Book 7, Question 30
Why Do We Count Seconds After a Flash?
Counting the seconds between a flash of lightning and the boom of thunder tells you how far away the storm is. That helps you know if the storm is coming closer or moving away. It is a safety habit, not a game to play outside.
From the book
Page from A Million Whys Book 7
More fun facts
- The sound of thunder travels about one mile every 5 seconds.
- Count the seconds from flash to thunder and divide by 5 to get the distance in miles.
- For example, 15 seconds means the lightning is about 3 miles away. Zero seconds means it is very close.
- Lightning can strike as far as 10 miles away from a thunderstorm.
- The National Weather Service slogan is: When thunder roars, go indoors.
- Stay inside until 30 minutes after the last sound of thunder.
Sources: National Weather Service, National Weather Service, NOAA
Questions kids ask
How do I know how far away lightning is?
Count the seconds between the flash and the thunder, then divide by 5. That's the distance in miles.
When is it safe to go back outside?
Wait 30 minutes after the last sound of thunder.