September 21 - Clocks of the Universe

Imagine that half of your wedding guests show up at the venue a month before the event because the government’s decision to add a month to this year’s calendar did not reach them. Turns out that such a scenario could not be completely ruled out in ancient Rome. Mihir Kulkarni, our speaker on Friday, opened our eyes to how the way we measure and keep track of time has evolved through history and how different cultures use different systems.

Until recently, no man-made device could match the regularity of celestial movements. As a result, we used the Earth’s spin, its rotation around the Sun and the Moon’s movements to measure time. These measurements became encoded in the calendars that helped regulate human activity, from seeding to religious festivities. Small differences between the actual movement of celestial bodies and that captured by calendars add to the point where they become noticeable and sometimes, disruptive. Such disagreements were often dealt with through ad-hoc adjustments, but ultimately they inspired calendar refinements based on more accurate astronomical models. This way, we learned about hard-to-measure phenomena such as the precession of the Earth’s rotation axis. As the axis wobbles not unlike that of a spinning top, the closest star to the north pole -called the North Star-, changes. This shift occurs on timescales of thousands of years, long compared with a person’s lifespan but measurable through history.

Finally, minute perturbations and secular changes to the Earth’s movement relative to the rest of the universe pose a fundamental limit to the precision with which we can measure time. To beat these limitations, our current time standards do not rely on astronomical calculations anymore, but that has not removed all implementation challenges, as the “Unix 2038 year” problem illustrates.

After the talk, Mihir answered many insightful questions from the audience. You can also find a detailed summary of the talk by Steven Fertig, of the Amateur Astronomers Association of New York, here.

Clouds prevented us from star gazing, but we had the opportunity of touring the Rutherfurd’s observatory facilities lead by Daniel and Matthew while Douglas discussed some counter-intuitive properties of black holes with the support of animations in our 3D wall.

-- Jose Zorrilla (graduate student)

Sept 29 - Galactic Archeology

Our speaker this week was Keith Hawkins, a Simons Postdoctoral Fellow based in the astronomy department here at Columbia. Keith is a Galactic Archeologist. He searches for clues to the past of our galaxy, the Milky Way, similar to the way an archeologist seeks to learn about ancient civilizations and cultures. 

Keith started by telling us about the "fossils" he uses to study the galaxy - stars! Stars are fossils in two ways. First, at the great distances involved on the scale of the Milky Way, we see stars not how they are but rather how they were up to hundreds of thousands of years ago, before humans even evolved on the Earth. This is because light moves at finite speed and needs time to reach us from the distant galaxy. Second, many types of stars live for hundreds of millions or billions of years and so their composition provides clues to what was going on at the time when they formed.

Next we learned about the tools used in galactic archeology. We heard about the methods used to measure distances, chemistries, and velocities of stars: parallax and spectra. Keith demonstrated parallax by having the audience hold up a finger and close each eye in sequence; the finger appears to move relative to the background. This is analogous to how astronomers measure distances, except observations taken on opposite sides of the Earth's orbit, 6 months apart, replace winking. The amount the star appears to move relates to its distance from us. Spectra, obtained by splitting a star's light and measuring how bright it is at different colors, contain a wealth of information. Dark bands in the rainbow are often visible. These bands correspond to light being absorbed by different elements in the star's atmosphere, so examining their pattern can tell an astronomer which and how much of the elements are in the star. The specific chemical signature of a star can pinpoint its place of birth or prove association with other stars. The bands in the spectrum may also be shifted to redder or bluer colors than normal; the direction and amount of shift is due to the Doppler effect and indicates the velocity of the star relative to us.

Keith finished his talk by describing his research's goal: a complete map of the Galaxy containing information on the positions, motions, and chemical content of millions of stars. He believes this "chemical cartography" will be key to deciphering the history of the Milky Way. 

After the lecture and a lively question and answer session, undergraduate students Briley and Harrison showed 3D astronomy animations on the 13th floor while graduate students Steven, Aleksey and Haley pointed the Rutherford Observatory's telescopes at the Moon, Ring Nebula, and the double star system Albireo.  

-- David Hendel (graduate student)

Mar 3 - Las Atmósferas Estelares

(This was our 3rd Annual Spanish-Language Lecture)

Turns out the Sun has an atmosphere, albeit very different from Earth’s. Alejandro Núñez, a graduate student at Columbia University, unveiled what is known about this gaseous envelope, layer by layer. He further described how a flotilla of space probes is helping scientists clarify some remaining mysteries by continuously gathering data from all angles and wavelengths. The most vexing of these unsolved questions is how the corona -the outer layer of the Sun’s atmosphere- can be hundreds of times hotter than the photosphere -its visible surface-, reaching temperatures in excess of a million degrees Celsius. While a detailed description of the heating mechanism still needs to be developed, it seems to be linked to the complex interaction between the Sun’s magnetic field and its atmospheric plasma.

Turns out the Sun is also a star. Thus, we can extrapolate what we learn about the Sun to other stars. As Alejandro explained, we need to do so with caution, for different stars can have diverse levels of magnetic activity. He illustrated this with a discussion on how the red dwarf at the core of the recently discovered multiple planetary system Trappist-1 seems to be much more active than our Sun, and the consequences that this could have for the habitability of the planets orbiting it.

This was the Spanish public lecture of this season, and the audience had the opportunity to stargaze at the Rutherford observatory on Pupin Laboratories’ roof after the talk. The night was cold and partly cloudy, but we managed to get a glimpse of some objects like the Moon and Mizar through some clearings.

-- Jose Zorilla (graduate student) 

Feb 3 - Earth in Human Hands

On Friday night, author and astrobiologist David Grinspoon shared his new book, "Earth in Human Hands", with us. He claimed we are entering a new era on earth called the Anthropocene - the age of humanity. For better or worse, we are reshaping our planet, and we have the capability to be aware of and intentional about the changes we enact. He also told us about another species living 2.5 billion years ago that caused catastrophic climate change: cyanobacteria learned to generate O2 through photosynthesis, which changed the composition of atmosphere and that destroyed many other bacteria that thrived on the previously methane-rich atmosphere. He also made the distinction between inadvertent vs intentional changes in climate. For example, when we began driving cars on a wide scale, we didn't initially understand the environmental impact that would have. However, in the 70s, the world responding to ozone depletion by banning chlorofluorocarbons (CFCs), intentionally working to recover that protective layer between the Sun and us. Finally, Dr Grinspoon believes we can positively affect future climate, even beyond reversing the effects of humans on the climate - we could avert a future ice age, for example, since we know those happen periodically even when the Earth is left to its own devices. 

After the lecture, Dr Grinspoon signed copies of his book, and then undergraduate Erin took the audience on a brief tour of the other planets in our solar system. Upstairs, undergraduates Richard and Cierra showed movies on the 3D wall, and graduate students Aleksey and Daniel led roof tours. 

-- Stephanie Douglas (graduate student)

Dec 16 - How to Hold a Dead Star in Your Hand

Our speaker, Kimberly Arcand, didn't come from an astronomy background. She began her science career as a biologist studying deer ticks, then moved into computer science before joining the Chandra X-ray Center (CXC), where she is now the visualization lead. Her job is to take the data and turn it into interesting and useful pictures. The data is beamed down from the telescope to NASA and then sent to the CXC as a lot of 1s and 0s. This is cleaned and assembled into black and white images; part of Kimberly's job is to determine how best to color these images to make them informative. Often, Chandra images are colored by the X-ray energy range or the dominant chemical/element.

Color has meaning. Kimberly spends part of her time studying responses to different color schemes, and choosing the right color scheme based on the audience for an image. Scientists think of blue as hottest, but culturally most people associate red with heat. Because Chandra images are important for outreach to the general public, her team picked red for the hottest parts of an image, rather than the blue that the scientists wanted.

Kimberly also told us about her work on visualizing the Cassiopeia A supernova remnant. Chandra (along with the Spitzer infrared telescope and Hubble Space Telescope) has observed this expanding shell of gas over many years, and you can actually see the gas moving outward in images taken several years apart. There is enough data that her team could use software borrowed from brain imaging to make the first 3D model of a dead star. She showed us a movie where we flew through the Cas A remnant. They also made a 3D printed model of the remnant - you can download the free file here if you want to hold your own dead star in your hand.

After the lecture, undergraduate Richard took us on a tour through all the scales of our universe, undergraduate Briley showed short astronomy movies on the 13th floor, and graduate students Alex and Aleksey led tours of the roof. Myself and graduate student Moiya also helped facilitate in the lecture hall.

-- Stephanie Douglas (graduate student)

Nov 4 - The Cosmic Origins of the Chemicals of Life

We start, as perhaps all good talks should, with Genesis. Daniel Wolf Savin took us through the first three days of creation, from the light of our universes first stars to the formation of water, and maybe even life, on planets like our own. In the lab his team has recreated the chemical conditions of the first stars and used it to infer some of the evolution and distribution of the chemicals that form the building blocks of life. On the way he also gave us pearls of wisdom such as the best way to ensure a healthy supply of Belgian chocolate in your laboratory, and jokes that even he admitted were "good science but bad comedy".

After his stellar ("good science") talk we also heard from astronomy graduate student Moiya McTier, about how space affects all of our everyday lives. Meanwhile up on the roof we had clear skies, with Stephen Mohammed, Jorge Cortés, Danielle Rowland, and Emily Sandford guiding our telescopes to the Moon, Mars and a proliferation of double star systems. And finally but fluently we had Erin Flowers explaining the wonders of the universe in all your favourite dimensions on the 3D wall.

-- Zephyr Penoyre (graduate student)

Oct 21 - Surviving the Misinformation Age

In the past, information was scarce, but generally high quality. Conversely, in the last 10-15 years, the amount of information produced by humanity has skyrocketed while simultaneously being made accessible to nearly every human being on the planet. Tonight, Professor David Helfand discussed the challenges that this firehose of data presents to society. 

The internet is full of mis-information that is easily accessible and appears vetted. Prof. Helfand told us about the tendency for people to cherry-pick data, i.e. selecting only evidence that fits their pre-determined argument, rather than assessing or even accepting all the available evidence. He also critiqued the "echo chamber" that can be created in online spaces. He urged the audience to be skeptical and listen to a variety of sources, and to search out the evidence behind claims they read or hear. Prof. Helfand's talk was based on his new book, "A Survival Guide to the Misinformation Age."

Despite the clouds, graduate student Aleksey Generozov and a team of volunteers showed off the big dome and telescope. On the 13th floor, undergraduate student Richard presented movies on our 3D wall. 

-- Stephanie Douglas (graduate student)

Oct 7 - Black Hole Duet

"We did it!" says the soundbite, and while the screen fills with fireworks the lecture hall fills with applause. This is the culmination of an almost century long journey between Einstein's first postulates of general relativity to our first detection of gravitational waves last September.

Maria Charisi, graduate student and guide through the fabric of space-time, took us through the last moments of the life of a binary black hole. The LIGO project has taken almost 50 years, from the first genesis of the theory to the eureka moment of detection, to find gravitational waves. By measuring the minuscule variations in space-time, a fraction of the width of the nucleus of an atom, we can observe the ripples from distant violent collisions between black holes. Since the first detection we've found 2.9 merger events (the last one we're only 90% certain of, the other results ring clearer than a bell) and when we restart it with improvements in a few years we might find as many as 50 more.

After the main lecture Jordan Borgman took us to Tatooine, Luke Skywalker's home planet to talk about how the planets of Star Wars match up with the exoplanets we're discovering in our galaxy. Meanwhile Erin Flowers guided us through 3D visualizations of the universe on all scales.

Up on the roof, Alex Teachey orchestrated a beautiful (mostly) clear night of viewing through the telescopes. In the able hands of Richard Nederlander, Aleksey Generozov and Rose Gibson we had telescopes pointing at Mars, the Moon, and the Double Cluster.

-- Zephyr Penoyre (graduate student)

May 13 - The History and Future of Black Holes

Last Friday, NSF Fellow and future NASA Einstein Fellow Dan D' Orazio gave us an engaging tour to the long history of the most exciting and mysterious astrophysical objects. Black holes are objects with very strong gravitational pull, that nothing can escape from them. John Michell was the first to suggest the idea of such a "dark star", in the late 18th century, although this idea went almost unnoticed at the time.

The story continues in the beginning of the 20th century, when Albert Einstein conceived the general theory of relativity, a revolutionary theory to describe gravity. Dan described the early advances of the theory, including the first solution of Einstein's equations for a spherical non-spinning black hole by Karl Schwarzschild, and the skepticism that followed, mainly driven by the famous British astronomer Sir Arthur Eddington. Dan later discussed General Relativity's golden era (the 60s), with several significant contributions by many great physicists, among which the solution of Einstein's equations for a spinning black hole by Roy Kerr and the suggestion that under specific circumstances black hole can emit radiation, the so-called Hawking radiation. Dan also mentioned the history of the term black hole, which was coined in one of NASA's centers, above Tom's Restaurant in our own neighborhood.

By the early 70s, astronomers acquired the first observational evidence for astrophysical black holes with X-ray telescopes. For instance, the X-ray binary Cygnus X-1, in the constellation of Cygnus hosts one of the most nearby black holes. Earlier in the 1950s, astronomers had discovered radio galaxies with very extended jets, which later realized that can only be powered by supermassive black holes, i.e. black holes with a million to a billion times the mass of the sun. A supermassive black hole resides in the center of our galaxy as well and was discovered by detailed observations of the motion of stars in the close vicinity of the galactic center. Dan finished this exciting journey of discovery by describing the most recent breakthroughs, such as the numerical solutions of Einstein's equations 10 years ago and the first direct detection of gravitational waves of two merging black holes by Laser Interferometer Gravitational Observatory (LIGO), just 3 months ago. Even though, so far we had strong evidence for the existence of black holes, the LIGO event serves as the first direct confirmation of black holes.

Unfortunately, due to bad weather stargazing was not possible. However, the audience had a chance to join tours of the Rutherfurd Observatory on the roof of Pupin, lead by graduate students Steven Mohammed and Steph Douglas. Additionally, undergraduate student Richard Netherlander, guided the audience to the majesty of the cosmos through the projections of 3D movies, while, at the lecture hall, Andrew Emerick presented a mini-lecture on reionization and showed a mesmerizing movie about the end of Dark Ages.

-- Maria Charisi (graduate student)

Mar 4 - The Gas that Fills Invisible Space

How do show something that's invisible? How can we view, model and understand those parts of our universe which are beyond the scope of our senses? How can we use a grad's students unwavering desire for pizza to explain our galaxies inexorable gas guzzling?

Yong Zheng took us on a journey from waking up and rifling through the fridge to building a massive galaxy by throwing swirling disks of stars and gas together. With delightful hand drawn cartoons and a many laughs she showed us that there's much more to the Milky Way than meets the eye, and by examining electromagnetic waves way out of the spectrum our eyes can see we can infer the private life of gas streaming in and out of galaxies. Culminating in beautiful films from the Illustris simulation she invited us to consider what interesting and varied information may be hidden just out of sight.

Afterwards Stephanie Douglas, gave a short talk on how clusters of stars passing near the milky way are ripped apart into long thin streams that we see cutting across the night's sky. Our 3D wall was showing off everything beautiful movies on topics ranging from the surface of our sun to collisions between galaxies. Patchy clouds and technical issues made observing tricky, but those who persevered were able to peer at the Orion Nebula and Jupiter using portable telescopes on campus. The roof was also open for tours but sadly conditions made it impossible to view the sky through it.  

-- Zephyr Penoyre (graduate student)

Feb 19 - Ripples in Spacetime

A record crowd packed into the lecture hall tonight to hear Jillian Bellovary talk about gravitational waves and how to detect them. Jillian's research focuses on supercomputer simulations of supermassive black hole binaries, but her presentation focused on much less massive binaries like those whose merger was detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in September. Gravitational waves are very small distortions in spacetime caused when massive objects are accelerated to high speeds. The distortions measured by LIGO were smaller than the radius of a proton -- and those were caused by two ~30 solar mass black holes merging together. Jillian showed simulations of how these ripples in spacetime are created by the two merging black holes.

Jillian also described how LIGO was able to detect these tiny distortions. LIGO is an interferometer, meaning it measures how light waves interfere with each other (either adding together or canceling each other out) after they travel a very long distance in two perpendicular directions. How the interference pattern changes with time tells LIGO scientists how the distance is changing in each direction. If the "arms" of the interferometer lengthen and compress in a particular pattern, then they know they've detected a gravitational wave!

The sky was cloudy, but graduate students Adrian Price-Whelan and Lauren Corlies, along with undergraduates Amanda Quirk and Cierra Coughlin, showed off the Rutherfurd Observatory. Meanwhile, undergraduates Richard Nederlander and Tze Goh screened short films on the 3D Wall. In the lecture hall, volunteers Stephanie Douglas, Maria Charisi, and Danielle Rowland played videos from PhD comics and from members of the LIGO team at CalTech, and answered audience questions about gravitational waves.

--Stephanie Douglas (graduate student)

Jan 29 - BLAST!

Our first event of the year didn't exactly go as planned as our scheduled screening of BLAST! was plagued by technical difficulties. On the other hand, a thoroughly overcast day miraculous cleared up right as our stargazing began so what might have otherwise been a disappointing night turned into one of the better observing sessions we've had this winter! Led by graduate student Yong Zheng, astronomers on the roof had telescopes pointed at the Orion Nebula, Jupiter and the Galilean moons, and the Pleiades star cluster. On the indoor side, undergraduate Gladys Velez-Caicedo, ran our 3D Wall for a packed house.

For those interested in seeing what actually happened with the BLAST experiment, we hope you'll give us another chance and come see us over the summer for our Film & Stargazing series. We will reschedule our screening of the film then (and will bring every back-up system ever invented).

Thanks to everyone who came out for their incredible patience throughout the evening.

-- Summer (Director of Outreach)

Nov 13 - The Dark Matter of Ghost Galaxies

Multiple galaxies are reported missing from around the Milky Way. The cops have no leads on where to find the missing satellite galaxies. The government is keeping tight lipped. Only one investigator, Jana Grcevich, has any clues to offer on where they have gone.

Dwarf galaxies hold the secrets, and dark matter is the prime suspect. Looking at the stars in these galaxies we can work out that there's less dark matter in their centers than we expect. After deep investigation (and at least one car chase) Jana believes that this can explain why we're not seeing these satellite galaxies, and what their absence can tell us about dark matter and our galaxy.

As well as this packed talk, witnesses enjoyed some hair raising on stage demonstrations of what happens when you crash the most massive galaxies in the universe together by Zephyr Penoyre. They we're able to explore the cosmos even deeper with Shy Genel leading them through a 3D exploration of the hearts of stars and the far edges of the galaxy.

And those who braved the cold and the clouds were rewarded with some stunning views of the Pleiades, Double Cluster, Capella and many others, as our brave team of student volunteers ducked and dove between the clouds, under the steady guiding hand of Steven Mohammed.

-- Zephyr Penoyre (graduate student) 

Oct 30 - Re-tuning the Hubble Diagram

Our lecture this past Friday was by Columbia Astronomy graduate student David Hendel entitled "Re-tuning the Hubble Diagram".  David used stunning Hubble images to demonstrate the diversity in galaxy shapes and discuss how astronomers classify them. He then went on to discuss why this organization, the Hubble Tuning Fork, can be misleading and how galaxies can be transformed from one classification to another.

After the lecture, some stayed for a lecture on our Local Group by Lauren Corlies and Mihir Kulkarni and Richard Nederlander ran the 3D wall and a discussion on stellar structure. Up on the roof, the weather was great for observing. Yong Zheng led volunteers Emily Sandford, Alex Teachey, Aleksey Generozov and Zephyr Penoyre in pointing the telescopes at double star Albireo, the Double Cluster, and the elusive Andromeda Galaxy.

Overall, it was a great way to kick off the Halloween weekend.

-- Lauren Corlies (graduate student)

Oct 16: Observing Variable Stars

Stella Kafka, Director of the American Association of Variable Star Observers (AAVSO), gave a dynamic talk on variable stars, terming them "the good, the bad, and the explosive". Good variable stars show very regular periodic signals that can be directly tied to physical processes - like stellar pulsations. Bad variable stars have messier variability, such as star spots rotating in and out of view as they evolve. Finally, some stars explode and suddenly brighten by orders of magnitude. They may explode once (supernovae) or experience smaller surface eruptions (classical novae).

The AAVSO has been collecting data on variable stars for over a hundred years since its founding at the Harvard Observatory in 1911. They are an organization of amateurs who observe variable stars, and their data contributes to professional astronomical research. Even interested members of the public without telescopes can contribute (website).

After Stella's talk, undergraduate Tanay Bhandarkar showed recent pictures of Pluto from NASA's New Horizons mission. Post-doc Shy Genel presented movies on the 3D wall. The team on the roof, led by graduate student Yong Zheng, were mostly thwarted by clouds, but managed to briefly observe the Pleiades.

-- Steph Douglas (graduate student)

Oct 2: The Glorious Past of Our Monster Black Hole

Last week, physics graduate student and NASA fellow, Shuo Zhang, introduced us to the monstrous black hole in the center of our galaxy. It is well established that every massive galaxy hosts a supermassive black hole in its center and Milky Way is not an exception. Astronomers analyzing the orbits of stars in the galactic center, enabled by advancements in observing technology, realized that the only feasible scenario for the dark object in the center is the galaxy is a black hole with mass of a few million times the mass of the sun.

The black hole is known as Sagittarius A-star (SgrA*), since it is located near the border of the constellations Sagittarius and Scorpius. Being the closest supermassive black hole we can observe, SgrA* is of great astronomical interest. But is it a typical black hole? SgrA*, is one of the quietest supermassive black holes among all the nearby galaxies. However, that wasn't always the case. Recently, the Fermi Gamma-ray Space Telescope discovered a bubble of gamma-rays surrounding our galaxy, which indicate that 2 million years ago, the black hole was very active, swallowing gas and expelling in at large distances. 

Shuo also mentioned her own work observing the black hole at the center of the galaxy with an X-ray telescope called NuSTAR (a NASA mission, in which Shuo's research group here at Columbia was a major contributor). Shuo observes sporadic X-ray flares, which last for a few seconds. During these flares the black hole becomes hundreds of times brighter and then returns to its quiet state. The origin of the flares is still unknown and it has been suggested that we observe the heated remnants of an asteroid that was ripped apart by SgrA*.

Unfortunately, the weather did not cooperate to allow stargazing. Whoever stayed after the lecture had a chance to see 3D movies of the galaxy lead by undergraduate student Richard Nederlander, or hear a short presentation by graduate student Emily Sanford, about the exciting discovery of water on the surface of Mars.

-- Maria Charisi (graduate student)

May 8: “Al Otro Lado del Espectro” (At the Other Side of the Spectrum)

Our last public outreach night of the semester took place on May 8th and it was a very special one since it marked the first Spanish-speaking outreach event in many years. The whole event was conducted in Spanish, including announcements, the presentation, and the activities that took place afterward. It was a mixed audience, consisting of regular attendees, people interested in practicing their Spanish, and Spanish-speakers in the community.  

Alejandro Núñez, a graduate student in the Astronomy Department at Columbia University, gave a talk titled "Al Otro Lado del Espectro" ("At the Other Side of the Spectrum"). Alejandro started the talk by describing the wave nature of light, and introduced concepts such as frequency and wavelength. Then he showed several spectacular images of celestial objects at different wavelengths, starting from the long-wavelength radio waves, all the way to the short-wavelength gamma rays. He included many images of the Sun, other planets, and our Milky Way.  He concluded by showing us the different telescopes capable of observing the different parts of the electromagnetic spectrum.

After the talk, many audience members went to the roof to see Jupiter and M3 through the telescopes, where they had the opportunity to talk with the Spanish-speaking volunteers.  Some  attendees stayed in the lecture hall asking Alejandro a few more questions. In addition, undergraduate student Gladys Velez-Caidedo  showed several movies on the 3D wall.  It was a good turnout and we expect to have similar events in the future.  

-- Ximena Fernandez (graduate student)

Apr 24: Galactic Synthesizers

Tonight Adrian Price-Whelan, Columbia graduate student and National Science Foundation fellow, showed us how he has used simulated galaxies to compose original music. First, he had to describe the basic shapes of galaxies an how stars move inside them since the motions of stars are the basis of his method. Starting with spiral galaxies, we heard about their three main components: a flattened disk of stars moving in orderly, almost circular orbits around the galactic center, a spheroidal bulge at the center of the disk where stars move in every direction with nearly random orientation, and an outer halo which surrounds the disk and spheroid, spanning an enormous volume but containing only 1% of the stars. The shapes of these spiral galaxies were contrasted with that of ellipticals, which are generally more "bloby" and whose stars move mostly with random orientations which are quite unlike the most prominent largest components of spiral galaxies, the disks themselves. Despite their relative featurelessness, ellipticals are typically triaxial - that is, they have different extents in different directions, which leads to a variety of orbits with different shapes including long-axis tubes, short-axis tubes, and box orbits. 

To turn galaxies into synthesizers, Adrian built a computer model of a galaxy of each type and populated them with stars. Each star moves with specific frequencies, both in and out from the center of the galaxy and around it; these frequencies were mapped onto scales, with low notes corresponding to short-axis tube orbits of the elliptical galaxies and halo stars of spiral galaxy, mid-tones made by the disk and long-axis tube stars, and high notes produced by box orbits and stars in the spheroid. As the simulation advances the stars ring their notes in a manner similar to plucking a guitar string, while encoding actual physical information about the shape of the galaxy they orbit in to sound. You can listen to his compositions over on Soundcloud: spiral galaxies, elliptical galaxies.

Following Adrian's talk, Columbia graduate student Emily Sandford presented some slides describing variety of Earth-Sun-Moon arrangements and how they lead to solar and lunar eclipses, which then smoothly transitioned into a discussion of the Kepler space telescope since it uses a very similar principle to find planets around other stars - it precisely measures the dimming caused by an extra-solar planet passing between its host star and the Earth. Upstairs, undergraduate Gladys Velez-Caidedo and post-doctorate researcher Shy Genel ran the 3D wall, illustrating a wide variety of astronomical phenomena.

-- David Hendel (graduate student)

Feb 27: Neutron Stars

This past Friday, Slovko Bogdanov, a research scientist at Columbia University, gave a great talk telling us all about neutron stars. While stars are kept from gravitational collapse by the burning of their nuclear fuel, when this fuel source runs dry, look out! The resulting supernova can outshine the light from an entire galaxy. Neutron stars are the result of this process -- when a massive star collapses, the remainder is so compact that it can fit the mass of the Sun into a star the size of Manhattan. We looked at a number of supernova remnants and learned out about the discovery of fast spinning pulsars. We also learned about an event in December 2004 where a starquake in a magnetar (a highly magnetized neutron star with magnetic fields more than 100,000,000 times stronger than anything scientists can create) released a blast of gamma-radiation so strong that it had the same ionizing effect on our atmosphere that strong solar flares do -- but from a distance of 50,000 light years. Yikes!

Afterwards, Columbia Post-Bac David Jaimes gave a slideshow on the recent Rosetta Mission, where after 10 years, we successfully landed a probe on Comet 67P. He showed us some gorgeous close up images of the comet, and described some of the science behind this amazing feat of engineering. Others wandered to our 3D-wall, where we screened several different movies showing simulations of colliding galaxies and more. Up on the roof, the skies were clear and we had clear views of Jupiter, the moon, and the Orion Nebula with our Big and Little Dome telescopes.

-- Jennifer Weston (graduate student)

Jan 30: Cosmic Stretchmarks

Tonight Princeton post-doc, and cosmologist, Renee Hlozek explained what light can tell us about the early universe. She showed us this map of light from the early universe, called the Cosmic Microwave Background, which is almost entirely uniform - the temperature fluctuations shown are only a few parts per million. But such uniformity, along with the observation that the universe appears perfectly flat, was a problem for theories about the universe's beginning.  For the temperature fluctuations to be so small, every part of the universe must have been in contact at the beginning. Renee used the example of communication across the big lecture hall - if she asks the person in the front row what the favorite band is of the person in the back corner, the front row person won't know unless she has talked to the other person. 

So scientists came up with the theory of cosmic inflation, which explains the Cosmic Microwave Background very well. But Renee also told us that scientists don't want their theories to simply explain existing data - good theories also make testable predictions for future observations.  And inflation theories predict that we should see a particular type of polarization (the orientation of light rays as they reach our detectors) that isn't produced by any other object in the universe. So if we detect that type of polarization, called B-modes, then we have good evidence for inflation!

Many experiments are studying the Cosmic Microwave Background, and last year one of them announced that they had detected B-modes, but a leaked press release for tomorrow indicates that their supposed detection was probably due to interference from dust in our Galaxy. Renee told us that this is a product of good science - the scientific method involves checking your own and other people's work, to make sure results are accurate.  Renee works on a collaboration using the Atacama Cosmology Telescope, one of many experiments studying the Cosmic Microwave Background. She showed us a picture of the telescope, and also of four women who built one of its instruments. Another instrument currently being added to ACT will also look for B-mode polarization - it may still be out there!

After the main lecture, graduate student Andrea gave a short slideshow on a few asteroids and comets that have passed by Earth recently, and undergraduate Erin showed movies on the 3D Wall.  Graduate students Adrian, Jose, and Emily, along with undergraduate Rasmi, braved an extreme wind chill to let our attendees see Jupiter and the Moon from two dome telescopes on the roof. 

-- Steph Douglas (graduate student)