Classroom Stories: Light as a Wave

By Stacy Palen

Typically, I lecture about light as a wave by showing students images of waves and describing wavelength, frequency, and velocity. Then I tell them that wavelength and color go together; that light of a particular color has a particular wavelength.

However, when we would get to the Light and Spectra activity, it was clear that they had not fully internalized this information. Given that I’m not lecturing at all this semester, I invented a short activity (which can be accessed by clicking here) that unpacks this relationship a bit.

The activity uses an LED light tower that I happen to have. You can find this specific one here, but the activity could be adapted for use with spectral tubes or images from the internet.

I cannot darken the room this semester, so being able to adapt this activity made it indispensable. I also could not use the spectral tubes for my students because they simply weren’t bright enough to see. I wound up using the online images from the light and spectra lab. Without this activity students would not have been able to use their spectrum glasses in the classroom at all!

Oh, and in case you were wondering, no, it doesn’t work to try to project the spectrum tubes using the document camera.

Despite the difficulties in using the online images, student performance on the light and spectra activity was better than in the past. They also seem to have acquired a clear understanding that color and wavelength are related.

You can check out the activity yourself by clicking here!

 

 


Classroom Stories: More Ruminations on a Theme: Fermi Warm-Ups

By Stacy Palen & John Armstrong

This week, we have a guest post from a colleague at Weber State University. John Armstrong is also teaching in the inadequate classroom. He is experimenting with a way to fill the time while he figures out what’s changed about the A/V situation since the last class two days ago… 

Thanks to some intermittent multimedia issues in my new “temporary” classroom, I’m forced to get creative with the first ten minutes of class every day. So, I start by giving a Fermi problem to my students. I ask the question and they can work on the answer while I jiggle cables and try turning things off and on again.

Physicist Enrico Fermi was famous for posing seemingly unsolvable questions that he would then proceed to solve with a few back-of-the-envelope calculations. The most famous of these—how many piano tuners are there in the city of Chicago—requires some educated guesses about population, the popularity of pianos, and the diligence of their owners, but you get surprisingly close to the “correct” answer without knowing much of anything.

In astronomy, this tool has been leveraged in the Drake Equation to estimate the number of civilizations in our galaxy, proving that even when you can’t know some of the parameters you need to measure, you at least have a framework for study. The first three terms of this equation—the number of new stars formed in the galaxy, the number of these stars that form planets, and the number of Earth-like planets in each system—were largely unknown when I started my studies in the mid-nineties. They now have pretty good estimates. We are now on the verge of an estimate of how many planets can evolve life, which is something that could happen in the next decade or so.

But when I reached this point in my class, going from a simple Fermi problem to the Drake Equation seemed like a heavy lift.

I’ve always started the semester with a formal activity on estimating the number of pebbles in a jar. We measure the volume of the jar, remove a few pebbles and systematically measure their volumes, and then divide the two. The amount of agreement between the groups is surprising.

But thanks to my A/V woes, I’ve started asking a question every day. How much does the mass of humans increase each year? How far does a bumblebee travel in a day? How much food energy do you consume in a year? And each day, more and more students seem to dive in. Better yet, some of them have come in after doing some of their own estimations. How many bricks are in their house? How much electricity do they consume every year? 

The answer to the last question turns out to be surprising: It’s about ten times the amount of energy that you eat in food.

While I’ve always seen the value in Fermi problems, their routine application is giving my students extra practice and increasing their numeracy. And they also seem to be sparking my students' interest in their own questions.

I can’t wait to get to the Drake Equation!

—John Armstrong


Current Events: "Not Just A Space Potato": NASA Unveils "Astonishing" Details of Most Distant Object Ever Visited

By Stacy Palen

According to this article on The Guardian, when the New Horizons spacecraft arrived at Arrokoth, it revealed a surprising world. Now, planetary scientists are beginning to reconsider their conclusions about the formation of the Solar System. This new discovery appears to favor a gentler model of planet formation than the hierarchical model.

Here are some questions, inspired by the arrival of the New Horizons probe at Arrokoth, that you can ask your students:

1) Where is Arrokoth located?

Answer: In the Kuiper Belt.

2) Why can observations of Arrokoth yield information about the early Solar System?

Answer: Objects in the Kuiper Belt remain essentially unchanged since the Solar System formed. They do not have the same history of impacts and geologic processes as objects in the inner Solar System.

3) In your own words, state the hierarchical model of planet formation.

Answer: Small bodies smash together to form progressively larger bodies.

4) In your own words, state the cloud collapse theory of planet formation.

Answer: Slightly denser regions of dust and gas clump together and then, all at once, collapse under gravity.

5) What would astronomers expect Arrokoth to look like if the hierarchical model is correct?

Answer: They would expect to see evidence of collisions, like fractures and varied composition across the body.

6) What would astronomers expect Arrokoth to look like if the cloud collapse theory is correct?

Answer: They would expect to see uniform composition and no evidence of smashing.

7) Which model of planetary formation is supported by the actual appearance of Arrokoth?

Answer: Because Arrokoth is relatively smooth and uniform, it supports the cloud collapse theory of planet formation.


Current Events: 7 billion-year-old stardust is the oldest stuff on Earth

By Stacy Palen

I recently stumbled upon this article from The Washington Post about stardust on Earth. Mineral dust in the Murchison meteorite shows traces of neon produced by cosmic rays as the dust traveled through space. The abundance of neon atoms indicates that the dust was formed 7 billion years ago—before the Sun formed.

Here are some questions to ask your students based on the article:

1) What produces neon atoms in grains of interstellar dust?

Answer: Cosmic rays smash into the grain and convert silicon into neon.

 

2) How does the rate of cosmic rays striking the dust change with time?

Answer: It doesn’t. This rate is constant.

 

3) Suppose that one grain of dust has twice as much neon as another grain. What can you conclude about the relative time each grain spent in space?

Answer: The one with twice as much neon was out there twice as long.

 

4) In your own words, describe how astronomers determine the age of a grain of interstellar dust.

Answer: Astronomers count the number of neon atoms and compare that number to the number of neon atoms in a grain of known age. If there are more neon atoms, the dust grain was roaming the galaxy longer.

 

5) How old is the Sun, and how do we know?

Answer: The Sun is about 4.5 billion years old. We know this from measuring isotope abundances in moon rocks.

 

6) Are these dust grains older or younger than the Solar System?

Answer: These dust grains are 2.5 billion years older than the Solar System.

 

7) Is this result consistent with the idea that stars recycle material from the interstellar medium when they form? Explain.

Answer: Yes! Because the Sun and planets formed from material lost from earlier stars (we know this because of the abundance of other materials. Some of that material is still floating in the Solar System, and some of it was lost from stars that died long before the Solar System formed.


Classroom Stories: Another Way to Do the Phases of the Moon

By Stacy Palen

The phases of the Moon are one of those topics that has been extensively studied by the astronomy education research community and is well-known to be more complex than most people think. There’s the change of perspective from Earth-view to space-view. There are multiple motions at once (the rotation of Earth and the Moon, and the revolution of the Moon around Earth). There’s the issue about light rays always traveling in straight lines and not bending. It’s complicated.

Last week, I pulled an old phases-of-the-Moon activity out of the archives, which can be accessed by clicking here, for my students to complete in addition to the activity, “Studying the Phases of the Moon” from the Learning Astronomy by Doing Astronomy workbook. This is not an appropriate activity for Learning Astronomy by Doing Astronomy because it requires students to have Styrofoam balls that have been colored black on one half. (I can’t make the classroom dark, so I can’t use the traditional “balls-on-sticks” approach.) But one thing that I like very much about this activity is that it leads them to figure out how to (approximately) tell time by the Moon, which means that I can ask them a question about it on my zombie-apocalypse midterm—insert evil laugh here!

The activity also asks them to consider the phases of other objects, such as the phases of Earth as seen from the Moon, or the phases of Deimos as seen from Mars or Phobos. Carrying the concept of phases away from Earth seems to help cement the idea that this is a phenomenon that is all about the relative location of the light source and the observer.

I followed this activity the next week with the “Studying the Phases of the Moon” activity from the workbook. I was interested to notice that students finished the activity in record time and were much better prepared for it. The two activities worked well together to really build their picture of how the phases of the Moon actually occur.


Classroom Stories: Energy and Kepler’s Laws: A Surprise for Me about Where the Difficulty Lies

By Stacy Palen

Recently, my students worked on the “Working with Kepler’s Laws” activity from the Learning Astronomy by Doing Astronomy workbook. In this activity, students learn about ellipses, consider the “simple” version of Kepler’s second law (a planet travels faster when nearer to the Sun and slower when farther away), and run some numbers for Kepler’s third law: P2=a3. To my surprise, Kepler 1 and Kepler 3 brought almost no questions from the students (aside from “Am I doing this right?”). It was Kepler’s Second law that brought the most substantive questions.

Over and over they asked “Yes, but WHY does it go faster when it’s closer?”

I used this question as the basis for a whole new activity.

Approaching this question as an energy problem, I had the students throw a ball straight up in the air and make pie charts representing how much kinetic energy, gravitational potential energy, or thermal energy the ball had at various points in its trajectory. Then they threw the ball to a friend and made similar pie charts (in this case the velocity is never zero, so the kinetic energy is also never zero). Then I had them consider a planet in orbit around the Sun and make a third set of pie charts.

Wow! This was so much harder for them than I expected!

First, it turned out that pie charts are a concept that most (but not all) of my students have in common. Who knew?

Second, we ran into the issue about where to put the “zero” of gravitational potential energy. This information was in the Background section, so it was invisible.

Third, we faced our biggest issue: Convincing students that when they threw the ball straight up into the air, the ball had zero speed at the apex of the trajectory. That alone was a 20-minute conversation!

Finally, even though I told them to describe what happens to the ball between the moment after it left their hand to the moment before they caught it, many students turned all the energy into thermal energy. I’ve edited the activity to try to correct these problems and will use it again in the fall in search of perfection.

Despite these problems, I was very happy about the conversations that I overheard as I moved around the room. Some students were completely unfamiliar with the conservation of energy. They made progress simply by learning how the energy transformations occur for a ball thrown in the air!

Other students rocked that part but were stuck when the questions about orbits showed up; this was often because they drew the Sun at the center of the orbit instead of at a focus. What a great opportunity to correct this problem!

Finally, some students spent a very long time arguing about whether they needed to account for energy lost to thermal energy in our current Solar System.

Overall, I was pleased by what I learned about how they think about energy as well as how well they grappled with this material. And I’ve now set them up to have a spark of recognition when they learn about planet migration later in the semester. This activity is a work in progress, but I will definitely try it again!

You can access the activity by clicking here!


Classroom Stories: Classroom Calculators

By Stacy Palen

Here’s the thing: all students have a calculator in their phone. And for a long time, I've thought, “They should use the calculator in their phone so they know how to use the calculator in their phone!” But here’s the other thing: a lot of those calculators are terrible. They don’t all do the order of operations the same way. They don’t all have the same “buttons” on them. They don’t all use the same notation. Therefore, any time I have students do any math at all in the classroom, I spend most of the time running around and helping them figure out how to put the “times ten to the” into their calculator. iPhone calculators are pretty good, but Samsung calculators don’t have the same functionality. Students must painstakingly type “(3 X 10 ^ 8)” rather than “3EE8.” That may not seem so bad, but if they forget the parentheses, the calculator doesn’t see their input as one number. So, if the problem includes division, the student is stymied. In addition, students' having their phone in their hand is distracting to the point of incompetence.

This semester, I had the idea to invest in a classroom set of calculators. I found a fairly simple solar-powered calculator that I could buy for less than $7, and I begged the chair of my department to use some of our lab fees to buy 60 of them.

When we have an activity involving a math problem, I invite students to borrow one, and I use the document camera to show them exactly how to punch things into the calculator. For Kepler’s Third Law, I show them how to square a number and how to take a cube root. For multiplying powers of 10, I show them how to put in “3 X 108” so the calculator interprets it as a single number (3EE8 or 3EXP8).

So far, this has been revolutionary. I spend far less time helping students with their calculators and far more time helping them think about their answers. Students can now help each other with the calculators, too, and they don’t need to wait for me to come around to them. Generally, this seems to be helping them be more patient.

Even for the many students who have their own favorite calculator, they sometimes don’t know how to use it for our specific purpose—it’s set up for stats, for example. While they have the option to borrow a calculator or use their own, I still spend some time helping these students find the “EE” or “EXP” key for scientific notation, but if they otherwise know how to use the calculator, they seem to remember this new function more easily. Looking back, I estimate that I could have bought only half as many calculators for the 70 students in the room, and even fewer if they work in pairs.

As I go along, I’m compiling a list of calculator instructions that I can print and tape to the cover. I may make a large poster of this information, instead, which might work better once we are back in our usual teaching space.

I have been pleasantly surprised by how much easier it is to manage the classroom when all my students have the same tool. In retrospect, it seems obvious that this method would be easier, but it took me nearly 20 years to think of it…


Classroom Stories: Teaching the Seasons in Inadequate Classroom Space

By Stacy Palen

Last week, we continued our struggle with the lack of AV equipment in our temporary teaching space. In order to teach the seasons in this space, I rewrote an old activity that used an overhead projector and a piece of cardboard with a hole cut out to help students understand why the angle of incidence matters.

Not having an overhead projector or cardboard handy, it occurred to me to have the students use their cell phone flashlights and the hole punched in their Learning Astronomy by Doing Astronomy workbook pages to accomplish the same purpose.

I always feel chuffed when I think of some new way to solve the problem!  

I very much liked the way students interacted with this activity.

In Part A, they have to assemble some of their own real-life knowledge about seasons on Earth. In Part B, they have to hold the WRONG idea in their head as if it were true, which is especially challenging! In Part C, they identify and explain the correct explanation. In the final part, they apply their understanding to seasons on Uranus and test their ability to extend their knowledge to a new situation.

It took most students about 25 minutes to do this activity.

When I teach it again, I’ll probably modify some of the language in Part B to make it even more clear that I expect them to write down things that they know are wrong.

This activity may eventually make its way into Learning Astronomy by Doing Astronomy because I’ve now figured out how to do it with no extra equipment!

You can access the activity by clicking here!


Classroom Stories: Teaching in the Trailer, or "This Will Have Been a Good Time"

By Stacy Palen

In my family, we have a saying, “This will have been a good time.” We use it to refer to upcoming events that will be stressful and potentially awful, but that we will remember fondly once they have passed. For example, when my snake-phobic husband and I went to the Amazon: he didn’t enjoy the trip while it was happening, but afterwards, he was glad to have experienced it. The whole time we were planning the trip, we kept repeating, “This will have been a good time.”

For years, I have taught Introductory Astronomy in the planetarium. This is a difficult space to work in because the chairs are comfy, the light levels are low, the board and projector space is limited, and working in groups of three or more is really difficult. The chairs don’t turn; the students have those little desks that lift out of the chair arm for them to write on; and it is almost impossible to get in and out of a row in the middle of class. If I want to access the computer, I have to go to the back of the room. It’s awkward, but I got used to it, and I figured out how to do both active learning and lecturing, even in this difficult space.

This semester, the planetarium building is being renovated so that we will have heating and cooling that actually work. That’s the plan, anyway. Don’t ask me why they couldn’t do this renovation over the summer. Figuring out the decisions of Facilities Management is above my pay grade!

My astronomy class has been moved into a “portable”—a double-wide trailer in the parking lot, which was furnished the day before classes started. The layout of the classroom is awkward, with students facing perpendicular to the long axis, and the computer being stationed in one corner. It’s like teaching in a hallway. The first week of class, none of the A/V equipment was working, so there were no projectors. During the second week of class, some of the A/V equipment worked, but intermittently—something about the HDMI cables, aspect ratios, and temporary equipment being incompatible with the University standards. I don’t expect this system to be stable for at least another week or two. I could complain about this (more!), or I could see it as an “opportunity” to try something new.

So now, I have jettisoned my long-time methods and materials, and I’m experimenting. I’ve reorganized the whole class to involve lots of mini-activities that can be done quickly in larger-than-usual groups, with lots and lots of peer instruction. For my students, there is really no choice but to read the textbook before they come to class, because it’s really not possible for me to lecture at all.

Today, we’ll negotiate the “points” restructuring, and my students will get to have a say in how much weight each component will have in their final grade. Now that we’ve done a few of the longer activities from Learning Astronomy by Doing Astronomy, a few homework assignments, and a few of the mini-activities, my students have a better sense of how much value each component should have. I’ve explained the experimental nature of what we are doing, and they are mostly cheerful about it.

This entire situation has got me going back and resurrecting things that I did a long time ago, such as using parts of Understanding Our Universe and Learning Astronomy by Doing Astronomy in ways that I haven’t before (it never occurred to me to tear the activities apart and do them over multiple days), seeking out new ideas and activities, and oh … let’s call it “innovating” … at breakneck speed. I expect a lot of this to be a mess, some of it to be useful in the long haul, and some of it to appear in future textbooks. It’s definitely a situation that “will have been a good time.”


Current Events: Image Release: Giant Magnetic Ropes in a Galaxy’s Halo

By Stacy Palen

A new composite image released by the National Radio Astronomy Observatory superimposes radio data on a visual image of a galaxy. Magnetic fields here are shown in blue and green, indicating alternate directions.

Here are some questions that you can ask your students based on this image:

1) What is the Hubble type of this galaxy?

Answer: A spiral.

2) How do you know?

Answer: Because there is a disk, viewed edge on.

3) What is the Hubble type of the large galaxy directly above the primary galaxy in this image?

Answer: Elliptical.

4) How do you know?

Answer: There is no disk.

5) The blue and green false color “hair” represents the magnetic fields of the galaxy. Blue indicates that the magnetic field points roughly away from us, while green points roughly toward us. These magnetic fields are described as “spiraling” and as “ropes.” Make a sketch of the magnetic field lines of the galaxy that fits these descriptions and observations.

Answer: This is a genuine question, not a test of their understanding. I am picturing a spiral for each blue/green pair that is roughly perpendicular to the disk. I wonder what students “get” from these descriptions?

6) Are the magnetic fields above the disk of the galaxy symmetric with those below the disk? What might cause this?

Answer: They are not. It could be because the magnetic field is being generated differently, or it could be because the observations are more resolved above the disk than below. That could happen if the galaxy disk was tilted so that the top of the disk is tilted toward us.