11 December

1972: On 11 December 1972, Apollo 17 astronauts Gene Cernan and Harrison Schmitt landed on the Moon for a three-day exploration.

This would be the final Apollo mission to the Moon.

1863: On 11 December 1863, Annie Jump Cannon was born.

A deaf American astronomer, Cannon specialised in the classification of stellar spectra. In 1896 she was hired at the Harvard College Observatory, remaining there for her entire career.

The Harvard spectral classification had been first developed by Pickering. In conjunction with Pickering, Cannon developed and refined the Harvard system. She reorganised the classification of stars in terms of surface temperature in spectral classes O, B, A, F, G, K, M and catalogued over 225 000 stars for the Henry Draper Catalogue of stellar spectra.

1796: On 11 December 1796, Johann Daniel Titius died.

Titius was a Prussian astronomer whose formula showing the distances between the planets and the Sun was confirmed by Bode in 1772, when it was called Bode's Law (now the Titius-Bode Law).

Titius suggested that the mean distances of the planets from the Sun very nearly fit a simple relationship of A=4+(3x2ⁿ) giving the series 4, 7, 10, 16, 28, 52, 100, corresponding to the relative distance of the six known planets, up to Saturn, and a 'missing' value of 28 between Mars and Jupiter.

Olbers searched for a planetary object at this 'empty' position, and discovered the asteroid belt.

Since the discovery of Neptune and Pluto, which do not fit the pattern, the 'law' is regarded as a coincidence with no scientific significance.