Hello, I’m Darrell Heath with the UALR College of Arts, Letters, and Sciences; welcome to
The Night Sky
For astronomers the moon is both a blessing and a curse.
It’s considered a curse when its bright glare drowns out the dim light from the
faint and fuzzy deep sky objects that we all want to either observe or photograph.
But at the same time it is also a blessing in that we have such a remarkable world right
in our very own backyard.
The moon offers so much astonishing beauty and detailed features that stargazers
of any level of experience will always be richly rewarded by spending a little time
with it.
And of course, the more you learn about the moon the more fascinating an object it becomes.
In this episode I have randomly chosen five different things that I personally find amazing
about the moon and that perhaps you might not have been aware of.
So, here they are, and listed with no particular order in mind.
Number one, the moon has both an atmosphere and water.
Okay, I’ve cheated a bit and worked in two amazing things under one heading.
Until recently, the conventional thinking was that the moon was both airless and completely
dry but new findings tell us a rather different story.
Granted, there isn’t much of an atmosphere.
To give you some perspective, at sea level here on Earth our atmosphere contains about
100 billion billion molecules per cubic centimeter.
On the moon, you would find only about 100 molecules per cubic centimeter, just enough
to distinguish it from the hard vacuum of space.
But keep in mind that even 100 molecules per cubic centimeter is about what you’d find
in some of the best lab created vacuums here on Earth.
The exact composition of the lunar atmosphere is still unknown but to date we have identified
sodium and potassium as well as argon, helium, oxygen, methane, nitrogen, carbon monoxide,
carbon dioxide, and radon.
The exact origins for this very tenuous atmosphere is also a mystery but lunar scientists suspect
that there are several different sources.
Outgassing, the release of gases from inside the moon is one possibility.
The solar wind and high energy particles colliding with the lunar surface and knocking off atoms
may be another.
Material being released from the impacts of meteorites may be another source.
NASA scientists have a special name for this kind of very thin atmosphere, they call it
an “exosphere”, and it's probably the most common type of atmosphere on various
kinds of small bodies throughout our solar system.
The evidence for water on the moon comes from a number of sources, including impact probes,
orbiting spacecraft, and from moon rocks collected by the Apollo astronauts.
Upon initial analysis of those rocks the verdict was that the moon was bone dry but some 40
years after that assessment, orbiting spacecraft detected the signature for water at the moon’s
poles.
Of course liquid water cannot exist on the moon but it may occur as ice within the permanently
shadowed craters located at the poles.
Elsewhere on the moon water occurs as the molecule hydroxyl (which is one oxygen atom
and one hydrogen atom).
Some of this water is found within the lunar soil and a re-analysis of those moon rocks
have shown that it is also trapped within tiny crystals of the mineral known as “apatite”.
How much water there is on the moon is still a matter of debate.
Some scientists say that there is as much as 64 parts per billion, two orders of magnitude
than previously thought.
This still means that the moon is drier than any desert on Earth.
Some of the moon’s water may have been delivered by asteroid and comet impacts but the most
important source may be due to the influence of the Sun.
The solar wind that I mentioned earlier is constant stream of particles being emitted
by the Sun.
Some of these particles are hydrogen protons.
When these hydrogen protons collide with the oxygen rich materials at the surface they
may cause free oxygen to be released and if a hydrogen proton collides with an oxygen
atom with enough force they may stick together to form water’s close cousin, hydroxyl.
Number two, MOONQUAKES.
A moonquake is the lunar equivalent of the earthquakes that we experience here on Earth.
During the Apollo missions from the years 1969 and 1972, astronauts placed seismometers
on the moon which sent data back to Earth up until 1977 when they were switched off.
They revealed to us that there are four types of moonquake.
1) Deep moonquakes that originate over 400 miles within the lunar interior
Secondly, there are quakes that are triggered by the impact of meteorites Third, thermal quakes triggered by the expansion
of the frozen crust when exposed to sunlight after having been in the deep freeze for two
weeks of lunar night and then fourth we have shallow quakes that occur about a dozen
miles or more beneath the surface
The first three kinds of quake are fairly minor but the shallow quakes were the strongest,
some of which reached magnitude 5.5 on the Richter scale.
Here on Earth that is enough to move heavy furniture around and crack plaster.
What’s even more interesting is their duration.
On Earth, strong quakes may last only a couple of minutes but on the moon these shallow quakes
can go on for at least 10 minutes with the moon ringing like a bell.
Why the difference?
Well, here on Earth rocks can become saturated with water and the energy from an earthquake
deadens as it tries to propagate through it.
The moon, lacking as much water as does the Earth, has rocks that are far more rigid and
quakes can keep them vibrating like a tuning fork for much longer periods of time.
If we ever set up colonies on the moon we had better have quake-proof housing.
As to why the moon experiences quakes it is still something of a mystery.
Some of them may be triggered by tidal interactions with the Earth while others may be caused
by the rims of young craters slumping in upon themselves.
Number three, if you were standing on the moon, you would see the earth go through phases.
The moon does not generate any light of its own, all of its light is reflected sunlight.
We see the moon go through a set of phases (new moon to full moon and then back to new)
every 29.5 days.
The reason we see these phases is because the moon and the Earth orbit around one another
and we see various portions of the lunar surface illuminated as the angle between the Sun,
moon, and Earth constantly changes.
But did you know that, from the moon’s perspective, the planet Earth would also be seen going
through a full set of phases?
However, the Earth’s phases would be the opposite of the phase that we are seeing for
the moon.
For example, during a waxing gibbous moon phase (which is when the moon is close to
being full) any astronaut on the lunar surface would see a slender crescent Earth.
A few nights later, when the moon becomes completely full here on Earth, our lunar astronaut
wouldn’t see the Earth at all.
At this time the moon, Earth, and Sun are all aligned with the Earth in the middle.
From the moon the Earth would appear to be lost in the Sun’s glare.
From here on Earth we see the moon rise and set because our planet revolves upon its axis
once every 24 hours.
But the moon has a 1:1 spin-orbit resonance.
In other words, it rotates once upon its axis for every time that it takes to orbit around
the Earth and the upshot of this is that the moon always presents one face towards us.
So, while we see the moon rise and set, from the moon the Earth would always appear to
be in one place in the sky, spinning around every 24 hours to show off it various features,
and slowly going through its phases just like the moon does.
Number four, no one can own the Moon.
Just because American astronauts have planted flags upon the moon does not mean that the
United States owns the moon.
Neil Armstrong and Buzz Aldrin planted a flag on the moon purely as a ceremonial gesture
and nothing more.
On January 27th, 1967 the United Nations adopted the Outer Space Treaty which states that free
access is granted to all celestial bodies and that “outer space is not subject to
national appropriation by claim of sovereignty, by means of use or occupation, or by any other
means.”
By the same token, the treaty also states that weapons of mass destruction and all military
activity is strictly prohibited in space.
That still hasn’t stopped certain enterprising individuals form laying claim to ownership
of the moon and some of them will even be glad to sell you some very nice lunar real
estate.
They claim a loophole in the U.N. treaty but Article VI of the Outer Space Treaty clearly
states that non-government entities are just as bound to its provisions as are all member
nations.
So, if you’ve paid good money for lunar property be aware that it is only worth the
paper it is printed on.
Number five, THE MOON IS LEAVING US
Yes, it is indeed true that the moon is moving farther away from the Earth.
Here’s why…
The answer has to do with tides and the gravitational embrace that is shared between the Earth and
the moon.
The side of the Earth that faces the moon feels a greater gravitational pull than does
the center of the Earth, and the side that is facing away from the moon feels an even
weaker pull.
The net effect of this is that the moon’s gravitational tug creates two tidal bulges
in our Earth’s oceans (one on the side facing the moon and one on the side facing away).
But these tidal bulges are not static, the Earth is rotating underneath them.
Now, keep in mind that these tidal bulges have mass and as a consequence they also exert
a gravitational pull on the moon.
So, as the Earth spins faster than the moon can orbit around us, these tidal bulges try
and drag the moon ahead in its orbit.
But the moon is having none of it, it pulls back and slows the Earth down in its rotation.
This pulling back and forth between the Earth and moon, combined with the tidal friction
that it generates, takes energy out of the Earth’s rotation.
In fact, the Earth’s rotation is slowing down by about 2 milliseconds every century.
Sure, not so much that you and I notice in our day to day lives but it is a measurable
effect and one that the U.S. Naval Observatory has to factor in every now and again to keep
our atomic clocks in check.
But this energy taken out of the Earth’s rotation has to go somewhere, it doesn’t
just disappear, so it ends up going into increasing the size of the moon’s orbit.
The end result of this is that the moon is moving away from the Earth at the rate of
about 1.5 inches per year.
We can actually measure this by bouncing lasers
off specialized reflectors the Apollo astronauts left on the moon's surface.
But don’t worry, it will take a very long time before anyone notices
and before we do the Sun will have likely swelled into a red giant star, engulfing the
Earth and moon and turning us into a charred cinder.
So yeah, there’s that.
Before we go I want to recommend two books about a group of extraordinary women whose mathematical abilities
paved the way for the human race’s journeys into space.
But, because of their gender (and in some cases, their race) history has ignored their contributions up until now.
The first book is “Rise of the Rocket Girls: The Women Who Propelled Us, From Missiles to the Moon to Mars” by Nathalia Holt.
The second book is, “Hidden Figures: The American Dream and the Untold Story of the Black Women Mathematicians Who Helped Win the Space Race” by Margot Lee Shetterly
Check your local library or bookstore for these two great reads.
That’s all for now.
Be sure and watch our web site for all the latest happenings in astronomy and be sure
to take just a little bit of time to step outside and look up in both awe and wonder.