# Teaching Students About Time Intervals

What is a time interval?

A time interval is the amount of time between two given points in time. An example is: “The time interval between three o’clock and four o’clock is one hour.”

What is time measured in?

Time intervals are measured in different units: every unit describes an additional amount of time, and certain teams will be better suited to specific lengths of time.

For example, if you were cooking something in the oven, you would measure the time in minutes or hours. If you were waiting for your birthday, however, you might measure the remaining time in days, weeks, or months (depending on how far away it was).

So, when we ask, “what is time measured in?” we are asking about what units are used to measure time.

The smallest amount of time we would use every day is a second. So there are 60 seconds in a minute and 60 minutes in an hour. And 24 hours make up one day.

These time units can be recorded with a watch or a clock. If you want to measure bigger units of time, you need a calendar.

There are, of course, more considerable intervals of time. Seven days make one week. A month is slightly different, as a month might be made up of 30 days, 31 days, 28 days, or (once every four years) 29 days.

Twelve months make up a year, and there are even units beyond that to describe the number of years!

• Ten years is a decade
• 100 year is a century
• 1000 years is a millennium

How were time intervals measured in the past?

Although we can use clocks and calendars to measure time intervals, there was a period in history when watches and clocks (at least as we know them) hadn’t been invented.

Before the invention of watches and clocks, there were various ways that people could keep track of time intervals. In ancient times, they relied on natural resources, like the sun’s position in the sky.

Ancient people would build thin, tall monuments called obelisks. With these, they could tell the time by the position of the obelisk’s shadow. They were nowhere near as accurate as our current technology, but it allowed them to tell when it was morning and afternoon.

The Egyptians were able to make the measurement of time more accurate. They created a shadow clock (also known as a sundial) as long ago as 1500 B.C.

With a sundial, the Egyptians could divide time into smaller chunks called “hours.” In addition, they could measure more accurately because they knew that shadows didn’t change position as the day went by, but also length.

Other civilizations also used water or sand to measure time. For example, water clocks used stone vessels with sloped sides. Water would constantly drip from a small hole into another boat, with markings to show how much water was inside and how much time had passed.

With water clocks, a person could tell the time at night when they could not use the sun to check the length and position of shadows.

Fun time interval facts

Although we have already looked at some of the ways to measure time intervals, did you know that, throughout history, the question “what is time measured in?” has had some very different answers:

• In Old English, the word atom meant 1/6 of a second. It was thought to be the smallest possible unit of time.
• Although an atom is a concise piece of time, the smallest unit of time nowadays is the zeptosecond, or one trillionth of a billionth of a second!
• When you tell someone “just a moment,” you probably don’t mean “give me 90 seconds”. But, in the Middle Ages, that’s what you’d be asking for 1/40th of an hour.
• You could ask for a quadrant if you need more than a moment. A quadrant means a quarter of a day. Or, more precisely, 6 hours.

The name for the accurate measurement of time is called chronometry. However, most people instead use the word time-keeping.

Although a day is said to be 24 hours, that isn’t accurate. For example, a complete revolution of the Earth – 1 day – is a little less than 24 hours: it’s 23 hours, 56 minutes, and 4.2 seconds.