WEBVTT 00:00:00.030 --> 00:00:06.540 Do shadows from other planets cause the phases of the Moon? Let's find out. Hey Deigo 00:00:06.540 --> 00:00:09.719 you what do you think causes the phases of the Moon? It's gotta be the shadow 00:00:09.719 --> 00:00:17.779 from Mars right? No it's got to be the shadow for Mercury. I'm so misunderstood. 00:00:17.779 --> 00:00:22.439 Might the phases of the Moon be caused by Earth's shadow? Let's look at the phases 00:00:22.439 --> 00:00:25.859 of the Moon as it orbits around the Earth over its twenty seven day period. 00:00:25.859 --> 00:00:29.250 Note that the Sun is to the right and Earth's shadow will be represented by the 00:00:29.250 --> 00:00:33.570 blue cone on the left. Here we see the first quarter and we see the Moon shadow 00:00:33.570 --> 00:00:38.940 has appeared. But the Moon isn't even in Earth shadow yet. As we move towards 00:00:38.940 --> 00:00:42.989 Earth's shadow we can see a full moon. If the Moon were in Earth's shadow we would 00:00:42.989 --> 00:00:48.149 see it here. As the Moon continues going past Earth's shadow we see a shadow 00:00:48.149 --> 00:00:53.340 growing as we approach third quarter. Finally, as the Moon comes between the 00:00:53.340 --> 00:00:57.989 Sun and the Earth, we see that the Moon is opposite of the Earth's shadow. But 00:00:57.989 --> 00:01:02.430 it's the side of the Moon that is completely dark to us. Therefore, the 00:01:02.430 --> 00:01:07.530 phases of the Moon cannot be caused by Earth's shadow. if you still don't 00:01:07.530 --> 00:01:11.490 totally understand the phases of the Moon try this for yourself. All you need 00:01:11.490 --> 00:01:14.970 is a ball, like a baseball, to represent the Moon and a lamp to represent the Sun. 00:01:14.970 --> 00:01:19.290 Your head will represent the Earth. Go into a dark room with your materials and 00:01:19.290 --> 00:01:24.840 turn off all the lights. And don't forget the lamp. In order to do this, your Earth- 00:01:24.840 --> 00:01:29.939 Moon- Sun system needs to be set up as so. Let's see if we can get the Earth's 00:01:29.939 --> 00:01:32.939 shadow to create some of the Moon shadows. Here we are starting at a new 00:01:32.939 --> 00:01:36.210 moon. Since the Moon has a slightly tilted orbit, the Moon should be below 00:01:36.210 --> 00:01:40.350 eye level for the new moon. The side of the Moon facing you is entirely in the 00:01:40.350 --> 00:01:45.210 shadow. Remember, your head represents the Earth. Where is your head's shadow? Is it 00:01:45.210 --> 00:01:50.460 possible for your head's shadow to be on the Moon for this phase? Nope. Therefore, 00:01:50.460 --> 00:01:54.659 the Earth's shadow could not cause a new moon. If we fast forward approximately 00:01:54.659 --> 00:01:59.130 seven days we will see the Moon in first quarter. Look around and find your head's 00:01:59.130 --> 00:02:02.820 shadow. Does it look like your head's shadow is falling on the Moon? We can 00:02:02.820 --> 00:02:06.659 repeat this step one more time as we move to a full moon. Because of the 00:02:06.659 --> 00:02:09.780 Moon's tilted orbit the Moon should be just above our eye line here. Let's take 00:02:09.780 --> 00:02:12.660 a look and see where your head shadow is. Does it look like your shadow causes a 00:02:12.660 --> 00:02:16.650 full moon? Finally, moving to the last stage we will 00:02:16.650 --> 00:02:20.819 demonstrate the third quarter. The Moon has moved back to eye level and as we 00:02:20.819 --> 00:02:24.700 can see Earth's shadow still isn't facing the Moon. 00:02:24.700 --> 00:02:29.560 How many of the phases were caused by the shadow of your head? Through this 00:02:29.560 --> 00:02:32.170 in-person exercise, it is apparent that the Earth's shadow could not possibly 00:02:32.170 --> 00:02:38.170 cause the phases of the Moon. In summary, we've learned the phases of the Moon are 00:02:38.170 --> 00:02:41.950 not caused by shadows from other celestial bodies. The shadows from 00:02:41.950 --> 00:02:46.450 Mercury and Venus are too short to reach the Earth-Moon system. The shadows from 00:02:46.450 --> 00:02:50.319 Mars and other outer planets are pointed in the wrong direction. The Moon is also 00:02:50.319 --> 00:03:05.050 spherical, that is how it tests half a shadow onto the Moon.