Weight is a measure of the pull of gravity on an object.

Neptune has the fastest winds recorded in the solar system.

Cyrus McCormick invented a mechanical reaper.

Pluto also rotates on its side.

Uranus, its rings, and fifteen of its moons rotate on their sides.

Saturn's largest moon, Titan, has it's own atmosphere.

General Robert E. Lee surrendered at Appomattox Court House, Virginia.

The first battle of the Civil War was won by the South at Fort Sumter.

South Carolina was the first state to leave the Union.

Eli Whitney invented the cotton gin.

The space shuttle was the first spacecraft designed to be reused.

Salyut 1 was the first space station.

Jonathan Goble was the first Baptist missionary to Japan.

The first American in space was Alan Shepard.

California was the thirty-first state to join the union.

Robert H. Goddard launched the first liquid-fuel rocket.

Another kind of telescope is the radio telescope, which receives radio signals from outer space that help it create stellar maps and images.

There are two kinds of telescopes: reflecting telescopes and refracting telescopes. The first uses mirrors, while the latter uses lenses.

Light travels at 186,000 miles per second.

Noah Webster wrote the first major American dictionary.