Hour

High school (ages 12+)
Mathematics & Numbers

Name:

Date:

Step 1 · Read the article

Open the article and read it at the level above. Then answer the questions below in your own words.

https://smallwhale.org/articles/hour

Write what each word means, using the article.

Do not copy the article. Write two things you learned, the way you would explain them to a friend.

Answers below are taken from the article’s stored facts, so they match what the student read.

1. What is the atomic definition?Defined as 3,600 SI seconds, based on atomic transitions
2. What is the historical variability?Originated as variable seasonal divisions (1/12 of day or night)
3. How did people measure hours before clocks?Before clocks, people used the sun. They divided the daylight or nighttime into twelve equal parts, so an hour could be longer in summer and shorter in winter.
4. Why do we sometimes add a leap second?The Earth spins a little faster or slower each day. We add or subtract one leap second to keep our clocks close to the real sunrise and sunset times.

Mean Solar Day: The average duration of a day, calculated over a year, used as a basis for timekeeping.
Coordinated Universal Time (UTC): The primary time standard by which the world regulates clocks and time.
UT1: A time scale based on the Earth's rotation, used for astronomical purposes and navigation.
Leap Second: An extra second added to UTC to keep it synchronized with Earth's rotation.