Theophilus [114 S 264 E

Theophilus (Figure 10.25) is one of the most photogenic craters on the Moon; not least because it forms a spectacular trio with the overlapping Cyrillus and, further south, Catharina. Theophilus is the youngest crater of the trio and, because of this, its features are the sharpest and least eroded. The triple (or quadruple) cluster of two-kilometer-high central mountain peaks is especially eye-catching. Perhaps the feature is especially spectacular because the whole trio is sandwiched between the

Figure 10.25. Theophilus, Cyrillus, and Catharina imaged in the dawn twilight on October 7th 2001. 37-cm Newtonian + Barlow. A single 0.03-sec and exposure at f/10 with a Starlight Xpress HX 516 CCD. Image: Mike Brown.

smooth Mare Nectaris to the east and the contrasting, rugged, Rupes Altai to the west. Theophilus is 26 degrees east of the Moon's central meridian and thus is best illuminated when the Moon is about four or five days past full or roughly six days after new. The Moon is usually available at a higher altitude in a dark sky in the former case but at a very sociable early-evening time in the latter case. Of course, seasonal effects mean that the first-quarter Moon is better placed in the evening in spring, whereas the last-quarter Moon is best placed in the morning skies in autumn. Because of this, most observers' best view of Theophilus will be in the spring evening sky.

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