Transcription
We have one more important topic that I want to cover about the phases of the moon. Many times when we think about the moon, we think of the moon as being an object for the night time. We see the sun in the sky during the day and we see the moon in the sky at night. But is that actually true?
Let’s go back to our little moon demonstration here, and what I’ve added is I’ve added times for a person on the earth here. So, for instance, if the person is standing here when the sun is pretty much directly overhead, that’s what we call noon, remember it’s local noon in the lecture we had on The Day. Then, if a person is over here when he’s exactly on the opposite side of the earth from the sun, the sun is not in the sky, it’s midnight. And now you can see, okay, now he’s going around. The sun appears for the first time, it’s sunrise. The sun gets higher in the sky, it’s noon. It transits and it’s lower in the sky until it sets, it’s sunset.
Now we can do a little bit with this. Let’s look over here. We have the new moon right now. The part of the moon that’s lit by the sun is the part that we do not see. So, to us, the moon looks completely dark. Let me ask you a question. If it’s over here at midnight, is the new moon in the sky? No. This guy can’t see the new moon because the earth’s in the way. When will he be able to actually see the new moon? He’ll be able to see the new moon for the first time right around sunrise. Then he’s able to see the new moon. And for him, the new moon is going to be high in the sky right around noon, and then it’s going to set right around sunset. We say the new moon basically follows the sun. It’s in the sky the same time the sun is. We can say that it rises at sunrise and it sets at sunset.
So, if someone, for instance, said, “Oh, okay. The reason why we can’t see the new moon in the sky at night is because it’s not lit.” Is that true? Let me repeat that. If someone says the reason why we can’t see the new moon in the sky at night is because it’s not lit. Is that true? If you think about what we’ve just learned, you’d realize that’s not true. The reason why we can’t see the new moon in the sky at night is not because it’s not lit. It’s because it’s not there. The new moon is not in the sky at night. The new moon is in the sky during the day time.
But watch what happens as we move to a different phase. Let’s say as we go over here to full moon. Now, what time of the day is the full moon in the sky? Well, the full moon is going to be high in the sky right over this guy’s head right around midnight. He’s first be able to see it right around sunset, and the full moon will set right around sunrise. So, we say that the full moon is completely opposite from the sun. It rises at sunset and it sets at sunrise.
A little public service announcement for you here. If you’re planning to get stranded in the wilderness, plan to get stranded in the wilderness around full moon. Because then, what will you see? During the middle of the night, it won’t be dark. You’ll still see the light of the moon lighting up the sky. On the other hand, if you are really into astronomy and you want to go and get the darkest sky possible, you don’t want to go out during full moon because the light from the moon creates a whole bunch of natural light pollution, kills out the stars. Instead, you want to go. In fact, astronomers almost fight it out to get observing time during new moon. Because new moon, the moon is not in the sky during the night time. It doesn’t mess up our telescope observation. It doesn’t create that light pollution.
As the moon goes around the earth, the moon rises about 45 minutes later each day. And that’s why the moon is in the sky at different times depending on what phase it is, about 45 minutes later each day. First quarter moon, it’s in the sky from noon till midnight. Third quarter moon, from midnight to noon. The ones that I’m going to want you to know are these two. You need to know when the new moon is in the sky. It rises at sunrise, sets at sunset. And when the full moon is in the sky. Rises at sunset, sets at sunrise. Completely opposite from the sun. I also would like you to know that the full, that the moon rises 45 minutes later each day. Be careful with this. Stars, we learned in the earlier lecture, rise what, 4 minutes earlier each day. So, it’s opposite. Stars rise 4 minutes earlier each day. The moon rises 45 minutes later each day.
Alright. I just want us to test a little bit of what we’ve learned in the two phases of the moon lectures. Here are five phases of the moon. What I’d like you to do is to stop the recorder, and when you stop the recorder, I’d like you to give me the names for all five of these phases. Be sure to include a waxing or waning if appropriate. And then I’d like you to put them in order starting with the waning gibbous. So, one of these phases here is the waning gibbous. Start with that one, and then tell me which of these five phases would you see next, and which one would come after that, and so forth. You may have to skip some phases because not all the phases of the moon are here. But put these five in order starting with the waning gibbous. Okay. Stop the video and try and answer those questions, and then when you have your answers, start the video again, and we will check your answers.
Alright. First, let’s check our moon phases. So, here are the five moon phases here. Let’s work through them quickly and hit the highlights. Well, quickly, you can tell, say, this first one on the left. You use the, which side of the moon is lit, to figure out is it waxing or waning. So, for instance, in this case, the left side is lit, which means it’s waning. More than half is lit, we’d say it’s a waning gibbous. Here, the right side is lit, which means it’s waxing. Again, more than half, so a waxing gibbous. Here, the right side is lit, so waxing. Half of it is lit, which we call a quarter moon. So, we call this a waxing quarter or 1st quarter. None of it lit, new moon. Right side lit, waxing. Less than half, a nice banana shape, we have the waxing crescent.
Let’s see how we do putting these in order. I said to start with the waning gibbous. What comes after waning gibbous? After waning gibbous, it should be getting darker and darker each day. Now, what really would come next would be 3rd quarter, or waning quarter, but that’s not one of our choices. Then we get waning crescent, which again is not one of our choices. And then we come back to new moon, the entire moon is dark. What happens after that? Well, a little bit of light starts to work its way across the moon. We have a waxing crescent. Then we have half the moon lit, a waxing quarter or 1st quarter. And then we have more than half the moon lit, a waxing gibbous. If you kept going, what would you have next? The next phase would be a full moon. Then you’d come back to waning gibbous again.
It’s very important that you understand how to identify the phases of the moon. Be sure to practice this. Use the website that was linked in the previous lecture to practice these phases of the moon because on the mid-term, you will certainly have a case, and maybe even the quizzes, where I’ll give you a picture and ask you to tell me what phase of the moon is this. I might give you a bunch of pictures and ask you to put them in order starting with a certain phase.