Nature keeps time
Events that repeat tell us how much time has passed.
Before clocks
Long ago, people had no clocks or watches. But they noticed that some things in nature happen again and again.
What could they use to keep track of time?
What this lesson covers
The idea
Many events in nature, such as sunrise and sunset, the phases of the Moon and the seasons, repeat after definite intervals of time, so their cycles can measure time; a day is one cycle of sunrise and sunset.
Before clocks
Long ago, people had no clocks or watches. But they noticed that some things in nature happen again and again.
What could they use to keep track of time?
- Events that repeat, like sunrise and sunset
- Things that happen only once
- Things that nobody can see
Watch them repeat
Pick an event. Watch it go round twice. Then pick the others.
Cycles are a clock
Each event came round again after a definite interval of time. People used these cycles for timekeeping. One cycle of sunrise and sunset is a day.
Many events in nature, such as sunrise and sunset, the phases of the Moon and the seasons, repeat after definite intervals of time, so their cycles can measure time. A day is one cycle of sunrise and sunset.
Notes
Many events in nature, such as sunrise and sunset, the phases of the Moon and the seasons, repeat after definite intervals of time, so their cycles can measure time. A day is one cycle of sunrise and sunset.
Check yourself
Which of these repeats after a definite interval of time?
A day is one cycle of …
Why can the phases of the Moon be used to measure time?
Which of these is a repeating event used to keep track of time?
- A single earthquake. An earthquake does not repeat after a definite interval of time.
- Sunrise and sunset — correct. Yes!
- A shooting star. A shooting star is not something that repeats after a definite interval.
- the phases of the Moon. One cycle of the Moon's phases takes much longer than a day.
- the seasons. One cycle of the seasons takes much longer than a day.
- sunrise and sunset — correct. Yes!
- They repeat after definite intervals of time — correct. Yes!
- They happen only once. The phases repeat. That is why they can be used to measure time.
- They happen at random. They repeat after definite intervals, not at random.
- A lamp being switched on. A lamp is switched on whenever someone wants, so it is not a natural cycle.
- The changing seasons — correct. Yes!
- A stone falling. A stone falling is not a cycle that repeats after a definite interval.