Is There a Dark Side of the Moon?

What we sometimes call the dark side of the moon isn't always dark, but it is somewhat mysterious. Learn why we only see one side of the moon from Earth (and why it's sometimes in shadow) in today's episode of BrainStuff, based on this article: https://science.howstuffworks.com/dark-side-of-moon.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio. Hey, brain Stuff,
Lauren vogelbaumb here. You've probably noticed that when you look
up at the Moon, you always see the same features.
You can see craters and patches of lighter and darker areas.
With a pair of binoculars or a telescope, you can

(00:22):
make out even more detail. But no matter how you
look at the moon, you're always seeing the same landscape.
But the Moon is a sphere. If we're only seeing
one hemisphere, then what's on the other side. This is
the so called dark side of the moon, the side
we never see because it always faces away from Earth.

(00:46):
For this reason, people also use the phrase the dark
side of the Moon to describe something mysterious or unknown.
This side of the Moon faces the cold, black, expansive space.
What could be on this side of the moon? And
is it really always dark? We actually know what it
looks like, and no, it is not permanently dark. We

(01:09):
have lots of images from various lunar missions, and in
nineteen sixty eight, astronauts aboard the Apollo eight spacecraft were
the first humans to set eyes on it in person.
But the popularity of the phrase means that there is
ample opportunity for people to jump to the wrong conclusion,
especially since we only ever see that one hemisphere, and

(01:30):
it's easy to misunderstand the cause of the phases of
the moon that we see from Earth. But mostly this
is a problem with terminology. The descriptor dark side suggests
that shadows perpetually cloak the surface of the side of
the Moon that faces away from us. It's fun to
imagine a dividing line between the light side and the

(01:52):
dark side, but that's not how it works. While it
is true that some part of the Moon is dark
at any particular or time, it's not always the same part.
That's because like Earth, the Moon rotates on its axis,
a meaning it has a daytime and a night time.
So if you were to set up camp on the
Moon and stay put, you would eventually see the sun

(02:15):
rise and fall. You'd experience both day and night. So
technically the moon does have a dark side at any
given moment, but it shifts. The dark side is the
part currently experiencing night. The side of the moon we
see is sometimes the day side, sometimes the night side,
and sometimes a bit of both. A more accurate term

(02:38):
to describe The side of the Moon that we always
see is the near side. The side opposite is the
far side. The near side will always be facing toward us,
and the far side will always face away. This is
true from anywhere on Earth. If you were to fly
from America to Australia or vice versa, you'd see the
same features that you're familiar with back home. But why

(03:02):
do we only ever see one side of the Moon
from Earth? Okay, it takes about twenty nine days for
the Moon to make one complete orbit around the Earth.
That's also how long it takes the Moon to make
one rotation on its axis. Because the Moon's rotation and
orbit take the same amount of time, we always see

(03:22):
the same face of the Moon no matter when we
look at it. The Moon just keeps spinning the same
side of itself toward us as it orbits around us.
This happens because of gravity. Earth's gravitational pull on the
Moon is so strong that our planets slowed the Moon's
rotation down to its current speed. Its rotational speed is

(03:45):
locked with the time that it takes to orbit the Earth. Interestingly,
the Moon is doing the same thing to the Earth,
just much slower because the pull of the Moon on
the Earth is much smaller, so if you've ever felt
like the days are getting longer, they are technically still.
In a few billion years, the Earth's rotation will match
the time it takes the Moon to orbit the Earth.

(04:08):
By that time, the Moon and the Earth will have
drifted apart from each other a little bit, which means
it'll take a little longer for the Moon to travel
around the Earth, to the tune of about forty days
or so, meaning that in the distant future, one Earth
day will equal forty of our current Earth days, or
about nine hundred and sixty hours. Once the Earth's rotation

(04:31):
matches the time it takes for the Moon to orbit
the Earth, the same side of the Earth will face
the Moon all the time. But okay, let's talk about
the phases of the moon. A common misconception about the
moon is that it appears as just a sliver sometimes
called a new moon, when the Earth is between the

(04:51):
Sun and the Moon, thus blocking the light from the
Sun and casting a shadow across the moon. But in reality,
during a new moon, the Moon is between the Sun
and the Earth. Imagine that you're in a room that's
dark except for one window that has sunlight shining into it,
and then someone walks between you and the window. You

(05:13):
would see the person in silhouette. They'd appear mostly shadowy,
but with a bright outline along their side facing the window.
That's exactly what a new moon is. A full moon,
in contrast, is when the Earth is between the Moon
and the sun. Going back to our example, imagine that
you're the person standing by the window. If you turn

(05:36):
to look into the room, anyone standing there would be
well illuminated. That's the same as us looking at a
full moon. But again, whether it's a full moon or
a new moon, you're still looking at the same side
of the moon, the near side. During a new moon,
you're looking at the near side during lunar night time,
and during a full moon you're looking at the near

(05:57):
sides version of noon. All of this being said, the
far side of the moon is still a little mysterious
because the Moon's bulk blocks radio signals to and from
the Earth from its far side. Engineers don't yet have
a good way for us to explore that far side.
In the future, we may see NASA and other organizations

(06:19):
build radio relay towers on the Moon's surface to make
exploration possible. Until then, we'll have to content ourselves with
being looney over the side that faces us. Today's episode
is based on the article what and Where is the
Dark Side of the Moon on HowStuffWorks dot com written

(06:39):
by Jonathan Strickland. Brain Stuff is production of iHeartRadio in
partnership with hostuffworks dot Com and is produced by Tyler
klang A. Four more podcasts my heart Radio, visit the
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