Make it Stick

I just read Make it Stick, about research-based results in how people learn and the implications for education. I loved it; it is filled with simple, straightforward ideas that will be useful in the classroom. For example, it is better to do many low-stakes quizzes than a few high-stakes exams. For another, it isn't useful for students to re-read the textbook, and it is useful for the lectures and the textbook to be misaligned. For another, students' perception of their learning is often wrong and misguided. For another, it is useful to interleave topics and not just do “massed practice”. It points out that it is very adaptive for learners to believe that their brains are plastic and their abilities are not innately limited. Luckily this also appears to be true. All of these things will come into my next pre-health (or other big) class. And I will explicitly explain to the students why.

My quibbles with the book are few. One is that they slag off unschooling, and then immediately follow with a long profile of a Bruce Hendry, who is a perfect example of the power of unschooling (he is entirely self-taught through self-directed projects of great importance to himself!). I also found the writing repetitive and a bit slow. But the book is filled with good ideas. Also, it is not just informative, it is responsible: The authors clearly differentiate between research findings and speculations or over-generalizations of them. This is a great contribution to the literature on teaching and learning.


emission lines from stars

At the end of Mike Blanton's brown-bag talk at NYU yesterday, Matt Kleban asked: Why don't stars produce emission lines; why only absorption lines? Maryam Modjaz said "because they are hotter on the inside and cooler on the outside". That's true! But it is slightly non-trivial to see why the consequence is always absorption-lines only. And does it mean that if the stars were cold, condensed objects bathed in a hotter radiation field, they would produce emission lines? (I think the answer here might be "yes"; think of a gas cloud bombarded with ionizing radiation.) Also Kleban pointed out that actually the very outside of the Sun is in fact hotter than the surface, which is true, but it must be that this is just so optically thin it barely matters.

In some ways, the biggest paradox about stars is that they aren't all the same temperature: After all, the "surface temperature" of a star is the temperature around the place where the photosphere becomes optically thin; shouldn't this be around 10,000 K for all stars? After all, that's the temperature around which hydrogen atoms recombine (see, for example, the CMB). I don't know any simple answer to this paradoxical question; to my (outsider) perspective it seems like the answer is always all about detailed atomic physics.