Video Transcript: Phases of the Moon

So when we consider the phases of the Moon, let's look at them all.  I mean, if we were to condense the whole month into one set of phases we could see it like this.  Now the Moon gradually gets more and more illuminated until it becomes a full Moon and then it gets less and less illuminated until it becomes a new Moon.  So those are kind of the two ends of the lunar cycle; a new Moon when the Moon is not lit at all, and then the full Moon we see the whole thing.  

Now, while the Moon is getting more and more lit up in this first part of the lunar cycle, we call that the waxing phase of the Moon.  Waxing meaning getting bigger.  And the picture to have in mind is like you're an old fashioned candle maker, and you're dipping your wick in the wax over and over again, and every time you dip it in the wax, another sliver of candle is added, it's waxing, it's getting bigger and the candle gets bigger and bigger.  By contrast, the second half of the lunar phase is when the Moon is getting less and less than illuminated is called the waning phase. 

So as we look at this picture, showing all the phases of the Moon, we can label now each of these phases.  When we have only a sliver of the Moon, we call that a Crescent Phase.  So these very first crescent phases we would call Waxing Crescent Moons.  And then we get all the way to the point where the Moon is half illuminated, that is one side, the right side in this case is illuminated and the other side is dark.  That we call it a Quarter Moon.  Quarter, maybe like, why do we call it a quarter Moon when half the Moon is illuminated?  Well, it's because we're a quarter of the way through the lunar cycle.  So we call that First Quarter because it's the first quarter.   Alright, and then we continue on.  When the Moon is more than halfway illuminated, it's this kind of oblong shape, we call that a Gibbous Moon.  Gibbous Moon, so this would be the Waxing Gibbous because it's still getting bigger.  So we go from New Moon to Waxing Crescent, First Quarter, Waxing Gibbous and then to full Moon.  

And once we're past Full Moon now we're at the same phase but now it's sort of reverse order, as we're waning, so we get the Waning Gibbous.  And we get the waning, nope, not the waning quarter. We call it the Third Quarter.  Now we had First Quarter.  Now we have Third Quarter.  That's right here in this picture.  And then we have the Waning Crescent.  So that's all the phases of the Moon there but the question remains, what causes these phases?  Well, I'd like to show you is what's called a lunation.  

Lunation.  That is, if you could keep your eyes fixed on the Moon every day for an entire month and just watch it like fast forward the whole month and see how the phases of the Moon change, you'd see another something which gives a clue as to what's happening here.  So it's difficult to actually make this observation, but we can have a little simulation of it.  So watch what happens here if I go through all of these pictures.  If you're looking in the gallery, this is a little animated GIF so it keeps looping.  But just if you look at these phases as they go by, you see the Moon gets bigger and bigger and brighter until it's full; but notice the Moons getting bigger as it gets full and then it's getting smaller as it goes back to New Moon.  And if you watch that in the gallery, you'll see getting bigger and smaller and bigger and smaller and that's actually what's happening to the Moon as its phases are changing.  Now phases is the really obvious thing, but there's a slight change in the apparent size of the Moon, as well. This is giving us a clue as to what's happening.  The Moon is getting a little closer and a little further as it orbits around the Earth. And that's the key; this orbit around the Earth. That's what's giving rise to these phases.  So let's take a look at a diagram or two to help us visualize this.  It's kind of a weird thing, you know, when we're living on this planet and something's orbiting around us.  To us, it looks like it's changing but really, it's our perspective on it that's changing.  So take a glance at this; it’s the fourth picture in the gallery, which shows the Earth in its motion around the Sun, but at the same time it shows the Moon in its orbit around the Earth.  And the key thing to keep in mind here is that the sunlight is always illuminating half of the Moon.  

There's always one side of the Moon that's facing the sun.  What's changing as the Moon orbits the Earth is our perspective on which side of the Moon we see.  In a sense, are we seeing the side that’s lit up or are we seeing the part that's darker? And that changes as the Moon orbits the Earth.  So at the very beginning of a lunar cycle, the Moon is between the Earth and the Sun, and so the lit up part - I mean, think about this.  Here's my hand, right?  My hand is the Moon.  And you're the sun.  All right?  So if you're the sun, right now I hold up my hand.  Okay, you're seeing the part of my hand that's lit up.  But I'm seeing the part that's dark.   I find I don't see it because it's so dark.  So if this is the Moon, this is the new Moon from my perspective as the earth because all I see is the is the dark side.  

But here's the thing.  Just because it's the new Moon, it doesn't mean that the Moon is blocking the sun.   If I put my hand here, you don't see my face anymore. That’s an eclipse.  That's not the same as a new Moon.  A new Moon can happen when the Moon is between the Earth and the Sun, it doesn't necessarily mean the Moon is blocking the sun's light.  You know what I’m saying?  Okay, so that's the new Moon.  

And then here, as the Moon orbits around, we reach the First Quarter where, from the Earth's point of view, you're seeing only half of the Moon illuminated.  Of course, it continues to orbit around.  And then we get to the full Moon, the place where the Moon is now behind the earth and from the earth’s point of view, I look up there and I say, “Oh, yep, it's completely illuminated.”  So there's our full Moon that continues to orbit around. 

So it's tempting sometimes to think that these phases are caused by the shadow of the Earth. Like a crescent Moon must mean that the Moon is passing through the shadow, but that's not the case.  Really, the shadows aren't involved at all.  It's always the changing illumination, that changing perspective that we have, as the Moon is orbiting the Earth.   

Ah, it's so confusing, Moon, Earth, Sun, all the stuff to keep track, but these visuals help keep track of it.  

Okay, so then, here's the interesting thing.  A lot of times we think of the Moon and the Sun.  I think of the Moon and the Sun which God has put in place; one to govern the daytime, one to govern the nighttime.  We always associate the Moon with nighttime.  But the Moon - think about this - have you ever noticed the Moon up in the daytime?  Is the Moon limited only to evening?  No.  The full Moon you mostly see at night but the other phases you frequently can see during the daytime.  This is a complicated drawing this last picture in the gallery but what it illustrates is the connection between the phase of the Moon, the time of day, and where you see the Moon in the sky.

So let me explain this drawing a second and then we could try to make some sense out of it. This is similar to the drawing that you saw before except now we're showing the orbit of the Moon around the earth, showing its location at multiple places all at once.  So the sunlight is these yellow arrows coming in from the right side of the picture, and then the earth, of course, is in the middle, and what this is showing is sort of where that phase of the Moon is at that given time of day, like when is that phase of the Moon straight overhead.  

So if you were to have a new Moon, that means that the Moon is between the Earth and the Sun, so wherever the Sun is in the sky, that's where the Moon is as well.  So in that case, if the sun is straight overhead, the Moon is straight overhead, the Moon is up in the middle of the day.  But when it is, you can't really see it because it's a new Moon.  It's not illuminated that much and it's daylight.  So it's faint, it's hard to see.  So you don't really notice it.  That's why we don't see the Moon as much in the daytime. But that's when it's a new Moon. 

As the Moon moves into a Crescent Phase, and even a Quarter Phase, that Moon is overhead in the afternoon.  So you may sometimes notice that crescent Moon kind of in the later evening as the sun's going down, maybe the Quarter Moon as the Sun sets, you'll see that Quarter Moon in the sky.

So you can see the Moon in the day.  Now, why is the full Moon something we often associate with the night?  Well, that's because the full Moon happens, that phase happens when the Moon is on the opposite side of the sky from the Sun.  So as the Sun is setting, the full Moon is rising.  It's why so often so striking, we see a sunset, and you may be turn around an hour later and big full Moon is rising.  Those two things go hand in hand; a full Moon rises as the Sun sets.

Okay, then some of these Waning Phases you'd only really see if you get up really early in the morning because those rise very, very late at night, early in the morning, and come up just before the sun.  So you'll see them early on, but not later.  So the Moon can be up during the daytime.  The phase you see in the daytime will depend on what time of day it is and you're really only going to see these Crescent and Quarter Phases in the daytime.

All right.  We've explored a lot about Moon phases.  I hope it makes good sense.  Yeah, and we'll see you next time.