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.
