Week 12: Conclusion

This semester I've learned a lot thanks to Astro 16. In class, we covered topics ranging from sidereal time to the interstellar medium to astrochemistry and astrobiology. We talked about the progression of stars' lives, different strategies for detecting exoplanets, how properties of stars determine stellar structure, and why we wouldn't notice for millennia if the Sun stopped its fusion. I got to use a real telescope, write about recent developments in the field of astronomy, and even draw some connections with evolution and anatomy.

Probably one of the most interesting topics I learned about this semester was planet formation. The planets in our Solar System are pretty diverse in terms of size and composition, but I never knew exactly how they formed or why they're arranged the way they are. It was cool to learn that the mass of the protoplanetary disk material that is needed to form a planet is often much greater than the mass of the "finished" planet. It was also interesting to learn that the temperature and density gradients are a large part of the reason why planets formed the way they did. Hopefully as our understanding of our own Solar System improves, our ability to interpret the planetary systems of other stars will improve correspondingly.

The biggest challenge I've faced in this class (and this was definitely true of Astro 17 last semester as well) has been writing the lab reports. I found lab to be a valuable part of the class, especially as preparation for the Exoplanet Challenge, but I hate writing lab reports. In our first lab, we measured the astronomical unit using the Sun's angular diameter, rotational velocity, and period. Our final calculation was off by a factor of 10...which means there have been better estimates of the Earth-Sun distance since the 1st century BC. I mean, I knew going into the lab that our findings wouldn't exactly be ground-breaking, but I kind of expected that our modern technology would give us a leg up into at least the 14th or 15th century. It doesn't exactly motivate me to do a lab write-up when I know that Ye Olde Lab Reporte would've been way more accurate. As for the second lab report...well, I haven't started, and it's due at the end of the week. So there's that.

Finally, the highlight of the course in my opinion was the astrobiology lecture. Although I've done some reading on my own about astrobiology, I'd love the opportunity to go more in depth on the Drake Equation, the RNA world hypothesis, habitable zones, and anything else that may be necessary to make a planet livable. I honestly wish Harvard offered an entire course or two on astrobio and/or astrochem, because they're such cool subjects and the perfect union of my (admittedly very strange combination of) interests. If I can't find anything here at Harvard, though, maybe the Universe will bring me back to astrobio one day anyway.

Thanks for reading!

Sources 
https://en.wikipedia.org/wiki/Astronomical_unit#History
http://wallpoper.com/images/00/34/00/68/calvin-and_00340068.jpg

Week 11: Live Blogging the Exoplanet Challenge

So tonight from 12:30 am to sunrise, Rodrigo and I are signed up for our first observing session in our quest to complete the Astronomy 16 Exoplanet Challenge. If we successfully observe a transiting exoplanet and write up a brief report on it, we'll automatically get A's in the class. We've chosen to observe HAT-P-37b, an exoplanet with a radius 1.2 times that of Jupiter and a period of 2.8 days, which is supposed to transit its star between 3:04 am and 5:24 am tonight. I'll be live blogging over the course of the night, which should be interesting--both because we'll hopefully be getting some cool data and because my mental faculties will probably be on a sharp decline by around 2:30 am. So here we go!

10:23 pm: Attempt to take a nap. Give up not much later because I only woke up 12 hours ago. Resign myself to being exhausted for the next 24 hours.

11:43 pm: Realize that Dunkin Donuts closes in 17 minutes. Make the sketchy walk from the Quad in the name of caffeine.

11:57 pm: Discover that Dunkin sits on a throne of lies and has closed before midnight. Shake fist and go to Starbucks instead.

12:30 am: Ready to get started! We're taking over the telescope from the group before us, which means that we don't have to worry too much about setup. This would be more handy if the beginning of our transit wasn't still two and a half hours away, but it is nice.

1:57 am: So it took a lot longer than I expected to get things set up, but we just finished up in the dome. Fortunately we're right on schedule--we planned to start taking images right around 2 am so that we'd be prepared when the transit starts around 3. We spent the last hour and a half getting the scope in focus, finding our star, fiddling with the exposure time, and finally setting up the computer to take a bunch of exposures over the next hour or so. Our first few images looked awesome, so I'm optimistic about the rest of the night!

2:45 am: I'm taking advantage of the fact that I haven't collapsed from exhaustion yet to be productive. Maybe this week I'll get all my blog posts done before the hour before they're due! (Sincerest apologies to the lecturers of my bio class, which is right before Astronomy and in which I have finished more than one last-minute blog post...)

2:53 am: *Gets excited all over again about how cool astrochemistry and astrobiology are*

3:13 am: Our first 30 images are done! The transit should have started around 10 minutes ago and it seems like there may have been a decrease in the number of counts on our star, but until we start fooling around with photometry, we won't be able to tell. We were pretty anal following the directions during setup and it's pretty clear out, so I'm really hoping that we can get good data tonight.

3:56 am: It's way past my bedtime.

4:05 am: I just finished the other two blog posts for this week. Now that those are done, I'll be watching some videos to learn how to use some genomic analysis tools for the infectious disease lab I work in. This is peripherally related because the program is called Galaxy, even though all the genomes we have to sequence reside here on Earth. Galaxy is just a cool word I guess.

Thanks for always validating me, Google Images <3

My mentor in lab will be happy that I'm working on this, but probably not happy when I show up 6 hours from now with my eyes taped open. Can't win 'em all, I guess.

4:29 am: Our second set of images is done and we're going to start doing some photometry! Fingers crossed that we like what we see...

5:12 am: Our data doesn't make any sense and now clouds are moving in and I want to go to bed and I haven't even made any progress on Galaxy and I think the last time I stayed up this late was to work on the lab report last semester. This is my life now. *Drowns sorrows in brownies*

5:33 am: So the thing is that we have two decent-looking reference stars with which to compare our star's magnitude (as in their magnitudes remain more or less unchanged in all of our images), but all of the other stars that we've chosen as references seem to follow the same changes in magnitude as our object. I'm pretty sure that the shallow dip that we see in our object's magnitude, since it's matched by the plots of most of the other stars, is not actually legit. At the same time, it doesn't make a lot of sense for two of the reference stars to have normal-looking magnitude profiles if there's something atmospheric or something affecting the brightness of all the other stars.

6:04 am: We just shut the telescope and the computer down and will figure this mess out later. Time to head to Kirkland and crash on my friend's couch until my 8 am meeting!

Epilogue (12:40 pm):

We are true scientists. 

Sources
https://en.wikipedia.org/wiki/List_of_transiting_exoplanets

Week 11: WS20 #1

1. The Earth resides in a "Goldilocks Zone" or habitable zone (HZ) around the Sun. At our semimajor axis we receive just enough sunlight to prevent the planet from freezing over and not too much to boil off our oceans. Not too cold, not too hot. Just right. In this problem we'll calculate how the temperature of a planet, T_p, depends on the properties of the central star and the orbital properties of the planet. 
a) Draw the Sun on the left, and a planet on the right, separated by a distance a. The planet has a radius R_p and temperature T_p. The star has a radius R_★ and a luminosity L_★ and a temperature T_eff. 

b) Due to energy conservation, the amount of energy received per unit time by the planet is equal to the energy emitted isotropically under the assumption that it is a blackbody. How much energy per time does the planet receive from the star? How much energy per time does the planet radiate as a blackbody? 

We know that the flux from the star at the distance a is given by \(F_\bigstar=\frac{L_\bigstar}{4\pi a^2}\). However, this is the total flux, and we want only the power received by the planet. If we multiply the flux by the cross-sectional area of the planet, we get the correct units for power (energy per time) and the proper dependence on the planet's radius.
\(P=\frac{L_\bigstar}{4\pi a^2}(\pi R_p^2)=\frac{L_\bigstar R_p^2}{4a^2}\)
In order to calculate how much energy the planet radiates as a blackbody, we simply use the Stefan-Boltzmann Law to find the flux, and then multiply by the planet's surface area in order to convert to power.
\(F_p=\sigma T_p^4\)
\(P=\sigma T_p^44\pi R_p^2\)

c) Set these two quantities equal to each other and solve for T_p. 

\(\frac{L_\bigstar R_p^2}{4a^2}=\sigma T_p^44\pi R_p^2\)
\(T_p=(\frac{L_\bigstar}{16\pi a^2\sigma})^{1/4}\)

d) How does the temperature change if the planet were much larger or much smaller? 

There's no dependence on the planet's radius in the above equation, so the temperature won't change if the size of the planet changes. This makes sense, because any extra radiation absorbed by the planet due to its increased cross section will be radiated away due to its increased surface area.

e) Not all of the energy incident on the planet will be absorbed. Some fraction, A, will be reflected back out into space. How does this affect the amount of energy received per unit time, and thus how does this affect T_p? 

Any reflected energy will correspond to an equivalent decrease in the energy absorbed by the planet, which will correspond to a decreased surface temperature.

Week 11: WS19 #2

2. Resolving organic chemistry in disks: It is debated whether the Earth's water and organics originated from material forming around 4 AU (asteroid-like) or 30 AU (comet-like). We would therefore like to know what the differences in the organic composition is between these two locations in protoplanetary disks. One of the interesting organics CH₃CN emits strongly at 239 GHz. How big of a telescope would you need to resolve a difference in chemical composition between 4 AU and 30 AU in the nearest star-forming region? How does the required telescope size compare with the biggest steerable radio telescope in operation, the 100 m Green Bank Telescope (GBT)? To the longest baseline in the ALMA interferometer of 10 km? 

First, we should figure out what the wavelength the acetonitrile is emitting at.
\(239GHz=239\times10^9s^{-1}\)
\(\lambda=c/\nu\)
\(\lambda=\frac{3.0\times10^{10}cm/s}{239\times10^9s^{-1}}=0.126cm\)
Let's assume that the nearest star-forming region is 150 parsecs away.

Since we're comparing the signal at 4 AU and 30 AU, the top will be the difference: 26 AU. In order to calculate the angle, we can use the small angle approximation.
\(tan\theta=\frac{26AU}{150pc}=\frac{26AU}{3.09\times10^8AU}\)
\(\theta=\frac{26AU}{3.09\times10^8AU}=8.41\times10^{-8}\)
Finally we can calculate the necessary diameter of the telescope.
\(D=1.22\frac{\lambda}{\theta}\)
\(D=1.22\frac{0.126cm}{8.41\times10^{-8}}=1.83\times10^6cm=18.3km\)
To get the necessary resolution for this, the GBT would be way too small. ALMA is also a bit small, but is the right order of magnitude.

Week 11: The Arecibo Message

On Thursday, our lecture covered astrobiology. While a lot of this field focuses on life as a more general phenomenon, the exciting part of astrobiology for most people is almost definitely the idea of finding intelligent life off of the Earth. However, since the only example of intelligent life that we have is ourselves (and even that can be questionable sometimes), we don't know anything about the culture, capabilities, or even biology of potential life elsewhere in our universe, and it can be difficult to be confident in our definition of intelligent life.

Given our lack of knowledge regarding what we might share with other civilizations, scientists wanted to come up with the most simple and universal way of demonstrating humanity's intelligence. Thus, in 1974, the Arecibo message was born. This message contained what Dr. Frank Drake (of the Drake equation, which we discussed in lecture) and Dr. Carl Sagan deemed the most important information about and known by humans, including the numbers 1-10, the chemical formulas of the nucleotides, Earth's location within our solar system, and the population of Earth. Once the information was assembled, the message was transmitted via an extremely powerful radio broadcast in the direction of a star cluster called M13.

A graphic representation of the Arecibo Message. Its dimensions were chosen as 73x23, because prime numbers would lead to minimum confusion when reconstructing the information. 

M13 was chosen because it has a large number of stars, is relatively big, and is relatively close. However, "close" in this case means about 25,000 light years away--which means that it won't be another 24,958 years or so before the Arecibo message reaches M13, and another 25,000 years or so after that before we could possibly get a response. While very little of the information encoded in the message has changed since 1974 (only the Earth's population and the fact that we have demoted Pluto from planethood), a lot can change in 50,000 years--the disappearance of the Neanderthal and all of recorded history are just two small examples of things that have happened in the last 50,000 years, for instance. It's unlikely that the Arecibo Radio Telescope, from which the signal was broadcast and which is represented in the message, will still be around in 50 millennia.

Our understanding of the universe will have changed a lot by then too. Just given how much physics has advanced since 1974 and the accelerating trajectory that that advance has taken, it's possible that at some point before 50,000 years have elapsed, we'll look back on this transmission with embarrassment. "Why did we think it was important to show that we knew how to count to 10? Any respectable civilization would have understood and included the unified field theory instead," we will lament, with the same emotions one feels upon looking at pictures of him- or herself from middle school.

In any case, the Arecibo message is less of an exercise in practical extraterrestrial communication than it is in thinking about what's important and how we can communicate with cultures unimaginably different from ours. That being said, if we haven't made contact with aliens by 51,974, it'll be a suspenseful year for anyone who remembers this transmission.




Sources 
https://en.wikipedia.org/wiki/Arecibo_message
http://phenomena.nationalgeographic.com/files/2014/11/AreciboMessage-e1417162442960.jpg
http://www.seti.org/seti-institute/project/details/arecibo-message
https://en.wikipedia.org/wiki/Messier_13
https://en.wikipedia.org/wiki/Neanderthal
http://outline-of-history.mindvessel.net/80-the-neanderthal-man-an-extinct-race/81-the-world-50000-years-ago.html

Week 10: The Edge of Space

While it has been over 60 years since the first dogs were launched into space by the Russians (clearly the most important part of the space race), recently a group of young students from England managed to do the same...kind of. Using a balloon, they sent a stuffed animal dog named Sam equipped with a GoPro up into space--in the name of science, of course. The video is pretty cool, especially listening to how much quieter things get as Sam increases in altitude. By the end, you can clearly see the Earth's curvature and its atmosphere, and beyond that, the blackness of space.

After I watched this video, I began to wonder exactly where the boundary of space began. There's no clear point where Sam clearly passes from being "in the sky" to "in space," but clearly that transition must happen somewhere. Turns out there are several different definitions that range from about 80 km to about 120 km. NASA, for example, defines the boundary as 122 km based on how vehicles are steered during reentry. Another definition, 100 km, is based on the fact that at this altitude, the velocity needed for atmospheric lift is greater than orbital velocity. A third definition is based on the transition from Earth winds to the winds of charged particles in space.

Unfortunately there's no altimeter included in Sam's journey (or at least not one that appears in the video), so it's hard to tell how many of those barriers he passed. However, it's inspiring to see the English space program making such great leaps forwards.



Sources 
http://www.usatoday.com/videos/news/have-you-seen/2016/04/11/82901316/
https://en.wikipedia.org/wiki/Animals_in_space
https://en.wikipedia.org/wiki/Outer_space

Week 10: Tourism...in Space!

I just read an article describing Bigelow Aerospace's plan to introduce inflatable habitations that could be used in space. The first one will soon be attached to the International Space Station for a two-year-long test, but the company hopes that these units, termed Bigelow Expanding Activity Modules (BEAMs), could eventually exist in space apart from the ISS. This could help ease the demand on the ISS from smaller space programs that don't get as much time on board as programs like NASA do. There is also hope that this will be an important first step towards the commercialization of space. Not only does it have the possibility of initiating space tourism, but it also may give rise to the development of new industries that don't necessarily have to depend on governments.

Leaked photo of actual space tourists. 

This would also be a great way to increase the number of opportunities for scientific research. Not only would there be a wider variety of places to choose from to do microgravity research in fields like biology or medicine, but I think as commercial space programs become more legitimate, on-the-ground research that supplements those programs will become more of a focus as well. We need to take steps forward in the space industry both for their own sake and to keep things moving forward here on Earth.

Finally, I think these habitations would be a really great way of increasing popular support for the space program. Like a true pioneer, Robert Bigelow, the founder of Bigelow Aerospace, really drew attention to what is truly one of the most important goals in the space industry today: "We would love to see Disney have a Disney space station. Wouldn't that be cool?"

It would indeed be cool, Mr. Bigelow.

Sources 
https://www.washingtonpost.com/news/the-switch/wp/2016/04/11/boeing-lockheed-to-launch-habitats-for-space-tourists-and-researchers/
http://graphics8.nytimes.com/images/2011/03/01/science/01orbit/01orbit-articleLarge.jpg
http://vignette4.wikia.nocookie.net/disney/images/4/40/Magic_Kingdom_Space_Mountain_Poster.jpg/revision/latest?cb=20110413013012