Moon is the earths nearest neighbor in space. In 1969, this huge natural satellite of the earth became the first object in space to be visited by human beings.

The moon is the brightest object in the night sky, but it gives off no light of its own. When the moon "shines," it is reflecting (casting back) light from the sun. On some nights, the moon looks like a gleaming silver globe. On others, it appears as a thin slice of light. But the moon does not change its size or shape. Its appearance seems to change as different parts of it are lighted by the sun.

The moon travels around the earth once about every 271/3 days. The average distance between the centers of the earth and the moon is 238,857 miles (384,403 kilometers). A rocket journey from the earth to the moon and back takes about six days.

Because the moon is relatively close to the earth, it seems much larger than the stars and about the same size as the sun. The moon measures about 2,160 miles (3,476 kilometers) across. This distance is about a fourth the diameter of the earth and 400 times smaller than that of the sun. If the moon were seen next to the earth, it would look like a tennis ball next to a basketball.

The earth is not the only planet with a moon. For example, Jupiter has 16 known satellites. The earths moon is the sixth largest of the more than 40 natural satellites of the planets. For more information on natural satellites, see the separate planet articles.

The moon has no life of any kind. Compared with the earth, it has changed little over billions of years. The moon has no air, wind, or water. On the moon, the sky is black--even during the day-- and the stars are always visible. At night, the rocky surface becomes colder than any place on the earth. In the day, the temperature of the rocks is slightly higher than that of boiling water.

Through the centuries, people have gazed at the moon, worshiped it, and studied it. The long-time dream of traveling to the moon became history on July 20, 1969, when astronaut Neil A. Armstrong of the United States set foot on it.

Space flights and moon landings have provided many facts about the moon. Moon exploration has also helped solve many mysteries about the earth, the sun, and the planets.