Astronomy › Section D · Earth, Moon, and sky › Topic D.3
Keeping time and the calendar
Clocks and calendars look like human inventions, but every one of them is built on astronomy: Earth's spin, the Moon's phases and Earth's trip around the Sun. The trouble is that these three cycles don't fit neatly together.
In this topic
- Two kinds of day
- Worked example: stars rise earlier each night
- Sundial time and mean solar time
- Time zones and the date line
- Worked example: local time between two towns
- The calendar problem
- Calendars around the world
- From Julius Caesar to Pope Gregory
- Worked example: how good is each calendar?
- Common mistakes to avoid
- Key takeaways
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