Seven days, named after celestial bodies in many languages — Sunday (Sun), Monday (Moon), Saturday (Saturn).
Quick check
How many days are in a week?
Where the names come from
- Sunday — the Sun
- Monday — the Moon
- Saturday — Saturn
- Tuesday, Wednesday, Thursday, Friday — named after Norse/Germanic gods (Tiw, Woden, Thor, Frigg) in English
Unlike the day (Earth's rotation) and the year (Earth's orbit), the 7-day week has no natural cause. It's a human convention thousands of years old, kept because everyone agrees on it.
Counting in weeks
Weeks make a handy mid-size unit: 2 weeks = 14 days (a 'fortnight'), 4 weeks ≈ 1 month, 52 weeks ≈ 1 year (with a day or two left over).