The Babylonians adopted a seven-day week due to the the seven celestial bodies they observed in the sky: the Sun, the Moon, Mercury, Venus, Mars, Jupiter, and Saturn. This image of a lunar eclipse over the Swiss Alps highlights four of the seven objects. The Moon is the brightest object to the left. Mars is located directly below the Moon. Saturn is near the middle. And Jupiter hovers to the right.
Kaustav Ghose/Flickr