Initial Moon Ideas

First day of the moon, I had students interview their partner about what reasons they can give for why the moon is sometimes only partially visible (or even not visible at all)? They were supposed to *not discuss their ideas* but act as a journalist, reporter–asking follow up questions, and taking notes to really get inside that person’s understanding. They then had to report out that person’s ideas to the rest of their group.

Students could then discuss and collaborate, and then white-boarded initial models. We then presented as a class. Here are my interpretations of ideas that came up.

Earth blocks Sunlight from Getting to Moon, casting a shadow on moon:

Version #1 (Moon configuration only):   New moon is when moon is behind earth receiving no light. Full moon is when moon is 180 degrees there, now getting the sun’s full light. Phases are when moon is in intermediate locations between behind earth and in front of the earth.

Version #2 (Moon configuration plus vantage point):  New moon is when moon is behind earth receiving no light from the sun, but a visible moon is anytime the moon is not in the earth’s shadow–what exact phase you see the moon in depends on your vantage point from the earth. For example, this group drew a “full moon” when moon just came out of the shadow. Then, whether you see  it as a full moon or another partially lit phase, depends on your location on earth.

Version #3 (Visible portion of lit portion):  New moon is when moon is behind earth receiving no light, therefore not visible. Solar eclipse is when moon is directly between earth and the sun, because moon is blocking sunlight from getting to earth. First quarter and 3rd quarter, are the result of the moon being at 90 degrees. Half of the moon toward the sun is lit, but only half of that half is visible from earth, making a quarter moon appearance. Crescents are caused when moon is just passing into the back of the earth (partially in the shadow), and this partial blocking effects that you might still only be able to see a part of the part that is visible (i.e., making less than a quarter).

Notes from presenting group: Full moon seems impossible to create, and so they are concerned that this mostly wrong. They also worry that their diagram suggests that a solar eclipse would happen all the time, and they know its more rare than that. They are also wondering about what is a lunar eclipse, and how that fits in.

Earth Doesn’t Block the Light to the Moon:

New moon is when moon is between earth and sun, because the lit part of the moon is facing the sun, not the earth, making it not visible to us. Full moon is when moon is on backside of the earth, where the lit side is facing the earth. This means that light must still get the moon somehow even when its behind the earth; so either light gets around the earth (due to its spherical nature, not wall-like nature) or the moon-earth-sun must not fall in a perfect line. This group actually began making a whiteboard the same as the group presenting version #1, but as they drew and discussed it they realized many of the same issues that group #3 discussed.

Other Commentary

As a class, we have very vague ideas about what causes configurations of earth-moon-sun to change–as some combination of earth’s rotation, earth revolution around sun, and moon revolution around earth. People seemed uncommitted and confused about what does what, and even confused about seasonal changes vs. lunar changes. We also have very vague ideas about the path of moon through sky, which is of course related to the confusion above.

Tomorrow we dive into our moon observations we’ve been collecting over the last 6 weeks, and working to put all our individual observations into a class-wide set of observations. Then I’m hoping we’ll do some work talking on issues of scale, and then revisiting our theories.

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