Wednesday, February 27, 2013

Sunday fun day at Leo Carillo State Beach (An Erin report)

We broke from our routine of having mellow Sundays and headed out for a family adventure! The day's journey lead us up the Pacific Coast Highway to enjoy a windy winter day at the beach. We explored tide pools and caves, walked on the beach, slid down steep sand dunes and even spotted some sea urchins and sea stars (don't you call it a starfish!) until our hunger took over. We made our way to Neptune's Net for a delicious seafood lunch - ordered a sampler platter and dug in.














Wednesday morning music break

Erin and I have been seriously digging on the Bombay Bicycle Club lately. Check 'em out.

Sunday, February 24, 2013

Beware the slippery slope of marriage equality

Eclecta Blog puts forth fairly compelling arguments for non-traditional marriage (via Dan Savage):
In these instances, I’m reminded that the tradition of marriage is so sacred to many Americans that the notion of Republicans being allowed to marry can offend their very being. “Imagine,” their smoldering eyes seem to be screaming, “My dear, normal child being forced to sit in a classroom being forced to learn about Newt Gingrich’s belief that marriage should only between a man and a woman who doesn’t have cancer.”
I'm usually pretty tolerant, especially when it comes to issues of marriage. But I don't know about this one. What's next, letting Tea Partiers marry each other? Can you imagine it? Just...yuck.

Imagine if both of these guys were republicans. I know, right? Ew!

Personally, I believe we should let the states decide whether republicans can marry other republicans. That is, unless the states vote in favor of letting them marry. In that case, I believe in turning to state referendum, funded by rich people outside of the state, like with Prop 8. If that doesn't work, I believe in federal legislation outlawing it, and otherwise denying republicans basic rights such as the ability to visit a loved one in the hospital, or deporting their loved one if their republican "partner" is from another country (like with DOMA).

So in summary: Let the states decide, then referendum, then federal law. Whichever step prevents it. It's the way our fine country works when it comes to the rights of minorities.

In all seriousness, I think that any group who wishes to deny rights to another group must use arguments that cannot be applied back to them. It's the whole "do unto others" idea that that radical, progressive hippy guy advocated 2000 years ago.


Friday, February 22, 2013

0.5 per year

0.5 year$^{-1}$. That's how many black americans earn Ph.D.s in astronomy each year. I was two years worth of data back in 2007. One of my primary goals as a professor is to increase that number to > 1 year$^{-1}$. An order-of-magnitude increase would do nicely.
Former Caltech summer undergraduate researcher, Keith Hawkins (center). 
During the summer of 2011 I had the pleasure of working with an outstanding young, black astronomer named Keith Hawkins. Here's an article about him that was featured on the Caltech website describing how he became interested in science and what he was working on with me and my student Tim Morton.

Keith is one of the best students I have worked with as part of Caltech's SURF/MURF program, and I'm proud to announce that Keith was awarded a prestigious Marshall Scholarship to pursue his Masters degree in astrophysics (M.Phil) at Cambridge University in England. Keith was one of three African American students, and one of 40 total students to win a Marshall scholarship this year.

Nice work, Keith!

Monday, February 18, 2013

The science of comic books

Ph.Detours and PhD TV are at it again. Owen and Marcus are WAY into the various Peanuts movies, and walk around saying things like "Good grief!" and calling each other blockheads. This video gave me the idea of buying them some Peanuts comic books.

Sunday, February 17, 2013

This Week's Astro Nutshell: How Many Photons?

(Actually, this is from Astro Nutshell two weeks ago)

Each week I work with first-year grad students Marta and Becky on "order of magnitude" problems at the blackboard. I put that in quotes because we tend to do many more scaling arguments than true OoM. The idea is for them to draw on what they've picked up in class and apply it to common problems that arrise in astronomy.

This week we asked

How many photons per second per cm$^2$ (photon number flux) do you receive from a star as a function of its temperature $T$, radius $R$ and distance away $d$?

Having such an equation would be extremely handy for observation planning. When determining the feasibility of a new project, observers tend to start with a statement of the expected signal-to-noise ratio (SNR) for an observation of an astrophysical object. In the limit of a large expected number of photons, the signal is the number of photons $S = N_\gamma$, and the noise can be approximated as $N{\rm oise} = \sqrt{N_\gamma}$. So SNR$ = \sqrt{N_\gamma}$. So this week's question comes down to, "What is $N_\gamma$ for a star of a given temperature, radius and distance away?"


We start with Wein's Law, which states that the wavelength at which a star's (blackbody's) emission peaks is inversely proportional to the star's temperature
$\lambda_{\rm max} \sim \frac{1}{T}$    (1)
This is Astro 101. The flux level at this peak wavelength can be evaluated using the blackbody function (Planck function), which is given by
$F_\lambda(T) = \frac{2hc^2}{\lambda^5} \frac{1}{\exp{\frac{h c}{\lambda k_{\rm B} T} + 1}}$    (2) 
This gives the energy per unit time (power), per area, per wavelength per unit solid angle, as a function of temperature and wavelength. If we evaluate this at $\lambda_{\rm max}$, and approximate the total flux, which is an integral over all wavelengths, as a box of height $F_{\lambda_{\rm max}}$ and with a 100 nm width (standard observing bandpass). We also need to multiply by the solid angle subtended by the star of radius $R$ at a distance $d$, which is $R^2/d^2$. This leads to
$F_{\rm tot} \sim \frac{T^5 \Delta\lambda}{e^{\rm const} - 1} R^2 d^{-2}$   (3)
Since $\lambda_{\rm max} \sim 1/T$, then $|\Delta \lambda| \sim 1/T^2$ (Wow, check out that calculus slight-of-hand! However, the same scaling falls out of actually doing the integral over $d\lambda$). Finally, the energy per photon near $\lambda_{\rm max}$ is $E_{\lambda_{\rm max}} = h c / \lambda_{\rm max} \sim T$. Dividing Equation 3 by the energy per photon, and replacing $\Delta \lambda$ we get the flux of photons 
$F_\gamma \sim T^5 T^{-2} T^{-1} R^2 d^{-2}$
$F_\gamma \sim T^2 R^2 d^{-2}$ 
Increasing the temperature or radius of the star results in more flux, which should seem fairly intuitive: hotter, bigger stars emit more photons. Also, there's the familiar inverse-square law with distance. Evaluating for the Sun at 10 pc results in
$F_{\gamma,\odot} = [5\times10^{4} {\rm photons}] T^2 R^2 d^{-2}$
(please check my math on this!)

For an M dwarf with 1/5 the Sun's radius and roughly half the temperature, at 10 pc it would emit 100 times less light, but most of these photons will be down near 1 micron in the near infrared. An A-type star like Vega, with twice the Sun's radius and twice the temperature will emit 16 times as many photons, most of them in the ultraviolet.

I hope you find this scaling relationship as handy as I do!

Owen throwing darts



Marcus' Haircut


Before

After

Saturday, February 16, 2013

Friday, February 15, 2013

Oh, Goatie!

And now for something totally serious, scientific and important: goats yelling like people (via Julie):

Quality of plot vs. desire to work a physics problem



Giant Meteor Explodes Over Russia

From CNN via Jonathan McDowell (@planet4589)

A huge meteorite [sic] flared through the skies over Russia's Chelyabinsk region early Friday, triggering a powerful shock wave that injured nearly a thousand people, blew out windows and reportedly caused the roof of a factory to collapse.
Multiple amateur videos posted online showed the meteor’s flaring arc across the western Siberia sky. Others from the scene included the sound of a loud boom, followed by a cacophony of car alarms. One video showed the hurried evacuation of an office building in Chelyabinsk.
“There was panic. People had no idea what was happening. Everyone was going around to people’s houses to check if they were OK,” Chelyabinsk resident Sergey Hametov told The Associated Press. “We saw a big burst of light then went outside to see what it was and we heard a really loud thundering sound.”
Videos here:

The Faculty Search Process

Here's an excellent Wiki page and post over at AstroBetter describing the faculty hiring process.
For a postdoc seeking a tenure-track academic job, the process can be mysterious, confusing, and sometimes terrifying (at least it was for me). The level of competition is known to be extreme, and there are a number of steps, including the selection of letter writers, the decision where to apply, how to craft your application essays and how to conduct interviews. There can be long-term consequences of how you approach early steps in the sequence, so it is useful to know ahead of time all the relevant steps in the application process and to start thinking critically and making some decisions.
Big ups to proto-Prof. Josh Pepper for getting this wiki started (actually, he's in the rare, short-lived transitional phase). Also, big ups for the best professional profile pic evar:

New-school proto-Prof. Josh Pepper, seen here at quarter phase. He sees the Matrix.

Wednesday, February 13, 2013

Do you see the Matrix? Derivation of Linear chi^2 minimization

This blog post is primarily for my Ay117 students. However, if you've ever wondered where chi-squared minimization comes from, here's my derivation.

Figure 1: Either a scene from The Matrix or the hallway in your astronomy building.
Yesterday in class we reviewed the concept of "chi-squared minimization," starting with Bayes' Theorem
$P(\{a\} | {d}) \propto P(\{d\} | {a}) P(\{a\})$
In other words, if we wish to assess the probability of a hypothesis that is expressed in terms of the parameters $\{a\}$ conditioned on our data $\{d\}$, we first calculate how likely we were to get our data under the hypothesis (first term on the right), and multiply this "likelihood" by our prior notion that a given set of parameters is representative of the truth.

Supposing that we have data that are independent from one another, and normally distributed, then our likelihood term can be written
$P(\{d\} | {a}) = \prod_i \frac{1}{\sqrt{2\pi \sigma^2}} \exp{\left[\frac{1}{2}\left( \frac{y_i - f(x_i)}{\sigma_i}\right)^2\right]}$
As for the priors, we'll make the fast and loose assumption that they are constant ($P(a_0) = P(a_1) = ... = {\rm const}$). It is computationally advantageous to compute the log-likelihood
$l = \ln{P(\{d\} | {a})} = C - \frac{1}{2} \sum_{i=0}^{N-1} \left[ \frac{y_i - f(x_i)}{\sigma_i}\right]^2 = C - \frac{1}{2} \chi^2$
Since our goal is to find the parameters that maximize the likelihood, this is equivalent to maximizing the log-likelihood, which is in turn equivalent to minimizing that $\chi^2$ thingy.

For the specific problem of fitting an Mth-degree polynomial, $f(x_i) = \sum_{j=0}^{M-1}a_j x_i^j$, and this results in a linear system of equations that can be solved for the best-fitting parameters.

In class, I got my notation all scrambled, and I neglected the measurement uncertainties $\sigma_i$. My bad! Here's what should have appeared on the board (worked out this morning over breakfast, so be sure to check my work!).


To be clear, the "weights" are $w_i = 1/\sigma_i^2$. Zooming in on the key part:


The first problem of the next Class Activity will be to write a function that takes abscissa and ordinate values, and the associated uncertainties, and computes the best-fitting coefficients for a polynomial of arbitrary dimension $M$. 

See also David Hogg's excellent line-fitting tutorial.

Modern Professing

Old-school. Prof. Max von Laue. "You likely don't understand this."
Erin gave me a profound insight this morning. The idea of being a professor used to entail "professing." Yes, we still profess today. But in the past, the professor was the one person, or one of only a few  people in the world who had expertise on a specific area of study. If you wanted to understand the nature of young stars and you were a student in the 1960's, George Herbig was one of only a few people in the world who could profess on the topic.

These days, things are very different. If you want to know about young stars (or planets, or galaxies, or any other topic) you can do a Google search and you'll find a Wikipedia page, a slew of PDF documents, and a bunch of crap. You could also go down to your library and find numerous books, or you could turn to NASA ADS and turn up hundreds, if not thousands of papers. The availability of all of this information in the modern age is orders of magnitude beyond what was available in 1970, but the sheer volume, variety and, importantly, the range of validity of all this information is overwhelming to a student just getting started.

Thus, these days the job of the professor is not so much to profess and serve as the primary source of information on a given topic. Instead, our job nowadays is to provide context, motivation and a more flexible means of understanding. It's that last part that I think often goes missing in University teaching today.

This revelation nicely complements something else I've been thinking on lately. In physics and astronomy in particular, there used to be only a small number of students who could learn the subject. By that I mean there were only a handful of students with both the specific talents and opportunity to learn. The study of physics in the 1920's was therefore a guild system, with only a chosen few who could and would make it as Ph.D.-trained scientists. Take this description of the German systems of physics graduate education in the 1920's from The Making of the Atomic Bomb:
Physics students at that time wandered Europe in search of exoptional masters much as their forebers in scholarship and craft had done since medieval days...If someone whose specialty you wished to learn taught at Munich, you went to Munich; if at Gottingen, you went to Gonttingen. Science grew out of the craft tradition...an informal system of mastery and apprenticeship over which was laid the more recent system of European graduate school. This informal collegiality partly explains the feeling among scientists of [that] generation of membership in an exclusive group..." [emphasis mine]
This attitude exists to this day, and not only among the older generation of professors. Some physics and astronomy professors see themselves as part of an elite group, members of a select corps. An extension of this view is that only a few individuals after you should be capable of accomplishing what you, the professor have accomplished. So only a minority of any group of students should be good enough, while the rest are simply not up to snuff. Only a chosen few get the A by exhibiting the same level of intellectual talent as the professor; the rest just aren't cut out for physics. The job of the professor is to profess, the students try their best to receive, and the few who do move forward with initiation into the guild.

A more modern conception of being a physics professor is to take the vast quantity of information available to the budding physics student and make it accessible and understandable. I see my job as not finding the one student out of 20 who can hack it, but to find a way for every student in my class to understand the material. The challenge, therefore, is not to first be the first to understand and then profess that understanding. The challenge instead is to find ways of making that hard-fought knowledge broadly accessible, not only to a wide variety of students and learning styles, but also to the general public.
New school: Prof. Joe Barranco
To my mind these ideas go a long way toward helping me understand the tension between old-school and new-school approaches to physics/astro education today. The old-school professors see Physics as an exclusive club that only a chosen few may enter, and only after a lengthy apprenticeship and a great deal of blood, sweat and tears. Those who pass the "hazing" of graduate school are strong, those who cannot are culled. The strong move on and become the next giants of the field. The rest should not let the door hit them on the back on the way out.

The new school looks at this approach and sees it as inefficient, and therefore an opportunity for innovation. They see students who are plenty smart enough to make an impact in the field, but these students struggle because they do not think like a traditional physicist (note that Richard Feynman did not think like a traditional physicist). They are creative and have strong physical intuitions, but, for example, they don't quite "see the Matrix," both literally and in analogy to the movie, where the raw mathematics are as intelligible as English. But when an explanation, example or exercise is used that meshes with the way they think, they get it the same as, or even better than the traditionalists.

This is a very good description of my learning style, and if it weren't for a number of new-school profs who have mentored me along the way I would not be where I am today. My experience, in turn, informs and guides the way I teach. My goal as an educator is to figure out the myriad ways in which my students learn and find methods that help them make sense of difficult physical concepts. I tell my Intro to Astro students that my goal is for every one of them to not only pass the class, but get As. Not because I give them As, but because I managed to help them learn, and they in turn respond by performing at a level commensurate with an A. Not everyone likes this approach. But fortunately, the students almost universally do. While the old school views this inclusive approach as "coddling" and "hand-holding," the new school sees an empathetic, and ultimately more challenging and rewarding approach to education.

Tuesday, February 12, 2013

Hey, check out that group of...um...

Via @shaka_lulu (Lucianne). Click to view larger version. Sarah Silverman suggests an entirely different branch (NSFW video).


Monday, February 11, 2013

Some budding yeast I used to know

If you can handle this played-out tune, the lyrics are pretty rad:

Sunday, February 10, 2013

Ask A Prof: To Post or not to Post?




I'm going to prototype a new series, which may spawn a separate blog, called Ask a Professor. The idea is that I get tons of questions about careers in science, and often I get the same questions from different people. So I figure I can broadcast the advice I can offer. Any question for which I can't give a good answer, I know lots of people who I can ask, and we can learn together in those cases.


IfA last-year grad student Brendan Bowler asks: "To post, or not to post; that is the question. That is, to the Rumor Mill.  Does it have any actual influence (either beneficial or harmful) on the  decision-making process of fellowship committees?"

One thing I can say right off the bat is that this question stirs a lot of strong and passionate opinions among professors (and postdocs, and students). For this question, I think I'll present my own opinion and then revisit the question after talking to some other profs. Also, if you have a strong opinion one way or the other, please sound off in the comments or send me an email!

My answer is based on my strong belief that it is important to market yourself as a scientist. I used to get uncomfortable with the concept of self-marketing, all wrinkling my nose and feeling the urge to take a shower after using that sort of language. But my opinion changed after reading Marc Kuchner's book on the topic, Marketing for Scientists. I'm certainly a fan of this book and I recommend you check it out. 

The basic idea put forth in the book is that as a job-seeker, you are offering a product (yourself, your skill-set and accomplishments) to someone who may give you a job in exchange for what you have to offer. It's simply an exchange of benefits, like almost every other human-human interaction. If I, as a prof, post a job ad for a postdoc to help me with my planet survey, I need someone with a specific set of skills. I also need someone who will integrate themselves quickly into my group and enhance our science. If a job candidate can demonstrate that they can bring these benefits to me and my group, then I give them gainful employment. 

A fellowship program or faculty search committee is looking for a similar beneficial exchange. They want someone who is excellent in many dimensions, ranging from productivity, quality of science, the ability to write strong proposals, a good communicator, diversity and leadership. Say what you will about perusing the rumor mill, but the people who light up the job listings every year---the ones pulling in Hubbles and Sagans and Einsteins left and right---well, these are people for whom the astronomy community has come to a firm consensus on (or at least several independent review panels have come to the same conclusion). These people, by virtue of getting many strong postdoc offers are prima facie excellent job candidates.

Now, of course, there are many excellent researchers who don't light up the Rumor Mill. So I'm not advocating that search committees base their decisions on the people who show up on the Mill, nor am I suggesting that they do. This would be like using your data as both your prior and your likelihood: you'll quickly converge to a solution, but the solution is likely incorrect because the logical process used was improper. And I strongly believe that search committees know and understand this, and therefore do not use the Rumor Mill to make any major decisions. 

But might an individual on one of those committees use last year's Rumor Mill to identify good candidates that should be in the pool? Sure, why not. But once an individual is identified in that manner, or any other,  rest assured that the committee will get on the phone and call their colleagues and ask their opinions about Dr. Rumor-Mill-Star. Also, people filling seminar, colloquium and science meeting schedules might very well look through last year's Rumor Mill for the brightest young talent to invite in for a talk. I've sat on colloquium committees, and I admit that I glanced at the Rumor Mill for young talent outside of my field. 

Based on all of this, it is my opinion that one go right ahead and splash their name all over the Mill should they get fellowship offers, or short-listed for their first professor position. First, it's just good marketing. Second, if you get lots of offers, you should take this moment to shine and revel in the accolades. This sort of positive feedback is hard to come by in astronomy, so take it while you can get it and hold your head high, rather than shoving your A+ exam into your backpack before anyone sees. Note, however, that those individuals looking to switch institutions in a faculty swap may not want this information floating around. 

Finally, posting gets valuable knowledge out to an information-starved portion of our community. Kudos to the various fellowship offices that post their short lists and offer lists to the Mill! Those poor applicants anxiously awaiting news, any news, surely appreciate the knowledge that there has been an offer and to whom it was made. This is the primary reason I'm a supporter of the Rumor Mill. 

Oh, and one last note: yes, there will be jealous people. Those people might even post obnoxious things to the Mill about your achievements. But that's their problem. There will always be haters, so let 'em hate. The people in the community who care about you will be thrilled to learn of your fellowship offer. 

Friday, February 8, 2013

Heavy, wet and energetic

Whenever the Moon's tidal field and the Earth's rotation  wind and land conspire to pick up the ocean and violently fold it over on itself, most people stay far away. A select few take the opportunity to slide merrily along the folded ocean on little boards, at the mercy of gravity and fluid dynamics.

Check out the video below and recall that there a little less than a metric ton per cubic meter of water. That's a lot of cubic meters of water over each surfer's head! I have no idea how a human survive having all that water savagely dumped on them. h/t Jon Swift.

Thursday, February 7, 2013

Airport logic (or lack thereof)

http://thedoghousediaries.com/4845

Ask a Professor: How does a prof spend their time?

I'm going to prototype a new series, which may spawn a separate blog, called Ask a Professor. The idea is that I get tons of questions about careers in science, and often I get the same questions from different people. So I figure I can broadcast the advice I can offer. Any question for which I can't give a good answer, I know lots of people who I can ask, and we can learn together in those cases.

This week's question is from Molly Peeples (UCLA), "What does a professor do all day?  I think most postdocs realize it's some combo of research+teaching+advising+committees, but don't realize how a faculty meeting can go for hours or how committee obligations (both within the department/university and broader community ones) are capable of sucking up so much time."


phdcomics.com
Well, as an observer, my answer to most problems is: We need some data. This case is no different, and fortunately I have the perfect data set to address this question. Way back in 2009 at the previous AAS meeting in Long Beach, I was attending the annual NSF Fellows seminar. The featured speaker was Prof. Lynne Hillenbrand, who is a colleague of mine at Caltech. 

At the NSF Fellows symposium, Lynne gave an excellent talk about being a professional astronomer with a focus on how to manage one's time. In the talk, she mentioned that she kept a log of how she spent her time every single day for several months. Last year I asked Lynne for her log and she gave me permission to share it. However, I totally dropped the ball and the logsheet (in Excel format) lay unused until Molly's question. Finding it in my email archive was like finding a twenty-dolar bill in an old pair of jeans.

So without further delay, let's dig into the data! Lynne's data set spans Oct 8 through Dec 16. The number of hours per week is shown in the figure below, with the mean of 68.5 hours per week shown as a dashed line. That's a lotta hours per week! But keep in mind that this was when she was the department chair (the "Executive Officer" or EO, in Caltech parlance). Thus, this is probably skewed high, but it's still fairly instructive, especially since most full profs eventually serve as chair of the dept.
She also kept track of what she was spending her time doing:

teaching (formal)      12%
teaching (mentoring) 8%
teaching (research) 5%
total teaching:        25%

research (funded)       5%
research (unfunded)    14%
research (read/talk)   7%
total research:        26%

admin    (chair)         16%
admin    (dept)         7%
admin    (campus)  1%
admin    (national)     8%
total admin:           31%

email                   7%
travel                  6%
misc                    4%
total other:           17%

So there you have it: raw, cold data. Of course, there are many caveats. This is just one data set for one prof. A particularly detailed one, for sure. But only a single sample. How does this compare to my breakdown of responsibilities? Let's take a look at how I spent my time two weeks ago (I was traveling last week), according to my Google Calendar and my memory.

The week of Jan 21 I worked every day of the week, including Saturday and Sunday (5 and 4 hours, respectively). On Mon, Tue, Thu I worked from 8am-noon, 12:30pm-5pm, and approximately 10-midnight, for 10.5 hours per day. On Wed and Fri I play basketball noon-1:30 and have lunch 1:30-2, so those days are shorter, only 8 and 9 hours each, respectively that week. That's a total of 57.5 hours, which is close to what I estimated in an earlier post.

The breakdown of activities, using slightly different categories, is: 18% teaching, 25% meetings (research and admin, on-camus and Skype/phone/telecon), 25% email/misc, 32% research (most of it in meetings with students/postdocs/collaborators, proof-reading, and my own 30-minute writing sessions). Looking at other weeks, the total time per week remains roughly constant, but the breakdown of what the time is spent on has a lot of variance. So my data point is less precise than Lynne's, but it agrees with a fairly even split among teaching, research, admin and email/misc. The caveat being that we work at Caltech, the land of the low teaching load.

Other profs: How do you spend your time? If you can lend some of your time, please take a look at last week's calendar and give us the breakdown in the comments.

Other questions? Send 'em to me in the comments, or via email/Facebook/Twitter.


Lake-front property, expansive view of faint, red sun that never sets

From right to left: Courtney Dressing, Dave Charbonneau and yours truly at the live CfA press conference. Photo by Kris Snibbe/Harvard Staff Photographer
Yesterday, I had the honor of participating in a live press conference today at the Harvard Center for Astrophysics (CfA). The event was to announce new findings by third-year graduate student Courtney Dressing and her advisor Dave Charbonneau, who studied the occurrence of planets around M dwarfs in the Kepler field. Dear Sara Seager, check it out! A woman with not only a big exoplanet press announcement, but a HUGE exoplanet press announcement! (But, yes, we need more).

Sound familiar? If so, it's because Jon Swift and I made a related announcement last month at the AAS meeting. But while we focused ont he bulk occurrence rate, finding 1.0 +/- 0.1 planets per M dwarf, Courtney focused on Earth-like planets. By Earth-like she means, "planets the size of the Earth that receive a similar amount of sun light as our planet." (As an aside, Jon and I were very much relieved and excited that Courtney's statistical analysis matched our result on the bulk occurrence rate.)

Her big results are

  • 6% of M dwarfs (=red dwarfs) have Earth-like planets.
  • This means that there are at least 6 billion Earth-like planets in the Galaxy since M dwarfs comprise 7 out of 10 of the Milky Way's stars
  • The nearest Earth-like planet is around an M dwarf within 13 light years of the Earth. Which one? We don't know...yet. We need to start searching, like, yesterday IMO.
  • At 95% confidence, there is a transiting Earth-like planet around an M dwarf within 100 light years.

Here's the CfA press release.

Here's a preprint of Courtney's paper, which will very soon be accepted by ApJ (referee report was positive and has been responded to).

Slide from Courney Dressing's press announcement showing the amount of "sun light" received by the planets around Kepler's red dwarfs. The locations of Mars, Earth, Venus and Mercury are shown along the top. Three of the planets around Kepler's red dwarfs are squarely in the "goldilocks zone".
Have done several of these types of press conferences over the past couple of years, I've started recognizing a pattern in the Q&A with the press. It goes a little something like this:

Astronomers: 6% of M dwarfs have Earth-sized planets in the HZ! (out of breath from all the hard work)
Reporters: But come on, can life really emerge on planets around M dwarfs?! What about flares and tidal locking and bears, oh my? (Ed. note: Okay, I added that third problem)
Astronomers: Ummmm...did we mention all the Earth-sized planets we found with temperate equilibrium temperatures? 

First, I'll admit that it's the fault of astronomers for playing it fast and loose with the term "habitable" in reference to the locations of certain planets around other stars. The habitable zone is an extremely idealized concept referring to the region around stars where the incident sun light results in planetary temperatures that would be like the Earth's. But this is under the assumption that the planet has an Earth-like orbit (low eccentricity), an Earth-like atmosphere (albedo), and a nice solid surface where liquid water could pool into lakes and oceans and the like. So reporters are correct to be skeptical.

Thus, when an astronomer says "habitable zone," there's no reason to conclude that the planet is inhabited, or that it even could be inhabited (despite what some astronomers believe). Instead, when you hear the term you should think "possible location around the star where, if a myriad set of conditions are just right, a planet could have liquid water on the surface." Habitable zone is just much easier to say. Also, the habitable zone is something that is easy to calculate based on the parameters of planets discovered by various techniques. We bag 'em, the astrobiologists tag 'em...er...to help us understand whether they could truly be habitable.

So my first point is for the astronomers. We need to be more nuanced when tossing around notions of habitability. My second point is to the reporters. The question "Are these planets truly habitable" is pretty much impossible to answer right now. Why? Because we don't even know the conditions for habitability on our own planet! Here's a long, yet incomplete list of factors/questions that may or may not be important for the emergence of life on Earth:
  • Our Moon maintains the Earth's moderate obliquity (axial tilt). Mars undergoes large obliquity swings because it has no moon, which wreaks havoc with its weather
  • We have plate tectonics to maintain a carbon-silicate cycle, which keeps CO2 in a stable equilibrium. Maybe. We think. 
  • If plate tectonics are necessary, is the high water content of Earth's mantle necessary for plate tectonics?
  • If the Earth formed "dry" then how was water delivered? 
  • Do we need a large ocean to maintain thermal inertia?
  • Is it important that we have just the right amount of water so as to not cover all landforms?
  • Is dry land necessary?
  • Is Jupiter a friend or foe? Does it hoover up comets or toss asteroids in?
  • Why do we have a hydrogen-poor atmosphere?
  • Is water the only suitable solvent for life?
  • Is it important that we lack a close stellar binary companion despite ~50% binarity of stars Galaxy-wide?
  • Do we need an especially "calm" sun?
  • Do we need a low eccentricity?
  • Earth is not too large as to have ended up as a mini-Neptune
  • Earth is not too small to end up like Mars with high atmospheric escape
  • What about Milankovitch cycles?
  • Do we need our nickel-iron core for magnetic field generation? 
This is just a partial list that I was able to come up with while Google chatting with Prof. Jason Wright. What did we forget?



Wednesday, February 6, 2013

WTF, Evolution?

An awesome Tumblr via Josh Peek's Twitter feed. (I never would have written such a sentence this time last year. The kids and their technology have me firmly in their grasp..."

Steinbit
The wolffish is actually modeled after evolution’s cousin Frank. Evolution has always secretly hated its cousin Frank.

Tuesday, February 5, 2013

Monday, February 4, 2013

On the Two-Body Problem

Figure 1: The two-body problem. Image taken from this blog

In academia there is something called the "two-body problem." The original two-body problem involves the gravitational interaction between two massive bodies, e.g. a planet orbiting a star. This is a problem in the mathematical sense, as in something interesting about the universe that we would like to figure out. This classical two-body problem has a solution, but interestingly it is in the form of a transcendental equation that can only be solved numerically. But when done so, it looks like this. Pretty nice, huh?

It turns out that there's an even more difficult two-body problem in science academia, but this one has to do with the attraction between two humans (cf Figure 1 above for a succinct description). The problem arises when one or both individuals are academics seeking post-graduate job positions. The problem, in a traditional sense of the word, is related to the fact that academia has been honed and perfected over the centuries to accommodate only a specific type of coupling. If you are an academic and in a relationship, there is a closed-form solution to the two-body problem if and only if the partner/spouse is not also an academic and has the ability/willingness to move every 2-3 years over the next six years while academic partner takes various postdocs and/or other job positions. Personally, I was fortunate to find this "solution." Most do not.

A further complication from the standpoint of young academic couples is that there is often only one or at most a few available/desirable job openings per institution per year. This means that it is highly unlikely that the coupled academics will find their ideal job position at the same institution. However, if they do solve the problem at the postdoc level, it is very unlikely that it'll happen again at the professor level. Think of multiplying two or more small probabilities; the result is a very small chance. On the other hand, if you have a traditional (read: 1950's-era) family, none of this is really a problem. One partner pursues their career, the other raises the family, and the solution is not only closed-form, but elegantly analytic.

However, in modern times there have arisen a whole host of complications. The primary one is that as more and more women enter graduate programs, more and more couplings are occurring within said grad programs---hot nerd-on-nerd action, if you will. In what follows, please allow me to apply a cold scientific analysis to an inherently human/emotional process (I'm already bracing myself or angry commenters noting that not all women date men in academia. Settle down nerds, I recognize and hereby acknowledge the difference between a simplifying assumption and reality, the difference between the mean and the dispersion of a distribution of human behavior.)

Since the male-female ratio in most grad astro programs is 2:1---which is very high among the sciences, but still far from parity---there will be more women with two-body problems than men, under the simplifying assumption that every woman couples to a man. For every 3 intradepartmental pairings, there are four men available (forced) onto online dating services, night clubs, etc. where they can meet a non-academic. As the male-female ratio increases, the frequency of two-body problems among women increases. This assumption is valid, in my opinion, given that astro grad students spend the majority of their waking hours in their offices doing problem sets, reading papers, and tracking down bugs in their data reduction and numerical integration codes, instead of hanging out where non-academic, single people congregate. And if one's soulmate is not in the same department, there's always Bio or Engineering across the street!

This hypothesis gives rise to a few predictions:

  1. The majority of women in science will be in a relationship with another academic. Here's a test providing confirmation of this prediction.
  2. The unequal male/female ratio will result in more women than men facing a two-body problem
  3. Societal norms and/or other pressures will result in the woman giving up her career more frequently than the man giving up his. Anecdotally, but very obviously, I've noticed that the men in two-body situations tend to be 1-4 years older than their partner, which means they are more established when the tough decision-time comes. With a man in an established job further along in his career, it is often the woman who gives up rolling the dice on a future opportunity in favor of the sure-thing right now with her partner’s job offer.
  4. There will be a higher attrition rate among women than among men in academia, causing the male-female ratio to increase from grad school, to postdoc, to professor.
  5. The refusal of science programs to acknowledge and address this problem will exacerbate the gender disparity among their faculty.

Based on my personal observations during travels to various institutions, these predictions seem to hold up. The vast majority of my female friends/colleagues are in relationships with another academics, quite frequently with other astronomers. And far from being just a cute name given to a societal phenomenon, the two-body problem is a Problem with a capital P.

Figure from Dual Career Academic Couples: What Universities Need to Know (PDF)
I can't imagine cutting my astronomy career short at this phase in my life, so I can only imagine how difficult it is for people to be forced to decide between their careers and their relationships. I've heard of women being told, "Your spouse has an excellent job opportunity here. Would it be so bad to give up your career?" I have to admit that I've entertained such thoughts in the past. But I find it doesn't work when I apply this reasoning to myself. When I think about my passion for astronomy, and how my research is what causes me to go to bed late and wake up early, there's just no way I could imagine giving up my career and still finding full satisfaction in life. I'm a trained slayer of hard problems, and I live to to drive big telescopes across the sky. I'm also passionate about undergraduate and grad education of the type that can only be implemented effectively as a professor. How could I just give that up? So, no, it's not at all an option to ask a coupled scientist to give up their careers.

When couples are able to hold onto their pursuits, long-distance relationships are very common, which puts strains not only on the individuals, but also on their science. Being away from one’s partner for extended periods of time leads to stress and anxiety, whcih negatively impacts day-to-day work. Excellent candidates pass up opportunities at top institutions (justifiably) to stay with their spouse. Top profs at leading institutions drop out at the peak of their games to find a solution to the two-body problem. Postdocs pass up fellowship offers to stay close to home. I really wish these weren't the choices that young scientists have to face. Our field would be much happier with a closed-form solution to the two-body problem.

As we in astronomy begin to embrace diversity as a key ingredient for excellence, we must find a robust solution to the two-body problem. To keep the conversation moving forward, here are some solutions I have heard suggested or come up with on my own:

  1. Make postdoctoral fellowships last 4-5 years, rather than 2-3. The extra years relieve pressure and stress on couples to immediately begin searching for the next job and reduces the number of times a postdoc must move before (hopefully) settling into a more permanent professorship.
  2. Restructure job searches to allow for two-body hires. I've heard it argued that this is undesirable because it would require sacrifices in "excellence" to hire a spouse that isn't as "excellent" as the primary hire. But what good is hiring an excellent individual when they will be looking for a more accommodating position from day-one after starting at your university? How much excellence can be traded for an unhappy, loosely-bound workforce? On the flip side, think about how much more loyal your employees will be if hired together. You better believe they'll work harder than anyone else in your dept, and be far less likely to be enticed by competive offers later (immunity to poaching is valuable, no?). Also, think of the message you send to your entire workforce when you demonstrate the value of family security in your workforce.
  3. Coordinate among departments to make mixed-academic hires. One department might have to make a bit of a sacrifice along the (percieved) excellence dimension this time, but think of what can be gained the next time around when their top applicant is coupled to another academic. Astronomy is not the only field facing the problem.
  4. Recognize the considerable uncertainty in judging excellence in the traditional sense. How many previously-identified excellent hires didn't attain tenure at your institution and other top universities in the past 20 years? If hiring committees can miss that badly in one direction, why not hire the person who is deemed an 8/10 on your scale in order to retain the 10/10 in your dept now, with the recognition that that 8.0 is really 8 +/- 1

What have I missed? Discuss!

Watching illness steadily encroach

Sometimes you get sick and you're all, "Whoa! Where'd that come from?" That's how I felt two weeks ago when I came down with some weird stomach virus. Fortunately, the whole thing was over within 48 hours.

Other times you start to sniffle, ache and sneeze and you're all, "Yep. I pretty much knew that was coming." In fact, on some of these occasions you can remember the exact moment in space-time when the disease was transmitted to you. Those times most frequently involve kids.

I love my children with a white-hot intensity equal to that of the Sun's core. However, dammit if they aren't the most effective disease vectors known to man. Ticks? Psht. Mosquitoes. Please.

Take tonight, for instance. I can feel the early stages of the flu coming on. My eyes burn, I'm coughing and I'm getting more and more weary every passing hour. I know how this happened. I was sitting in the living room Friday when Owen, who had been sneezing all day, started to tell me something while sitting next to me on the couch. He said, "Daddy?" and I turned to look at his cute little face. And before he could get the next words out, he sneezed. In my face. Just full-on: yep, that's where those fluids go. In your facial region, Dad.

First it was Marcus, then Owen, then Erin (poor thing is still down for the count). Now it's my turn.
So I imagine I'll be down for a while (I sure hope I'm wrong!). Fortunately for you, dear reader, I have a full slate of blog posts queued up and ready to auto-publish throughout the week.

Ugh.

Sunday, February 3, 2013

The upside of procrastination

I've long wondered about the problem arising at the intersection of interstellar space travel and Moore's Law. Moore's Law is an empirical rule that states that technology doubles in speed (or other metric) every 18 months. The laptop that I'm typing this post on right now will be half as fast as the next Macbook Pro 18 months from now.

I doubt I'm the first person to think about this, but imagine a large crew of space settlers at the halfway point to alpha Cen. They might be the second or third generation aboard the space craft, having known nothing but their trip to the nearest stellar system. Out comes the bubbly, but in the middle of the celebration there's an announcement: "Captain, there's something showing up on our radar, approaching fast!" As the object flies by, the crew can just make out the relativistically shortened form of a brand-spanking-new, next-generation space craft, zipping past using the latest technology on the way to alpha Cen.

So if Moore's law guarantees that there will be a better, faster, more efficient space craft if you wait a couple decades, then you should wait for the new ship rather than starting the journey with today's technology. But there must be a break-even point. The solution to traveling to the next star over can't be to just sit around twiddling our collective thumbs. Right?
Figure from Gottbrath et al. 1999

Well, it turns out that this problem has been solved back in 1999...by astronomers (PDF here). The specific problem in their cas was whether to start a long computation with today's computer, or instead wait until Moore's Law brings along a much faster machine.


Saturday, February 2, 2013

C'mon U Penn!

The senior faculty of the Department of Africana Studies recently RSVP'd to U Penn's annual diversity dinner, saying thanks, but no thanks to this year's event (h/t Claude). The reason is that at last year's dinner they demanded to know why the president had not appointed a single minority to the upper administration during her tenure.
Her response was that she would not just bring in someone who is not qualified, a comment implying that none of the people in the room were qualified to serve in these positions, even though many of them serve in administrative capacities in departments and centers. In her closing remarks, President Gutmann reiterated her dedication to diversity within Penn’s administration, admitting that “a show beats a tell.”
President Gutmann’s “show” came on Jan. 17, when she announced the appointment of the new dean of the School of Arts and Sciences. Yes, a show beats a tell every time, and once again, she has shown that her commitment to diversity does not include her own administration. When presented with yet another opportunity to increase diversity at the highest levels of the University, she failed to do so after nine years at the helm.
The rest of the op-ed RVSP is here (see also this). While U Penn has made considerable progress in enhancing the diversity of its student body, diversity campus-wide is crucial. As one professor put it, “If you’re not diversifying the faculty that that student body sees, then what’s the point?” I wholeheartedly agree with this notion. Diversifying a university works best when done from the top down. It is hugely valuable for students of color, as well as women in the sciences, to see many examples of people like them in the positions of authority, such as professors and the administration, and not just as admins and custodians. As the authors of the op-ed put it:
The annual “diversity dinner” is indicative of cosmetic — not substantive — progress on diversity that we believe President Gutmann must address. Our decision not to attend this year’s dinner — and to share that decision with the Penn community — is not a petty one, nor is it one we’ve made lightly. Rather, it is based on a long overdue decision to forgo these meaningless gestures toward progress on diversity.
Only when issues of diversity are substantively engaged at the highest levels of our administration, not simply promoted as social events, will real change occur...

Astro Memories

On the road on the way up to the Mauna Kea summit
Sometimes I try to remember specific events from my recent past, say in grad school, and I can't remember the dates, ordering of events, and other details. It's amazing how 10 years can smear out important details in your memory. However, there's one event that I can clearly remember and even assign a specific date to. On the eve of the start of the Iraq war back on March 19, 2003, I was driving from Hale Pahaku to the summit of Mauna Kea, from 9000 feet to 14,800 feet. Prof. Mike Liu was driving and Mike Fitzgerald and I were passengers of the CFHT-issued Chevy Suburban. BBC radio was on and I was listening to reports of bombs falling on Bagdad, with a sinking feeling in my gut. Both because of the realization there was nothing I could do to stop my country from getting into the war, and because of the ride up the mountain.

What I remember very vividly was Prof. Liu had that Suburban was going very quickly along that Mars-terrain-like road. I remember the date, the people involved, the color of the SUV (blue with tan interior), the clearness of the sky, and the distinct feeling that we were moving up the mountain along that dirt road not unlike this:



That's what I remember. I don't remember the details of the vast majority of the science talks I attended, much of the content of the courses I took, even the conversations at the Triple Rock Brewery after work. But I definitely remember getting the back end of that SUV loose around those mountain roads with no guard rails between us and sharp, volcanic boulders. I also remember the exquisitely clear nights we had once at the summit. Astro memories!

Friday, February 1, 2013

Fund me maybe

Filmed at the January 2013 American Astronomical Society meeting in Long Beach, CA. Big ups to Emily and Niall!