In February 2007, the space shuttle was on the
launch pad when a thunderstorm suddenly
struck. The storm hammered the space shuttle.
Winds blew over 100 kilometers per hour. The
shuttle's fuel tank was damaged. However, the
winds were not responsible for the damage. The
damage was caused by hail. The hail made over
7,000 dents on the fuel tank.
Hail is one type of precipitation. Precipitation
is water that falls from the air to Earth. Water is
always present in the air. For example, a cloud
is a collection of millions of tiny water droplets.
These water droplets fall to Earth as
precipitation.
The most common type of precipitation is rain.
A raindrop begins as a water droplet that is
smaller than a period. The droplet collects more
water. It gets bigger and bigger. It gets to be
more than 100 times its original size. The water
droplet becomes heavy. Then, it falls to Earth as
a raindrop.
Precipitation can also be snow or sleet. Snow
forms in cold temperatures. The water droplets
in a cloud change to solid crystals. The crystals
can join to form snowflakes. Sleet forms when
rain from a cloud passes through a layer of
freezing air. The rain freezes to produce falling
ice, or sleet.
Hail falls to Earth as balls or lumps of ice. Hail
forms in big clouds. Winds move water droplets
up and down in the cloud. The winds carry the
raindrops high in the cloud. The temperature is
low up there. The raindrops freeze. As they fall,
they begin to melt. The winds push the droplets
up again. More water freezes on the droplets.
The droplets then become hail. The cycle
continues, and the hail becomes bigger. Pieces
of hail can become as large as golf balls.
It was golf ball-sized hail that hit the space
shuttle's fuel tank. Fortunately, the damage was
repaired in time to send the shuttle into orbit.