The Science of Lightning
Lightning can be a beautiful sight but it is
also very dangerous. Lightning strikes can
be fatal or cause lifelong injuries, including
brain damage. Rare forms of lightning can
occur from volcanic eruptions or forest
fires. However, most lightning comes from
thunderstorms. To form, thunderstorms
need moisture and motion in the
atmosphere—typically caused by
differences in temperature or pressure
between nearby air masses. Storms can
occur at any time of the year, but they are
most likely to occur during warm months.
Lightning is caused by a difference in charges
between areas within the clouds or between
Places with colder winters tend to have
clouds and the ground.
less moisture in the air during these times,
resulting in fewer storms. As a storm
grows, electrical charges build up in the clouds and on the
ground. When the difference in these charges gets too strong, a
sudden discharge occurs in the form of lightning.
There are two main types of lightning. Intra-cloud lightning
happens between two oppositely charged areas within a cloud.
Cloud-to-ground lightning happens
between opposite charges in the cloud and
on the ground. The first step of cloud-toground lightning is called a leader. A
leader sets the path that the electric
discharge will take. After a leader comes
the return stroke. The return stroke is the
discharge of electricity seen as lightning.
The leader and the return stroke happen so
quickly that human eyes cannot tell the
difference. Scientists have been able to
study lightning and its paths using high
speed cameras. The branches on some
lightning strikes are the charges trying to
connect to the ground in the most efficient
Not all lightning strikes the ground. Some stays
within the clouds.
way.
Thunder is a sound caused by lightning. Lightning heats the air
around it to about 50,000 ˚F—about five times hotter than the
Sun’s surface. Air expands quickly when it is heated. The air also
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The Science of Lightning
cools rapidly. This extreme heating and cooling produces a
sound wave that can travel up to ten miles. Rumbling thunder
indicates that lightning strikes are occurring farther away. Loud,
sharp cracks of thunder indicate that lightning is striking
nearby. The time it takes for a
person to hear thunder after a
flash of lightning can determine
how far away the storm is. It
takes the sound of thunder about
five seconds to travel one mile.
Counting the number of seconds
between the flash of lightning and
the sound of thunder and then
dividing by five reveals the
distance to the lightning in miles.
In the United States, the chance
that lightning will strike any one
person in his or her lifetime is
Lightning can damage trees, buildings, animals, and people.
about one in ten thousand. Only
10% of all people who are struck by lightning are killed; others
are left with various injuries. From 1981 to 2010, an average of
fifty-four lightning-related deaths were reported each year.
Being struck by lightning can stop the
heart, cause burns, and cause brain
damage that can lead to memory loss,
depression, and personality changes. The
best protection from lightning strikes is to
avoid being outside during storms. The
safest places to be are inside enclosed
vehicles or buildings. Vehicles or buildings
that are not fully enclosed, like golf carts,
porches, open garages, and motorcycles,
are not safe. It is also important to avoid
water (sinks, bathtubs, faucets) and
If a person cannot make it indoors, an enclosed
vehicle is also a safe place during a
electronic devices (computers, telephones)
thunderstorm.
once inside. Paying attention to the
weather helps people plan ahead in case a
storm arises. Knowing where safe buildings or vehicles are
located in case a storm suddenly arises is also important to
staying safe. Listening for thunder can provide clues as to
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The Science of Lightning
whether a storm is approaching the area. If someone is struck,
observers should call 911 immediately and wait for help. The
victim is not charged with electricity, so medical professionals
will not be shocked when they touch the person.
Lightning strikes can also cause
damage in the area surrounding a
direct hit. When lightning hits the
ground, the charge is spread across
the surface. This creates a ground
current of electricity in the area near
the strike. Ground currents from
lightning strikes kill many farm
animals each year. Ground currents
are more dangerous if there is more
space between contact points. For
example, a person standing on the
ground has two contact points (each
foot) close together. A person lying
on the ground is more vulnerable to
Livestock can be injured or killed by lightning strikes or
ground currents.
ground currents because the two
contact points (head and feet) are
farther apart. Many farm animals like cows and pigs have their
contact points (hooves) spread apart, increasing the chance of
injury or death by the ground current.
The United States experiences about
twenty five million lightning strikes
each year. The number of deaths caused
by lightning strikes has decreased in
recent years, but it is still a dangerous
force of nature. Being aware of the
danger and aware of the weather in the
area can help people prevent lightningrelated accidents. Nature cannot be
controlled, but people can learn to live
within its rules. Taking storms seriously
and finding safe places when a storm
occurs will help continue to decrease
the number of deaths and injuries in the
years to come.
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Lightning may be unavoidable, but people can be
safer during storms if they are aware of the danger.
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