The moon is the Earth's closest neighbor in space, and it is the only natural satelliteorbiting Earth. The Latin word for moon is "Luna," so when you hear the term "lunar" you will know it is referring to the moon. This cold, rocky body is about 384,403 kilometers (238,857 miles) away. This distance is similar to going around the earth 10 times, or lining up 30 earths in a row. If you were to drive from the moon to the Earth at 65 mph (just over 100 kph), going 24 hours a day, it would take you 153 days (about 5 months), to get here.
The moon is 3,476 kilometers (2,160 miles) in diameter. It is about 400 times smaller than the sun, but it is also about 400 times closer to Earth than the sun. Because things that are farther away tend to look smaller, when viewed from the Earth, the sun and moon appear to be the same size.
The moon is very old! Scientists believe that about 4.5 billion years ago a Mars-sized body hit Earth and the resulting debris (from both Earth and the impacting body) accumulated to form the Moon. Scientists believe this because they studied the lunar rocks that were collected by astronauts who went to the moon. The moon and the earth are made of the same material.
Other planets in our solar system have moons too. Earth has only one moon, and Venus has none, but Jupiter, for example, has 79 moons! Our moon is the fifth largest moon in the solar system. Find out more about other moons at NASA Space Place.
You can read more about the moon at NASA's StarChild, a Learning center for Young Astronomers.
What's it like on the Moon?
The maximum temperature during the day is 253° F (123° C), which is hot enough to boil water! At night the temperature can reach -387° F (-232° C), much colder than anywhere on Earth.
The moon has no atmosphere, so the lunar sky is black. On Earth, the sky is blue because of the atmosphere. On the moon, there is no wind, rain, sound, or breathable air. Astronauts must carry their own air for breathing when they visit the moon.
The surface of the moon is covered in craters or holes that have been created by space rocks or meteors that hit the ground. The lack of atmosphere there allows the rocks to crash into the surface, and allows the craters to remain as they are for billions of years. An atmosphere like the Earth's would prevent most meteors from reaching the surface, and any craters would be changed by weather and erosion. You can see craters on the moon with a pair of binoculars. You can also see dark and light areas. The dark areas are plains formed by hardened lava, and the light area are highlands or mountains.
No rivers, lakes, or oceans exist on the moon. But in 2018, water ice was confirmed on the surface of the moon for the first time.As shown in the photos above, these frozen ponds are located at the cold, dark, north and south poles of the moon. Scientists believe that the ice may be the remnant of a comet that crashed into the moon long ago. The discovery is important because it is possible that future lunar expeditions might have a readily available source of water.
If you weigh 60 pounds on earth, you would weigh 10 pounds on the moon because gravity is 1/6th as strong on the moon. That's why astronauts could leap and jump so high on the moon.
The gravity of the moon causes the rise and fall of the ocean tides on Earth. The gravitational pull of the moon on Earth causes high and low tides around the globe, with the time between high tides being about 12 hours 25 minutes. Learn more about the moon's effect on ocean tides from NOAA.
The Far Side of the Moon
The same side of the moon always faces Earth. The other side of the moon is always turned away from us. Because the moon rotates on its axis in about the same length of time it takes to orbit the Earth, we only ever see about 60% of its surface. The side that we see is called the near side, while the other side is called the far side.
Below is a NASA photo of the far side of the moon. Until humans sent spacecraft around the moon, no one had seen this side of our neighbor. In 2019, the first rover landed on the Moon's far side.
The moon has no light of its own. It shines because sunlight is reflected off its surface.
What is "moonrise"? The Earth rotates once a day on its axis, which makes it appear as if the moon rises over the eastern horizon and sets over the western one. Sunrise and sunset are the same kind of phenomena.
Phases of the Moon
Why does the moon appear to change shape each night? The moon orbits, or revolves, around the Earth about once every 27 days, 7 hours, 43 minutes. As it orbits, the Sun lights up different parts of its surface, and our view of the sunlit moon changes. This movement causes the moon to cycle through a series of phases: New, Waxing Crescent, First Quarter, Waxing Gibbous, Full, Waning Gibbous, Last Quarter, Waning Crescent and back to New again. This diagram shows the phases of the moon, from a new moon, which you can hardly see at all, to a full moon and back again, in just over four weeks.
Sometimes the moon passes through some portion of the earth's shadow and the Earth blocks part or all of the sun's rays from reaching the moon. This is called a lunar eclipse and can only occur at Full Moon. A schedule of upcoming lunar eclipses can be found on NASA's website.
Almost three hundred sixty years after the Italian astronomer Galileo Galilei made his first observation of the moon with a telescope telescope in 1610, astronauts from the Apollo 11 mission first landed on the moon on July 21, 1969. The first person to walk on the moon was the American astronaut Neil Armstrong, who stepped out of his landing craft with these famous words: "That's one small step for man, one giant leap for mankind." Don't miss the great Apollo 11 story from NASA complete with audio, video, and photos.
During NASA's six Apollo missions of 1969-1972, 12 American astronauts walked on the moon and used lunar vehicles to travel on the surface. They brought back 842 pounds (382 kilograms) of lunar soil and rock to Earth for study.
This photo (right) offers a close-up view of an astronaut's footprint in the lunar soil. Because there is no atmosphere, astronauts' footprints on the surface of the moon remain and are not blown away. Find more moonwalk photos at this NASA site.
Moon exploration continues today with rovers, orbiters, and robotic missions sent by many different countries throughout the world. NASA has compiled a chronology of moon missions, starting with the USA's and USSR's first missions in the late 1950s. Check out NASA's current plans for future moon exploration. Maybe you will visit the moon someday!