Monday, October 31, 2011

On Parenthood

Erin recently sent me this amazing post On Parenthood. A snippet:

As an adult, you may think you've roughly mapped the continent of love and relationships. You've loved your parents, a few of your friends, eventually a significant other. You have some tentative cartography to work with from your explorations. You form ideas about what love is, its borders and boundaries. Then you have a child, look up to the sky, and suddenly understand that those bright dots in the sky are whole other galaxies. 
You can't possibly know the enormity of the feelings you will have for your children. It is absolutely fucking terrifying. 
When I am holding Henry and I tickle him, I can feel him laughing all the way to his toes. And I realize, my God, I had forgotten, I had completely forgotten how unbelievably, inexplicably wonderful it is that any of us exist at all. Here I am with this tiny, warm body so close to me, breathing so fast he can barely catch up, sharing his newfound joy of simply being alive with me. The sublime joy of this moment, and all the other milestones – the first smile, the first laugh, the first "dada" or "mama", the first kiss, the first time you hold hands. The highs are so incredibly high that you'll get vertigo and wonder if you can ever reach that feeling again. But you peak ever higher and higher, with dizzying regularity. Being a new parent is both terrifying and exhilarating, a constant rollercoaster of extreme highs and lows.
This is so well put that I have a lump in my throat and goosebumps on my arms.

On the flip side, I was recently describing parenthood to a childless friend. Before relaying what I said, I have to issue the disclaimer that it was at the end of a particularly rough day with Owen and Marcus. Here's how I explained it:
To imagine parenthood, imagine extreme happiness. But imagine that happiness coupled with the following. Imagine doing a task that you don't want to do, something like unloading the dishwasher or scrubbing a counter. Now imagine that you can't do this task because a little life form is demanding your attention, screaming about some inconsequential circumstance, or impatiently insisting on your help in finding an item that they, the little life form, misplaced despite your warnings about losing things. So there you are, not able to do a task that you don't want to do because...well, because you decided to do something as crazy as having a kid.
I love my kids dearly. Being a parent has transformed me into a better person, a better man. But it's important to keep in mind that my decision was not made based on logic or reason. It was a crazy decision. I gave up my life. The moment Owen was born, life was no longer about me and my hopes, dreams and concerns. There's no logic in that decision. There's just this thing called love, and I'm eternally grateful to know it.

So, yeah, parenting is a wonderful mishmash of contradictions that somehow sums to net happiness. As the author above notes at the beginning of their post, it's that 1% that makes all the difference:

Sunday, October 30, 2011

Dragons and Space Dust

My teaching assistant, Jackie Villadsen, recently completed an excellent podcast for 365 Days of Astronomy. The audio and transcript are here. Here's an excerpt:
Stars are the dragons of the Universe. Their massive fiery bellies boil with an inconceivable heat. This heat comes from nuclear reactions. When we set off a nuclear bomb on Earth (which is a very unfortunate and unnatural process), we create for just a tiny moment and in a tiny space the high temperatures needed to fuse together four hydrogen atoms and make helium. By comparison, this process of fusion chugs along constantly, and completely naturally, in the belly of the Sun for 10 billion years! Imagine 10 billion years of continuous nuclear bombs… how strong that is!
The rest of the post takes the reader through the fascinating process of stellar nucleosynthesis, or the way in which all of the elements heavier than lithium are processed in the centers of massive stars and blown back into outer space through supernova explosions. These elements then form the seeds of planetary systems, some of which eventually give rise to life.  We are star stuff!

Sunday, October 16, 2011

Sunday Morning Music Break: 8-bit edition

Q: How many marimba-ists does it take to reprise an 8-bit Nintendo song?
A: As many as it takes to result in this level of awesomeness:

Tuesday, October 11, 2011

Feynman Science and Beauty and Doubt

Oh, internet...

I was looking for exoplanet-related pictures using a Google Images search, and I stumbled upon this bit of awesomeness:

(The sine of the angle b divided by the tangent of b is the cosine of b, or cos b.)

Friday, October 7, 2011

Monday's guest astronomer

Oops, I meant to post this to my Ay20 class blog. Oh well, enjoy it anyway!

Monday we'll be joined by an esteemed visitor, Dr. Jon Swift:

Dr. Swift was my graduate student mentor at UC Berkeley and we both ended up at the University of Hawaii together as postdocs, where he was a Sub-millimeter Array Postdoctoral (SMA) Fellow. His research focus is on massive star formation and he uses interferometers to study molecular clouds where these behemoth baby stars are born.

Dr. Swift is also a professional musician, photographer, poet and an accomplished surfer.

Come prepared with questions for our guest. We'll also be learning about blackbody radiation, so stay tuned for the worksheet, which will be posted this weekend.

Wednesday, October 5, 2011

Monday, October 3, 2011

My students' writing

A friend and colleague of mine, Prof. Andrew West, gave me the idea of having my students maintain research blogs, both as a way for him to keep up with what they are doing and for the student to practice writing. 

This has worked so well for my mentees that I decided to use it in my Intro Astro course. I was further encouraged by this article, in which the author Prof. Cathy Davidson notes
Given that I was teaching a class based on learning and the Internet, having my students blog was a no-brainer. I supplemented that with more traditionally structured academic writing, a term paper. When I had both samples in front of me, I discovered something curious. Their writing online, at least in their blogs, was incomparably better than in the traditional papers. In fact, given all the tripe one hears from pundits about how the Internet dumbs our kids down, I was shocked that elegant bloggers often turned out to be the clunkiest and most pretentious of research-paper writers. Term papers rolled in that were shot through with jargon, stilted diction, poor word choice, rambling thoughts, and even pretentious grammatical errors (such as the ungrammatical but proper-sounding use of "I" instead of "me" as an object of a preposition).
But it got me thinking: What if bad writing is a product of the form of writing required in college—the term paper—and not necessarily intrinsic to a student's natural writing style or thought process? I hadn't thought of that until I read my students' lengthy, weekly blogs and saw the difference in quality. If students are trying to figure out what kind of writing we want in order to get a good grade, communication is secondary. What if "research paper" is a category that invites, even requires, linguistic and syntactic gobbledygook? 
I've already found this to be true. Remarkably true, in fact. Check out the first handful of blog posts from my students. I was anticipating that I'd have to give a lot of feedback and corrections on their initial posts, but they all came out of the starting blocks blogging like pros!

Daniel Lo: The Night Beckons
David Vartanyan: Abstrosizics
John Pharo: Looking Up
Juliette Becker: Starstruck
Lauren Gilbert: Ay20
Mee Wong-u-railertkun: CQ, this is W9GFO. 
Monica He: Ay20
Nathan Baskin: Star Stuff
Tommy Heavey: A Chemist in Astronomy

Please leave comments if you really enjoy any of these posts. They need all the encouragement and feedback they can get on their way to becoming professional scientific researchers. 

Sunday, October 2, 2011

Order of Magnitude Astrophysics

From the Ay20 blog, here's a solution to one of the week 1 worksheet problems.

Estimating The Luminosity of a Sun-like Star

by: John A. Johnson, Jackie Villadsen


We present the solution to Worksheet problem #2, from week 1, estimating the power output of a Sun-like star. Each group should submit one to two of these per week. Decide amongst your group members who will be first author, second author, etc. Acknowledge people and resources used in your solution. Cite ancillary information. State your assumptions clearly. Write your solution such that a frosh could duplicate your steps and arrive at the same solution.


The oldest astronomical instrument is the human eye. A marvel of evolution, the eye has both high sensitivity and a large dynamic range. A classic study of the eye's response to light conducted in 1942 showed that of order 10 photons need to impinge on the eye in order for the brain to register detection (Hecht, Schlaer & Pirenne 1942). In other words, the eye has a gain of 10 photons/DN. In this contribution we use this fact as a starting point for estimating the luminosity (power output) of a Sun-like star. As additional input for our calculation we note that a Sun-like star at 100 light years is just barely visible to the naked eye if the star is viewed from a dark site. (As a side note, this corresponds to a G2V star with an apparent magnitude of V=6).

Order of Magnitude (OoM) Calculation

We start with a rough estimate of the aperture area of the eye. Fully dilated, an eye has an entrance diameter of roughly Reye = 0.5 cm, corresponding to an area of 0.25 cm^2. From here on we consider only a single eye since it is unclear how two eyes would combine for the detection of a faint star, and since we will only incur a factor-of-two error at most, which is insignificant for our OoM calculation. As an additional assumption we ignore absorption by the Earth's atmosphere and set interstellar reddening to zero.

The star is at a distance of 100 light years. Light travels at 3x10^10 cm/s, and there are (π x 10^7) seconds in a year. A light year is therefore D ~ (10 x 10^10 x 10^7) = 10^18 cm. The star emits some number Nemit photons isotropically, and the eye subtends a tiny fraction of the area of a sphere with a radius of D = 10^20 cm and receives 10 photons. This fractional area is (AD/Aeye), where Aeye is the area of the eye and Ais the area of the sphere surrounding the star. Thus

We are interested in the power output of the star, which is the energy emitted per second. We can get the energy corresponding to Nemit photons with 
where \lambda is the wavelength of light. We can assume that the eye's spectral response is well-tuned to the peak of the Sun's spectral energy distribution, which corresponds to about 550 nm (we'll learn more about this after we estimate the Sun's temperature and learn about black body radiation). Thus

where I have used cgs throughout (note that 550 nm = 550 x 10^-7 cm). Now we need to figure out the time interval. The eye detects the 10 photons at a certain "readout rate." This can be estimated by noting that movies are typically shot at 24 frames per second. At a slower rate the eye would notice a distinct slowing of the movie scenes (imagine watching a movie that shows one frame every second, i.e. a slide show), and at a faster rate the movie studio would be wasting film. So the time the brain takes to "read out" the eye is about 10 milliseconds or 0.01 seconds, to an OoM. Thus, the power output of the Sun-like star is

This compares well to the actual luminosity of the Sun, which is 3.862 x 10^33 ergs/s. 

Summary and Discussion

We have performed an OoM calculation of the Sun's luminosity by noting that a Sun-like star at 100 pc is barely visible to the naked eye. Our final answer is correct to within a factor of 4, demonstrating the usefulness of OoM calculations. By not worrying about the exact numbers, but instead focusing on the problem-solving process, we are free to concentrate on the physics of the problem knowing that we can perform the exact calculation using the same reasoning and a bit more time/effort. 


We thank Owen and Marcus Johnson for playing nicely with each other for the 45 minutes it took Daddy to write this. We made use of WolframAlpha when our initial estimate of the photon energy was off by two orders of magnitude, and when we couldn't remember Planck's constant in cgs. WolframAlpha helped us realize that we needed the wavelength of a green photon in cm rather than meters. Duh. The equations were generated using CodeCogs online LaTeX editor.

Dreaming of a Basketball Future

Owen, Mar and I have been watching a Youtube video of Monta Ellis and Stephen Curry, the two fleet-footed guards on the Golden State Warriors. Owen likes to imagine himself as the shooting guard Ellis, and Mar is the point guard Curry. The music is nice, too.

A vision of things to come? At the very least we'll be at the Warriors vs. Clippers (pre-season) game later this month!