Theophilus and Cyrillus (Bruce Rohrlach)

Contains: Solar system body or event

Theophilus and Cyrillus

Acquisition type: Lucky imaging

Theophilus and Cyrillus

Acquisition type: Lucky imaging

Theophilus (upper-left) and Cyrillus (lower-right) craters, named after two 4th century Coptic popes (Theophilus of Alexandria and Saint Cyril of Alexandria), located on the NW side of Mare Nectaris (‘Sea of Nectar’; top) and on the southern margin of Sinus Asperitatis (‘Bay of Roughness’; left of Theophilus). These craters are illuminated along the lunar terminator typically around 5-7 days after each new moon.

The 100-km-wide Theophilus is the crowning glory of a trio of craters of Eratosthenian age (3.2 to 1.1 billion years). The 98-km-wide Cyrillus crater is older, and part of its outer wall has been decimated by the impact of Theophilus.

Theophilus is well-known for well-developed impact melts that are widely distributed outside of the crater on its northern flank (left on image) - where impact melt had ponded in low depressions on the lunar surface. The kinetic energy from the impact that created Theophilis and its 2-km-high rebound peaks in the centre of the crater, created a 100-km-wide lava sea of molten rock within the 4200m deep crater. Soon after impact, major slumping of the crater walls of Theophilus down into the lava sea created a tidal wave of lava that raced towards and washed over the opposite crater wall, and drained down the northern external slope of the crater. Much of this tidal wave of impact melt flooded down into Sinus Asperitatis. However, residual pools of impact-melt filled depressions in the lunar topography on the northern flank of Theophilus form smooth pools of solidified impact melt. Such features are also seen at Korolov X and Tycho.

Imaged 20-01-2021 from our backyard in Melbourne (SW 8 inch/f5 Newtonian, ASI224mc astrophotography camera, focal length ~7000mm).

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Theophilus and Cyrillus

Theophilus and Cyrillus

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Theophilus and Cyrillus

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