Category: communicating science

Six-legged spiders

Here’s a quiz for you: what’s wrong with these pictures?

Black widow spider
Black widow spider
Advent calendar
Pyramids at Giza

Did you find anything wrong? Surely you noticed the black widow spider has only 6 legs, not 8.  Here’s the original – I amputated one leg with photoshop for the pic above. If you rolled-over the pyramids picture and saw the reference to National Geographic, you might suspect the pyramids are in the wrong locations. Not in this picture, though: there’s nothing wrong it. (source)

What about the picture from the advent calendar? If you’re at all familiar with this blog and my passion for teaching astronomy, you might have guessed I’m going to tell you about the Moon and its incorrect phase.

And you’d be right.

The November 25, 2011 edition of the Guardian carried the story, “Your moons are rubbish, astronomer tells Christmas card artists.” The offending advent calendar shows the Moon in the waning crescent phase:

As astronomer Peter Barthel correctly points out, this phase rises around 3:00 am and sets around 3:00 pm. No matter if this Moon is rising, setting or somewhere in between, you’re not going to find people caroling in the town square. The artist got the wrong phase. In fact, Barthel has done much more than point out this one flawed calendar. In an article submitted to the journal Communicating Astronomy with the Public, he finds errors in artists’ depictions of the Moon in everything from Dora the Explorer to Christmas wrapping paper, from the Netherlands to North America.

The responses to the Guardian story, and its offspring like this Globe and Mail piece, seem to fall into three camps:

  1. “Oh, puh-lease! It’s just a picture on a calendar! Gimme break, you grinch!”
  2. “Oh, c’mon! Everybody know the Moon cannot be in the waning crescent phase in the evening!” (I suspect the Guardian reporter might fall into this camp because he writes, “[t]he phases of the moon are easy to grasp.” As someone who teaches astronomy and studies astronomer education, let me tell you, for the vast majority of people, they’re not.)
  3. “Oh, dear.  Another case of scientific illiteracy.”

Me? I’m in Camp 3. Why can’t an artist do some fact-checking before drawing the Moon? Does the artist think to himself, “I wonder if that’s the right phase? Ah, screw it, whatever.” I doubt it. It’s more likely a lack of recognition that the phases of the Moon follow a predictable, understandable pattern. That is, most people don’t even realize you can ask a question like, “when does the waning crescent Moon rise?”

Or worse yet, there’s a distinct possibility that people (yes, now I’m talking about more than this one, particular artist — the problem is widespread) are completely unaware of the Moon, other than the fact that we have one. Why, just recently a colleague said to me, “I have no idea about phases. I never look at the Moon.”

Which brings me back to the six-legged spider. If you bought a book for your kid with a six-legged spider, you’d see the error. Would you draw in a two more legs? I would.  Even your kid would see the error and tell you the book is rubbish. Why the difference between spiders and the Moon, then?

“Because spiders are something everyone sees every day.” Uh-huh, like the Moon.

“Because spiders are icky and gross and awesome. And the Moon is, like, science-y. Boooorrrring…”  Damn.

What do I think we should do about it? I’d like people to learn some astronomy, sure. More than that, though. I want people to think scientifically. I want to live in a world where people have the awareness (and freedom) to stop and ask, “Really? Are you sure about that?”

That’s a tall order so let’s get on it. We can start by modeling scientific awareness for our kids,  students, friends. Show them it’s okay to be passionate about math. Show them it’s okay to step off the sidewalk onto the grass to look at a bug or an interesting stone. Read them stories that engage their brains. Don’t buy books, wrapping paper or calendars with incorrect science. And if you accidentally do, don’t laugh it off with a “whatever…” It only takes one or two of those for kids to learn the science is dumb and only grinches point out mistakes. Instead, take the opportunity to talk with them about how we should always be curious about how things work.

A society of scientifically-literate people? That’s a world I’d like retire in.

A misconception about extrasolar planets

A couple of weeks ago in the introductory “Astro 101” class I work in, the instructor and I confirmed that many students hold a certain misconception. I was, still am, pretty excited about this little discovery in astronomy education. If my conversations over the following few days had turned out differently, I probably would be writing it for publication in the Astronomy Education Review. Maybe I still will. But for now, here’s my story.

Our search for life in the Universe and the flood of results from the Kepler Mission have made the discovery of extrasolar planets an exciting and relevant topic for introductory “Astro 101” courses and presentations to the general public.  Instructors, students, presenters and audiences latch onto “the transit method” of detection because it is so intuitive: when an extrasolar planet passes between us and its star, the planet temporarily blocks some star light and we detect a dip in the brightness of the star. The period and shape of the dips in the record of the star’s brightness encode the characteristics of the planet.

When an extrasolar planet passes between us and its star (when it "transits" the star) we detect a dip in the brightness of the star. (Kepler/NASA image)

Our students do a nice 50-minute, hands-on lab about how to decode these “light curves” which I hope to share at the ASP 2011 conference (#ASP2011 on Twitter) in July. In a class following this lab, the instructor posed the following think-pair-share clicker question. We wanted to assess if the students remembered that the size of the dip is proportional to the area of the star blocked by the planet’s disk, which scales as the square of the diameters:

Clicker question to assess the students' grasp of the transit method of detecting extrasolar planets.

The bars in this histogram record the number of students who chose (from left to right) A to E:

Students' responses for (left to right) choices A to E to extrasolar planets clicker question.

About 60% of the class chose answers (C and E) with a 1% drop in brightness, the correct drop, and about 40% chose answers B and D with a 10% drop. This second group didn’t remember the “proportional to area” property. So, not stunning results, certainly a good candidate for pairing and sharing.

The misconception

What is stunning, though, and the source of my excitement, is that 97% of the class feels you see a black spot moving across the star. Which is not true! We only detect the drop in the brightness of the star. We can’t even see the disk of the star, let alone a tiny black spot!

Okay, okay before you jump to the students’ defence, let me (with the help of my great CAPER Team colleagues) jump to the students’ defence:

  1. The question says, “…by observing it pass in front of the distant star.” Of course the students are going to say we see a dark spot – that’s what we just told them! Perhaps I should be worried about the 3% who didn’t read the question properly.
  2. The question is vague about what we mean by “size.” Diameter? Area? Volume? Mass? “The star’s diameter is 10 times bigger than the planet’s diameter” is a much better question stem.
  3. My colleague Aaron Price points out
  4. Astronomers may not see a “dot” crossing the star right now, but they can see something comparable. Through speckle imaging, radial topography and optical interferometry we have been able to see starspots for decades. CHARA’s recent direct observations of a disk of dust moving across epsilon Aurigae shows what is being done right now in interferometric direct imaging. I predict within 10 years we’ll have our first direct image of a “dot” in transit across another star.

  5. Aaron, Kendra Sibbernsen and I all agree that the word “see” in “What would you see?” is too vague. The question I wanted to ask should have used “observe” or “detect”. Kendra suggested we write “A) a dark spot visibly passing in front of the star” and perhaps following up the question with this one to poke explicitly at the potential misconception:

With current technology, can astronomers resolve the dark spot of an extrasolar planet on the disk of a star when it is in transit? (T/F)

Was there a misconception?

Did the students reveal a misconception about transiting extrasolar planets. Nope, not at all. It’s not like they took the information we gave them, mixed it with their own preconceived notions and produced an incorrect explanation. Instead, they answered with the information they’d been given.

A teachable moment

It seems that we’re not being careful enough in how we present the phenomenon of transiting extrasolar planets. But as it turns out, this is a teachable moment about creating models to help us visualize something (currently) beyond our reach. We observe variations in the brightness of the star. We then create a model in our mind’s eye — a large, bright disk for the star and a small, dark disk for the planet — that helps us explain the observations.

This is a very nice model, in fact, because it can be extended to explain other, more subtle aspects of transiting extrasolar planets, like a theoretical bump, not dip, in the brightness, when the planet is passing behind the star and we  see detect extra starlight reflected off the planet. The models also explains these beautiful Rossiter-McLaughlin wiggles in the star’s radial velocity (Doppler shift) curve as the extrasolar planet blocks first the side of the star spinning towards us and then the side spinning away from us.

These wiggles in the radial velocity curve are caused by the Rossiter-McLaughlin effect (from Winn, Johnson et al. 2006, ApJL)

Want to help?

If you’re teaching astronomy, you can help us by asking them this version, written by Kendra, and letting me know what happens.

An extrasolar planet passes in front of its star as seen from the Earth. The star’s diameter is 10 times bigger than the planet’s diameter. What do astronomers observe when this happens?

A)  a dark spot visibly passing across the disk of the star
B)  a 10% dip in the brightness of the star
C)  a 1% dip in the brightness of the star
D) A and B
E) A and C

In conclusion

I don’t think this qualifies as a misconception, not like the belief that the seasons are caused by changes in the distance between the Earth and the Sun. We’re just need to be more careful when we teach our students about extrasolar planets. And in more-carefully explaining the dips in the light curve, we have an opportunity to discuss the advantages and disadvantages of using models to visualize phenomena beyond our current abilities. That’s a win-win situation.

Thanks to my CAPER Team colleagues Aaron, Kendra and Donna Governor for the thoughtful conversations and the many #astro101 tweeps womanastronomer, erinleeryan, uoftastro, jossives, shanilv and more who were excited for me, and then patient with me, as I figured this out.

#eqjp, a teachable moment

In my current assignment through the Carl Wieman Science Education Initiative in Physics and Astronomy at UBC, I’m working closely with a senior astronomy professor to help him better teach his general-education “Astro 101” course. It’s a mixture of providing resources, mentoring, helping him clarify what he wants the students to learn, and coaxing (sometimes dragging – he’s a great sport!) his teaching to a learner-centered approach.

Today was supposed to be the first class in the last, big section of the course, comparative planetology. That is, the characteristics of the planets and other bodies in our Solar System and, more importantly, what their similarities and differences tell us about the formation of Solar System some 4.5 billion years ago. Traditionally, one follows the textbook’s lead. Chapter 10: Mercury. Chapter 11: Venus,… Chapter 15: Saturn,… Chapter 20: Other Crap, Chapter 21: [finally!] Formation. And by this time, nobody remembers Mercury, Venus, or gives a damn. I’m glad to say we long ago scrapped that approach and instead, focus on the gathering and analyzing the evidence that points to a single formation event. Our learning goal states that a student will be able to

deduce from patterns and properties of the planets, moons, asteroids and other bodies that the Solar System had a single formation event.

Where was I? Oh, right, teachable moment.

Last night (March 10), there was a massive earthquake in Japan. Magnitude 8.9, one of the biggest earthquakes recorded. The ensuing tsunami(s) devastated parts of Japan. I pay attention to these things, perhaps more than others, because my home, Vancouver, is on the list of places expecting The Big One. And we can be hit by tsunamis caused by earthquakes around the ring of fire. Thankfully, the west coast of Canada and the U.S. were spared this time.

It occurred to me, on the bus ride to work this morning, we could use last night’s earthquake in class today. Seismic activity tells us about the structure and evolution of the Earth. Similar signs of earthquakes and volcanoes on other planets, or lack thereof, tell us about their structure and evolution. Not seeing volcanoes on a planet is just as telling as seeing them. Using the earthquake to introduce this last arc in the course would set the tone for the next month of classes: we don’t care about the exact surface temperature on Mercury or the exact density of Neptune. We care about patterns in the physical properties of the planets. And we care about how we find, collate and reconcile those patterns.

Shortly after this “A-ha!” moment, my brain countered with, “Is this a teachable moment. Or are you exploiting the earthquake because you can’t think of an interesting way to teach comparative planetology?”

So I tweeted…

…and, as usual, was overwhelmed by the quick and intelligent response of the great tweeps who follow me. Thanks @TanyaCNoel, @penmachine, @snowandscience, @cpm5280, @derekbruff, @erinleeryan, @cosmos4u. The overwhelming advice was take advantage of the teachable moment:

Good idea. Understanding is always helpful.
teachable moment. everyone’s talking about it anyway…
Definitely a teachable moment

I’m also thankful to @ptruchon for putting words to something that bothered me:

Tough one…Do some of them have family in Japan? If so, are they ok?

So, I went for it. And by went for it, I mean I decided to convince the prof to use the earthquake in today’s class. I proposed he could run the “Earth’s Changing Surface” lecture-tutorial but he decided against it. Instead, he used the earthquake to segue from “here are the 3 or 4 key patterns that support a single formation event” to “how do we know all that, anyway?” Through open questions  like, “What does the earthquake tell us about the structure of the Earth?” and “What does this picture [of Mars’ Olympus Mons] tell you about this planet?” he lead a nice discussion with the 170-or-so students in class today. Many students, men and women, from the front and the back of the lecture hall, participated.

A very successful class, in my opinion, one that demonstrated to me and himself and the students, how “agile” this prof is getting. I was proud that we were able to adapt our presentation so quickly and help the students learn about something they care about.

P.S. A special hat-tip to @cpm5280 who reminded me about that this earthquake was predicted, yes predicted, by the Super Moon wingnuts. I gave the prof a quick summary, just in case. And sure enough, at the end of class, a gaggle of students came down and asked him if he knew anything about the Moon being super-close on March 19. He hit them with a few, key scientific facts (in particular, that because gravity follows an inverse-square law, the tiny decrease in distance won’t do very much) and told them that the whole earthquake-prediction thing was, “a load of crap.” He used their language and they, like, totally got it.

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