First astronomical observation recorded The earliest known case of an astronomical observation with a definite time assertion is recorded in the register of the cathedral of Léon in northern Spain for the lunar eclipse on 17 February 1421. It reads: This day, six hours after midday, the moon began to darken, and the eclipse continued until half past seven or later, so the eclipse lasted two clock hours. It is unclear whether a cathedral clock was used for this observation. Futher Reading Matthes, D. and R. Sánchez-Barrios. September 2017. ‘Mechanical clocks and the advent of scientific astronomy’ in Antiquarian Horology 38(3): 328–342 (see especially p. 329, nos. 4 and 5). Image Credits Catedral Gótica de León. David Jiménez Llanes, CC BY-SA 3.0, via Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Catedral_G%C3%B3tica_de_Le%C3%B3n.jpg Reloxo da Catedral de León. España. Luis Miguel Bugallo Sánchez (Lmbuga), CC BY-SA 3.0, via Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Reloxo_da_Catedral_de_Le%C3%B3n._Espa%C3%B1a-32.jpg
