Clocks of long ago
Shadows, water, sand and candles told the time.
How long has it been?
A day is long. People also wanted to know smaller bits of time within a day. They made devices for it.
What could they use?
What this lesson covers
The idea
Sundials tell time by the changing position of a shadow cast in sunlight, water clocks by water flowing out of or into a vessel, hourglasses by sand flowing between bulbs, and candle clocks by marked candles burning.
How long has it been?
A day is long. People also wanted to know smaller bits of time within a day. They made devices for it.
What could they use?
- Shadows, flowing water, flowing sand and burning candles
- Only calendars
- Only the stars
Run the old clocks
Pick a device and run it. Try all four.
Four ways
The sundial used a moving shadow. The water clock used flowing water. The hourglass used flowing sand. The candle clock used a burning candle.
Sundials tell time by the changing position of a shadow cast in sunlight, water clocks by water flowing out of or into a vessel, hourglasses by sand flowing between bulbs, and candle clocks by marked candles burning.
- Device | What changes
- Sundial | Position of a shadow
- Water clock | Water flows out of or into a vessel
- Hourglass | Sand flows between bulbs
- Candle clock | A marked candle burns
Notes
Sundials tell time by the changing position of a shadow cast in sunlight, water clocks by water flowing out of or into a vessel, hourglasses by sand flowing between bulbs, and candle clocks by marked candles burning.
Check yourself
A sundial tells time by the changing position of …
Which device uses sand flowing from one bulb to another?
Which device uses a candle with markings?
Why can a sundial not tell the time at night?
- a flame. A flame is used in a candle clock.
- a water drop. Water is used in a water clock.
- a shadow — correct. Yes!
- An hourglass — correct. Yes!
- A sundial. A sundial uses a shadow.
- A candle clock. A candle clock uses a burning candle.
- A water clock. A water clock uses flowing water.
- A candle clock — correct. Yes!
- A sundial. A sundial uses a shadow made by sunlight.
- It is made of stone. Being made of stone is not the reason. A sundial works with a shadow cast by sunlight.
- It has no marks. Sundials have marks. They need sunlight to cast a shadow.
- It needs the light of the Sun to cast a shadow — correct. Yes!