A tropical storm becomes a hurricane when its wind speed reaches

Clouds are formed by __________ air motion and shaped by __________ air motion.

The troposphere derives energy by means of

The horizontal movement of air is called

An air mass forming over the Gulf of Mexico would be classified as __________.

__________ is an extremely large collection of stars bound together by mutual gravitational attraction.

The four basic types of clouds are cirrus, cumulus, stratus, and __________.

The Sun, like other stars, radiates energy because of nuclear __________ of hydrogen nuclei into helium nuclei in the 15 million K temperatures of its core.

The Greenwich, England meridian is also known as the __________.

The solar system is a complex system of moving masses held together by __________ forces.