A thunderstorm is approaching, and suddenly you see lightning followed by a deafening sound of thunder. His voice sounded close -- very close. Calculating your distance from lightning can give you a sense of security if you're in a safe place, or it can help you know if you need to find a safe route as soon as possible. So how close are you to a lightning strike? Read on to find out.
Step
Method 1 of 1: Calculating Distance from Lightning
Step 1. Watch for lightning flashes in the sky
Step 2. Count the number of seconds until you hear thunder
If you have a digital or analog watch, start counting as soon as you see lightning and stop as soon as you hear thunder. If you don't have a watch, do your best to count the seconds precisely. Say "one second, two seconds, …" in your head as you count.
Step 3. Calculate the distance from the lightning in miles or kilometers
Sound travels a mile (1.6 km) every five seconds and a kilometer every three seconds. So if you want to know how far you are from lightning, divide the number of seconds by 5 if you want the answer in miles and divide by 3 if you want the answer in kilometers. The difference between when you see lightning and when you hear thunder occurs because sound travels much slower than light. Here's what you do:
- Suppose you count 18 seconds. To find your distance from lightning in miles, divide 18 by 5 to get 3.6 miles. To find your distance from lightning in kilometers, divide 18 by 3 to get 6 kilometers.
- While you can't get absolutely accurate results because the weather may have varying temperatures and humidity, which will slightly affect the speed of sound, it's a good way to estimate how far you are from lightning.
Step 4. Calculate the distance from the lightning in feet or meters
Sound travels at a speed of about 344 meters or 1,129 feet per second. To calculate your distance from lightning in meters, just round 344 down to 340 and multiply the number of seconds by 340. To calculate your distance from lightning in feet, just round up 1.129 up to 1130 and multiply the number of seconds by 1130. Here's how you do it:
Suppose you count 3 seconds. Multiply that number by 340 to get your distance in meters. 3 x 340 = 1020 meters. Multiply that number by 1130 to get your distance in feet. 3 x 1130 = 3,390 feet
Tips
- If there are frightened children around you, calculate the distance of the lightning strike and tell them. This will help reduce their fear and then, they are more likely to ask "How did you find out?"
- Tell people about this method. Many people still believe in the myth that the number of seconds you count equals the number of lightning distances in miles (1.6 km).
- Sound travels through the air at slightly different speeds, depending on the air temperature and relative humidity. However, the difference is quite small and won't really affect your calculations. For more information, see the sound speed calculator in the external links section below.
- This calculation can also be used to teach students how to calculate distance, speed and time.
- If lightning strikes a point 1 mile (1.6 km) away, you will see approximately 0.00000536 seconds after the strike, whereas you will hear it approximately 4.72 seconds after the actual strike. If you calculate the difference between these two events, a person will hear a lightning strike approximately 4.71999 seconds after the strike actually occurred. Thus, 5 seconds per 1 mile (1.6 km) is a rough estimate.
- Of course, there is ample room for error in this way. If possible, calculate the distance from multiple lightning bolts and average them for better accuracy.
- If you have a map and compass, try to describe the location of each lightning strike by drawing a line on the map according to the direction of the lightning, and a cross at the distance you calculated along this line.
Warning
- Lightning is dangerous and deadly. Check out the wikiHow article on lightning for more information on staying safe in a thunderstorm.
- If you notice lightning is less than 1 mile (1.6 kilometers) away, make sure you find/have cover immediately. Lightning may strike you.
- This is not an exercise to be done outdoors. If you're close enough to hear thunder, you're close enough to be struck by lightning. Lightning can travel very quickly and has struck people more than 16 kilometers from the storm. If possible, take cover immediately.
- Because of the way sound propagates and the many types of objects, such as mountains and buildings, interact with sound waves not most reliable way to predict lightning distance. Don't let your life depend on this prediction. Listen to local weather experts.
- If you don't see the lightning strike directly, the sound you hear may be the reflection of sound from a building or mountain, which increases the time between the two events (flash and sound, making the lightning appear farther away than it really is). Take into account the effects of objects/obstacles that are near you (especially large ones) as sound inevitably bends and bounces off of these objects. All indirect lightning paths are definitely longer than the distance you're trying to calculate.
