14. The Babylonian Calendar
The Babylonian calendar uses days, months and years. The month begins after sunset on the evening when the lunar crescent becomes visible for the first time after New Moon.
15. The Day Begins
The Babylonian day begins and ends at sunset. Observations follow a tripartite division of the night. Either they take place during "the first part of the night" beginning at sunset, later in "the middle of the night," or before sunrise during "the last part of the night."
15. TheSky Astronomy Software
Representations of the sky were created using TheSky astronomy software. It uses state-of-the-art routines capable of picturing the celestial sphere seen on any night by sky-watchers in Babylon.
17. Normal Stars
For Babylonian astronomers, the major frames of reference were the horizon and a fixed celestial frame of some 33 bright stars. These so-called normal stars are distributed around the ecliptic within a few degrees of the paths of sun, moon and planets.
18. An Ancient Observation
A typical Diary inscription names a celestial body, notes its position, and gives the (Babylonian) date of the observation and an indication of the time.
Diary No. -567 reads: Line 8: Month II, the 1st (of which the 30th of the preceding month), the moon became visible while the sun stood there, 4 cubits below fl Geminorum; it was thick;
The observation was made the first day of Month 2, when the crescent of the moon first became visible near the western horizon at sunset. The moon was close to the normal star beta Geminorum. The lunar crescent was thicker than a sliver, and it was visible while the sun stood there above the horizon.