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Title: Moon
Author: NASA
Attribution: Public Domain

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Moon.nasa.gov is NASA's deep dive resource for lunar exploration from astronauts to robots.

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Title: Earth's Moon
Author: NASA
Attribution: Public Domain

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Overview The brightest and largest object in our night sky, the Moon makes Earth a more livable planet by moderating our home planet’s wobble on its axis, leading to a relatively stable climate. It also causes tides, creating a rhythm that has guided humans for thousands of years. The Moon was likel…

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Title: Solar Lunar Eclipse Diagram
Author: Tomruen
Original Source
Attribution: CC BY SA

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Title: Moon Phases
Author: Anondee
Original Source
Attribution: CC BY SA

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Title: Moon
Author: Pavel Kazachkov
Original Post
Attribution: CC BY

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Title: Does the Moon Spin
Author: Astronomic
CC BY

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Title: Episode 17: Where does the Moon Come From
Authors: Fraser Cain & Pamela Gay
Attribution CC BY

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Fraser Cain: One of our listeners, Dave Hine, asked a great question: how did the Earth get its Moon? Instead of answering this on the forum, we have turned it into an entire show. So, Pamela, why do you think that this is a great question?
Dr Pamela Gay: Well, our Moon is a big mysterious object. It's not an asteroid, as so many other moons in the solar system are, nor a big potato-shaped thing that was captured and held in place, but it's not the same as Earth: its density is lower, its contents slightly different, and it does not have things like water.

But at the same time, some of the isotopes that we can use to figure out where things formed in the solar system - like the oxygen isotopes â€" are absolutely identical to the Earth's, and these things don't all fit together in a nice neat way.

So the moon is not like many of the other moons, it kind of stands out, and its composition is really confusing. It's had people scratching their heads for as long as people have been trying to figure out what put it there.

Fraser: So what were the main theories for where the Moon came from?

Pamela: Initially there were three main theories. The first was a fission theory, that said that the Earth formed and was spinning really fast, and it just happened to fling off part of its surface. People point to the Pacific Ocean trench as where the Moon could have come from.

But it doesn't explain everything we see. This idea means that the Moon should be similar in composition to the Earth. I mentioned that the Moon lacks water, and water is a volatile. To get rid of volatiles, you have to heat something up, and the theory of a fast-spinning Earth flinging off the Moon doesn't explain how the moon lost its volatiles or how the heating took place to make the Moon the way it is.

Fraser: Did the Earth spin fast enough when it was forming that this would be plausible?

Pamela: We don't know how fast it was spinning initially. It does spin unusually fast, but there's no reason to suppose it was spinning much faster in the past using modern theories. We can't get there from here.

Fraser: And something would have to have slowed it down to its current rate of rotation.

Pamela: Well, there are tidal forces that are slowing down all the planets; Venus rotates remarkably slowly because it's so close to the Sun compared to the Earth. So we are getting slowed down, but we don't know how to get from spinning so fast that we heave parts of the planet into space, to our current, more sedate 24 hour rotation.

Fraser: So the problem with this theory is that it would mean that the Moon would be formed from the same constituents as the Earth, but it's not.

Pamela: It has many of the same things, but it's missing the volatiles. It has the same oxygen isotopes but the water isn't there. So we have to figure out how to bake the Moon, and this doesn't explain it.

Fraser: So it's as if, once the Moon had formed, nothing would have been hot enough to give it that final baking to remove the volatiles.

Pamela: It needed to be put under a sun lamp that didn't also affect the Earth.

Fraser: ...because we would have lost our volatiles as well. OK, so next step!

Pamela: So then there's the capture theory: you have the Earth and Moon formed near to each other so that they are made of similar things and they gravitationally pass and somehow the Moon grabs on to the Earth and starts orbiting.

This all sounds good, but it doesn't quite work when you try to figure out how the orbits work. If there's something as big as the Moon that's coming towards the Earth, it must be moving really slowly in order for the earth's gravity to be able to grab hold of it. To get the Moon moving that slowly if it's on a normal orbit, you require a third large object nearby that gravitationally slows the Moon, and there's no third object.

Fraser: I see. If the Moon was coming towards us so slowly, in most situations it would just be flung away, so you need a third big body and in the interactions between the three you can end up with the Moon going around the planet.

Pamela: And that third body isn't there. The Earth and Moon had to be formed at very close to the same distance from the Sun in order for them to have the same isotopic abundance of oxygen in both worlds. This [theory] doesn't take into account how the Earth and the Moon could have the same oxygen isotopic abundances, nor is there any third body.

Fraser: So that's out! Next?

Pamela: The next theory's the condensation theory: the Earth and the Moon formed where they are, out of the same stuff and they're in the same place and everything seems to be accounted for, but it's not. The problem is, that you end up with the Earth and the Moon having the same isotopic abundances, but you still haven't baked the moon, so our problem with the lack of water in the Moon is still there.

You also create a new problem: the Moon does not have an iron core like the Earth does. It has a really low density compared to the Earth, and if you have two things forming out of the exact same distribution of materials, how do you get two things that don't have the exact same composition? How do you form the Earth with an iron core but the Moon without an iron core?

Fraser: So if they had formed out of the same cloud of material, some would have ended up on the Moon, and some on the Earth, but they would have been distributed quite equally.

Pamela: Exactly!

Fraser: But then you're still not explaining why the Moon got baked and the Earth didn't.

Pamela: Yes, so with the condensation theory you get the same isotopic abundances, you get them in the right place, but how do you form it such that they don't have the same composition in terms of iron, and how do you bake it to get rid of the water?

So, three theories, and none of them match all of the observables. We have a lot of the scientific community scratching their heads.

Fraser: OK, so how did our current thinking come about then?

Pamela: Well, in the mid '70's, after all the lunar rocks dashed all of our hopes (because now we knew what the moon was actually made of), scientists sat around, scratched their heads and started talking to one another and the idea of a giant impactor came up.

So, what if you take a giant hunk of planet about the size of Mars or, for instance, take Mars' evil twin and put it on an orbit very similar to the Earth's orbit but not identical, such that the two of them end up colliding with one another?

Well, assume this Mars object hits the side of the Earth with a speed relative to the Earth of 10 kps (so they're both orbiting the Sun going at a bazillion miles an hour, but the difference between their two velocities is such that the Mars object catches up to the Earth at a closing rate of 10 kps), then you can end up with a giant splash.

The heavy parts of the two planets collapse down, form a big iron core, and the light parts of the planets â€" the mantle, the crust â€" get flung up and form a disk around the Earth and - over time - that disk coalesces into a moon.

Fraser: Right, so I guess that solves some of your problems, because you can keep the heavy material in the Earth, and you've got the lighter material that splashed out, and a reason why the Moon got baked.

Pamela: It's the energy from the collision that baked out the water from the parts that got splashed. So, basically, the high energy got the *expletive* smashed out of its stuff, thrown into space, all of the water, all the volatiles come out of it, it forms a disk and that disk â€" over time â€" builds itself into the Moon. And the time period over which this happened was probably only about a year.

Fraser: So what would have happened to the Earth then?

Pamela: The entire surface of the Earth would have gotten redone. The core of the Earth would have been redone. Our entire planet changed itself when this happened: we went from being smaller to being suddenly larger, we became much denser in the centre and we lost some of our mantle â€" it became the Moon. It was a point at which the Earth was essentially erased and started over.

Fraser: So it would have been absolutely catastrophic if there had been life on Earth.

Pamela: This was potentially the biggest impact that has happened in our entire solar system in terms of the effects of what happened. This was during the period of the Great Bombardment, or Heavy Bombardment (most likely the Late Heavy Bombardment).

While everything was going on, you have comets and asteroids crashing into things, and in this case we had another planet crash into us, which is rather catastrophic. It hit the reset button, and everything on Earth got to start over again at that moment. But what was cool, was that the Moon that we were given potentially allowed life to exist on our planet.

Our Moon is basically the great attractor of all things that want to hit the Earth. Its is completely covered in craters, most of which represent the catching of some object that might otherwise have hit the planet Earth.

We also have tides, which aren't just fun to play in and surf on, they also slosh about the oceans, and who knows what effect that has on the evolution of biological life on the Earth.

So, not only did it hit the reset button, it started the planet Earth on a completely different direction.

Fraser: Now, apart from not looking so battered, would the Moon have looked very similar to what we see today?

Pamela: Well, it would have been much smoother, it wouldn't have had the Old Man in the Moon lava basins that we see now. It took time for all of those things to form.

No one is exactly sure why the lava flows on the Moon are the way they are, lots of people have tried to figure out why the dark features that we see as the Old Man in the Moon are predominantly on the side of the Moon that faces the Earth, and no one can really explain why that is the case.

They're not the lowest points on the planet, and basic physics does not allow us to get an exact solution that says it's because that's where there is higher gravity from the earth; there's just not that much difference in gravity. But it took time for all those volcanoes to erupt for unknown reasons predominantly on the side of the Moon that we see all the time.

We also would have had a completely smooth Moon initially; it took time for all the craters to build up on the surface.

Fraser: Why do we see only one side of the Moon?

Pamela: It's because of something called tidal locking. The Moon creates tides on the Earth. Its gravity pulls on the Earth such that the gravitational pull is higher on the side closest to the Moon and lower on the side furthest from the Moon, and this squishes our planet a little bit.

The same thing is happening on the Moon; the Moon is getting squished a little bit and, if the object is rotating, the rotation carries the bulged part (the squished-out, flat part) away from the other object. So as we rotate, the high tides are slightly ahead of the Moon's position.

Now, the Moon is pulling on those bulges, trying to prevent them from rotating away. The Moon is a smaller object, so the effect of a pull on a bulge on the Moon is much more dramatic and so initially the Moon was probably rotating compared to where we stand on the Earth. Currently, it does rotate relative to the stars, so the Sun gets to see every face of the Moon during every lunar cycle, but we only see the exact same side because our gravity has locked it in the place. If it was rotating, it would squish out and we would grab the bulge and pull on the bulge so that the bulge was always faced towards us.

The Earth is getting slowed down currently; as we rotate, the Moon pulls on our tides. It pulls on the high tides,even the rocks have tides: did you know that mountains can move by as much as 30 centimetres as they get pulled towards the Moon?

Fraser: I had no idea!

Pamela: It's one of those cool things. We see the ocean tides, but the mountains are moving as well.

Fraser: So was there a time, long ago, when the Moon freely rotated? I guess it would have been a lot closer to us, right?

Pamela: It would have been a lot closer. Due to conservation of momentum and a lot of other neat stuff, the Moon was initially closer but, as we've been slowing down its rotation, it has been been moving faster in its orbital velocity, so its been slowly creeping further and further away from the Earth.

Fraser: How fast is it moving away from us?

Pamela: Only a couple of centimetres a year, but it adds up in time, and what's neat is that we can actually measure this using lasers. There's a group out at McDonald Observatory in West Texas out in Fort Davis, that shoot giant green lasers off the mirrors that the Apollo astronauts planted on the Moon, and they measure the amount of time it takes the laser light to go up to the Moon and come back, and they an measure the distance to the Moon to just millimetres and they can measure changes in the orbit and very minute changes in the distance of the Moon from year to year.

Fraser: But if the moon is moving away from us, how is it that the Moon and the Sun are the same size in the sky? We can have a total eclipse of the Sun and the Moon just perfectly covers the Sun.

Pamela: This is one of those strange coincidences. In general in science we say that we do not live in a special time or place, but when it comes to the Moon and the Sun, we actually do live in a special time.

In the far distant past, when there were probably no human beings walking on the Earth, the Moon appeared much larger in the sky and could more than cover the face of the Sun when it passed in front of it but now, as the Moon's moving further and further from the Earth, it's getting smaller in size.

Currently we have two types of solar eclipses: one is a complete, and the other is an annular eclipse.

With an annular eclipse, the Moon is further away from the Earth in its orbit, and it only sort of covers the Sun, and you end up with this small annulus of the Sun visible around the Moon. In time, that's going to be the only type of solar eclipse we ever get.

Currently, when the Moon is on the closest part of the orbit, if it happens to be a new moon that exactly lines up with the Sun, you get a full solar eclipse, but eventually, when the Moon is at its closest position to the Earth, it will no longer be able to block the Sun, so we'll always have this doughnut of Sun left behind during a solar eclipse.

Fraser: Have there been any other examples of these kinds of large collisions in the solar system that might explain other moons?

Pamela: Well there are all sorts of examples of collisions all over the place. When we look at the asteroid belt - which is fairly close - some of the larger asteroids have small chunks of rock which orbit them. In some cases, those small chunks have been knocked off the parent asteroid and now orbit it.

If you look at the distribution of what asteroids are made of, you see clumps where all of the asteroids are made of very similar materials, and were probably once a larger body that got broken up during collisions.

As we look further out across the solar system, when we look at Pluto and Charon, there's a chance that there's another example of a place where something big got hit and turned into two smaller bodies.

Fraser: So we've got a very similar situation there with the non-planet and the moon...

Pamela: ...the dwarf planet and the other dwarf planet!

Fraser: Yeah, where they have a similar type of material but one is lighter than the other. I guess we're going to wait for New Horizons to make it out there and help answer...

Pamela: ... And the more we can learn about the other moons of Pluto and Charon, the more we'll know about that particular system.

Fraser: So what does the future hold for our Moon? It's moving away from us, so what's in the far future?

Pamela: Well, eventually the Earth is going to become tidally locked with the Moon as well. So if I can see the Moon and it's low down on my eastern horizon, you - who live further west â€" may not be able to see the Moon at all because it's over your horizon. So only half the planet will ever be able to see the Moon.

It's also going to be rough on those of us who like 24 hour days, because when this happens, the Earth is going to rotate once for every time the Moon orbits the Earth, and that's going to take a thousand hours or so. So the days are going to be substantially longer.

Luckily it's going take about a trillion years for that to happen, so we have a good long wait but, until then, our days are slowly going to get a little bit shorter each year and the Moon's going to get a little bit further away each year, until at some point the Earth and the Moon are completely locked together, at which point they stop moving apart and the days start lengthening, and we're trapped looking at the exact same aspects of one another.

Fraser: Wow! That's quite a future. I think that it's interesting to see that what we see right now is just a moment in time. The Moon is getting further away, our days are getting longer, and what we think has always been is something that is happening on scales which are so long that we just can't comprehend it.

Pamela: Everything is always evolving and changing and we don't live in a stagnant place; it's a very dynamic universe. Saturn's rings could disappear, it's possible that Mars will develop rings. Everything is changing and we just happen to live in a unique time when we have a 24 hour day and full solar eclipses. It's a pretty good to time to live in, I think.

Fraser: So, there you go Dave Hine, I hope that answers your question, and I hope that gives the rest of you some hope that, if you ask us questions, send us e-mails, suggest show topics, or post in the forums, we'll try to turn them into shows if we think there's enough material there.

Next week we'll be tackling black holes, big and small. Thanks again Pamela.

Pamela: See you later, Fraser.

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Fraser Cain: One of our listeners, Dave Hine, asked a great question: how did the Earth get its Moon? Instead of answering this on the forum, we have turned it into an entire show. So, Pamela, why do you think that this is a great question?Dr Pamela Gay: Well, our Moon is a big mysterious object.

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What if the Moon didn't Exist? (a podcast)

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What if the Moon didn't Exist? (a podcast)

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Title: March 28th: What if the Moon Didn't Exist?
Authors: Patrick McQuillan
Attribution: CC BY

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Date: March 28, 2009

Title: What if the Moon did not exist?

Podcaster: Patrick McQuillan

Organization: Incorporated Research Institutions for Seismology (IRIS)
www.iris.edu

Description: We often take the Moon for granted. We assume it will always be there. Circling the Earth month after month with regular precision. But what would our world be like if we didn't have a moon? The length of the day, the tilt of the planet, the number of meteors impacting the surface are just a few of the things that would all be vastly different if the Moon did not exist. Not to mention all of the familiar cultural references that would no longer make sense.

Bio: Patrick McQuillan earned a B.S. degree in Physics from the College of William and Mary. His senior research project involved determining the period of variable stars, most notably Alpha Auriga. This was at a time when collecting data meant going to the roof of the physics building, locating the research star by hand, and tracking the star manually by following a guide star in the finder scope. No GPS-auto-guiding-from-a-climate-controlled-remote-location! In the twenty plus years since then, he has explained astronomy to the general public as a Planetarium Director, the Education Manager for Challenger Center for Space Science Education, a NASA Solar System Ambassador, and currently explains Earth Science as Education and Outreach Specialist for IRIS. You can view current earthquake activity using the Seismic Monitor located on the IRIS website.

Today's Sponsor: This episode of "365 Days of Astronomy" is sponsored by Astrocamp Summer Mission of Idyllwild, California. Help introduce a child to the world of Astronomy. Learn more at www.astrocamp.org.
Transcript:
Hello, I'm Patrick McQuillan, Education and Outreach Specialist with IRIS, the Incorporated Research Institutions for Seismology, a NASA Solar System Ambassador and a former Planetarium Director. Welcome to the March 28th edition of the 365 Days of Astronomy podcast: What If the Moon Did Not Exist?
One of my favorite comic books growing up was a Marvel comic entitled What If...? The comic usually began with a brief replay of a notable event from the story of superhero in Marvel Universe. At a critical story point, one which could have sent the story in several vastly different directions, the writers explored what would have happened if events had taken a different course. For example, what if Spiderman's Aunt had died instead of his uncle? What if the Fantastic Four had not gained their super powers? What if Captain America lived during the American Civil War?

In almost every one of these stories the change led to something bad, or at least worse than the original story. Which of course led you to believe that the writers had made the best choice when they directed the paths of the original stories. And it led my friends and I to have long, heated arguments about the moral, social and philosophical implications of the various versions of the stories. Well... as much as you can argue about fictitious characters when you are twelve.

In science it can often be instructive to ask What If? Such thought experiments have been used for centuries to explore science concepts, usually when the actual experiment was too expensive or even impossible to actually perform.

So to take a page from Marvel comics, in today's podcast we look back to the early days of the Solar System. We see the early Earth forming from the cloud of gas and dust surrounding the young Sun. An object, perhaps as large as Mars, is on a collision course with our future home. This giant collision destroys the incoming body and ejects large amounts of debris into orbit around the Earth. This cloud of debris eventually forms the body we know today as our Moon.

Now let us pause and pose our philosophical question...What if this collision NEVER HAPPENED?
We see the early Earth forming from the cloud of gas and dust surrounding the young Sun. An object, perhaps as large as Mars, is on a seeming collision course with our future home. They just miss. No collision. No cloud of ejected debris. No Moon. And I will give away the bad answer... No Earth as we know it!

Yes that is correct. Without the Moon, life on Earth would not be life as we know it.
The first thing that would be different are eclipses. They would be no more. No more solar eclipses, no more lunar eclipses. In fact there would be no more solar eclipses anywhere in the solar system. The earth is the only planet where, from the surface of the planet, one of the planet's moons seems exactly the same size as the Sun and can just cover it, causing an eclipse.

There would be more consistently dark skies for astronomical observing if there was no moon. Astronomers would still have to compete with human created light pollution.

If we had no moon there would be no tides. Well not exactly. There would still be tides; they would just be smaller. Both the Sun and the Moon create tides on the Earth. There are two high tides and two low tides each day.

Tides occur because the gravitational force between two bodies decreases with distance. Gravity tugs on nearby objects more strongly than on distant objects. The oceans on the side of the Earth closest to the Moon feel the greatest attraction to the Moon (and to the Sun). Being fluid, the nearby oceans move upward in response to the Moon's pull, until there is a balance between the upward force from the Moon and the downward force from the Earth. The high tide on the far side of the Earth occurs because the oceans on the side of the Earth farthest from the Moon feel less gravitational attraction to the Moon. They are left behind as the Moon pulls the other parts of the Earth toward itself with greater force.

This difference in gravitational attraction on the near and far sides of a body is officially known as tidal force. The word "tidal" does not refer to actual moving ocean tides, although this force does give rise to them. The strength of tidal forces fall off according to an inverse cube law. (Remember gravity falls off according to an inverse square law.) The inverse cube relationship means that tidal forces are more dependent on distance than gravity.

In simple terms, since the Moon is 400 times closer to us than the Sun, and even though the Sun is more massive than the Moon and thus has more gravity, the much closer distance of the Moon makes its tidal forces on the Earth much larger than the Sun's. The tidal effect of the Sun is just under one half the tidal effect of the Moon.

With both the Sun and the Moon rising tides in the Earth's oceans the actual height of high tide at any one location is complicated. First let us ignore the effects of local geography, which can cause really high tides due to the shape of the land into which the tide is moving. When the Sun, Moon and Earth are all lined up, the tides from the Sun reinforce those from the Moon and we have higher high tides. This is called a spring tide. It has nothing to do with the season of Spring. When the Sun, Moon and Earth are lined up in a 90-degree angle, the tides from the Sun partially cancel those from the Moon and we have lower high tides. This is known as a neap tide.

Thus, if we had no moon we would still have tides. They would be simpler. And they would not be as strong. So surfing would not be as exciting. Bummer.

But it gets worse. Due to the effects of tides, the Moon is gaining angular momentum from the Earth. The Moon's orbital velocity is increasing and it is moving away from the Earth. Due to conservation of momentum, the Earth's period of rotation is slowing down. The day is getting longer. The day increases by 0.002 seconds each century. Which doesn't seem like much, but over billions of years it adds up.
This exchange of energy occurs mostly because the eastward rotating Earth is rubbing against the westward moving tides. This causes friction, which slows the Earth's rotation. Since the total energy of the Earth-Moon system must remain constant (conservation of Momentum), the Moon's velocity increases. As a body's orbital velocity increases, it must move farther away from the object it is orbiting in order to remain in orbit. The Moon is receding from the Earth about 2 inches per year. This has been confirmed by bouncing laser beams off reflecting mirrors left behind on the lunar surface by the Apollo astronauts and measuring the round trip travel time of the laser light.

If the Earth is slowing down, it must have been rotating more rapidly in the past. By counting growth rings in 400 million year old coral fossils and in 3 billion year old stromatolites, geologists calculate that the Earth was rotating four times faster when it formed than it is today. The tidal effects of the Moon and, to a much lesser degree, the Sun have lengthened the day from six hours to 24 hours.

By the way, the closest the Moon could have been was about 7,300 miles above the Earth's surface. This is 1/20th the Moon's present distance. Any closer the tidal forces created on the Moon by the gravity of the Earth would have ripped the Moon apart, turning it into a ring. This limit on the Moon's distance is consistent with the theory of lunar formation by giant collision.

Ok, so with no Moon to slow the Earth down, the only tides would be from the Sun. The Earth's rotation would still slow down, by not nearly as much. The six-hour day at the time the Moon should have formed would increase to an eight-hour day at present time with no Moon. Not good for life on Earth!

The faster a planet rotates, the faster its winds blow. Just look at Jupiter. The largest planet in the solar system rotates once every 10 hours. Winds are pulled into east-west flowing patterns with wind speeds between 100 and 200 miles per hour. The Earth would be rotating once every eight hours, so 100 mile per hour wind speeds would not be unreasonable to expect. Hurricanes would have even higher wind speeds.
Try to imagine what life would be like with only three to four hours of sunlight each day. Life forms on Earth have evolved with biological clocks set to the familiar 24 hours of rotation. Many activities are regulated by internal biological clocks. Waking, sleeping, hunger, and mating depend on these circadian rhythms. Animals with a 24-hour internal clock would quickly get out of sync with an eight-hour day. Think about how you feel after an airplane trip that crosses multiple time zones.

Of course life would have evolved to fit the conditions of a shorter day. It just might not have included humans. Which I guess would be ok, there are so many things I don't get done during a 24 hour day, I would not even like to speculate how little could be accomplished in an 8 hour day.

Let's not forget that the mere presence of the Moon caused less life ending impacts to occur on the Earth. Without the Moon's helpful goal keeping, the Earth would have experienced a higher rate of impact from space debris as the solar system, and life, was forming. Which might have led to the absence of humans on Earth today.

And even if humans did exist on this wildly rotating, wind tunnel of a planet, think of all the cultural references to the Moon that would not exist.

The word "month" would not exist. With no Moon as a reference, there could be no lunar calendar. Time keeping would be more difficult. The Sun would be the next best reference point.

There would be no "lunatics". Well, they would still exist; we would just need another word for them. Nightatics just doesn't seem to cover it.

There would be no lunar fables. Gone would be werewolves, humans who change into the form of a wolf during full moons.

With no moon to travel to, our first foray off the Earth to a distant world would not have occurred. Mars would be the nearest destination. A trip to Mars is a much more complicated three year journey compared to the, although difficult, but much shorter, two week trip to the Moon.

For those with romantic inclinations, there would be no full moon to park beneath. Somehow, I think a night under a bright Venus would not elicit the same response.

And think of all the wonderful songs that would either not exist or would have been written differently. Familiar favorites such as: Nothing River, Blue Nothing, Fly Me to the Nothing, Nothingshadow, Blue Nothing of Kentucky, Nothing over Bourbon Street, Bad Nothing Rising, By the Light of Silvery Nothing, Nothingdance, and my personal favorite: Pink Floyd's Dark Side of the Nothing.

So while we often forget it is around, we should take time out every now and again to reflect on how different the Earth would be without our nearest neighbor. And if you take along a close friend the contemplation could be doubly enjoyable.

365 Days of Astronomy
=====================
The 365 Days of Astronomy Podcast is produced by the New Media Working Group of the International Year of Astronomy 2009. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow...goodbye.

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March 28th: What if the Moon did not exist?

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Date: March 28, 2009 Title: What if the Moon did not exist? Podcaster: Patrick McQuillan Organization: Incorporated Research Institutions for Seismology (IRIS) www.iris.edu Description: We often take the Moon for granted. We assume it will always be there. Circling the Earth month after month with regular precision.

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Neil Armstrong Describing the Moon's Surface

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Neil Armstrong Describing the Moon's Surface

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Author: NASA
Public Domain

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Title: High School Earth Science/Earth's Moon
Attribution: CC BY-SA

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High School Earth Science/Earth's Moon - Wikibooks, open books for an open world

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Astronomers have carried out computer simulations showing that the collision of a Mars-sized object with the Earth could have resulted in the formation of the Moon. Additional data shows that the surface of the Moon dates to about 4.5 billion years ago, suggesting that the collision occurred during the heavy bombardment period, about 70 million years after the Earth formed.