Popular Astronomy

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2011-01-02

A mighty Moon crater

Copernicus ranks among the impact showpieces of the Solar System. Bright rays surrounding it can easily be seen with the naked eye just beneath Mare Imbrium when illuminated by a mid-morning to early evening Sun.

Copernicus is thrilling to observe. Masses of debris were flung out from the impact some 900 million years ago, the heftier fragments of which produced secondary impact craters, grooves and crater chains arranged radially around Copernicus. In places, the ejected material is many tens of metres thick. Copernicus’ floor lies 3,760 metres beneath its rim. The floor’s southern parts are rougher than the north, but small telescopes cannot resolve this terrain, and they appeari smoother but darker than the north. Mountains occupy the centre of the floor, and so much detail on the inner west wall can be seen that only a brave and confident observer would ever attempt to draw the whole lot during a single observing session. Copernicus A (2.5 km) sits snugly on the middle terrace due east of the central peaks, and to its east the rim displays a marked kink protruding towards the craterlet.

Copernicus, observed by Graham Sparrow on 15 November.

Added by:  Graham Sparrow