ay20: long exposure of the stars at night (Default)
I'm Lauren, and this is my blog for Ay 20, fall 2011. I'm a third-year -- not saying junior, because I know full well I'm not graduating in four years -- at Caltech, majoring in physics. My research interests are experimental high energy physics; basically, I've thought hep-ex was super cool and the best career possible for, er, five or six years? And three summers of research does not appear to have convinced me out of this idea, so I'm sticking with it for the time being.

Some notes on blog administration:
  • Anonymous commenting is turned on, as I doubt anyone save myself in Ay 20 is going to be Dreamwidth-based.
  • Play nice in comments. This is not a democracy.
ay20: (mountaineer and a mosquito)
While Ay 20 ended two terms ago, I thought I'd take a quick moment to congratulate our lovely professor John Johnson and TA, Jackie Villadsen. Both were honored at the ASCIT teaching awards last night, and they were both completely and utterly deserved.

Nearly half of the class was there because they'd nominated either Prof. Johnson or Jackie, and considering that we could only nominate one person, I think that says a great deal. Thank you both for all of your hard work and dedication to this class, and to teaching in general.
ay20: long exposure of the stars at night (Default)
Courtesy the Dabney social veeps,

Spherical chickens exist, if only in plush animal form.
ay20: (Saturn)
And here's my tenth blog post in a week, nine of which were problems from the worksheets. However, this is a write up of possibly the most important of the worksheets, as it derives the equations of stellar structure.

cut for ~65 lines of math; you have no idea how tired I am of LaTeX )
ay20: (xkcd)
An administrative note: this blog finally has a title other than "Ay 20 Fall 2011". It's titled Aubade, which is both "a poem or song about lovers parting at dawn" (obvious astronomy parallel is obvious) and a poem I am particularly fond of. (Warning: Philip Larkin, so contains references to suicide.) The previous several sentences may or may not be related to rereading all of the Larkin.

So I realized today (while cursing at my inability to write up a post without multiple LaTeX errors) that I never wrote up the lab in which we measure the astronomical unit from only a photo of the sun. Specifically, using this photo of the sun, with Mercury silhouetted against it:



The sinusoidal pattern is due to the parallax.

cut for math-in-images; contains trigonometry, also my lamentable drawing skills )
ay20: (Saturn)
(for people who have this RSSed: I apologize for the spam. I have two more write-ups after this in order to have blogged every set, and then this will go back to business as usual.)

And now for my least favorite set of the term, on the path of a photon created inside the sun.

cut for math-in-images )
ay20: long exposure of the stars at night (Default)
In order to prove that hydrostatic equilibrium prevents the Sun from collapse, we need first to find the differential equation for hydrostatic equilibrium. We assume that the Sun is spherical and of density ρ(r). We can calculate the differential of mass from the density & differential of volume.

cut for math-in-images; also minimal calculus )
ay20: long exposure of the stars at night (Default)
As I mentioned in my last post, I've decided to make sure I've blogged at least one problem from each worksheet in Ay 20. While I've done a decent job blogging recently, I missed a few of the early worksheets. Therefore, determining basic properties of the sun from afar:

cut for math-in-images )

Second protip: if you're feeling like you haven't done much this term, redo sets from the beginning of term. This was so much easier than the current sets. I didn't have to number the equations to make it comprehensible!
ay20: long exposure of the stars at night (Default)
I am supposed to be making some ridiculous quantity of brussel sprouts, and am absently writing up solutions from one of the early worksheets (new goal: blog at least one problem for every worksheet). Instead, I appear to be looking at astronomy-related fashion.

cut for images )
ay20: (xkcd)
I did say I was writing up all the blogs. Now: star formation!

Second authors: Nathan, Eric

cut for math-in-images )
ay20: (mountaineer and a mosquito)
Second authors: Nathan, Eric

(I'm behind on blogging so am catching up by doing all the blogs.)

We start with the expressions for radial velocity. While I am not going to fully derive it here, Nathan has a lovely post on radial velocities you should read.

cut for math-in-images )
ay20: (Saturn)
Second authors: Nathan, Eric

The habitable zone of a star describes the range of semimajor axes where liquid water can exist. Logically, this scales with stellar mass, as demonstrated below.

cut for math-in-images )
ay20: (mountaineer and a mosquito)
Second authors: Nathan, Eric

While it is true to a first approximation that a planet orbits a star, it is more accurate to say that a planet and star orbit the center of mass of the system. However, we will prove that for a star the mass of the sun, and a planet the mass of Jupiter, this is not a very significant effect (in comparison to the total distance between the sun and Jupiter).

cut for math-in-images )
ay20: Amy Pond! (Amy Pond)
So, last week I got a chance to talk to Kip Thorne.

Let's pause for a moment to make high-pitched squeeing sounds. OMG OMG OMG I GOT TO MEET KIP THORNE EEEEEEEEEEEEEEEEEEE.

For those who are unaware, Kip Thorne is, in my opinion, the second-most famous astrophysicist in the world (second only to Stephen Hawking). He was definitely the second astrophysicist I'd ever heard of -- I read A Brief History of Time (although I didn't understand it nearly as well as I thought I did) some ten years ago, and it was all downhill from there. Kip Thorne also helped found LIGO, did his PhD under John Wheeler, lead the Caltech cosmology group for over 20 years, does a lot of really cool science I don't understand, wrote the book on gravitation, and is now screen-writing in Hollywood.

Oh, and he's Blacker '62.

I originally emailed him to interview him about a career in astrophysics, but he said he wasn't entirely suitable for such an interview -- he claims he's only 1/3 of an astrophysicist, because he's only spent 1/3 of his career doing real astrophysics. (For the record, I disagree on this point.) He very strongly identifies as a physicist, not an astronomer or astrophysicist. He felt that majoring in astrophysics was limiting; that majoring in physics gave you more options.

He also had a fair bit to say about Tech -- namely, everything is easier than undergrad at Tech. Grad school is easier than Tech. Postdocs are easier than Tech. Being a professor is easier than Tech. Coming from a man whose post-Tech career has been distinguished to say the least, this is both encouraging and discouraging. It does mean that I feel slightly more justified in my stress level, but I still have a couple more years of this.

When Kip Thorne was in undergrad, his future career field didn't entirely exist. He did a couple SURFs in observational astronomy, and headed to Princeton to work under John Wheeler on the newly developing field of numerical cosmology. Caltech offered him a job, and he happily returned. He's a pen-and-paper theorist; he doesn't code (oh, physicists who graduated undergrad before 1985), but he does employ people who do. However, he's not completely disassociated from experiment -- he helped create LIGO and did some early design work. He also did a lot of the quantum theory of measurement. The quantum theory of measurement sounds really, really cool -- I have my issues with LIGO as a project, but I am tempted to figure out what faculty work on the theory of measurement, and bother them for a SURF. As LIGO grew beyond just a few people, he brought in Barry Barish, my former SURF advisor, to administer the project.

LIGO sounded like an exercise in frustration, though, and Kip Thorne even admitted this. The theoretical work behind LIGO was done in the 1970s, but Advanced LIGO won't come online until (at best) 2014. Forty years is a long time to wait for experimental evidence to prove or disprove your theory, especially when he feels like LIGO was doable with 1970s-era technology. It wouldn't be as good as it is now, obviously, but had the funding been there, it might have been possible to detect gravitational waves by 1980.

At this point, he's relatively disassociated from academica, and has instead run off to Hollywood to become a screenwriter. He spent nearly 30 years advising and working with undergrads, and he wanted to work on something else. Specifically, he's working on a film with working title "Interstellar". He wrote the original screenplay, and it's based on real science. (He did said he played a bit fast and loose with science in areas that had many competing theories, but said everything in the film was at least possible.) They're aiming for a 2014 release date, and IMDB claims that it's to be directed by Steven Spielberg.

We talked briefly about combining a career in writing with one in physics. It sounds like it's very hard to make grad school anything but pure science (unless you end up in HPS, or something), but after grad school, anything is possible. He chose to do pure science, and for a long time, the only writing he did was textbook writing. However, it is possible to focus on writing -- Leonard Mlodinow is an example of this. He does very little research, and is basically a full-time writer. I'm not sure what the right balance is for me, but I certainly have time to figure that out.

I wish I had been at Tech about five years ago, because I think Kip Thorne would have been an amazing adviser. (Not that I don't love my adviser, Maria Spiropulu!) And I'm really, really glad I got to meet him.

(I should also note that he had no opinion on the new hazing policy, and had no interest in finding out about it, although I suspect that might change if he understood what the hazing policy will do to Blacker House. He very much identifies as a Mole still. He's going to be at Blacker dress dinner, so I am sure someone will rant at him about it.)
ay20: long exposure of the stars at night (Default)
In order to gain a better understanding of what science beyond undergrad looks like, Prof. Johnson told us to go talk to one (or two, or three) professional astronomers or astrophysicists. Earlier today, I had a chance to talk with Fabian Schmidt, a postdoc in cosmology at Caltech, about his career path & what it's like to be a professional astronomer.

I should first note that Dr. Schmidt is a physicist more than an astronomer. He works on theoretical cosmology, although he has worked on experimental high energy physics in the past. (I swear, I didn't know that until I interviewed him! Although his research is really cool, and is, in fact, why I emailed him.)

What struck me the most as I was talking to Dr. Schmidt today was the flexibility available, and the number of times he had reinvented his career. I tend to think that I need to decide my subfield now, and that I can't change my mind. Wrong! Very wrong! Dr. Schmidt did start out in physics (unlike our guest in class today), but didn't realize that astronomy was a real career choice until he was 20. I'm just 20 now; clearly I can still change my mind!

Dr. Schmidt did his undergrad in Germany, and did his undergraduate thesis on a cosmic ray experiment. Rather than staying in Germany, he decided to come to the US for graduate school, because German graduate schools make you choose an adviser right away, and if you change your mind, you have to start your whole PhD over again, basically! He wasn't completely sure what he wanted to do, so he didn't think that was a great option. Many of his colleagues in Germany are still working on what they decided on when they first graduated from undergraduate. He, however, chose to go to cold and snowy Chicago, where he transitioned from working on a cosmic ray experiment studying ultra-high energy cosmic rays, to working on theoretical astrophysics.

He described graduate school as being completely different from undergrad. Instead of focusing on classwork, you focus on your research, and only take a few classes. I knew that, but I didn't realize just how little you took class-wise -- he said that he only spent 15 hours or so a week on classwork. He did, however, spend another 15 - 20 hours a week on TAing. Since he went to Chicago, where most of the students are not science majors, he spent a lot of TAing for people who didn't know much about physics. He particularly recommended this -- not only did it reinforce his knowledge of basis concepts to teach them over and over again to people, he really enjoyed being able to pass on his interest in astronomy to students who might not otherwise care much about the subject.

We talked briefly about graduate school admissions -- while he agreed it's really hard to deal with senior classes, writing a thesis (which I really want to do!), and applying to graduate school, he didn't suggest the usual Caltech option of delaying for a year, and working at a lab. If you're in graduate school, you get your own project; at a lab, you have to work on someone else's. This is possibly more of an issue for theorists than experimentalists, though, because experimentalists are (obviously) not going to all have their own experiments, so you end up working on someone else's project. I'm not quite sure -- clearly I need to find out more about the advantages/disadvantages of taking a year off between grad school and undergrad.

Interestingly, he didn't feel like I was out of the running for being a theorist, even though I have a much weaker math background than many other Techers. He thought that it was enough to have a reasonable math background -- which I do, with calculus, linear algebra, vector calculus, differential equations, and complex analysis -- but you needed a strong physics background. I was somewhat encouraged by this statement. I'd pretty much given up on being able to do theory by this point, because I'm terrible at pure math. ... all right, so I don't particularly want to do theory, but it's nice to know I might still have the option! However, he did say that he felt this was not always the case in high energy physics, my prospective research area, and that astro was less strict about keeping theory and experiment separate.

He also thought that I shouldn't worry too much about graduate school, despite having a highly questionable GPA. Since I have good recommendations, especially since I have recommendations from a couple of the schools where I plan to apply (Harvard, Stanford), he told me I shouldn't worry too much about it. That's easy for him to say -- he's long-since done with the process! He even said that applying to graduate school was the most stressful thing he's ever done -- which, I suppose, is heartening in a way. If I can get through that, I can probably get through the rest.

That sounds more negative than I actually feel about doing physics professionally, I think. I am worried about getting into graduate school, but I really love physics, and want to do it for the rest of my life. Fortunately, it sounds like graduate school will be right up my alley, as I both enjoy and am very good at research. (I am decidedly less good at classwork, making the next couple years a bit more of a challenge.) And being a postdoc sounds like a ton of fun: you get to do science! All the time! And have your own projects and budget and be only nominally under anyone else's supervision, and SCIENCE. That, I think, is a job worth striving for.

(more of this series to come when I have a chance to talk to another astronomer or two.)
ay20: long exposure of the stars at night (Default)
Particularly academic this is not, but I came across this on the Internet today and it made me laugh:

ay20: long exposure of the stars at night (Default)
Since I missed one of the recitation sessions this week, I thought I would blog another problem to make up for it. This problem is about opacity -- that is, what is "optically thick" (most photons absorbed or scattered) and what is "optically thin" (most photons pass through it).

  1. The path from the center of the sun to us for an optical photon is optically thin. Most photons of visible light (that are emitted in the correct direction) make it to the Earth; there is very little in space to stop them.
  2. Neutrinos are not stopped between the center of the sun and the Earth. Optically thin/thick is obviously not an entirely applicable term, but they pass through both the sun and the earth without difficulty.
  3. The Cosmic Microwave Background has a frequency that lies in the microwave range. Most microwaves pass through Earth's atmosphere, so it is optically thin to them.
  4. A photon of energy 13.7 eV is needed to ionize hydrogen. As there is little hydrogen in the atmosphere, the atmosphere is optically thin. However, just to prove this, I'll do some calculations.

    E = hν = 13.7 eV = 2.19 * 10-18 J
    &nu = 2.19 * 10-18 / 6.62 * 10-34 = 3.51 * 1015 Hz
    c = λν
    λ = c / ν = 3 * 108 / 3.51 * 1015 = 8.55 * 10-8 m = 85 nm

    The earth's atmosphere is optically thin to this wavelength.
  5. The Earth's atmosphere scatters most optical photons on a cloudy day, but does not absorb them. Thus, it is optically moderate.
  6. As it is still possible to get a sunburn from near-UV light on cloudy days (as I can personally attest), the Earth's atmosphere is optically moderate for near-UV rays on cloudy days.
  7. Your clothes are optically thin to the new airport scanners. However, a watch or a belt is not. (As my TA was somewhat amused, I feel it is required to link to Fourth Amendment Wear, which sells clothing whose text shows up on the scanners. You can therefore buy a shirt that has the Fourth Amendment, and have that text show up to the person reading the scanner.)
  8. Your body is not optically thin to the backscatter scanners.
  9. Your flesh is optically thin to medical X-ray scanners.
  10. Your bones are optically thick to medical X-ray scanners; hence why they show up on readouts.
  11. Since a black hole is a near-perfect black body, and black bodies are perfect absorbers, a random astrophysical object with the frequency distribution of a black hole is optically thick.


Many thanks to Daniel Lo, Joanna Robaszewski and Cassi Lochhaas for their assistance with this problem.
ay20: Amy Pond! (Amy Pond)
A black body, for those who don't recall, exactly what it sounds like -- a perfectly black body that absorbs any electromagnetic radiation, and a perfect thermal emitter. The properties of the emitted radiation depend only on the temperature of the black body.

The energy density is thus also dependent on the frequency of the emitted light & the temperature of the black body, and is given by:

cut for images; also math )
ay20: Amy Pond! (Amy Pond)
So, I have mixed feelings about astronomy as a subject.

Given that, it is perhaps unusual that I decided to take Ay 20 as an elective this term. My bias against astronomy came from a truly lousy experience the time I did an intensive summer program in astronomy (SSP, for any alums reading this). However, this was mostly unrelated to the actual research, and decidedly more related to the fact that the staff was unwilling to deal with a chronically ill student, and repeatedly tried to get me to leave for being such. (No, really. There was a required medical form, which I sent in two months in advance. They got around to reading it two days before I arrived, and then tried to get me to leave within half an hour of arriving at the program.)

So, yes, irrational bias! But I like(d) the subject, and certainly, I think the history of astronomy is super cool; Hum/H/HPS 11 remains one of my favorite classes I've taken at Caltech. My research is also not unrelated; HEP and astro have a lot of overlap. I just did a SURF in neutrino physics, and besides the fact that they may go faster than light, a lot of neutrino physics experiments are astrophysics in disguise (e.g. the solar neutrino problem). It seems extremely useful to be at least vaguely familiar with astrophysics, even if I don't particularly plan on becoming an astrophysicist. (Pre-SSP, I even considered research in the subject -- I think I have a first edition of Carroll and Ostlie somewhere that I was reading through in high school. And, since Caltech is one of the best astro programs in the country, it seemed sensible to take advantage of that.)

Handily for me, the professor for Ay 20 is really enthusiastic about his subject. I've been through a few too many physics classes that nearly killed my interest in the subject, where the professor was clearly uninterested in teaching undergrads, and didn't want to be there in the least. A class like that in astrophysics would... perhaps not have helped me remember that astro is actually really cool. But it is science! And it involves looking at pretty things! And, er, hopefully moderately less swearing at computers than HEP, but given the stories I've heard from friends who have done SURFs in astro, I'm not holding out much hope for the latter.

There are a couple other ideas for posts floating around in my brain, but they need a bit more thought; notably, the perception and presentation of science (particularly astronomy/astrophysics) in science fiction (... OK, this is mostly because I am absently watching Farscape while writing this entry), order-of-magnitude estimates in physics (and when they are/are not useful) and teaching styles that do/do not work for me in science and mathematics. Hopefully I will have time to write about those in the near future -- although it is term, and "spare time" is... er, rare.
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