Tag Archives: sundial


Ancient Egyptian water wristwatches never caught on

Egyptian water clocks

Sundials tell time during the day, when it’s sunny. How did the Egyptians tell time at night?

Way back around 1500 bc (over 3,500 years ago) some clever Egyptian invented the water clock so they could tell time at night. A water clock is a jar with sides that taper from a wide brim to a small base. Almost at the bottom is a small hole. The idea is: you fill the jar with water and water leaks out the hole. There are marks on the inside of the jar for every hour. As the water level slowly sinks, it reaches each mark and that’s how you know what time it is.

It sounds like a swell idea, but I have a few problems with it. Number One: I don’t know exactly how big these jars were, but it doesn’t seem like there’d be nearly enough water inside them to last all night long. Even if the hole at the bottom were a mere pinhole, I think the water would run out in an hour. Did they wake up every hour to refill the water clock? That seems like a pain in the neck.

Number Two: to function as an accurate time-measurer, that jar would need to be filled precisely on the hour. You’d need to coordinate with a friend outside looking at a sundial so he could tell you the moment to fill it up.

Number Three: where did the water go after it leaked out? Did they just let it run all over the floor; did they collect it in another jar?

Number Four: Did their dogs see puddles of water on the floor and think, “What the heck, it must be okay to pee in the house now?”

Number Five: Didn’t the sound of dripping water keep them from sleeping?

This one has a cute little baboon sculpture. But how much water could you put in the reservoir? What is it, an egg-timer?

Dots on the inside walls mark the time as the water level sinks.

Egyptian sundials


An Egyptian lady catching some rays from Ra.

Let’s travel west from Sumer, away from the MidEast, along the northern coast of Africa to Egypt. About 1,000 years after civilization was up and running in the Tigris-Euphrates valley, the Egyptians got started on their civilization which thrived from 3100 bc to 332 bc. Like the Sumerians, Egyptians depended on a river—the Nile—and a system of irrigation to water their crops to keep the economy going. Their writing system was hieroglyphics—symbols that represented sounds, or ideas, or things. Their government was monarchical—they had a single ruler, called a Pharaoh. The Egyptians worshiped a pantheon—which means a bunch of gods and demi-gods. The Pharaoh was worshiped as a god, too.

The Sumerian culture must have influenced the Egyptians somewhat. The Egyptians divided the day into two halves, each having 12 hours—twelve is an easy Base Sixty number. The Egyptians are thought to have invented the sundial. The earliest example of a sundial has 12 hours marked using lines on a semi-circle, 15° apart.



A fragment of a limestone sundial. The gnomon goes into the hole at top.


This sundial is a half-bowl cut out of a block of stone.

A sundial is a simple way to measure the passage of the Sun. There’s a post (called a gnomon, pronouced NOM-ON) sticking up from a flat, horizontal surface. Lines are drawn on the flat surface, radiating out from the gnomon. When the Sun is shining, the gnomon casts a shadow on the lines. Each line represents the passage of an hour.

The Egyptians built huge obelisks—big stone monuments. These were sundials, too. The obelisk cast a shadow on the ground, which was marked for every hour. As the Sun moved across the sky, the shadow would move along the dial, showing the time. Of course, sundials only work when there’s daylight. How did they tell time at night?