> Have you ever wondered how people measure the height of a mountain? > They don't do it by climbing the mountain and measuring with a ruler > as they go! The height of a mountain is found by...
Measuring temperature
For thousands of years, people judged the temperature by how they felt. To check the heat of an oven, cooks put a hand into the oven. If the weather felt cold, people put on more clothes. Long, long...
Measuring speed
The mighty Superman can move faster than a speeding bullet---but how fast is that? A tiny snail creeps along at what is called a "snail's pace"---but how slow is that? There's an easy way to measure...
Minutes, seconds, and nanoseconds
> Atop a tower in the town square hung a big bell. At each side of the > bell was a large iron statue of a man. Each statue held a hammer in > its hands. > > Suddenly, one of the statues seemed to...
Water clocks and sand clocks
Measuring time by the sun or the stars is all very well, but people soon needed a better way. And this need led to the invention of the water clock. The first water clock was just a large clay or...
Sun clocks
A clock certainly seems nothing like a ruler. Yet, a clock and a ruler do the same kind of job. They both measure something. A ruler measures length and a clock measures time. People of long ago...
Twenty-four hours a day
Why do we have twenty-four hours in a day? Why not twenty hours? Or sixteen hours? As a matter of fact, we have twenty-four hours in a day simply because the Egyptians did. They invented the...
The birth of the calendar
A year is a long time. So, long ago, people decided to divide it into shorter time periods. About five thousand years ago, the Sumerians divided the year into twelve "moons." Each moon had thirty...
Measuring time by the stars
People of long ago lived out of doors most of the time, so they were used to seeing the stars at night. And they knew that the stars moved across the sky during the year. Because the stars always...
Suns and moons, winters and summers
If you want to know what time it is, you look at a watch or a clock. If you want to know the date, you look at a calendar. A clock measures time during a day. It lets you know when to turn on a...
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