Explore the Moon
FAQ: Moon Facts
What is the Moon?
The Moon is our closest neighbor in space. It is a rocky, airless world that orbits Earth. The Moon is Earth’s only natural satellite. Most of the other planets in our solar system also have moons.
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼Is there any sound on the Moon?
Sound needs something to travel through to get from one place to another. On the Moon, since there is no air, sound cannot travel above the surface. So, there are no sounds on the surface of the Moon. When the Apollo astronauts were out on the Moon’s surface, they could only talk to each other, and to mission control, by using the radios in their air filled helmets. Even when the astronaut in the photo to the right, hit a metal tube into the ground with a hammer, no sound was made.
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼Is there any water on the moon?
Yes! Water was identified in the plume of material thrown up from the surface of the moon by the impact of the LCROSS mission. More investigations are need to determine the exact amount of water present in the lunar soil. (Suffice to say, the moon is extraordinarily dry, and astronauts can’t expect to dig wells or melt ice sufficient to support life.)
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼Why is there no air on the Moon?
The Moon has no air because its gravity is too weak to hold an atmosphere. The gravity on the Moon is about six times less than the gravity on Earth, so any gases on the Moon (except for the very heaviest) would eventually float away into space. Because the Moon has no air, astronauts who go out onto the Moon’s surface must carry their own air supply. They also must wear helmets and protective clothing.
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼How old is the Moon?
By studying data from rocks that the Apollo astronauts brought back from the Moon, scientists have found that the Moon is about four and a half billion years old, which makes it about the same age as Earth. The rocks to the right are among the oldest rocks brought back from the Moon.
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼How long is a day on the Moon?
A day on the Moon is 27 days, 7 hours, and 43.2 minutes long (in Earth time). This is how long the Moon takes to complete one full rotation on its axis. The reason why a day on the Moon is so long is because the gravitational forces between Earth and the Moon slowed the Moon’s rotation until the same side of the Moon always faced the Earth. This means that one day on the Moon lasts for the same amount of time that it takes for the Moon to make one complete orbit around Earth.
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼How much would I weigh on the Moon?
Because the Moon has one sixth the gravity of Earth, you would weigh six times less than what you weigh on Earth. This is why the astronauts were able to move easily in their heavy space suits. They were able to hop around on the surface of the Moon, but they had to be very careful to keep their balance and not fall. In the photo to the right, John Young, commander of the Apollo 16 lunar landing mission, jumps up from the lunar surface as he salutes.
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼What is the temperature on the Moon?
Because the Moon has no atmosphere to block some of the sun’s light or to help trap heat, the temperature on the Moon’s surface ranges from extremely hot during the day to extremely cold at night. During the day the temperature on the Moon can reach 253 Fahrenheit (123 Celsius), while at night it can drop to -387 Fahrenheit (-233 Celsius). The Earth, which has an atmosphere, has much more comfortable temperatures. The DIVINER instrument on LRO will be mapping the temperature variations across the surface of the Moon. Some places on the moon are particularly cold because they are in constant shadow! The amount of incident light and composition of the Lunar surface both effect temperature.
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼How fast does the Moon travel around Earth?
The Moon travels around Earth at a speed of 2,288 miles per hour (3,683 kilometers per hour). During one complete trip around Earth (one orbit) it travels a distance of 1,423,000 miles (2,290,000 kilometers) in about 27.3 days.
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼How big is the Moon?
The Moon is much smaller than Earth. It has a diameter of 2,159 miles (3,476 kilometers), which is about four times smaller than the diameter of Earth. Its volume is just over fourty-nine times less than the volume of Earth. This means that forty-nine Moons could fit inside our Earth with a little room to spare. The Moon is also much less massive than Earth having about 81 times less mass (amount of material) than Earth does.
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼How do we know how far away the Moon is?
Today, the distance to the Moon is measured by bouncing laser beams off special reflectors which were left on the lunar surface by the astronauts of the Apollo 11, 14, and 15 missions. Since we know how fast the light of the laser beam travels, and can measure the time it takes for it to travel to the Moon and back, we can figure out the Moon’s distance from Earth with great accuracy. Before lasers were used, people used geometry to calculate the distance to the Moon.
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼How far away is the Moon?
The Moon is at an average distance of 238,897 miles (384,467 kilometers) away from Earth, which is about the width of 30 Earths. Because the Moon does not orbit Earth in a perfect circle, but instead travels in a slightly elliptical (oval shaped) orbit, its distance from Earth varies between 225,740 miles (363,300 kilometers) and 251,970 miles (405,500 kilometers).
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼How does the Moon stay up in the sky?
The Moon stays up in the sky because it is in a stable orbit around Earth. The Moon is pulled towards Earth by Earth’s gravity, but because it is so far away and is moving so fast around Earth, it will never fall down. If the Moon were moving a lot faster it would escape Earth’s gravity and fly off into space. If the Moon were moving much more slowly, gravity would pull it down to the Earth. So, the Moon is traveling at the right speed and distance to keep it in orbit around Earth.
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼How did the Moon get there?
Many astronomers think that the Moon was formed after a Mars-sized object smashed into Earth over four and a half billion years ago. This collision caused material from both Earth and the colliding object to be thrown into orbit around Earth. This material eventually gathered together to form the Moon. At first the Moon was closer to Earth than it is now. Over time, it gradually moved farther away. The Moon is still moving away from Earth at a rate of about 1.5 inches or 3.8 centimeters a year.
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼Why doesn't our Moon have a name?
Our Moon actually has a name. It is simply called “the Moon”. Until Galileo discovered that Jupiter had moons in 1610, people thought that the Moon was the only moon that existed. After other moons were discovered, they were given different names so that people would not confuse them with each other. We call them moons because they orbit planets the same way that the Moon orbits around Earth.
Galileo Mission Sun Spots and Spacecraft Surveyor Program more ▼