You’re lecturing to your introductory college astronomy
class about Newton’s law of gravitation. You’ve carefully explained
that the gravitational force depends on the product
of the two masses involved and on the inverse square of the
distance between them. You’ve shown a few examples or perhaps
videos and animations to help your students connect
the abstraction of an equation to the real physical world. You
may assign thoughtful homework problems, and you encourage
the students to ask questions if they don’t understand, either
in class or during your office hours. You’re known as a
good lecturer, and your students always rate you highly at
the end of the term. Yet when you give your exam, you’re dismayed
to see how many of them can’t answer straightforward
questions of the type you covered in class and assigned
as homework. So why does the same thing happen to instructors
all over the country?
Astronomy-education researchers have been working to
solve that problem and many others facing instructors of astronomy
survey courses for nonscience majors. Such courses
are commonly called Astro 101. During a series of investigations
conducted at the University of Arizona, education researchers
have developed conceptual questions used to assess
students’ understanding of core topics in such courses. Two of
the questions are “At what location between the Earth and
Moon does the net gravitational force on a spaceship become
zero as it travels between the two bodies?” and “Would a waxing
gibbous Moon ever be above the horizon during daytime?”
After traditional lecture-based instruction, one student
(Jennifer) stated in response to the gravity question, “halfway,
because exactly halfway causes the Moon’s and Earth’s gravitational
pulls to cancel out.” In response to the lunar-phase
question, another student (George) answered, “No, because
this phase only occurs when the Sun illuminates it during our
nighttime.” Those responses indicate that after instruction Jennifer
and George still had conceptual and reasoning difficulties
common among their peers prior to instruction.1
By the second time Jennifer and George answered those
questions, they had both participated in an interactive learning
activity designed to help Astro 101 students confront
common misconceptions. After completing the activity on
gravity, Jennifer correctly answered, “Closer to the Moon
than to Earth, because Earth has a greater force on the space