Theophilus 11.4°S, 26.4°E
Cyrillus 13.2°S, 24.0°E
Catharina 18.0°S, 23.6°E


A trio of craters demonstrating the principles of superposition on the surface of the moon.

All three craters are of approximately the same size but increase in age from Theophilus in the north to Catharina in the South.

(Image Martyn Kinder: Celestron 11" Edge HD, ZWO asi224mc camera - 20230327 - 2027UTC)

The image isn't especially sharp but does demonstrate that the neatly terraced walls of Theophilus overlap the partially slumped walls of Cyrillus so that Theophilus must have been formed after Cyrillus.

Catharina is showing evidence of significant erosion not present in either of its two more northerly neighbours. All three craters are approximately the same size and should show evidence of similar features. However, the Catharina central uplift has gone and the crater floor has several additional craters present which must have formed after Catharina was formed.

The crater walls of Theophilus are 'neat' and have a clear multi facetted edge (not circular) which is typical of craters of this size and era. The crater floor is devoid of secondary or impact craters. The central uplift is clear and showing no signs of collapse. The double uplift in Cyrillus is rounded and there is at least one large secondary impact crater on the crater floor. The slumping on the walls of Cyrillus is far more pronounced.

The Catharina central uplift has been destroyed by subsequent impacts.

Note that the secondary crater chain to the east of Catharina which appears to be younger that Cyrillus as the chain appears to overlap Cyrillus.