## Friday, December 16, 2011

### Transiting Santa

Merry Xmas! Where X stands for star crossing...

## Sunday, December 11, 2011

### Impostors Welcome

From the AAS Women In Astronomy blog (in my RSS feed):

http://womeninastronomy.blogspot.com/2011/12/impostors-welcome.html
Eleanor Roosevelt said, "No one can make you feel inferior without your consent." We must not allow ourselves to retain feelings of inferiority. Had I succumbed to that response 30 years ago, I would not be writing here today.

## Saturday, December 10, 2011

### Post Finals Post

Nice job on your Ay20 finals, everyone!

Juliette

Daniel

Monica

Iryna

Erik

David

Joanna

Lauren

Mee

John

(Sorry, Tommy, I totally forgot to get your picture! Please don't feel bad, I almost forgot everyone's picture, and Jackie kept reminding me)

Cassi

Nathan

Details here.

# Western U.S. states to see unusual total lunar eclipse early Saturday morning

The moon exhibited a deep orange glow June 16, 2011, as the Earth cast its shadow in a total lunar eclipse as seen from Manila, Philippines, before dawn. The last total lunar eclipse of the year is Saturday, Dec. 10, 2011. And there won't be another one for three years. Viewers in the western half of the United States will have the best views Saturday well before dawn, Pacific and Mountain Standard Time. (Bullit Marquez - AP)
While the East Coast misses out, residents in central and western states will catch a unique total lunar eclipse Saturday morning. Where visible, the final lunar eclipse of 2011 promises to be eye-catching.
The eclipse will officially begin at 3:30 a.m. Pacific Standard Time (PST), but not until 4:45 a.m. PST will Earth’s umbral shadow start darkening the moon’s edges. Total eclipse is set to begin at 6:06 a.m., and last for 51 minutes.
Sky watchers in Northern California and the Pacific Northwest will see the fully eclipsed moon emerge from Earth’s shadow just before sunrise. Assuming clear conditions, the eclipsed moon will appear impressively large and low in the sky. Over the Rocky Mountains and northern Plains, the full moon will still be entirely in Earth’s shadow as it sets along the northwestern horizon. Farther east, from the Ohio Valley into the Southern Plains, observers will see the partially eclipsed moon set before it reaches totality.

## Wednesday, November 30, 2011

### Sunday last day for blog posts

Jackie here. I don't want there to be pressure on you to write blog posts during exam week, and I need to eventually win the race to grade blog entries faster than you all post them, so I'm not going to grade any blog posts that are posted after Sunday evening 12/4 (ie if they say Monday 12/5, they're still awesome but they're not for points). If you think you really really need to post more blogs next week in order to get the grade you want to get, let me know. But currently you are all pretty much doing fantastic, so don't stress about it too much.

### Prof. Johnson on TV

Tomorrow at 6pm and 9pm on the National Geographic Channel. Yes, this will be on the final (just kidding).

#### Finding the Next Earth

Join astronomers as they enter the final lap in a race to find a planet capable of sustaining life, a world like ours, the next Earth. See the launch of Frances CoRot and Americas Kepler missions, and the smoking hot worlds they discover. See a controversial and tantalizing discovery of a planet where life could exist in a strange twilight zone, that is, if the planet really exists. Astronomers are working to determine what conditions are necessary for life to exist, and they are building the radical James Webb Space Telescope, a spacecraft that can look at the atmosphere around a planet and reveal whether or not life as we know it actually exists. It could be the greatest discovery in human history and it could change how we see ourselves.

## Tuesday, November 29, 2011

### TQFR

Please be sure to fill out your TQFR (Teaching Quality something something) surveys at the end of the term. We will listen closely to your feedback, which we'll incorporate into adjustments to the Ay20 course in future terms. Thanks!

## Wednesday, November 23, 2011

### Essential Topics

Essential topics from the class to study for your exam:

• What is the relationship between telescope diameter and resolution?
• Celestial sphere: when will a star at a given RA and dec be visible in the sky?
• What are the equations of stellar structure, and the story of each one?
• Scaling relations (what they are and how to derive them): M-R, M-L, M-Teff
• Use scaling relations to derive the slope of the main sequence in the H-R diagram (log L vs -log Teff)
• Derive the slope of the white dwarf main sequence
• Equilibrium temperature of a planet as a function of semimajor axis and stellar properties
• Blackbodies! Flux, luminosity, Rayleigh-Jeans Law (kT >> h*nu), Wien's Law (kT << h*nu), peak wavelength (relationship between photon energy and temperature)
• Color and brightness of a star
• Virial theorem - what does it mean? apply it to:
• typical temperature in the Sun
• derivation of Kepler's 3rd law
• How do we find planets?
• Relationship between velocity amplitude of a Doppler signal and mass of planet, period of planet, mass of star

## Sunday, November 20, 2011

### Optional Lab: Exoplanet Transit

The Las Cumbres Observatory Global Telescope Network has a program called Agent Exoplanet where you go through real astronomical images from their telescopes, measure the flux from stars, and then identify stars with transiting planets based on a dip in flux. If you would like to earn extra points, or if you're just curious, please go play with their tools and then blog it up!

### Transit Probability

Many of you had some trouble with the worksheet problem about the transit probability of a planet. Consider the sketch below:

The star is the big orange circle in the middle, and the filled blue circles show two extreme planet-orbit inclinations, above and below which the planet does not transit. Note that the orbit planes for the two configurations are parallel to the blue solid lines, not the black lines. The two orbit configurations are separated by and angle of approximately 2 Rstar/(purple trace), obtained using the "skinny angle" property that the sine of a small angle is the small side over the long side.

With those definitions in mind, the transit probability is related to the solid angle traced out by the two extreme transit configurations, which is
as well as the total solid angle at a semimajor axis a, or:

The probability is the ratio of these two solid angles:

$p({\rm transit}) = \frac{2\pi \times 2 R_\star}{4\pi a} = \frac{R_\star}{a}$

For more on all things transit, including eccentric orbits and other properties of the transit geometry, see Prof. Josh Winn's (MIT) excellent book chapter here:

## Wednesday, November 16, 2011

### RV Plots for Thursday's Worksheet

Here are the radial velocity time series for two exoplanets. The mass of the star is listed under each plot. Problem 1 on the worksheet asks you to measure the masses of the planets in each system (assume e = 0, and i = 90 degrees).

## Monday, November 14, 2011

### Josh Carter's Exoplanet Talk

Tuesday 3pm in 370 Cahill:

Josh Carter
, Harvard-Smithsonian Center for Astrophysics

Kepler's Multi-Eclipsing Hierarchical Triples: Accurate Masses and Radii, Transiting Circumbinary Planets
The Kepler mission has opened a new era of high-precision time-series photometry. It has allowed for the wholesale detection of planetary systems and the detailed characterization of both stars and planets. The Kepler data quality and restricted mission scope has also led to the unveiling of novel events.  Amongst these are the discovery of hierarchical multi-eclipsing systems including those with transiting circumbinary planets (e.g., KOI-126, Kepler-16). These systems are observationally biased to have small periods and period ratios and, consequently, have short (Kepler mission lifetime) secular variation timescales. This dynamical information is encoded in variable eclipse morphologies.  I describe photometric-dynamical fits to the these light curves.  I present results from these fits; namely, I report accurate absolute bulk parameters (stellar and planetary masses and radii) that are determined free of typical model-dependencies.  I compare these parameters with theoretical expectations and comment on the efficacy of stellar models. I briefly address the search for additional transiting circumbinary planets in the Kepler data and discuss future applications of this work.

## Thursday, November 10, 2011

The final exam will be a half-hour oral exam with Professor Johnson and me (and maybe a guest scientist!), sometime during the exam period from Dec 7-9. Please follow this link to fill out a form indicating your preferred exam times.

## Monday, November 7, 2011

### LaTeX Math Symbols

It's great seeing so many people use online LaTeX editors! Here's a handy guide to LaTeX math symbols:

http://web.ift.uib.no/Teori/KURS/WRK/TeX/symALL.html

Also, FYI, LaTeX is pronounced "Lay-Tek." My fellow grad students and I at Berkeley once spent the better part of a Stellar Structure study session debating this point. Somehow we all did well on the final...

## Sunday, November 6, 2011

### Prof. is back

Hey everyone, I'm finished with my battle against bronchitis. Short story: I won. Yay! I'm looking forward to being back in the classroom.

Juliette stumbled upon my most recent Astrobites contribution about preparing for grad school. I wrote that post this past summer, and I didn't think to connect it to our course. But it makes perfect sense to do so, so check out Juliette's blog and follow the link from there.

I wrote another Astrobites post last year that went viral, at least throughout the astronomy community. I think all Caltech students should check it out, and talk to me if it strikes a nerve.

Finally, we had our first two blog posts come in as part of the Professional Astronomers series. Write your first post soon, with your initial thoughts and impressions about what the process of going pro is all about. Then get going on your interviews! Talk to me if you need recommendations for interview subjects. But don't wait.

## Thursday, October 27, 2011

### TALC moved to 9-10:30 am next Tuesday

Next monday (10/31) is Halloween, so we will not have TALC that morning. Instead, we will have TALC from 9-10:30 am on the following Tuesday morning (11/1). The week after that, TALC will continue at the regular time on Monday evenings.

## Tuesday, October 25, 2011

### Visitors for Wed and Fri

We'll be joined in class Wednesday by Dr. Ryan Foley (Harvard CfA). Come prepared for a brief Q&A with Ryan at the beginning of class Wed.

On Friday, Dr. Samaya Nissanke will visit us once again and bring a worksheet on GR for us to play around with.

### Major Blogging Assignment

One of the main goals of Ay20 as stated on the course website is that, "Students will understand what it means to be a professional astronomer." Jackie and I put a lot of thought into these goals and we fully intend to meet them by the end of term.

Pursuant to this goal, your assignment is to team up with 2-3 of your classmates and put together a series of 3-4 blog entries on the overarching topic of: "What does it take to be a professional astronomer." This topic, as stated, is broad and a bit ill defined by design. Tackle it as you see fit. However, here are some concrete suggestions:

1. Write down your impressions as of right now. What does it take to be a professional astronomer. What is the ultimate goal? What is your goal? This can form the basis of your first post.
2. Interview a grad student and a postdoc, perhaps several. Or interview a junior faculty member, or well-established prof. Write a friendly yet professional email to your prospective interviewee, invite them to lunch or out for an afternoon coffee/tea at the Red Door. The Q&A (questions in bold, responses in normal text) can form the basis of a second blog post. What is the typical career arc of a pro? What is a postdoc? Where did they apply to grad school? Where did they start out as an undergrad? What do they know now that they wish they knew at your age? What are their career aspirations?
3. What are alternative career arcs? What are the prospects in engineering, working at observatories, national labs, or in industry?
4. Find articles on this topic online. Check out the discussions on astrobetter and read the career development posts on astrobites. What have you learned and how has your impression from step 1 changed now that you've researched the topic? This can be your third (or fourth) post.
Share the various tasks (interviewing, reading, writing) among your team members. Meet regularly to compare notes. Use Google Docs to write collaboratively. Talk to Jackie and myself.

This assignment is due before the end of term, the sooner the better. What ever you do, please do not wait to do this all in one or two nights. Start now! And have fun with it.

## Friday, October 21, 2011

Please send me your pictures from our Palomar trip. I'd like to compile them into a post here on the course blog.

Thanks!

### Monday's Visitor

Monday we'll be joined by Dr. Phil Muirhead, a postdoctoral scholar here in Cahill who is an experimental astrophysicist. Here's his webpage. Check him out and come to class with questions for him.

## Friday, October 14, 2011

### Spectroscopy

In case you don't get the reference in the first poster on the wall...

## Thursday, October 13, 2011

### Lab 2 deadline moved to Wednesday

In response to feedback from students (which is very helpful!), the lab 2 deadline has been moved to next Wednesday, 10/19.

## Wednesday, October 12, 2011

### Reminder: Palomar trip this weekend

Don't forget the Palomar trip is this Sunday, 10/16! We will meet at noon at Cahill (eat lunch beforehand), drive the three hours out to Palomar, and stay there through evening to do a bit of observing/stargazing. You should pack a "night lunch" (dinner) since we will get back late.

### Lab 2

Lab 2 has been posted on the course web site: http://www.astro.caltech.edu/~jrv/Ay20/labs/lab2_theAU.pdf. In this lab, you will use an image of Mercury's transit of the Sun, taken by the TRACE mission, to estimate the distance to the Sun. This builds on our measurement of the radius of the Earth (but feel free to use a more accurate value than the one we got). The lab is due Sunday night by midnight.

## Monday, October 10, 2011

### The Known Universe

Here's the video I showed in class Monday. Enjoy!

Read C&O Chapter 3.3-3.5 (The Nature of light, Black bodies)

### iObserve

Right on the heels of our celestial sphere lessons, here's a post at Astrobetter about a handy tool for planning your observations.

## Sunday, October 9, 2011

### Monday's Guest

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 (SMAFellow. 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.

## Thursday, October 6, 2011

### Carnegie Observatories Open House

Oct 23, 2-5pm
Santa Barbara St.
http://obs.carnegiescience.edu/Events/openhouse2011

## Wednesday, October 5, 2011

### That rock

Here's an example of a mid-level (~3 points) lab/HW writeup. A 5-pointer will go into much more detail.

On the Mass of That Rock
by: John A. Johnson

Abstract

I can't remember numbers very well, but I like to calculate stuff. Here's an example of how using street fighting mathematics can help people with poor memories make order-of-magnitude calculations.

Introduction

Hey, how much does that rock weigh (see Figure 1)? Let's figure it out on the way to lunch at Chandler.

 Figure 1: A rock
Solution

Well, we know the density of the rock will be comparable to the average density of the Earth. The density of the Earth depends on the mass and radius of the Earth. I used to have both of these quantities memorized, but the process of learning all the Ay20 students' names forced these constants out of my cache.

From my most recent frequent flyer statement I know that the distance from LA to NY is about 3000 miles, which is 4800 km =~ 5e8 cm. There are about ~5 United Stateses around the globe (maybe 6), and this distance divided by 2pi =~ 6 is the radius of the Earth, or R =~ 5e8 cm.

The acceleration of an object dropped near the surface of the Earth is about 10 m/s^2 or 1000 cm/s^2 (I can remember 10!).

The density is the mass divided by the volume, or ~7 g/cc. That rock is about a meter cubed, or 10^6 cc, so it must contain 7 million grams, or 7 metric tons. That's a lotta rock!

Epilogue

It turns out that the average density of the Earth is more like 5.5 g/cc, and the density of the rock in Figure 1 is likely less than this average value, unless it's solid lead or some such. This table gives the density of various materials in kg/cc. Most surface rock is around 2.5-3.0 g/cc, so I'm off by a factor of 3. Which means I'm dead-on to an order of magnitude!

Acknowledgements

I extend my gratitude the lady with the stroller (not pictured) for jumping out of the way just before I snapped this picture.

## Tuesday, October 4, 2011

### Palomar Field Trip

We will have a VIP tour of Palomar Mountain and its facilities Sunday Oct 16. We'll leave from Cahill at 1pm and we'll stay until after sunset (provided that the weather cooperates). Please find someone with a car and reserve your seat. I'll have 3+2 seats available, where the +2 seats are for people under 5'4".

## Monday, October 3, 2011

First, watch this nice intro to the topic:

Then read Chapter 2 of Gray's Stellar Photospheres. Read enough to understand Figure 2.4 (this was incorrectly labeled as Figure 2.8 in a previous version of this post. Fortunately the hyperlink went to the correct figure.), which you should memorize for life.

We'll think about telescope optics and astronomical instrumentation mostly using 1-d visualizations. As additional reading you can check out this introduction to FT for 2-dimensional functions (images).

## Sunday, October 2, 2011

### Worksheet 2

Worksheet 2: The Celestial Sphere and Observation Planning

Note that this was originally going to be assigned Friday, but we'll put it off until Monday. Your group's write up of one or two of these problems is due by next Sunday (Oct 9). There will be a help session Monday evening. Together with your time in class, this gives you about 2.5-3.0 hours to work on the problems.

Also, I'm having trouble with URLs in LaTeX containing characters such as "_" and "~". Here are the Keck targets for you to organize.

http://www.astro.caltech.edu/~johnjohn/outgoing/keck_targets.txt

### Estimating The Luminosity of a Sun-like Star

by: John A. Johnson, Jackie Villadsen

Abstract

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.

Introduction

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.

Acknowledgements

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.

## Saturday, October 1, 2011

### On the Earth's radius, the beach, and balance

I hope you all enjoyed this lab as much as I did. We may or may not get an accurate measurement of the Earth's radius. However, either way, we had an opportunity to get to know each other better, which will no doubt help us work collaboratively and learn more from the class.

On the way back to Pasadena one of you told me, "This will probably be the last time I go to the beach for the next 9 months." I really hope this isn't the case. One of the most important things I want you learn in this class, besides the virial theorem and radiative transfer, is how to introduce balance in your lives. Your success as scientists depends on it.

If you feel like you can't get back to the beach sometime in the next month, please come talk to me or Jackie. We're both extremely busy, with teaching, our research, taking classes, etc. However, one of the reasons Jackie and I have made it to this point in our careers is that we have aspects of our lives that compete with astronomy for our time, and we often let those non-astronomy things win. We'd like to help you out if you need it.

Right now, I have a paper I need to write. However, my son's soccer game is competing for my time. This morning, soccer is going to win.

Here are some pics from Lab 1. I wish I took more. Let me know if you have any that you'd like to share.

## Friday, September 30, 2011

### Palomar Field Trip

I'd like to take the Ay20 class up for a VIP tour of Palomar Mountain sometime this term. Please fill out this poll to let me know your availability.

http://www.doodle.com/zabfpysa9fbwgie7

## Wednesday, September 28, 2011

### Insignificance

Mee had a great post on humility in science. Here's a fun, related comic:

http://www.smbc-comics.com/index.php?db=comics&id=2223#comic

### Abstrosizics: Flames and Hot Gases

We have a winner! David identified the Flame nebula, and even some of the associated physics. Here's his post:

Abstrosizics: Flames and Hot Gases

'via Blog this'

## Tuesday, September 27, 2011

### Introducing... Me!

Hi all!

I'm super excited to be the TA for this class. This is my first time as a TA. But I do have a couple prior teaching experiences. In particular, as an undergrad I spent a summer in China running technology summer camps for high school students there. That gave me the experience of being in front of a classroom. For me, a lot of the meaning of science comes from the impact it has on people, and so teaching is a crucial aspect of making science meaningful.

What do I want to get out of this class? I guess one of the things I want is to learn how to teach. Professor Johnson is a great person to learn from, because he's full of lots of creative ideas and lots of energy. I also want to share my love of science. It's so fun to interact with people who also get that thrill from learning to understand our universe. I also want to learn. When I signed up to TA this class, I didn't realize that would really be involved. But it turns out there's so many levels of understanding, and when you ask yourself, "How can I teach this?", you have to dive down a few levels below where you've been before.

I'm here to help you guys out. One major thing is if you have any suggestions or questions or concerns about the class, or about Professor Johnson, you should feel free to bring them up with me. The goal is that this way, nothing we see on the course evaluation forms at the end of term will be a surprise, since we'll already be working with you guys to implement your suggestions for the class while it's still going on.

See y'all bright and early tomorrow :)

Jackie

Chapter 1 Carrol & Ostlie

And by "for Friday" I mean read this chapter before coming to class Friday. You never know when you might have to have a conversation with someone (for instance a TA or Prof) about the celestial sphere while hanging out in Cahill 219...

### On Points and Posts

Please create your blogs and make your initial posts. Introduce yourself to the class, muse about something astronomical, ask a dumb question and try to answer it. Whatever you do, start writing and then continue writing.

Blog posts will typically range from 1-3 points. Exceptional posts will receive 5 points. Here are some examples:

1-pointer (short, sweet, shows that I've been thinking about astronomy while eating my Froot Loops)
2-pointer (this might be a 3-pointer)
2-pointer (more if accompanied by writing. Don't get me wrong, though, I love this!)
3-pointer (this student is thinking about the day-to-day aspects of an astronomy career)
3-pointer (whoa, this student has been checking out astro-ph abstracts!)
5-pointer (straight out of Sky and Telescope! :)
5-pointer (AstroBites for the win!)

Points will be a bit subjective, but the Central Limit will likely prevail and wash out injustices whenever they may occur.

### The power of dumb questions

Fun fact: back in the summer of 1999 I, Prof. Johnson, was a SURF student working in the LIGO group for Prof. Libbrecht and Dr. Phil Willems. It's crazy to me that these great scientists are now my peers! But it's proof positive that SURFers go on to do great things.

One of my most vivid memories from that summer took place in the basement of Robinson Hall. I went to visit a fellow SURF student on whom I had a crush. In her office was a poster of M33, not unlike the one pictured here. After staring at it for half a minute, I asked her A Stupid Question: "Um, what are all these really big, bright stars outside of the galaxy? Fortunately, my fellow SURF student didn't roll her eyes, or laugh, or sigh.

Instead, she jumped up from her chair and seized the opportunity to teach a fellow student about something she was passionate about. She told me that the big stars were actually normal-sized, but that they were closer and in our own Galaxy. In the picture, we were looking past stars in the Solar Neighborhood, out through our galaxy, and into a very distant galaxy composed of stars so far away and so numerous that they blurred into structure of what we call M33.

At first I was embarrassed that I had overlooked such an obvious explanation. But then, suddenly, right before my eyes the image of M33 took on a three-dimensional shape that I had never seen before in an astronomical image. For the first time, I sensed the structure of the Milky Way. I felt how enormous it is. I realized how gigantic M33 really is. HFS, I can see!

This event illustrates the power of "stupid" questions. Stupid, obvious questions are my favorite variety. Science works when people challenge the obvious, revisit "old" knowledge that everyone "knows," and ask dumb questions. Please keep this story in mind during the semester and let it guide how you approach Ay20.

Let me start off asking a dumb question about the image of M33. Take a look at some of those foreground stars. Those stars are points of light, with no discernable dimension. The only reason they have any shape is due to the limitations inherent in the optics we use to view them. They are point sources. And yet, any astronomer will tell you that we know a great deal about those tiny points of light. We can measure their temperatures, radii, masses, magnetic fields, chemical compositions and search for planets around them. We know a bit about how they form, why they shine, how long they'll live, what their internal structures look like.

The dumb question that forms the basis of Ay20 this term is: Seriously? Are you seriously telling me we can know all of this from a point of light in the night sky?

Do you buy it? You shouldn't at this point. But by December I think you will, and I hope you'll remain as amazed as I am about it!

## Monday, September 26, 2011

### Times for Problem Solving Sessions

I'll be in Cahill 219 two evenings a week to host problem solving sessions so you can work together on the lab and problems leftover from class. Participation highly encouraged. One session will be Thursday 8-10 pm. The other session will be either Monday or Tuesday evening.

Please comment on this message to let me know whether Monday or Tuesday evening is better, and what time window is the best.

Jackie

### Ay20 class times

Hi Ay20!

Jackie here, your faithful TA. Our first Ay20 class meeting is 3-4 pm today in room 219 in Cahill. Since class participation will be very important in the structure of the class, it's crucial that everyone attend class.

This morning at the organizational meeting, we scheduled class for Mondays 3-4 pm, Wednesdays 9-10 am, Fridays 9-10 am.

Class updates will be posted to this blog. You should save the link to this blog and add it to your RSS feed. If you have Gmail, you can do this by going to the top of the screen in Gmail and clicking on "Reader", which takes you to Google Reader. Then click on the "Add a Subscription" button in the top left of the screen, and type in "ay20class.blogspot.com".

Can't wait to meet you all!

PS - If due to some scheduling mishap you can't make it to class today, please email me (jackievilladsen@gmail.com) and Prof. Johnson (johnjohn@astro.caltech.edu) to let us know asap.

## Sunday, September 25, 2011

### Welcome to the Ay20 Blog

Welcome to the Ay20 course blog. Please add this to your favorite RSS reader so you can stay up to date on the latest class announcements, problem set hints, in-depth articles about topics we will only have a little time to cover, student contributions and much, much more. If you don't have a favorite RSS feeder, open up a Google account and use Google Reader.

All Ay20 students should also create their own blogs. Just go to blogger.com, login with your Google account, set your URL to ay20-FIRSTNAME.blogspot.com, and give yourself a clever title. You should then invite your friends and family to follow your blog. Outstanding posts will be reposted to this site, and possibly reposted again to the main Cahill Astronomy blog (coming in November 2011). Write in your own voice, but use proper grammar and spelling. You can be humorous; indeed, humor is encouraged. But all posts should reflect what you are learning in this class and others here at Caltech. Be creative by including your own photography, music, comic strips, drawings and poetry. Keep your posts concise and focused, and update often (at least twice a week).

While your grade depends on the quality of your posts, since your blog is open to the world I hope you put a lot of work into your writing simply because so many people will likely read it. If you'd like to get a sense for what goes into a good science blog, check out some of my favorites:

AstroBites
AstroBetter
Cosmic Variance
An Illumination
Hogg's Research
Female Science Professor