This transcript is not an exact match to the audio file. It has been edited for clarity.

This transcript is not an exact match to the audio file. It has been edited for clarity.

Artist's illustration of the dwarf planet Eris. Image credit: NASA

Astronomers have been searching for the mysterious Planet X for hundreds of years. It was the search for a theoretical planet beyond Uranus that turned up Neptune, and then again for Pluto. And even now there are some astronomers who think there's a more distant planet out there. Oh, and there are a bunch of pseudoscience cranks trying to freak people out about the end of the world. Don't worry, we'll make time for them too, but first let's start with some real science.

Surveyor Lander. Image credit: NASA

Let's continue on our journey to the Moon. Last week we talked about the physical characteristics of the Moon, its appearance in the sky and how it interacts with the Earth. This week we're going to take a look at how scientists have expanded our understanding of the Moon. From ancient astronomers using nothing more than their eyes and the first telescope observations of Galileo to the exploration by robotic spacecraft. And of course, the first tentative steps by the human explorers of the Apollo program.

Ep. 114: The Moon, Part 2 – Exploration of the Moon

Before we went…

• Aristotle, Galileo and the Moon — Galileo Project
• Lunar mare – Absolute Astronomy
• Lunar Basalt – Wiki
• Franz von Paula Gruithuisen — Internet Encyclopedia of Science
• Finding craters on Earth with Google Earth — Google Earth Blog
• Nomenclature of Lunar craters – NASA

Early Missions to the Moon

• NASA's timeline of lunar missions
• Russian Luna 1 ( 1959 flyby), Luna 2 (1959 impact), Luna 3 (1959 probe)
• US Pioneer 4 (1959 flyby)
• Ranger missions (1961-1965)
• Huygens probe to Saturn's moon Titan
• Surveyor missions (1966-1968)

Apollo

• Apollo missions overview (1968-1972)
• Book:  A Man on the Moon by Andrew Chaikin
• Movie:  From the Earth to the Moon
• Movie:  Apollo 13
• Movie:  In the Shadow of the Moon
• Movie:  When We Left Earth

Subsequent robotic Moon exploration

• Hitan (1990)
• Clementine (1994)
• Clementine Color Mosaics of the Moon
• Lunar Prospector (1998)
• Smart-1 (2003)
• The Magic of Ion Engines — ESA
• Kaguya (SELENE) 2007-present
• JAXA's Kaguya site, includes Hi-def movies of the moon
• Chang'e 1 2007- present
• More on Chang'e 1 from the Planetary Society

Download the transcript

Transcript: The Moon, Part 2 – Exploration of the Moon

Fraser Cain: Let’s continue on in our journey to the Moon. Last week we talked about the physical characteristics of the Moon, its appearance in the Sky and how it interacts with the Earth.

This week we’re going to look at how Scientists have expanded our understanding of the Moon from ancient Astronomers using nothing more than their eyes and the first telescope observations of Galileo to the exploration by robotic Spacecraft.

And of course, the first tentative steps by human explorers of the Apollo Program. So, let’s go right back to the first discoveries that humans have made about the Moon. I guess in the beginning we just had eyes.

Dr. Pamela Gay: Well and initially it’s not like we didn’t know the Earth had a Moon. It is probably one of the first things people noticed – Oh, there’s a giant bright object in the Sky that changes phases.

Fraser: Who discovered that?

Pamela: Yeah, I don’t know his name. [Laughter] It’s not in Wikipedia. But the main record that Western thought bases itself on in studying the Moon goes back mostly to Aristotle and Plutarch. Aristotle in looking at the Heavens saw all of the heavenly bodies as perfect spheres because well, the sphere is the perfect shape therefore everything in the Sky must be the perfect sphere.

However, when you look at the Moon it is mottled in color. There’s the ‘Old Man’ or the ‘Rabbit’ in the Moon depending on your cultural perspective and many other shapes as well.

When Plutarch looked up, what he saw instead was that the dark places were corrupted. They were chasms, they were craters (well they didn’t know what craters were back then) they were pits; they were cut-aways from rivers. They were places where the Sun wasn’t able to reach the bottom in and instead we’re looking into deep shadow.

So, we have these two completely different views. Aristotle going: spheres, perfect wonderful it’s in the heavens. Plutarch going: no, corrupted body, deeply shadowed, large chunks missing that the Sun can’t reach the bottom of. So there is this wonderful dichotomy. Most people listened to Aristotle.

It wasn’t until Galileo and his “well let me look up with the telescope” way of looking at the Universe that we started to realize that for certain the Moon wasn’t a perfect sphere.

The Moon had mountains; it had these weird round pits. It had all of these different surface features and he was able to say for certain that the two different colors were two different surfaces. That’s kinda cool.

Fraser: And how are they two different surfaces? What’s the difference between the parts that are dark and the parts that are lighter from our point of view?

Pamela: We didn’t know that for a long time. He was simply able to say that the dark stuff is not a giant pit. He was able to say that’s just a surface. It wasn’t until we went and started exploring it that we were able to confirm for certain that the dark stuff is basalt, it is lava. It’s melted rock that has been cooled and solidified. It’s either from actual volcanic type stuff or just more oozing of lava out through the surface or from re-melting of the surface during cratering. The light stuff is in the inner highlands, it’s just rock.

What’s kind of cool to me is we look at the Moon – and having grown up learning about Asteroids at about first or second grade, the difference between a Meteor a Meteorite or a Meteoroid – we look at the Moon and see the round spots as craters. But it wasn’t actually until the 1820s that a man whose name I’m going to horribly mispronounce, Franz von Paula Gruithuisen got the idea that maybe these things were Meteor strikes. He thought maybe these round pits with crater walls are actually crater marks on the Moon.

Fraser: And there’s an object like that here on Earth, the Meteor crater in Arizona which looks very similar.

Pamela: Right and now that people are starting to peer through all sorts of satellite imagery there are major craters that look like craters all over the planet Earth.

There are actually all sorts of projects in Google Sky or Google Earth as the case may be, to try and locate other potential crater walls scattered around the Planet. And that’s just cool our Planet is pock-marked too.

Fraser: Well, after Galileo you can imagine that every Astronomer worth their salt was pointing their telescope at the Moon when they weren’t discovering the Rings of Saturn [Laughter] or something. Beyond that what kinds of discoveries started to pour out?

Pamela: Mostly we were happily mapping the surface of the Moon, naming things in all sorts of different ways. There were many different naming conventions that were used. The one that was eventually settled on is the idea that large naked eye blobs on the surface are named as seas (mare). The little spots that you can only see through telescopes which we now know are craters are named after philosophers and I just like this dichotomy.

Since then we’ve broken it and so there’s shackles and craters and things like that. It wasn’t until 1753 that we realized that the Moon doesn’t have an atmosphere. Up until then people had randomly thought maybe there was life on the Moon.

It was actually Plutarch who started that idea. As early as essentially the beginning of Western Civilization there was the concept that maybe there was life on the Moon. Then in 1753 we realized no, there’s not, there’s no atmosphere there. Then as I said in the 1820s we realized that the craters were made by Meteor strikes.

From then on, we basically mapped and that was all we could do without having any solid compositional data. Even with the mapping we could only map a little more than fifty percent of the Moon because the Moon, as we talked about in the last episode is tidally locked to the Earth. We can only see one side of it.

The Moon has what we call vibrations. It vibrates a little bit and we can see around the edges a little bit as it oscillates slightly. But we mapped the one side we could see really, really well. Then we waited for manned Space flight and unmanned Space flight to get invented so that we could start looking at other things as well.

Fraser: So then fast forward, I mean beyond just mapping, [Laughter] fast forward to the first attempts to actually reach out with Spacecrafts and explore the Moon. So what were the first attempts to get to the Moon?

Pamela: Well, back as early as 1959 actually we were flinging things at the Moon. It was initially mostly the Soviets flinging things. There were three different Luna missions, one, two and three, conveniently named in 1959 as well as one Pioneer mission from the United States.

The Luna missions were off to first take pictures of the Moon and second to go land on the surface and find out what the surface is made of. So the first mission was intended to land on the surface – well impact on the surface – landing is a bit strong of a statement. But it missed. It flew by, took pictures and then it kept going.

It was actually the very first object to end up orbiting the Sun instead of the planet Earth. Then after that the United States launched its Pioneer mission. That again was a fly-by, took pictures, and happily explored the environment. It did a radiation experiment and then we went back to the land of the Luna missions. We had Luna 2 which did manage to successfully hit the surface of the Moon and then

Fraser: It landed.

Pamela: It landed.

Fraser: The hard way [Laughter]

Pamela: But they intended to land the hard way. So it was alright.

Fraser: Right, that was all part of the plan.

Pamela: It was all part of the plan and then finally, Luna 3, toward the end of 1959 allowed us to see for the first time – this was a Soviet mission – it returned the first ever pictures of the back side of the Moon, the unknown, the dark side of the Moon that really does get lit up as much as the front. So finally in 1959 we were able to see this mysterious other side of the Moon.

What’s cool is the back side of the Moon is radically different. It is cratered completely differently. It has much, much less lava on it so it’s coloration is very different. And so that was just a fabulous moment. Then no one went back to the Moon for a year.

Fraser: [Laughter] Right, now I’m assuming that you’re glazing over all of the failures, all of the rockets that exploded on the pad and crashed into the atmosphere and so on.

That’s fine, we don’t want to repeat – we had a lot of complaints on the Mars episode about the failure after failure so we’ll gloss over the failure after failure.

Pamela: But the thing is those four missions I just named, according to the NASA Lunar Exploration Timeline which does list lots of failed missions – those were the only four.

Yeah, Luna 1 missed and kept going but it still returned data. So the Moon doesn’t have quite the same curse that Mars suffers from.

Fraser: Right, okay so we’ve gotten to the point that we’ve seen the far side of the Moon for the first time. What about landing?

Pamela: There was a gap. Here’s where the United States started to get involved again with things that didn’t like to fly in the 1960s with the Ranger program, it was not one of America’s more successful programs. It had two attempted test flights in 1961 and both of them failed.

Then we had in 1962 an attempted impact and we missed. Ranger 4 did successfully find and crash into the surface. It was designed to transmit pictures. It was able to do this for about 10 minutes prior to impacting the surface.

What’s kind of cool is one of our goals was to basically shake the Moon to collect data on what happens when you have a rough landing. This is sort of like when we landed the Huygens Probe on Saturn’s Moon Titan. We wanted to find out what the surface is like.

One way to do that is to land a bit more violently than you might like and Huygens didn’t really do that. But then to see what shakes, what is the impact like, if you have a nice slow deceleration then you landed on something squishy.

If you have a bit abruptive landing that means you landed on something a bit more solid than you might have liked. So there are reasons to fling yourself into the surface of a foreign body.

Fraser: Well the surface of the Moon is a bit of a mystery, right? I mean they knew that it was covered with dust probably from billions of years of micro-meteor impact but they didn’t really know how hard this stuff was going to be.

Pamela: Right. This is the problem with the Regula. The Moon is constantly being barraged by micro-meteors. Fred Hoyle was one of the people who put forward the idea that “yeah you’re going to land and you’re just going to sink into the dust.”

We eventually ended up building an entire series of missions – the Surveyor missions – that started launching in 1966 with a goal to land purposely, land softly and send back data. They had Solar Arrays, TV cameras, all the nice little things including arms to dig into the surface. You can see these as kind of the baby precursor version of our current Mars Polar Lander.

These happy little tiny robots that are really quite darling. They look like tripods that have been overburdened with electronics. These little robots successfully landed in many cases and were able to send data back to the planet Earth.

So, now instead of impacting the surface, we’re purposely landing on the surface. We did our first purposeful landing May 30^th of 1966; tried again in September – didn’t work so well – kept trying and these were the precursors to the Apollo landings.

Fraser: Right, so these were the ones that really sent out the first pictures of the surface of the Moon, tried to dig around and see what the surface was like, but you already kind of mentioned the next big plan which was the Apollo mission. Maybe rewind a bit and talk about that.

Pamela: This all started with John F. Kennedy from my home state of Massachusetts. When he became president he wanted to give our Nation a vision and part of that vision was violently beating the Russians to the Moon (well, not with violence but peacefully) beating the Russians to the Moon.

He put this idea forth very eloquently in his speech where he said: “We choose to go to the Moon. We choose to go to the Moon in this decade and to do other things. Not because they are easy but because they are hard. Because that goal will serve to organize and measure the best of our energies and skills because that challenge is one that we are willing to accept, one we are unwilling to postpone and one which we intend to win and the others too.” He goes on it’s a really cool speech.

Then they start throwing resources at it. That was the cool thing, NASA didn’t have a lot of money but they did a lot of deficit spending. Nowadays I don’t think NASA would be quite so allowed (not even a strong enough a word) no one would allow NASA to keep going if they went into the same amount of deficit spending that we had during the Apollo era.

They were able to in less than 10 years go from not really being able to get things consistently to the Moon to landing human beings on the Moon and returning them with a lot of rocks. Rocks don’t weigh small amounts and that’s just cool.

We accomplished an amazing amount of stuff – all of this before I was born. The last crewed landing on the Moon occurred in December of 1972, more than a year before I was born. This is I think part of why people of my generation are a bit, yeah NASA, do something now please because we haven’t seen any really cool accomplishments.

No one has landed on the Moon in our lifetime. But in that one brief wonderful deficit spending period of time, NASA went from missing the Moon to successfully landing and returning people.

Fraser: I don’t think we have the time in this episode to really go into the details of how the Apollo program worked but there are some wonderful documentaries and TV shows and movies that you can watch that will show you them. “From the Earth to the Moon” is amazing.

Pamela: It’s a must see. I make my students watch it.

Fraser: Apollo 13; there’s a new one by the Discovery channel which is “When we Went to the Moon”. There’s a lot of great material out there to be able to sort of bring you up to speed on all of the missions. Yeah, “From the Earth to the Moon” I think is the most entertaining, comprehensive accessible look at the Apollo mission.

So, if you’re older and you want to get your kids into the Apollo missions, that’s the show to watch. They really make it quite entertaining, very much in the style of Apollo 13 as well. It all kind of mixes together quite well.

Pamela: What’s really cool about this stuff is how much history is involved in it. So, if you have a friend who thinks, yeah science, I don’t care, but is interested in politics and history, the Apollo mission is the way to suck them into science as well.

We’re dealing with personalities, how to fund all of this, dealing with everything else that was going on in the world at that time. It’s just very fascinating to watch. While America so far is the only nation that has managed to successfully get people to the Moon and back, the Soviets also helped returned rocks. Returning rock – if you’re not into rocks and I admit to not being into rocks – really doesn’t sound that all exciting because they’re rocks.

The thing about Lunar rock is you can use it to start dating different surfaces. So by sending people to different areas on the Moon and by sending Lunar Return Landers to the Moon, we were able to gather rocks that we could bring back and we could use carbon isotope dating to say, this region that has very few craters is this age. This region that has this number of craters is this age.

Using the rocks gathered on the Moon and assuming that impact crater rates are fairly consistent across the Solar System (which we think is a reasonable thing to assume) we’re able to make rough estimates of the ages of all the rocky non-weathered bodies in the Solar System. That’s just really cool.

Fraser: So, July 19, 1969, Neil Armstrong and Buzz Aldrin step out on the Moon for the first time and stay out there for a few hours and come back. Several missions after that leading up to 1972 I think Gene Cernan was the last person to walk off the Moon.

Humans haven’t set foot on the Moon since then. But that’s not the end of their exploration of the Moon. There have been missions ever since and right now. So, let’s not get stuck in 1972 [Laughter] let’s get going and talk about some of the other missions.

Pamela: The NASA timeline which includes everything else – it’s on the NASA.gov website shows how in January 1973 there was a Soviet Rover. In 1974 there was a Soviet Orbiter and Lander.

In 1976 there is another sample return mission. Then the Moon gets ignored until 1990. Through pretty much my entire child adolescence there was nothing to do with the Moon anywhere.

Fraser: Right it’s all about the Space Shuttle.

Pamela: It was all about the Space Shuttle and the Space Shuttle is cool but it only goes 300 miles up which in terms of exploring the Universe is nowhere.

Fraser: Fine, the Voyagers.

Pamela: The Voyagers were awesome. They were out on the edge of the Solar System. They were what got me excited in Astronomy.

Fraser: Me too.

Pamela: But, we ignored the Moon and then the Japanese got involved. They sent this wonderful little mission that was called Hiten – I’m sorry I’m going to mispronounce things because they don’t teach you about this in graduate school.

It translated into Flying Angel. A wonderful little mission that went out and it was taking pictures and basically re-opened the door. It got us back exploring the Moon a second time. This wonderful little Japanese craft was mostly out there looking at dust. It checked out the Lagrange Points.

It eventually ran out of fuel and they crashed it into the Moon which doesn’t sound all that exciting. But when you hit things into the surface of the Moon you can make the Moon vibrate. The way they vibrate allows us to start probing the density of the Moon, probing how it reacts to different things.

The Apollo Astronauts left mirrors on the Moon so when we hit the Moon with things like this cute little Japanese Spacecraft it makes the Moon vibrate and we can see those vibrations in laser light reflected off these mirrors. That again is just kind of cool. So, in 1990, the Japanese re-opened the doors to Lunar exploration.

A few years go by, nothing much happens and then America gets back in the game. We go out and start doing detailed imaging again. Here we have the Clementine mission. This is the point at which the United States starts thinking again about going out and figuring out how do we get people back on the Moon.

Mapping the Moon in great detail is one of the first ways to do this. The Clementine mission had lots of different ways of imaging the Moon. It had a laser imaging detection and ranging system. They were flying over the Moon bouncing laser light up and down which allows you to get very accurate altimetry of the Moon, very accurate altimetry of the Moon and very accurate measurements of the rise and fall of the surface.

They had radar, high-resolution cameras, they had ultra-violet invisible cameras and they were even able to detect charged particles coming up off the surface of the Moon.

Fraser: Yeah, Clementine REALLY mapped the Moon to within an inch of its life. [Laughter] Nothing had ever been mapped at that level, to that detail; like just REALLY amazing contour maps.

I was actually doing some work on this recently and all of the Clementine maps have been turned into these really amazing mosaics. You can search for like Clementine, Moon Map or Mosaic on Google and you can get access to these really detailed maps that have been stitched together of the images that Clementine took of the Lunar surface. It’s quite amazing.

Pamela: They weren’t the perfect images. They weren’t high enough resolution that we could start looking for ice down in the bottoms of craters. We’re going to do better in the future. But it was a great start to getting back.

The resolutions were less than about 5 meters when the Orbiter was in its closest approach. It was great work. We were able to get great measurements of altitude of different surfaces. It was a wonderful way to get back and get started and start figuring out this little body so close by one more time.

From Clementine we’ve gone on to there was a Lunar Flyby with a mission in 1997 – not so exciting, I’m going to move on. Then we had Lunar Prospector in 1998 which was another mission to go out and in this case it was looking out in all sorts of ways that you wouldn’t think to look.

We had a Gamma Ray Spectrometer, a Neutron Spectrometer, and an Alpha Particle Detector that detects high energy Helium Nuclei flying off. They had a Doppler Gravity experiment. They had all sorts of different ways of looking at it other than through photography.

This allows you to start probing for what’s below the surface. It starts allowing you to probe for how the surface reacts when it gets hit with a Coronal Mass Ejection and flares from the Sun. All of these things start to give us hints of the chemistry of the Moon at the density structure of the Moon. This allows us to start trying to figure out is there water on the Moon.

Fraser: The goal here with Lunar Prospector is just with its name, to beyond mapping the surface but to try and map the locations in quantities of chemicals and minerals on the surface of the Moon.

Are there vast stockpiles of water ice? What elements are there? Are there elements that reacted with other chemicals in the past? You really just get a sense of what’s there and where it is.

Pamela: So the Neutron Spectrometer is perhaps one of the most important instruments for this search for water. Using it, Scientists were able to detect the Neutron emissions that you would expect if there’s water hiding under the surface.

The frustration we’re having is as we look for it with other missions we can’t directly image it and we talked about this in the last show. So, any water there is on the Moon appears to be trapped in different things.

According to the Lunar Prospector data, there should be about 3 billion metric tons of water ice in the polar crusts of the Moon. Now we just need to figure out how to get to it.

So Lunar Prospector got us to yeah, the Moon has a lot of really interesting chemistry for why we should go back. Then we went another span of several years without visiting the Moon until the European Space Agency went back with Smart-1.

Fraser: This is the coolest mission ever.

Pamela: [Laughter] Why do you say it is the coolest mission ever?

Fraser: Because the way they used to get to the Moon is that they used an Ion Drive. We’ve talked about this in the past. This is where instead of having a chemical rocket where you shoot it out really fast – you turn on this Ion engine which accelerates with electricity – Ions out the back of the Spacecraft.

You don’t need to carry very much fuel so you can launch with a very low Mass. It’s fairly inexpensive. It doesn’t let you go very quickly – accelerate very quickly – but over very long periods of time you can accelerate.

What they did with Smart-1 is they turned on this engine and increased the size of the orbit around the Earth slowly. It just kept getting bigger and bigger elliptical circles around the Earth for like the better part of a month [Laughter] until the ellipse was so big that it included the Moon.

Then they just turned it the other way and slowly brought the orbit back down until it was only orbiting around the Moon. So while normally a Spacecraft just takes from the Earth to the Moon it does it in 2 days, Smart-1 took the better part of a month to make its journey from the Earth to the Moon.

But it did it at a fraction of the cost that any other Spacecraft would do which I though was just wonderful.

Pamela: And what was amazing was just how tiny this little mission was. It had a mass of just 367 kilograms – about 800 pounds. A hundred kilograms of that was propellant related they were using Xenon. But still we’re looking at like a 600 pound (once you get rid of the propellant) Spacecraft that’s tiny. We have like random laboratory equipment hanging around here that is way, way bigger than that.

Here again we’re looking at detecting stuff in a lot of different ways. There was a standard CCD Imager that looked at my standard optical wavelengths of light and took images with about 80 meter resolutions so each pixel in the image is about 80 meters across.

They were doing x-ray spectroscopy trying to study the chemicals. They were also using an x-ray Solar monitor to just keep track of what the Sun was up to because depending upon what radiation from the Sun is hitting the Moon, you’re going to get different data.

Lots of really good science including the discovery of Calcium came out of this mission. So Smart-1 again, following up on Prospector we’re starting to now study the chemistry of the Moon.

That was back in 2003 and then we had another gap, four years this time from 2004-2007 happened and then everything started happening all at once last year. We had…

Fraser: This is about the coolest time of Lunar exploration I think – apart from some of the early discoveries.

Pamela: It was like we suddenly re-discovered there was a rock nearby that we could go land on. So then just one after another we start seeing all these missions.

There was the Kengoya or Selene missions launched out of Japan. Japan returned. They have a high-definition camera on their mission. It’s producing some of THE coolest videos ever.

Fraser: They did a re-creation of the Earth rise images. They did it like a movie though. It’s just beautiful and if you just want amazing pictures of the Earth and the Moon these are some of the most beautiful ones ever done.

Pamela: They’re all designed for today’s High-Definition television set so go buy your wonderful high quality Japanese TV and watch your wonderful high quality Japanese Lunar videos – it’s a great combination.

Fraser: But not just Japan, China is there.

Pamela: China is there as well with Chang’e 1 which had the result last week I believe, that no we can’t find visually the water ice on the Moon which is kind of frustrating.

And then just 2 or 3 weeks ago, another mission took off. In this case from India. The Chandrayaan-1 took off October 22 and is off imaging more chemistry experiments.

Then we’re looking in 2009 here in the United States to launch the Lunar Reconnaissance Orbiter and LCROSS which is going to careen itself into the Moon and then into the Moon again.

Fraser: Oh, oh, we’re out of time. That’s what we want to talk about next week [Laughter] which was the future of Lunar exploration including the plans to send humans back to the Moon. So save that part.

Ep. 113: The Moon, Part 1

Moon Phases

• Understanding Moon Phases – Moon Connection
• Phases of the Moon — US Naval Observatory
• Virtual Reality Moon Phase pictures (see what the moon looked like/will look like on any day, past or future — US Naval Observatory
• Waxing moon – Universe Today's Guide to Space
• Waning moon – Universe Today's Guide to Space
• Listen to the pronunciation of waning — Yahoo Education (does YE seem like an oxymoron?)
• A moon phase module that can be put on your website

Eclipses

• Lunar eclipses for beginners — Mr. Eclipse.com
• Lunar eclipses – Starry Skies
• The path of the ecliptic — GSFC
• Solar eclipses for beginners — Mr. Eclipse.com
• NASA's Eclipse website

Tides

• Lunar Tides — UTK
• What causes high tide and low tides? — HowStuffWorks
• Tide predictor website

The Moon Illusion

• Bad Astronomy's Moon Illusion page
• Moon Illusion Mystery — U of Pennsylvania

The Moon Itself

• The Primal and Future Moon — Starry Skies
• Why Doesn't the Moon Rotate? – DigiPro
• Is the moon moving away from Earth? — Cornell U
• Conservation of angular momentum — UTK
• The Moon — Nine Planets
• Universe Today's Guide to the Moon
• Geology of the Moon – Wiki
• Surface Properties of the Moon — UTK
• The Lunar Mare (names and locations)– Ames Research Center
• Star Stryder post about the composition of the moon
• Crater Counting to determine age — Wiki
• Radiocarbon dating – Wiki
• Fred Hoyle — Wiki
• Moon dust problems here and here – Universe Today
• Kaguya Doesn't Find Water on the Moon – Universe Today

Download the transcript

Transcript: The Moon, Part 1

Fraser Cain: The Moon!

Dr. Pamela Gay: The Moon – just in time for Halloween!

Fraser: Exactly you know we’ve been doing this show now for 113 episodes and we haven’t even done ‘The Moon’ yet. We did an episode on where did the Moon come from. Yeah, but people ask are you ever going to do any episodes? Huh!

Pamela: [Laughter] No, we just going to forget important topics.

Fraser: Wait until you hear our topic for next week. [Laughter] Let that be a surprise. Okay today we look at our closest Astronomical companion – the Moon. What impact does the Moon have on our lives? Where did it come from? Who walked on it? Are we ever going to walk on it again?

We’re going to learn about the phases, the tides and even a little bit about NASA’s troubled [Laughter] plans to send humans back to the Moon. Let’s start with the phases. We look at the Moon and sometimes we see it in shadow and other times we see it a full Moon or various crescents. What’s going on?

Pamela: Well basically it’s just the Moon is illuminated by the Sun. The Sun is on one side of the planet Earth, the Moon keeps switching which side of the Earth that it is located on and as it moves around in the light of the Sun you see different aspects of it lit up.

Now one of the really common misconceptions about the Moon and the Sun and how all of these crazy phases work is that the reason that we see part of the Moon in shadows is because it’s actually passing into the Earth’s shadow. That has ABSOLUTELY nothing to do with it.

The Moon in general stays completely out of the Earth’s shadow. The only time the Moon gets involved with Earth’s shadow is during Eclipses which occur about every six months.

Fraser: So like the Moon is always illuminated, just half of it, right? Just one half whichever side is facing the Sun is being illuminated. If you could like hold the Moon and turn it around you could just see yeah one half of the Moon is illuminated. The other half is in shadow.

Pamela: With half the Moon always, always, always illuminated there is always half of the Moon illuminated, what’s changing is what part of the Moon we’re able to see. So when we use the phrase ‘dark side of the Moon’ which is a great Pink Floyd CD…

Fraser: Completely wrong [Laughter]

Pamela: Completely wrong. The dark side of the Moon gets lit up just as often as the well, non-dark side of the Moon. What’s dark about it is our ability to see it.

So we’re lacking information. We’ve sent probes all over, we’ve taken maps, and we just generally haven’t seen it with the human eyeball.

Fraser: Right that’s the far side of the Moon. That’s totally different.

Pamela: And so the far side of the Moon that’s the side that is never facing the planet Earth and it gets just as much sunlight as the side that we see all the time. Here’s where the phases come from. When you take the Moon and put it between us and the Sun, the side of the Moon that’s getting illuminated is the side of the Moon that’s closest to the Sun. We don’t get to see that side because we’re on the other side of the Moon from the Sun.

When you have the Moon located probably below or above the Sun in the Sky, they’re basically on a line between us and the Sun, on a sheet of paper between us and the Sun.

Then you end up with what we call a ‘New Moon’ a Moon where we don’t see any of the surface of the Moon illuminated. As it moves away from the Sun, as it orbits back to the left in the Sky from the Sun, what we end up seeing is a ‘Crescent Moon’.

So we have, if you’re looking down on the Earth-Moon-Sun System the Moon is going around the Earth in essentially counter-clockwise direction. If you start off with a nice polite line with Earth, Moon, and Sun then the Moon is going to move up in a counter-clockwise direction. It’s going to become what we call a ‘First Quarter Moon’.

In this situation, we still have half the Moon illuminated but we now have a right angle where you have the Sun off to one side, the Moon straight up from the Earth and the Earth is forming that right angle part of the triangle.

We’re going to stick lots of pretty diagrams in our show notes. In this right angle situation half the Moon is illuminated but we only see a quarter of that part that’s illuminated.

This is why we call it a ‘Quarter Moon’. It looks like half the Moon illuminated but you have to remember when we look at the Moon we see half of the Moon and half of a half is a quarter.

This is one of those things that gets really muddied to think about but ‘First Quarter Moon’ is when you go from ‘New Moon’ to being able to see half of half the Moon illuminated in the Sky.

Fraser: Right and when the Moon is increasing in illumination we call that ‘Waxing’.

Pamela: So, we’re gonna have wax on wax off. In the case of wax off it’s a ‘Waning Moon’ – the fancy word we use for it. We go from ‘New Moon’ to ‘First Quarter’. The Moon keeps going in this counter-clockwise direction around the Earth and eventually gets itself lined up so that it’s either above or below the Earth on the Sky when you draw a straight line between the Sun the Earth and the Moon.

In this case, it’s the Earth that’s between the Moon and the Sun. So, in this case we’re able to look at the Moon and see it fully illuminated and this is what we call a ‘Full Moon’. You’re actually seeing two quarters or half the Moon and we call it a ‘Full Moon’.

One way to think of this is to imagine you’re on stage with another actor. When you’re facing the spotlight and the actor that you’re talking to is standing in front of you with his or her back to the audience, their back is illuminated by the spotlights and the side of them that you see is in darkness.

The audience sees you completely illuminated. Now if you reverse positions so that they’re facing the audience and your back is facing the audience, you see them fully illuminated by the spotlight and they see you in darkness.

A ‘Full Moon’ is straight overhead at midnight when we’re fully having our back to the Sun and the Moon is facing the Sun – our audience in this case.

Fraser: Right and then this I guess leads to the question which is that if the Sun and the Moon are on opposite sides of the Earth, why doesn’t the Moon go into the Earth’s shadow? You’d think that if it was perfectly lined up it would be in shadow.

Pamela: And this is why I said it’s above or below. The Moon’s orbit is tilted in relationship to the Earth’s equator. The Earth itself is also tilted. So when you get all of these crazy angles together what you end up with is the Moon is generally in the Sky above the Earth so that you could be standing on the Moon and look over the top of the Earth or under the bottom of the Earth at the Sun off in the distance.

It’s this tilt where you’re going in a loop-d-loop around the Earth that crosses the Equator once when it’s going toward the Sun and once when it’s coming back away from the Sun. It is generally getting carried above or below the Earth so that you can always see the Sun above or below.

Fraser: But they DO line up in the shadow sometimes.

Pamela: Twice a year and that’s where it becomes important that yeah the Moon does cross the Earth’s equator twice on every orbit – once going up and once coming back down.

Twice a year it lines up typically so that you get the Moon planting itself in Earth’s nice large shadow and often you also get twice a year the Moon putting itself between us and the Sun so that the Moon’s very small shadow is able to get cast somewhere on the surface of the Earth as it blocks out the Sun.

This precise lining of what we call the Nodes – this precise lining up of where the Moon’s orbit crosses the Earth’s equator typically only happens twice a year.

Just to make this clear, it’s not the crossing of the Equator that necessarily causes the Eclipse – although that can happen if you precisely have one at a Solstice. It’s actually the crossing of the Ecliptic which is the line that the Sun is on at the Sky that causes the Eclipses.

So it crosses the Equator twice per orbit and it crosses the Ecliptic twice per orbit. It’s this crossing of the Ecliptic that leads to Solar and Lunar Eclipses.

Fraser: Right and we have plans to do a whole show about Eclipses down the road but that’s sort of the geometry that’s involved with the Moon and the Sun and the Earth. That’s why we see Eclipses and that’s why we see the Phases. Now, let’s talk about more of the Moon’s influence which is the tides.

Pamela: Tides are caused by – well water slushes – and in fact rock slushes too, we just don’t usually think of it this way. When the Moon is straight overhead, it’s able to exert an extra pull on whatever is directly below it, the ocean the rock the mountains, the earth and it tries to pull this stuff up towards it.

Now the Earth is rotating so stuff is getting pulled up and carried away at the exact same time so ‘High Tide’ is always actually a little bit ahead of where the Moon is.

If you’re looking down again from some mythical location in Space at the Moon going counter-clockwise around the planet Earth and the Earth is also rotating counter-clockwise, if you can look down on the System you’ll see the Earth rotating and carrying ‘High Tide’ in front of where the Moon is located.

Fraser: But is it actually like the Moon’s gravity reaching down and just pulling the ocean towards it? I’ve seen pictures and it looks like there’s bulges on both sides of the Planet.

Pamela: That’s the kinda cool part. On the other side you actually have less Force. So since you have less Force things aren’t getting squished as much. It’s the way the Forces add up everywhere.

You sort of end up with when you’re at a right angle plus the rotation of the Earth thrown in to make things more complicated you are halfway in-between ‘High Tide’. This is where we have the ‘Low Tides’.

In this case the Forces are at their mid-point when you have the Moon straight overhead plus a little bit for the rotation of the Earth you have the most Force getting exerted on you. You end up with a ‘High Tide’.

When you are on the opposite side of the Planet – plus a little bit thrown in for the rotation – you have the least Force on you and this also leads to a ‘High Tide’ because things aren’t getting squished as much. It’s kinda weird to think about.

Fraser: That’s why we get two high tides and two low tides every day. We’re passing through the high tide and then the low tide and then the other high tide and then the low tide and then back to the starting point again.

Pamela: So if you hang out on the beach notice when you see the Moon straight overhead and then notice when you see the ‘High Tide’.

Fraser: Cool. Alright and there’s one last thing I want to talk about which is the Moon Illusion. [Laughter] Have you ever seen it?

It’s totally true you see the Moon down at the horizon and it looks gigantic. Then later on when you see the Moon really high overhead, it’s teeny tiny.

Pamela: But you can always block it out with the tip of your finger.

Fraser: Yeah, one of the great experiments – I think Phil told me this – is you hold an aspirin at arm’s length and that’s how big the Moon is. You can see that the Moon if you hold out as you said your pinkie finger, your nail should just cover the end of the Moon. Then try it again when the Moon is way overhead and it’s the same size.

Pamela: What’s happening is when our brain has trees, cars, and all this other stuff that it can contextualize the size of the Moon with it goes ooh, large pretty Moon – beautiful.

But then when the Moon is lost in a sea of nothingness up in just hanging out in the middle of the Sky, without anything around it our brain goes, ooh, little tiny thing. It’s just completely an illusion – that’s all it is.

Fraser: Just completely trick of the brain, wow.

Pamela: The human mind is a strange and scary place. [Laughter]

Fraser: Okay so now we mentioned earlier on in the show that there’s a near side of the Moon and a far side of the Moon. What’s going on there? Maybe we can talk a bit about the Moon’s orbit around the Earth.

Pamela: Once upon a time, long, long ago in the Solar System we live in the Earth was a large blob. We talked about in a former episode that the Moon was formed by something roughly the size of Mars coming along and splashing into what used to be the Earth colliding and flinging the lighter stuff up into Space.

That lighter stuff re-congealed in the form of the Moon. It was closer, it was rotating and over time this new body that formed out of this collision, this new Moon that formed around the Earth formed with a very strange asymmetry.

If you were able to take the Moon cut it in half and put an ‘X’ down where the center of mass is and where the center of its shape is, the center of mass is actually off to one side.

This is sort of like you can imagine having a basketball that has a lead weight off slightly to the side of the center of it. It’s not perfectly centered but off to the side. When you try and spin it, it’s going to wobble in strange ways.

In this case as it tries to rotate this extra mass, this extra density on the one side is always getting yanked by the Gravity of the Earth.

This off-center yank had the effect of over time slowing rotation of the Moon. The Moon is trying to rotate and every time that extra mass isn’t pointed directly towards the Earth, the Earth’s gravity yanks on it and says “no, point that extra mass this direction” it’s exerting a torque.

Over enough millions and millions of years this extra torque, this extra yank on this non-spherical distribution of mass stopped the Moon’s rotation so that the Moon always keeps this extra dense region pointed directly at the planet Earth.

What’s kinda cool is when you actually map the entire surface of the Moon the two sides look VERY different. This is because it was easier for lunar lava to leak out on the side of the Moon that’s not facing towards the planet Earth.

We get much more lava and much more of this black stuff – the salts; Lunar Mare is what they call it.

Fraser: But those are like the Seas, right? The big black blotches on the face of the Moon. So those aren’t on the far side of the Moon as much?

Pamela: No, we see at a few percent level that on the far side of the Moon, inside the deep craters there is this lava there as well. But on the near side of the Moon, over 30 percent of the Moon is covered in this black lava flow; whereas it’s only a couple percent on the far side of the Moon.

Fraser: That’s pretty cool. Now if I remember correctly, the orbit of the Earth – because right now the Moon that is tidally locked to the Earth, that’s always showing the same face to the Earth – but the Earth isn’t tidally locked to the Moon.

We rotate in 24 hours while the Moon takes 27 days to go around the Earth. We’re actually slowing down, right to become tidal locked to the Moon?

Pamela: Right, our own Planet also isn’t a perfectly symmetric distribution of stuff. If we were, the entire Planet would have the exact same thickness of the ocean everywhere; the exact same distribution of metals everywhere and we don’t.

As a result of differences in density in different parts of our Planet as we rotate there’s a tidal friction that is slowly trying to torque our Planet as well. As a result of all of this the Moon actually appears to be moving away from the Earth a few centimeters a year.

What’s happening is the Earth’s rotation is slowing down just a very little bit. This slowing of the Earth’s rotation with conservation of angular momentum requires that the Moon move to a larger distance away from the planet Earth.

So over time the Earth’s rotation is going to slow and slow and the Moon is going to as a result move further and further away. This means that we actually live at a pretty special time in the history of the planet Earth where the Moon is uniquely located such that most of the time when it passes in front of the Sun it fully blocks the Sun out.

Over time as the Moon moves further and further away, its size on the Sky is going to get smaller and it will reach the point where Solar Eclipses get such that what you’re actually creating is a donut of Sun instead of a completely blocked out Sun.

Fraser: You’ll be seeing transits, right? Where they just zip across the face of the Sun but you don’t actually get that big block that we do now.

Pamela: We already get this some of the time with what we call Annular Eclipses where you’re left with an annulus of Sun. But the size of the annulus and the frequency of Annular Eclipses is going to increase until all we have is Annular Eclipses and as the Moon gets further away, yeah transits may be a better word for it.

Fraser: The Annular Eclipse that’s because the Moon changes – you know it’s in an elliptical orbit around Earth – and it changes its distance, how close it gets to the Earth and if things time out right the Moon is at its farthest point when it passes in front of the Sun.

Visually it’s the smallest in the Sky and so you get the black Moon with a ring of sunlight around it. That would be pretty amazing to see I think.

Pamela: And we’re getting there, just hang out for a few more billion years.

Fraser: I think it’s 50 billion years when the Earth and the Moon become tidally locked to each other.

Pamela: But our Sun is going to crispify our System first so I’m not real worried about it.

Fraser: Yeah, I knew we had an appointment before then. [Laughter] Okay so I think that kind of explains the orbit. What is the Moon made out of?

Pamela: Swiss cheese.

Fraser: Don’t say Swiss cheese, aw I knew it! [Laughter] I guess I flubbed up on that one, didn’t I? Fine, apart from vast quantities of Swiss cheese, what is the Moon made out of?

Pamela: The tactical words we use for it is it’s made out of basically the lava stuff is the salts. It’s mostly I guess, avoiding all the geophysics and a lot of vocabulary words where I have to admit I’ll be in way over my head – I’ve been teased by more than one geophysicist for how badly I pronounce the names of minerals.

It’s made out of a lot of different minerals that are really lacking in water. That’s one of the things that we keep finding over and over. You take a lunar rock, look at what’s in it and water is not one of the ingredients.

Fraser: Right it’s like Silicon-Oxide, Titanium-Oxide, lots of Oxygen but no Hydrogen.

Pamela: It’s lacking in volatiles as well. What gets neat is when you start looking at how the surface was made. The surface is generally composed of two different regions.

There is the Lunar Mare – this is the section that is made primarily of lava either from volcanoes or from the surface liquefying during an impact event. Then there are also the Terrae, the Lunar Highlands. These are the light areas of the Moon.

The entire surface of the Moon has just been completely pulverized with craters. We can start to age different parts of the surface by looking at the number of the craters. We’re looking at the impact of large craters that we can generally see and determine a particular section has been hit by so many objects while another section has been hit by a different number of objects.

The majority of the stuff that’s hitting the Moon is little micro-meteorites. With all the impacts that have occurred over all of the millennia, this has led to the surface of the Moon basically becoming granulated. We talk about the surface of the Moon being what we call Regula which is basically dusty pulverized rock.

The thickness of the Regula varies depending on what type of surface you’re on with the older surfaces have much thicker regula and the younger surfaces have much thinner regula. We have a surface that has been blasted, is constantly getting impacted – the largest impacts ended up melting the surface, flipping the surface – we end up aging the surface by looking at the craters.

We look at the density of the craters in different places and looking at the structures that the craters have. Can we still see the rays? Have the craters themselves had craters placed on top of them? This is how we end up aging the surfaces.

Then what’s cool is we can actually say we know one section is older than another section due to the number of craters. Then we’ve actually sent people to go pick up rocks and use radio-carbon dating to put absolute numbers on the ages of the sections tested.

Fraser: When the Apollo mission was being planned, scientists weren’t sure that the Lander would be able to sit on top of the Regula. One of the fears was the Lander would land and it would just sink into the Regula like it was a snow bank.

Pamela: That was one of the fears put out by a man by the name of Fred Hoyle who has alternately come up with some of the greatest ideas in Astronomy and also some of the most wrong ideas in Astronomy.

What’s cool is he was consistently trying to think outside of the box and just make people aware of what they might be walking into as they explore new worlds and built new scientific ideas.

This was one of those things where as we contemplated what’s it going to be like to land on the Moon we had to contemplate what’s it going to be like to land on really thin pulverized dust.

Is it going to be like landing on powdery snow where you sink straight down or is it going to be more like landing on nice wet soggy snow where you can compact it and stand on the surface?

Fraser: It’s kind of both, right? The very top few centimeters is this really light powdery stuff almost like talcum powder. Below that it’s actually pretty dense.

The Astronauts had a little trouble you know they had to use hammers and chisels to actually dig out samples from the Regula.

Hoyle was thinking that they would sink into the Regula and that was wrong. But this dust is actually pretty nasty stuff.

Pamela: It is and it’s one of the things that NASA is working the hardest to try and figure out how to cope with as we look to landing on the Moon in the future. One of the more fascinating women that I interviewed when I was at the Lunar and Planetary Sciences conference last March was a Biologist who is working on trying to figure out how to mitigate the effects of dust on human beings.

You get the dust on your spacesuit, bring your spacesuit in with you and strip it off and no matter how careful you are you end up getting this dust into the atmosphere of the crew area.

It’s extremely abrasive. As you said filled with different metals and silicates, this is like the finest nastiest glass-based sand that you’ve ever encountered.

A lot of the lunar surface when it gets liquefied and re-solidifies as an effect of an impact it becomes glass. Imagine living in a low Gravity environment – Gravity on the Moon is one 6^th of what it is here on Earth – where this glass-based dust can suspend itself in the air. You’re getting it in your clothing and it is rubbing on your skin between you and your shirt.

They are actually investing money in trying to figure out what type of apparel will cause Astronauts to get the least damaged by getting dust in their clothing.

Fraser: Well but they’re going to get it in their lungs. That’s the trouble right? It’s like little pieces of glass going into your lungs.

Pamela: Being an Astronaut isn’t safe.

Fraser: No, no but I think this is not what they were anticipating and now when they’ve had a chance to really look at this stuff under the microscope, yikes, it’s really dangerous.

There was a new announcement this week which we thought we’d report on. We’ve covered this in the past which is: “Is there ice on the Moon? Maybe in some of the craters at the southern and northern poles?” There might be deposits of water ice.

Pamela: The basic idea is the Moon just like the planet Earth has gotten creamed with Comets now and then. It’s gotten basically hit with watery things that should have deposited their material on the surface of the Moon and there are places on the Moon that never see any daylight.

There are also places of the Moon that never see darkness because the mountains extend out so they’re always in sunlight. There are craters that go down deep and sunlight is never able to get inside of them at the two poles.

We’ve thought that maybe one of the craters – Shackelton is the one getting explored lately – maybe in Aitken’s Basin and Shackelton Crater, in one of these polar craters, maybe a Comet hit.

Maybe it left its ice; maybe that ice is still there and we can land and use that water to help fuel a colony, provide water – we need water, it’s just that simple. However, we can’t find it.

Fraser: NASA’s Lunar Surveyor found evidence of water. It is more like found chemical evidence of it. It wasn’t actually able to take pictures of water at the southern pole but yeah, the news isn’t good.

Pamela: No and so right now we can’t completely eliminate the fact that maybe there is water maybe there isn’t water.

What we can say is if there’s water, it’s not hanging out sitting on the surface where it’s nice and shiny and easy to take pictures of.

Fraser: Right, yeah the Japanese spaceship Kaguya just took pictures of the bottom of Shackelton crater and nothing.

Pamela: Nothing – no go.

Fraser: No go – just dry dusty shadowed Moon just like the rest of it.

Pamela: If there is water ice on the Moon it’s either covered in dust so that we can’t see it or something else has happened so that it just looks just like the rest of the lunar surface. The Moon is still keeping its secrets or it has no water.

I think a lot of us are going please, please let there just be hiding the water because otherwise it’s going to be a lot harder to start putting colonies on the Moon.

Fraser: The plan was that we were going to talk about some missions, but we’re out of time. So I think we’ll stretch this out to next week.

So, next week we will talk about past and future missions to the Moon.

Pamela: And we will save our cool show to be two weeks from now. We’ll have a really cool show coming your way.