In satellite images of Earth's atmosphere, it's easy to spot the large, spiraling clouds of hurricane. These powerful storms are fueled by warm seawater, so they form over oceans near the equator. They can become larger and stronger as they cross the tropical seas. What you can't see in a satellite picture is the hurricane's incredible power. For a storm to be a hurricane, its winds must be blowing more than 74 miles (120 km) per hour .

Definition: rotating storm with winds at least 74 miles (120 km) per hour
Cause: oceans warmed by the Sun and Earth's rotation
Measurement: The Saffir-Simpson Scale is a 1 to 5 rating based on a hurricane's wind speed (1 is the weakest and 5 is the strongest)
Deadliest U.S. hurricane: On September 8, 1900, some 8,000 people were killed in Galveston, Texas.
Cool Fact: Tree rings record hundreds of years of hurricane history.

Image credits: main image,, © AMNH.