We get asked a lot of questions about the moon. Our lunar neighbor is so evocative that it’s no surprise that we want to know so much about it.

The most common question we get is ‘how many craters are on the moon?‘ which we answered some time ago.

In this article, we supply moon facts aplenty as we answer 22 of the most common lunar queries we receive.

## 1. How Many Moons Can Fit In The Earth?

Quick Answer: We can fit about 50 moons inside the Earth.

One of the best ways to understand the sizes of celestial objects is to calculate how many of one fits into the other. We do that by working out the volume of the two spheres by taking their diameter and using the formula 4/3πr3.

Our planet‘s diameter measures 12,742 km through its center. The moon’s diameter is 3,474 km, just a little short of the width of the United States.

The volume of Earth (using the formula 4/3πr3) = 4/3 x 3.14 x (12742/2)3 = 1,082,657,777,102 cubic km

The volume of Moon = 4/3 x 3.14 x (3474/2)3 = 21,941,577,089 cubic km

1,082,657,777,102 / 21,941,577,089 = 49.343

Which all means that if we assume both our planet and the moon to be perfect hollow spheres, the ratios of their volumes is 49.343, i.e. Earth’s volume is 49.3 times that of the moon’s.

Thus, we can fit 49 moons inside our planet!

Another way of tackling the question is to ask how much more surface area the Earth has than the moon.

We work out the surface area of a sphere using the formula 4πr².

This tells us the surface area of the moon is 37,895,642 km² and that of the Earth is 509,805,891 km².

Working out the ratio between the two gives us 509,805,891 / 37,895,642 = 13.5. So Earth has 13.5 times as much surface area than the moon (assuming they are both flat and perfect spheres).

## 2. How Long Does It Take Light To Travel From The Moon To Earth?

Quick Answer: Light takes about 1.28 seconds to cover the average distance from the moon to the Earth.

If you have watched any of the videos of moon landings, you might have noticed that there is a slight delay in the transmission of astronaut’s responses.

This is because light and radio signals need time to zip past the 250,000 miles that exist between Moon and Earth.

The distance that light travels in one second is 186,282 miles and the approximate average distance of the moon is 239,000 miles.

Applying our standard formula of time = distance/speed, we can say that light travels from Moon to Earth in 239,000 / 186,282 = 1.28 seconds.

At its closest, the moon is 221,500 miles away. At that point, light gets to us in just 1.19 seconds. When it is at its farthest from us, light takes 1.35 seconds to cover the 252,100 miles from our lunar sibling.

## 3. How Did The Lunar Maria Form?

Quick Answer: They were formed by the eruption and spread of lava from meteor impacts and volcanic activity.

Like any other celestial body, the moon was volcanically active during its formation, around 3.9 billion years ago, which was also a period when meteorite impacts were high.

Meteor hits on the moon formed huge craters on its surface. Afterwards, volcanoes that erupted filled these craters with lava from the moon’s interior. It is the action of this lava spreading, cooling and solidifying which is believed to have formed lunar maria.

Maria, incidentally, is the Latin word for seas. Although they may well look like flat oceans from our perspective, lunar mare have no water in them.

## 4. How Long Is A Day On The Moon?

Quick Answer: A lunar day, i.e. the time it takes the moon to rotate once about its axis, is just over 27.32 Earth days.

Our Moon is tidally locked to Earth, which is why we only ever see the same surface facing us. As a result of this tidal locking, it takes the same amount of time for the moon to complete one orbit around Earth as it takes to rotate around its own axis.

In other words, a lunar day lasts as long as the moon’s phases from new, through full and back to new again, i.e. 27 Earth days, 7 hours, 43 minutes and 12 seconds.

## 5. How Long Would It Take To Walk Around The Moon?

Quick Answer: At NASA’s maximum expected lunar walking pace of 5km/h, it would take 3 months (91 days) of constant walking to complete a walking lap of the moon.

The Apollo astronauts walked at about 2.2 km/h, partly because of low lunar gravity. They would have taken almost 5,000 hours to walk around the moon at that pace, or 206 days.

A 2014 NASA study claims that you can walk a maximum of 5 km/h. At this rate, you would need 91 days of walking to travel the 10,921 km circumference of the Moon.

In reality, you would need to sleep at some point. Assuming you could walk for 10 hours per day, you’d cover 50 km per day and make it around the moon in 218 days, or about seven months.

And what if you could walk as fast on the moon as you can on Earth?

Assuming a decent walking speed of 4mph (6.44km/h) but still with only walking 10 hours per day, you’d make it back to where you started on the lunar surface after 169 days, or a little over five and a half months.

## 6. How Is A New Moon Different From A Lunar Eclipse?

Quick Answer: A new moon is caused by sun being on the far side of the moon from Earth’s perspective; the far side is lit while the side facing us is dark. A lunar eclipse happens during a full moon. The sun is lighting the surface facing Earth but Earth’s shadow causes the moon to go dark.

A new moon occurs when the moon is placed between the sun and Earth such that the side illuminated by the sun faces away from us. The moon is still there; we just can’t see it.

This is one of the phases of the moon that occurs with every orbit around the earth with a periodicity of 29 days, i.e. a new moon happens every month.

A lunar eclipse, on the other hand, can only happen during the full moon phase, when the sun is shining on the side of the moon facing Earth.

The eclipse occurs when Earth moves in between the moon and the sun, blocking any of sun’s light from reaching the moon.

The cause of a lunar eclipse is the alignment of the inclination of the lunar orbital plane around Earth with that of Earth’s orbital plane around the sun. It is not periodic but lunar eclipses do happen regularly.

## 7. How High Can You Jump On The Moon?

Quick Answer: With 1/6th the gravity of Earth, you can jump 6x higher on the lunar surface. The world record high jump on Earth is 2.45m, meaning it could be 14.70m on the moon.

The moon’s gravity is just one sixth that of Earth’s, so you can jump six times higher on the moon than you can on Earth. Each time to you jump, you can stay in the air for about 4 seconds before surrendering to gravity.

Jumping on the moon’s surface is something the world witnessed the lunar explorers do back in the 1970s.

The high jump record would become 14.70m on the moon (12.54m for women). The record standing jump of 1.616m (see video, below) would become 9.70m on the moon.

## 8. How Many Times Does The Moon Orbit The Earth In A Year?

Quick Answer: The moon orbits Earth just over 13 times per year.

The moon completes an orbit around the Earth every 27 days, 7 hours, and 43 minutes. Divide that into 365 days and you get a little over 13.3 lunar orbits per Earth year.

However, it takes 29.5 days for a complete lunation, i.e. the period between two new moons (see next question), so it appears from our perspective that the moon orbits 12.4 times per year.

On average, every 2.7 calendar years, there is a month which has two full moons in it. The second full moon in the same month is known as a blue moon, so the expression ‘once in a blue moon’ means about once every three years or so – if taken literally.

Every 19 years or so, there is a blue moon in both the January and March of the same year. This happens when there is no full moon in February, see ‘How Often Is There A Month With No Full Moon?’, below.

## 9. How Long Does It Take The Moon To Complete One Cycle Of Phases?

Quick Answer: It takes 29.5 days for the moon to complete one series of phases from new moon, to full and back to new again.

You may be wondering why it takes 29.5 days to complete all phases but only 27.3 days to orbit the Earth (previous question).

These two measure represent the sidereal and synodic months. The sidereal month is the time it takes the moon to go around the Earth, i.e. 27.3(ish) days.

The synodic month acknowledges that during those 27.3 days, the Earth has also been travelling around the sun. This creates an extra bit of distance the moon needs to cover to get back to appearing ‘new’ from our perspective. The time needed to cover that extra distance is about 2.2 days, making a total of 29.5 days between two new moons.

## 10. How Many Days Does a Full Moon Last?

Quick Answer: To us as observers, the moon looks for for around three days but, in reality, the full moon lasts but a moment, on the turn from waxing to waning.

A full moon occurs when the Earth is directly between the sun and the moon. We see a full moon when the lunar hemisphere facing us is more than 95% sunlit.

A full moon only occurs once per lunation and appears to last for approximately three consecutive days.

## 11. How Often Is There A Month With No Full Moon?

Quick Answer: It is impossible for any month except February to pass without a full moon occurring. Roughly every 21 years, February has no full moon, causing the January before and March after to each have two.

The table below shows the range of times that a lunation can last for.

The longest lunar month is four hours shorter than 30 days, so there must be one full moon in every month – except February, because every other month is longer than this.

February is shorter than the shortest lunation in both leap years (29 days) and non-leap years (28 days).

From the year 2000 to 2999, inclusive, there are 12,368 full moons. Of those, 952 occur in February. Since a thousand years contain thousand Februaries, it is evident that 48 of these Februaries miss a full moon. This is approximately one every 19 years.

The last Feb without a full moon was in 2018, the next will be in 2037.

Each time a February misses a full moon, January and March experience two full moons!

## 12. How Cold Is The Dark Side Of The Moon?

Quick Answer: This is a bit of a trick question because there is no ‘dark side’ per se. However, at night on the moon, temperatures can plummet to -280°F (-173°C).

The dark side of the moon is a loose term for the side of the moon which we never see. In reality, all points on the lunar equator experience equal amounts of day and night, light and dark.

Daylight and darkness last for thirteen and a half days each on the moon. Since there is no atmosphere on the moon to trap the heat, temperatures reach minus 280 F when the sun goes down.

During the day however, the temperature can reach a hotter-than-boiling 260°F / 127°C.

## 13. How Many Phases Does The Moon Have?

Quick Answer: The moon has eight recognised phases. Four are based on degrees of surface illumination: 0% for a new moon, 50% at first and last quarters, and 100% illumination at full moon. The remaining four phases are the transitions between these first four.

Since the moon shines by reflecting sunlight, what it looks like from the Earth depends upon the angle at which sun’s rays are hitting it. Thus, the moon has eight phases depending on how much amount of its area is illuminated by sunlight.

New, full and first and last quarters are moments in time signifying zero illumination (new), total illumination (full) or half illumination (first and last quarters) of the moon’s surface.

The other four phases are the transitions between the four above. They are comprised of a mix of waxing (growing) & waning (shrinking) and crescent (less than 50% illuminated) & gibbous (more than 50% illuminated).

The transition from new to first quarter is a waxing crescent; from first quarter to full moon is a waxing gibbous. From full moon to last quarter is the waning gibbous phase and from last quarter to new moon is the waning crescent phase.

## 14. What Phase Is The Moon During A Lunar Eclipse?

Quick Answer: It is always a full moon when a lunar eclipse occurs.

A lunar eclipse occurs when the moon enters Earth’s shadow for a brief period of time. This can only happen when the moon is directly opposite the sun with the Earth in the way.

The side of the moon that faces us would be fully illuminated by the sun if Earth wasn’t in the way, which creates a full moon

## 15. What Phase Is The Moon During A Solar Eclipse?

Quick Answer: Solar eclipses only happen at the new moon phase.

In the opposite scenario to the question above, the moon is now in between the sun and Earth. A solar eclipse is caused when Earth travels through the moon’s shadow.

Since the sun has to be directly behind the moon from our perspective for a shadow to be cast onto Earth’s surface, the moon has to be in its new phase.

## 16. What Do Waxing And Waning Mean?

Quick Answer: Waxing means the moon’s disc is getting ‘fatter’, which happens between new moon and full moon phases. Waning describes the disc thinning, as happens between full moon and new moon phases.

As the moon orbits around the Earth, we notice different phases which are named after the amount of moon’s area lit by sunlight. As it moves from a new moon to a full one, the area illuminated by sunlight gradually increases, also known as the waxing phase.

As it goes from a full moon to a new one, this illuminated area decreases, known as the waning phase.

In the Northern Hemisphere, the moon waxes from right to left until it is full, and wanes (i.e. the illuminated part diminishes) from right to left.

## 17. What Direction Does The Moon Revolve Around The Earth?

Quick Answer: The moon’s orbit is a prograde motion, i.e. it travels in the same direction as Earth’s rotation.

Like the moons of most planets, our moon exhibits prograde motion, meaning that it orbits Earth in the same direction that Earth rotates on its axis.

This also happens to be the direction in which the Earth revolves around the sun, and the direction that sun rotates on its axis.

While all the planets in the solar system orbit the sun in the same direction, Venus and Uranus orbit about their own axes the opposite way, which is known as retrograde rotation.

## 18. Why Doesn’t The Moon Have An Atmosphere?

Quick Answer: The moon’s gravity is too weak to hold onto an atmosphere and it has no magnetic fields protecting any atmosphere from being blown away by solar winds.

Atmospheres on any celestial body are subject to gravity and temperature.

Earth is massive enough for the gravity to hold on to our atmosphere. In added defence, our planet’s molten core generates strong magnetic fields that prevent the solar flares from eroding our atmosphere.

The moon, on the other hand, is a tiny little satellite with a weak gravitational pull that it can’t keep an atmosphere.

It does have a very thin atmosphere – so thin that the molecules in it never collide at all! A major source of this wispy atmosphere is outgassing from the moon’s interior due to radioactive decay.

## 19. Why Does The Moon Have More Craters Than Earth?

Quick Answer: Volcanic activity, weathering and plate tectonics (the movement, destruction and creation of land) on Earth’s surface erode nearly all craters. Moon’s surface has no such activity and, with nothing to erase craters, there are many more lunar ones than terrestrial.

If Earth has stronger gravity than the moon, shouldn’t our planet attract more meteors and have more craters than the moon?

While it is true that both Earth and moon been hit numerous times in their 4.5 billion year lifetime, most of the evidence has been erased by our planet.

Why is that?

Earth has three processes that the moon does not. Erosion, plate tectonics, and volcanism.

Weather, water, and plants on Earth act together to wear down the ground over a period of time. The Moon has no weather, no water and certainly no plants, so its ground is unchanging. Even the footprints of astronauts who walked there in 1971 are still present today!

Plate tectonics cause the rocks in our planet to shift around, discard old ones and form new ones. However, because the moon is much smaller, its interior cooled down much earlier than Earth’s and so it has not been geologically active for billions of years.

What scars the Moon, stays on the Moon.

Finally, on Earth, volcanic flows cover craters by filling them up with lava. While Earth has always been volcanically active, this has not been the case with the moon for many millions of years.

However, the lunar mare are examples of newer ground that is not as scarred as the rest of the surface. See ‘How Did The Lunar Maria Form?’, above.

If you have more crater questions, check out our dedicated article about lunar craters.

## 20. Why Doesn’t A Lunar Eclipse Occur Every Month?

Quick Answer: Lunar eclipses only require the sun, Earth and moon to not only be in a straight line but also in the same horizontal plane. Most months, the moon’s orbital plane takes it out of horizontal alignment with Earth, so no eclipse happens.

A lunar eclipse only occurs when the orbits of Earth, the moon and the sun are perfectly aligned and in the same horizontal plane.

This does not happen every month because the moon’s orbit is slightly tilted with respect to Earth’s orbit. The tilt in its orbit means that the moon can be behind Earth with respect to the sun, but above or below it in the horizontal plane, which means it can still be hit by sunlight.

## 21. Does The Moon Have Day And Night?

Here on Earth, we experience a day when we are on the half of the Earth that’s facing the sun. When the ground we are on does not face the sun, we experience night.

The same logic follows for the moon.

However, since the moon takes 28.5 days to spin about its axis, one day on the moon is 28.5 Earth days, with 14 being in ‘night’ and 14 being in ‘day’.

## 22. Does The Moon Produce Its Own Light?

Quick Answer: No. As bright as it can appear, all the light we see is reflected from the sun.

It does not, for the same reason that Earth cannot produce its own light. It is not big enough to make the fusion necessary to generate light.

It may be the brightest object in the sky after the sun, but all the light we see coming from the moon came from the sun to begin with, the moon just reflects sunlight back to us.

During a new moon, we can see earthshine, which is the moon reflecting light from the Earth’s surface (which itself is reflected from the sun).

Improve your moon observing skills, with our Guide to The Lunar 100