Moon Questions
Click on one of these sections below to see questions about the moon.
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.
Image Credit: NASA
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.
Artwork by Joe Tucciarone
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.
Image Credit: NASA
How far away is the Moon?
The Moon is at an average distance of 238,897 miles (384,467 kilometers) 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).
Image Credit: NASA
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. The image to the right shows one of the laser reflectors which was left on the Moon's surface by the Apollo astronauts.
Image Credit: NASA
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 fourty-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.
Image Credit: NASA
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.
Image Credit: NASA
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 a much more comfortable range of temperatures.
Image Credit: NASA
How much would I weigh on the Moon?
Because the Moon has only 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.
Image Credit: NASA
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.
Image Credit: NASA
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.
Image Credit: NASA
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 must also wear helmets and protective clothing.
Image Credit: NASA
Is there any water on the Moon?
Scientists do not know if there is any water on the Moon. There is some evidence that there may be water in special places on the Moon, but no water has been found yet. One possible place where water may exist is deep within craters near the Moon's poles. Sunlight cannot reach these extremely cold places, so if there is water inside these craters, it is probably in the form of ice. Future manned bases on the Moon will need water, so NASA is planning missions to search for water on the Moon. One of these is the Lunar CRater Observation and Sensing Satellite (LCROSS) shown in the artist's drawing to the right.
Image Credit: NASA
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.
Image Credit: NASA
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.
Image Credit: NASA
Surface Features
Why is the Moon covered with craters?
The Moon is covered with craters because throughout its history it has been bombarded by a lot of meteorites. All of the moons and planets in our solar system have been hit by meteorites. This was especially true in the past, when there was much more debris in our solar system than there is today. On Earth, we only see a few meteorite craters because most have been eroded away by wind, rain, and other forces. Also, since Earth has an atmosphere, most meteors burn up due to friction with the atmosphere before they reach the ground. On the Moon, where there is no atmosphere, there is nothing to prevent meteorite impacts and there is no wind or rain to erode the impact craters away. Even the footprints of the astronauts who landed on the Moon over 30 years ago are still there.
Image Credit: NASA
What is the largest crater on the Moon?
The largest known impact crater on the Moon is over 1,300 miles across. It is called the South Pole-Aitken basin because it stretches from the south pole of the Moon to the Aitken crater on the far side of the Moon. The crater was formed when a large object, the size of an asteroid or comet, crashed into the Moon's surface. The false-color image on the right shows the lowest parts of this impact crater as purple. Higher regions are shown as blue, and the highest areas are shown as yellow and red. The image is from the Clementine spacecraft.
Image Credit: Naval Research Lab, Clementine Project
What are the dark patches on the Moon?
The dark patches on the Moon are large plains which were formed by lava flows early in the Moon's history. In the past, the Moon was heavily bombarded by the material leftover from planet formation. Some of the objects which hit the Moon were very big and formed large impact basins. These basins were then flooded by the darker volcanic material from the Moon's interior. The lava flows covered any craters in their path, so these plains have very few craters compared to other places on the Moon. People once thought that these dark patches were seas on the Moon, so these regions were given the name "maria" which is the latin word for seas. The maria cover about seventeen percent of the Moon's surface and are found mainly on the side of the Moon facing Earth.
Image Credit: NASA
Are there mountains on the Moon?
There are several mountains and mountain ranges on the Moon. Several lunar mountains are well over 10,000 feet tall. Most of the mountains on the Moon are on the rims of large craters formed by meteroite impacts. The Moon does not have jagged mountains, instead the Moon's mountains are round and smooth. The image to the right shows a range of mountains at the edge of a crater.
Image Credit: NASA
What is the far side of the Moon like?
This photo of the far side of the Moon was taken by the astronauts on board Apollo 16 as it circled the Moon. As you can see, the far side of the Moon is heavily cratered. Also, it does not have as many of the large, smooth, dark basins (called maria) as the side of the Moon facing us has. The crust on the far side of the Moon is thicker than it is on the Moon's near side, so it was probably more difficult for lava to break though this part of the Moon's surface to form maria. The far side of the Moon was first photographed in 1959 by the Soviet spacecraft Luna 3.
Image Credit: NASA
The Moon's Appearance
Who is the man in the Moon?
When some people look at the Moon, they imagine seeing a face made out of the dark and light areas on the Moon's surface. Just like when you try to see shapes in the clouds, the man in the Moon comes from peoples' imaginations and is not real. Of course, there were men on the Moon for a short time when the astronauts landed during the Apollo missions. But there have not been any people on the Moon since then.
Image Credit: NASA
Why don't we see the other side of the Moon?
From Earth, we cannot see the other side of the Moon because it always faces away from us. Long ago, the gravitational forces between Earth and the Moon slowed the Moon's rotation until it was locked with one side always facing Earth and the other side always facing away from Earth. This does not mean that the Moon does not rotate. The Moon rotates once in the same amount of time that it takes for the Moon to travel once around Earth. So, the Moon's rotation is synchronized with its orbit around Earth, causing it to always keep the same face towards us.
Image Credit: NASA
How does the Moon shine?
Even though the Moon is the brightest object in the night sky, it does not make its own light. The light we see from the Moon is actually sunlight that is reflected from the Moon's surface. The Moon only reflects about seven percent of the sunlight that reaches it. The rest is absorbed by the Moon's surface.
Image Credit: NASA
Why is the Moon gray?
It is true that the Moon is not very colorful. In the color photo on the right you can see that the Moon's surface really is different shades of gray. This is because the materials that make up the Moon's surface are mainly volcanic in origin and are naturally gray in color. In the past the Moon had a lot of volcanic activity. Most of the rocks on the Moon came from the inside of the Moon during these volcanic eruptions. The darker gray regions on the Moon's surface are old lava flows which filled in impact basins. If you have ever seen a volcanic region on Earth, you may have noticed that volcanic rocks and soil, and places were lava flowed can be very gray.
Image Credit: NASA
Why does the Moon change its shape?
The Moon does not really change its shape. It just seems to change its shape, or go through phases, because we only see the parts of it that are lit up by the Sun. The portion of the Moon that we see depends on where the Moon is in its orbit around Earth. When the Moon is between the Earth and the Sun, the side facing us is dark. We call this a new moon. Gradually, as the Moon orbits Earth, more and more of the side facing us is lit up by sunlight. When the Moon reaches the opposite side of the Earth as the Sun is, the side of the Moon facing us is completely lit up by sunlight and we see a full moon. Then we see less and less of the Moon until it becomes a new moon again. The time that it takes for the Moon to change from one new moon to the next new moon is about 29.5 days.
Image Credit: NASA
How does a lunar eclipse happen?
As Earth orbits the Sun, it sometimes comes between the Sun and the Moon. When this happens the Earth blocks out some of the sunlight that would normally reach the Moon and creates a shadow which travels across the Moon's surface. This is called a lunar eclipse. A lunar eclipse can be partial or total. A partial lunar eclipse occurs when, during the passage of Earth's shadow, the entire Moon is never completely shaded. A total lunar eclipse happens when Earth's shadow completely covers the Moon. The part of the Moon covered by the Earth's shadow is usually still faintly visible because it is lit by sunlight that has been bent by Earth's atmosphere. This light gives the Moon a reddish glow during the eclipse. A lunar eclipse can last for more than an hour and only occurs during a full moon.
Image credit: Mr. Eclipse/Fred Espanack
Exploring the Moon
When was the first picture of the Moon taken?
The first picture of the Moon was taken in 1839, shortly after the invention of photography, by John Draper. The image to the right is the very first picture of the Moon that he took using a 12 inch telescope. He had to expose his photographic plate to the moonlight for 20 minutes to create this picture.
Image credit: John W. Draper
When were telescopes first used to study the Moon?
In 1609, the Italian scientist Galileo Galilei was the first person to use a telescope to study the Moon. Using a telescope with a magnification of twenty times, he was able to see the mountains, craters, and rough surface of the Moon. During Galileo's time, people believed that the Moon's surface was smooth, so his observations caused many arguements. Since photography did not exist at the time, Galileo sketched what he saw through his telecope. To the right is a set of four of Galileo's engravings of the Moon, showing what he saw through his telescope.
How long does it take to get to the Moon?
How long it takes to get to the Moon depends on how fast a spacecraft travels. The Apollo missions took about three days to reach the Moon. The fastest mission which flew by the Moon (but did not stop) was NASA's New Horizons Pluto mission, which took only 8 hours and 35 minutes and traveled at speeds of over over 58,000 km/hr. The longest trip to the Moon, by the ESA SMART-1 lunar probe launched in 2003, took 1 year plus 6 weeks. It used a new, very fuel efficient, ion engine.
Image Credit: NASA
When did the first spacecraft land on the Moon?
The Soviet spacecraft Luna 2 (Lunik 2), launched on September 12, 1959, was the first spacecraft to reach the surface of the Moon. It crashed onto the Moon's surface on September 14, 1959. Fortunately, it was an unmanned spacecraft, so there were no astronauts on board.
Image Credit: NASA/GSFC/NSSDC
Who were the first people to land on the Moon?
The first people to land the Moon were were the Apollo 11 astronauts Neil Armstrong and Buzz Aldrin. They landed on the Moon on July 20, 1969. Neil Armstrong was the first to set foot on the Moon and he was followed shortly afterwards by Buzz Aldrin. They spent 21 hours on the lunar surface and collected 46 pounds of Moon rocks to bring back to Earth for study. The third astronaut of the Apollo 11 crew, Michael Collins, remained in orbit around the Moon piloting the command module. The picture on this page shows (from left to right) astronauts Armstrong, Collins, and Aldrin.
Image Credit: NASA
How many astronauts have walked on the Moon?
Twelve astronauts have walked on the Moon. The first astronauts landed on the Moon in 1969 and the last astronauts landed on the Moon in 1972. These astronauts were part of the six Apollo missions which each landed two astronauts on the Moon's surface.
Image Credit: NASA
Which astronauts walked on the Moon?
The tweleve astronauts who walked on the Moon were:
Neil Armstrong - Apollo 11 - July, 1969
Edwin "Buzz" Aldrin - Apollo 11 - July, 1969
Charles "Pete" Conrad - Apollo 12 - November, 1969
Alan Bean - Apollo 12 - November, 1969
Alan Shepard - Apollo 14 - February, 1971
Edgar Mitchell - Apollo 14 - February, 1971
David Scott - Apollo 15 - July, 1971
James Irwin - Apollo 15 - July, 1971
John Young - Apollo 16 - April, 1972
Charles Duke - Apollo 16 - April, 1972
Harrison Schmitt - Apollo 17 - December, 1972
Eugene Cernan - Apollo 17 - December, 1972
Image Credit: NASA
When was the last time people visited the Moon?
The Apollo 17 mission was the last manned mission to the Moon.. The crew included Eugene Cernan, Harrison Schmitt, and command module pilot Ronald Evans. They landed on the Moon on December 11, 1972 and left the Moon three days later on December 14, 1972. Both Eugene Cernan and Harrison Schmitt walked on the Moon, but Eugene Cernan was the last to return to the lunar module and is the last man to have walked on the Moon. The Apollo 17 astronauts explored the Moon using the Lunar Roving Vehicle (Lunar Rover), collected rock and soil samples, and set up experiments. To the right is a picture of the Apollo 17 crew.
Image Credit: NASA
Where did the astronauts land on the Moon?
The landing sites for the six Apollo missions which landed astronauts on the Moon are shown on the image to the right. The numbers on the picture are the Apollo mission numbers. For example, 11 shows where the first astronauts landed on the Moon during the Apollo 11 mission. All of the landing sites are on the side of the Moon facing Earth. Astronauts landed on this side of the Moon so that they could send radio messages and television signals back to Earth. They could not do this from the far side of the Moon.
Image Credit: NASA
When were lunar rovers used on the Moon?
Between 1969 and 1972 the astronauts who landed on the Moon were able to use lunar rovers. By driving around in the lunar rovers, astronauts were able to travel much farther and explore more of the Moon. Before the use of lunar rovers, the astronauts could only travel by foot. Lunar rovers were used during the last three Apollo missions to the Moon (Apollos 15, 16 and 17). The Soviet Union also sent two robotic rovers to the Moon (called Lunokhod 1 and 2) in 1970 and 1973. These rovers were operated by remote control from Earth.
Image Credit: NASA
How fast and far could the lunar rover travel?
The lunar rovers were designed to have enough power to travel a distance of about 40 miles and to reach speeds of up to about eleven miles per hour. The lunar rovers usually traveled at speeds up to 6 to 8 miles per hour. The Apollo 16 astronauts conducted performance tests with the lunar rover, at one time getting it up to eleven miles per hour (eighteen kilometers per hour), which still stands as the record speed for any wheeled vehicle on the Moon.
Image Credit: NASA
How many Moon rocks were brought back to Earth?
Astronauts who landed on the Moon collected 2,415 samples of Moon rocks weighing a total of 842 pounds (382 kilograms). Most of these rocks were collected during the Apollo 15, 16, and 17 missions. In addition, three unmanned Soviet Luna spacecraft brought 0.66 pounds (326 g) of lunar samples back to Earth.
Image Credit: NASA
When will people go back to the Moon?
NASA is planning future manned missions to the Moon and even the construction of manned lunar bases. No dates have yet been set, but NASA hopes to land astronauts back on the Moon by about 2020. To the right is an artist's concept of a small lunar outpost.
Image Credit: NASA
Can you see more stars from the Moon?
On the Moon, there is no atmosphere and no clouds to blur or block our view of the stars. The sky on the Moon is always black, even during the daytime. From the Moon, you would be able to see many more stars than you could see from Earth. You would also see the Earth in the sky, and it would appear much larger and brighter than the Moon appears to us. Earth would also go through phases, like we see the Moon do from Earth. Many astonomers think that the Moon would be a great place to have an observatory. In the image to the right, you can see the Earth rising as seen from the Moon. There are no stars visible in the image because the camera exposure used was not sensitive enough to show the stars against the bright lunar surface.
Image Credit: NASA