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Why does a week have seven days?
Even though it would be perfectly possible to imagine a week having five, six or even eleven days, most cultures in the world have seven-day weeks. The reason for this is that seven celestial bodies were known to the ancients: the Sun, the Moon, Mars, Mercury, Jupiter, Venus and Saturn. These celestial bodies are visible to the human eye and people in ancient times were able to observe how they moved across the sky. This is also where the term 'planet' comes from - it is derived from a Greek word meaning 'wanderer'.
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Last update: 13/01/2009 14:21:34
Exhibition "Out of this World"
International Year of Astronomy 2009
CosmicDiary - Astronomy Blogs
Daily Podcasts at 365 Days of Astronomy
ESA - IYA2009
Planetariumshow "Touching the Edge of the Universe"
Archive: Astronomy Questions of the Week