This week was mostly devoted to informal formative assessment (I’m really beginning to hate those words). Students were asked to explain aspects of a stick’s shadow’s behavior in terms of, for example, Sun’s diurnal and annual motions. Example questions would be something like:
“In one sentence, explain why a stick’s noon shadow changes length during a year.”
“In one sentence, explain why a stick’s sunrise shadow changes direction during a year.”
“In one sentence, explain how you know that the ecliptic and celestial equator cannot possibly coincide. Cite specific observational evidence.”
The third question can then be used for something quite profound, namely to establish that two fundamental celestial reference planes which cannot actually be seen on the sky MUST not overlap (they intersect, of course). This is related to the infamous “twenty-three and a half degrees” that most all introductory astronomy students claim to know all about. Yet, when questioned, they cannot articulate what the entities are that share this angle and furthermore, they cannot articulate how this angle is even measured. Thus, by all reasonable definitions, they do not know anything about it. By the way, in my course students actually complete a WebAssign assignment in which they use noon shadows to measure this angle, but most do not realize that’s what they’re doing at the time.
There’s a lot of reasoning behind these questions, and that reasoning is the main “thing” I want students to take away from this course. I assert that such reasoning is virtually absent from traditional introductory astronomy (there may be exceptions I don’t know about). In the next chapter, these questions will be extended to ones like:
“In one sentence, explain why the time of sunrise varies throughout the year.”
I would much rather have student learn to reason through the explanations for these observable events, which they’ve all noticed in their lives, than memorize facts and figures about anything. From some of my experiences, I’m in the minority.
Comments and feedback welcome!