A High-Albedo Impact on the Western Shore of Tranquillitatis

Feature Profile & Selenographic Data

Feature type

crater

Coordinates

2.77° N · 17.29° E

Diameter

17.25 km

IAU approval

1935/01/01 00:00:00

LAC quadrangle

LAC-60 · Julius Caesar

Geological Chronicle

Dionysius occupies the western margin of Mare Tranquillitatis, just northwest of the crater pair Ritter and Sabine and near the northwest-trending rille network known as Rimae Ritter. Measured at 17.25 kilometers in diameter, the crater exhibits a generally circular rim that shows little sign of wear.

The formation stands out under high solar illumination because of its high albedo. Around the bright central halo, its ray system extends across a radius of over 130 kilometers, accompanied farther out by relatively rare deposits of dark rays.

The feature honors the first-century Greek astronomer Dionysius the Areopagite. In 1651, Giovanni Battista Riccioli used the name for the crater now designated Delambre, before the International Astronomical Union officially adopted the name for this crater in 1935.

Chronology & Exploration

1. 1651 Riccioli Nomenclature

   Giovanni Battista Riccioli introduces the name S. Dionysius, originally assigning it to the crater now known as Delambre.

2. 1935 IAU Adoption

   The International Astronomical Union officially adopts Dionysius for the crater on the western margin of Mare Tranquillitatis.

Scientific Sources & References

• IAU Gazetteer of Planetary Nomenclature — Registry coordinates, diameter, and namesake confirmation.
• Wikipedia (en) — Source text for crater morphology, albedo characteristics, and naming history.

Name Origin

St. Dionysius the Areopagite; Greek astronomer (fl. 1st century A.D.).