's limb, next to his co-author's Grimaldus.
Almagestum Novum (The Greatest New) was not only considered by Riccioli himself as a follow-up to Ptolemy's Almagest. It was with its 1500 pages in two volumes also considered by the scientific community the largest compendia of astronomical knowledge of that era. Francesco Maria Grimaldi contributed to the work, especially regarding the lunar maps.
Fig. 5: Cassini and Jeaninet: Grande carte del Lune, 1788 National Library of AustraliaFig. 4: Homann and Doppelmayr: Tabula Selenographica, 1742 David Rumsey Historic Map Collection
Later lunar map publications like Tabula Selenographica by Homann and Doppelmayr in 1742 and Grande carte del Lune by Cassini and Jeaninet in 1788 preserved the Galilæus name at its original location near the crater Reiner, only changing the diphtong æ to e as Galileus.
Renaming in 1834: Reiner γ
Fig. 6: Johann Heinrich Mädler: Mappa Selenographica, 1834 Library of Congress
183 years later, Johann Heinrich Mädler's much more detailed Mappa Selenographica published by Wilhelm Beer in 1834, replaced the name Galilæus with a simple γ as third minor feature of nearby crater Reiner. The original name he modified from nominative Galilæus to genetive Galilæi and moved its location 150 km north-west, to a small crater that was not drawn on any previous map.
The reason and potential discussion for this change is undocumented and speculated to be a strict formalism he introduced with his map to only name surface relief features like craters, ridges, and graben. The feature he labeled Reiner γ was visible in his improved telescope as flat albedo-only marking without surface relief. Most likely he considered Riccioli's naming of a flat albedo-only feature a scientific mistake he had to correct, especially as previous observers were misinterpreting the color variations as relief.
Official Name Adoption in 1935: Reiner Gamma
Fig. 7: USGS, science for a changing world: Gazetteer of Planetary Nomenclature
Another 101 years later, the International Astronomical Union (IAU) adopted Mädler's naming and made Reiner Gamma the official name in 1935 for the global scientific community as the IAU's lunar nomenclature was considered the naming authority and still is today. The name Galilaei was kept at its new crater location 150 km northwest from Ricciolis intent, now known as Reiner Gamma.
A Historic Mistake
Fig. 8: Galilæus at same latitude as Reinerus in Almagestum Novum, 1651 e-Rara Swiss digitized rare books platform
It's clearly visible in all pre-1834 maps, how Galilæus was located at the same latitude as crater Reiner and not 150 km NW. The crater now known as Galilaei was not shown in any pre-1834 map as it was most likely invisible in early small telescopes.
Mädler in 1834 most likely suspected a scientific mistake by Riccioli due to the early weaker telescope. But today with our insight into all published maps of that time and even higher resolution photos, we can see how Riccioli was correctly seeing something at the same latitude as crater Reiner. He really saw the swirl we today name Reiner Gamma and honored his mentor Galileo Galilei by naming it after him.
Riccioli became later known, together with Grimaldi and Cassini, with their first proof of Kepler's elliptic orbit model by precise measurements at the long meridian line in the church Santa Maria degli Angeli e dei Martiri in Rome. Michal J. A. Paszkiewicz, the author of the 2023 Almagestum Novum english translation, speaks about those details in his 2025 presentation Riccioli: Sentinel of an Unshaken world.
The reason for Mädler's change was not documented by him. Such documentation would be considered today as minimum requirement to consider the renaming as scientific process.
Fig. 9: Galilaei Impulsus at same latitude as Reiner, crater Galilaei 150 km NW in LROC WA/NAC photographic map of Reiner Gamma, 2011
Given all that, my proposal is to revert the 1834 name relocation and the 1935 name adoption and return the honoring of Galileo Galilei to the original 1651 location.
To avoid confusion during future lunar excursions, I recommend to keep the name Galilaei at the small crater in the north-west and rename the lunar swirl from Reiner Gamma to Galilaei Impulsus.
Furthermore, the name component Impulsus could be introduced as new feature type name for all lunar swirls as for this type of albedo feature, no naming type yet exists.
A Natural Protective Force Field
Fig. 10: Simulation and visualization of the local magnetic field at Reiner Gamma NASA Scientific Visualization Studio, 2019
The underlying secret of the lunar swirls remained unknown until the Apollo missions in 1969. Only with the Apollo sub-satellite magnetometer measurements we know about the lunar magnetic anomalies which are located at each visible swirl. Not all magnetic anomalies produce a swirl, but the reverse is true.
Reiner Gamma is the largest and most prominent of all swirls with its albedo markers matching the pattern of iron filings above a bar magnet.
The surface brightening at the swirl location is a direct effect of the local magnetic field. It's 1000 times weaker than the magnetic field at Earth's surface, but still reflects about 50% of incoming solar wind ions back into space, as was measured by Japan's Kaguya probe.
Fig. 11: Jan Deca Solar Wind interactions with Lunar Magnetic Anomalies: Reiner Gamma, 2016 Reflected ion measurements by Japan's Kaguya, 2007
With half of all ionizing radiation reflected back into space by this natural force field, at the Reiner Gamma surface location, the ionizing radiation impact on future human explorers at this location would be reduced to half compared to the surroundings. A significant health benefit for humans on the Moon!
Rover Landing in 2026
Fig. 12: Lunar Vertex Rover landing with IM-3 in 2026 at Reiner Gamma JHUAPL, Intuitive Machines, NASA
Later in 2026, the NASA CLPS Lunar Voyage 2 Mission with its Intuitive Machine's Nova-C Lander in their IM-3 project will land at Reiner Gamma. It will carry the Lunar Vertex Rover to measure the local magnetic field in all three dimensions while it travels several kilometers through the swirl. This will provide the first actual surface measurement of the potential health benefit for humans at the Reiner Gamma location.
When it is confirmed to be the healthiest human landing location on the Moon, it definitely deserves to be returned ot its original name, as it would provide a new scientific impulse for future lunar research, much like Galileo Galilei sparked with the first telescope observations. It deserves to be named Galilaei Impulsus.
https://en.wikipedia.org/wiki/Reiner_Gamma quote:
In early lunar maps by Francesco Maria Grimaldi, this feature was incorrectly identified as a crater. His colleague Giovanni Riccioli then named it Galilaeus, after Galileo Galilei. The name was later transferred northwest to the current crater Galilaei.
https://en.wikipedia.org/wiki/Galilaei_(lunar_crater) quote:
Initially, the name Galilaeus had been applied by Giovanni Battista Riccioli, an Italian Jesuit who produced one of the first detailed maps of the Moon in 1651, to a large and bright nearby albedo feature (now known as Reiner Gamma). The name was transferred to its present location by Johann Heinrich Mädler in his influential Mappa Selenographica, published in collaboration with Wilhelm Beer in four parts between 1834 and 1836. Mädler's motive for this change was the fact that his lunar map did not name albedo features, forcing him to transfer Galileo's name to an insignificant nearby crater.