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August 2018

Reading Astronomy News: Neutron Stars and General Relativity

by Stacy Palen.

Here is a nice little article from NRAO that corresponds to material in Chapter 13 of Understanding Our Universe and Chapter 18 in 21st Century Astronomy:

Questions for Students:

  1. Make a sketch of this triple-star system to show how the three objects move in their orbits as time passes.

    Answer: A sketch with a pair of stars in a small orbit around each other and the combined system making a much larger orbit around a third body.
  2. Anne Archibald says that they can “account for” every pulse since they began their observations. What does she mean by that: does she mean they observed every pulse or they can calculate the time of every pulse?

    Answer: The astronomers can calculate the time of every pulse.

  3. Think back to Ole Roemer’s observations of the speed of light. Roemer observed that the moons of Jupiter passed behind the planet sooner than expected when Jupiter was closer to Earth in its orbit because light did not have as far to travel from Jupiter to Earth. In addition, he observed that the moons passed later than expected when Jupiter was farther from Earth in its orbit. That’s because light had a greater distance to cover. From this, he was able to measure the speed of light to fair accuracy.  The experiment conducted in the article used a different type of “clock”, created not by orbiting moons, but by a rotating neutron star. Explain how the experiment described in the article is related to Roemer’s experiment. Remember, we now know the speed of light quite precisely.

    Answer: This experiment solves the problem “backwards”. It used the known speed of light with the early arrival of a pulse to determine that the pulsar is closer.  A late arrival means the pulsar is farther away.

  4. “Gravitational binding energy” can be thought of as analogous to “nuclear binding energy”. Where in this course have you seen “nuclear binding energy”?

    Answer: Nuclear binding energy appears in discussions of nucleosynthesis, the proton-proton chain, the CNO cycle and the enrichment of the galaxy in heavier elements.

  5. Why is it important to test a scientific idea over and over again?

    Answer: It’s important to repeatedly test a scientific idea because there may be limits in which the idea fails.  These limits become more accessible over time as technology improves.

  6. Suppose that the result had been different. Imagine if the neutron star fell differently than the inner white dwarf. What would astronomers conclude about Einstein’s Equivalence Principle?

    Answer: Astronomers would conclude that the Equivalence Principle might be wrong for very dense objects. They would test this again in another system, if possible, as well as further test some of the alternative ideas mentioned in the article.


What other questions would you ask your students, based on this article? Feel free to leave suggestions in the comments!

How-to: A Day One Strategy for Improving Classroom Engagement

By Stacy Palen.

We often wish that students were more engaged in class. Sometimes we complain that students won’t ask questions, or that they won’t answer the ones we ask.

This is a training problem: we have to train students to know what our expectations are. Think of it this way: expectations are different in every classroom. In some classrooms, especially large ones, students are expected to sit passively and quietly, taking notes, watching videos, or just letting the professor “get through” the material. In some classrooms, students are expected to “discuss.” In others, they are expected to “do.”

How does a student know which kind of classroom they are in? On day one, you can make your expectations clear to students, but it may require allowing yourself to be pretty uncomfortable on that first day! 

First, tell students that you expect them to contribute during class. Then, give them an immediate opportunity to do so! Ask your students what they want to learn in the class, and then stop talking.

Let them tell you. Make a list on the board or screen, where you faithfully show that you hear their contributions. This is not the time to say, “Well, we aren’t really going to talk about constellations.” This is the time to say, “Constellations. Good.” And write that down and then say, “What else?”

This lets students know that you are not looking for a “right” answer. You are taking their input seriously, even if it’s “aliens.” It takes courage for students to speak up in front of their peers and risk being wrong. They need help with that.

Second, tell them that you expect them to answer questions. Then, give them an immediate opportunity to do so! Ask a question that has no “wrong” answer. For example, ask about a recent astronomical event. At the moment, the solar eclipse is a good one.

“How many of you heard about the solar eclipse?” Hands will go up.

“How many of you witnessed it?” Hands will go up.

Ask those students to share their experience with the group. Then ask a question that clearly has a “right” answer: what causes a solar eclipse? WAIT, for a long time if necessary.


For a long time.

I sing “Happy Birthday” to myself to force myself to wait long enough for students to know that they have to take responsibility for answering the question. Sometimes, I even tell them this is what I’m doing--they think it’s hilarious.

Often, in the first few days, as I wait, a student will speak up and say, “Wait. What was the question?” That's because their attention drifted away. They did not know that I was expecting them to stay focused and answer questions--because they didn’t know what kind of classroom they were in.

WAITING is particularly important in the first few days of class. It’s how you show that you actually expect your students to respond to you, unlike those other professors who ask rhetorical questions. Wait. Every single time. How will students know it’s not a rhetorical question, unless you prove it to them by waiting, even though it makes you uncomfortable?

That’s enough for you to try to keep track of on the first day! Try it out and let me know how it goes in comments below.