march: sidereus nuncius

When Galileo drew five sketches of the Moon in his ground-breaking book Sidereus Nuncius (the Starry Messenger) he omitted to mention the time and date of each observation. This is a great pity: various versions of his book have included poorly copied, incorrectly oriented and mis-ordered images. These, coupled with misinterpretations of terms such as 'second quadrature' (actually second quarter, the gibous phase before full moon) have led to a great deal of confusion over the features he depicts.

The image above is the second image from the original version, showing a roughly seven-day Moon. The large oval ¼ of the way down from the north lunar pole is the Mare Serenitatis, with the Caucasus and Haemus mountains extending onto the dark half of the disc.

The large crater bisected by the terminator has prompted many suggestions to its identity. Tycho and Copernicus are popular candidates, though their size and position are a poor match, doing a great disservice to Galileo's draughtsmanship. Ptolemy, Albategnius and Deslandres are a far better fit.

Image: Rice University Galileo Project.