How do you measure time?
Since the start of time, human beings have looked to the sky to tell time.
Think of Earth as a rounded (“but not perfectly round”) sphere. Looking down on a sphere, you see a circle that contains 360 degrees (360°). Scientists also know that the Sun appears to move 15° across the sky every hour. (Of course, we know the Earth is actually rotating, which makes the Sun appear to do the moving.)
If you travel 15° in one hour, how long would it take you to go through all 360° on the Earth? You must travel a distance of 15° 24 times to move through the entire 360° (to travel around the Earth). We have 24 hours in a day that are matched with 24 time zones around the Earth. At the end of a day, the Sun has appeared in all 24 time zones. An “additional” 25th time zone is created in the Pacific Ocean by the international date line.
Earth’s longitude lines separate time zones, which are 15° wide. Sometimes, a longitude line will run through a state or a city and could place the two parts of the state or city within two different time zones. Usually, the longitude line at the edge of the time zone goes “around” a state along its border. This way, an entire state or city would stay in the same time zone. These time zones extend from the North Pole all the way to the South Pole, and that is why Virginia residents are in the same time zone as people near the Panama Canal or in Miami Beach.
Time zones begin at 0° longitude. This line is called the Prime Meridian. Time in this zone is called Greenwich Mean Time (GMT), which is named for the city of Greenwich, England where you find the Prime Meridian). This time zone is about 75° from the time zone for Virginia; 75° divided by 15° equals 5 hours (75/15 = 5), which means that time in England is 5 hours earlier than Virginia time. In other words, because England is east of Virginia, you would add five hours to the clock to know the correct time in England.
If it is 6:00 PM in Virginia, it is 11:00 PM in England (add 5 hours to 6:00 PM). For places west of Virginia, subtract hours from your time.
The United States is so large it has several time zones: Atlantic, Eastern, Central, Mountain, Pacific, Alaska, and Hawaii-Aleutian. As an example, if it is 6:00 PM in the Eastern time zone, it is 5:00 PM in the Central Time Zone, 4:00 PM in the Mountain Zone, and 3:00 PM in the Pacific Time Zone. It is noon in Hawaii (6 hours “behind” Virginia).
NASA will take a new clock—an atomic clock—into the sky and put it on the Space Station. The orbit of the Space Station will help make keeping track of time easier.
Clocks work because of pendulums that measure beats of time. We call the beats seconds. The atomic clock works with lasers. A laser shines on atoms to cool them. The atoms move slower and the beats are easier to measure.
Many things happen on Earth that change the way atoms work. Atoms fall quickly on Earth. In space, atoms float around in their containers, just like astronauts; therefore it is easier to measure time in space than on Earth.
We already use atomic clocks on Earth. They help drivers find their way. Sailors, truck drivers, soldiers, hikers, and pilots use atomic clocks. They are even used in some cars. You might have seen one. The car has a map display on the dashboard. This map is drawn by using atomic time signals. Farmers use atomic clocks, too. The clocks tell the farmer’s tractor when to water crops and when to put insecticide on the plants. Atomic clocks will make it easier for people to schedule tasks that have to be done on a regular basis.
KSNN™ thanks NASAexplores as a source of information.For more information about this topic and additional teaching resources go to http://www.nasaexplores.com
National Teaching Standards:
NCTM Standards for Pre-K-2-Measurement; Problem Solving; Connections; Representation
This activity demonstrates how to tell time and how to understand the concept of elapsed time.
NOTE: Educators/Parents should consider reading the entire text to their children, if necessary, as they assist them with the activity.
All grade levels need a pencil, scissors, worksheets
NOTE: All worksheets are located at the end of this activity.
Activity for Students in Kindergarten
- What do you think “time” is? There are many different answers to that question. This activity will help you understand time in several ways, including easy ways to help you understand how to tell time.
- Use Worksheet A, Part 1 to make a clock.
- Write the correct numbers in the blank circles. Notice that two numbers have already been placed in circles for you. These numbers represent hours on the clock. You can look at a clock in your classroom or home to check your work.
- Cut out the arrow hands on the worksheet.
- Notice that one of the arrow hands is longer than the other.
- The short arrow hand will show time on the clock in hours. The long arrow hand will show time on the clock in minutes.
- Place the dot on the long arrow hand on top of the dot in the center of the clock face. Point the arrow to 12 on the clock.
- Place the dot of the short arrow hand on top of the dot in the center of the clock face. Point the arrow to 1 on the clock.
- Can you tell what time is shown on the clock? Remember, the number the short arrow points to is the hour number.
- Repeat this procedure with all numbers on the clock.
- Complete Worksheet A.
Activity for Students in Grade ONE
NOTE: Conduct the Kindergarten Activity before you begin this listed Activity.
- Understanding how to tell time is much more than knowing how to read a clock when the hands only point to a certain hour.
- This activity will help you understand how to read time when the hour hand does not point directly at numbers on the clock.
- Point the minute hand (long arrow) towards 6 on the clock. This position of the long arrow shows that the hand has moved halfway around the clock’s circle of numbers.
- Remember that each number on the clock equals one hour of time.
- Look at the clock drawn below. Notice that there are many small lines between each number. Each line shows that one minute of time passes as the minute hand (long arrow) moves around the clock face.
- Point the hour hand (short arrow) to a place halfway between the 1 and 2 on the clock.
- What time is shown on the clock? We are 30 minutes past 1:00 on the clock. This time is called one-thirty (1:30), which is a shorter way of saying 1 o’clock plus thirty minutes.
- Move the hour hand to a place halfway between the 2 and 3 on the clock. What time is shown on the clock? Some people will still say this time is “half past 2 o’clock” instead of calling it “two-thirty” (2:30).
- Complete Worksheet B.
Activity for Students in Grade TWO
NOTE: Conduct the Kindergarten and Grade One Activities before you begin this listed Activity.
- Place the hour hand on the clock so that it points towards 1 on the clock.
- Place the minute hand on the clock so that it points towards 12 on the clock.
- Notice there are five marks or lines that you must move through to travel from one number to the next number.
- How many minutes pass as you move the minute hand from the 12 to the 1 on the clock?
- We can say the time is now one-oh-five (1:05) or five minutes past 1 o’clock.
- Move the minute hand so that it points to the 2 on the clock. This position shows that five minutes have passed. Add these five minutes to the previous five minutes. What time is now shown on the clock?
- Complete Worksheet C, Part 1.
- The clock is also designed to help us understand what is called “elapsed time” or how much time passes when we do something.
- For example, if we start our class at 1:00 and the class ends at 2:00, it means that one hour – or sixty minutes – passed while we were in class.
- Now, YOU try a problem. You begin your lunch at exactly 1:00. You finish eating when the minute hand points to the 6. How long were you eating lunch? Remember to use the paper clock if you need it.
- Here’s another problem to solve. Your soccer practice started after school at 4:30. Unfortunately, practice ended at 4:45 when a thunderstorm began. How long was your soccer practice that day? Editor’s note: Past tense is preferred here.
- Complete Worksheet C, Part 2.
EXTENSION ACTIVITIES FOR ALL GRADE LEVELS
- Practice reading a clock when the hands are located in many different positions. Let an adult help you know if you telling time correctly.
- Investigate how time was kept in the past. HINT: We didn’t use the same clocks we use today.
- What would happen to you if you could not tell the time?
- What other ways can let you know the approximate time of the day without using a clock?
- This is the clock and arrow hands needed for the Kindergarten Activity.
- Draw the hands on the clock to show the correct time.
- Write the correct time below each clock.
- Draw both arrow hands on these clocks to show the correct time.
- Write the correct time below each clock.
- Determine the elapsed time for each problem. The first question is already answered.
- two in the afternoon to 8 p.m. = _6_ hours
- seven in the morning to three in the afternoon = ___ hours
- 9 a.m. to 9 p.m. = ___ hours
- three in the morning to eleven in the evening = ___ hours
- 7 a.m. to 5 p.m. = ___ hours
- noon to four in the afternoon = ___ hours
- Fill in the correct time for the problems below. Make sure you include a.m. or p.m. in your answer.