Earth’s Moon
In 1609, the Italian scientist Galileo Galilei heard about a telescope, a device that could observe distant objects by making them appear closer.
Galileo soon made his own telescope and used it to look at the moon and other planets in the solar system.
What Galileo saw astounded him! Instead of the moon being a perfect sphere imagined by the Greeks, he saw that the moon has an irregular surface with a variety of remarkable features.
Features on the moon’s surface include maria, craters, and highlands.
The moon’s surface has dark, flat areas, which Galileo called maria, the Latin word for “seas.”
Galileo incorrectly thought that the maria were oceans.
The maria are actually hardened rock formed from huge lava flows that occurred between 3 & 4 billion years ago.
Galileo saw that the moon’s surface is marked by large round pits called craters.
For a long time, many scientists mistakenly thought these craters were made by volcanoes.
Scientists now know that these craters were caused by impacts of meteoroids.
The maria have few craters compared to the surrounding areas. Most of the craters were formed early in its history before the maria was formed.
On Earth, such craters have disappeared. They were worn away by water, wind and other forces.
Galileo could also see what he called highlands or mountains. The lunar highlands are actually shadows cast by the rims of craters.
The moon is 3,476 kilometers in diameter, a little less than the distance across the United States.
Temperatures range from a torrid 130 degrees in direct sunlight to a frigid -180 degrees at night.
Temperatures on the moon vary so much because it has no atmosphere.
Gravity is also so weak that gasses can easily escape into space.
The moon has no liquid water but there are large patches of ice deep within craters located near the poles where sunlight never reaches.
The moon’s origin: The collision-ring theory.
Scientists theorize that a planet-sized object collided with Earth to form the moon.
Material from the Earth’s outer layers was ejected into orbit around Earth, where it formed a ring.
Gravity caused this material to combine and form the moon.