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) 

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)

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)

Dec 4 - On the Care and Feeding of Black Holes

Aleksey Generozov, a 4th year PhD student in the astronomy department, introduced us to the majesty of black holes. Black holes are regions in space-time, where gravity is so strong that nothing (particles or even light) can escape from inside; we could make a black hole if we squeezed the entire earth into the size of our fingernails.

Aleksey next described the discovery of a supermassive black hole at the center of our galaxy, the Milky Way. Observing the orbits of stars very close to the galactic center, with very high precision, astronomers concluded that an object very massive (with mass a few million times the mass of the sun) and very compact (that would fit in a sphere with radius smaller than the radius of our solar system) must be hidden in the galactic center. The only feasible explanation was a huge black hole. These days, we are actually on the verge of seeing the radius of the black hole (the event horizon), with a network of radio telescopes positioned around the globe.

And although the black hole at the center of our galaxy is relatively quiet, this is not the case for every galaxy. In the '60s, astronomers discovered some very bright radio sources, equally bright as some nearby stars, which they named quasars (quasi-stars). Later, when the size and distance of these objects were measured, it was realized that the enormous amount of energy is produced when gas falls onto a supermassive black holes at the center of a very distant galaxy. The gas is brought to the central black holes, when two galaxies collide. This also explains why our own supermassive black hole is quiet; It's starving! However, there is some evidence from observations of very high energy photons, that our own black hole had a more spectacular past. The talk concluded with Aleksey and the audience singing along "twinkle-twinkle quasi-star".

After the lecture, the audience had the chance to hear about the K2 mission, which is the second phase of NASA's Kepler space telescope, lead by graduate student Stephanie Douglas. Moreover, they had a chance to further explore galaxies and black holes by watching 3D movies, guided by undergraduate Briley Lewis. The clear sky and the mild temperature gave us a wonderful opportunity for stargazing on Pupin's roof with the help of Adrian Price-Whelan, Emily Stanford, Daniel De Felippis, Rasmi Elasmar, and Richard H Nederlander. Attendees were treated to views of the Andromeda Galaxy, the Pleiades star cluster, and the Red Giant Betelgeuse.

-- Maria Charisi (graduate student)

Nov 7: Juggling with Black Holes

This week, Hubble Postdoctoral Fellow Andreas Kupper described the dynamics of multiple massive objects in the same system.  When two massive objects are near each other, they exert gravitational forces on each other and their motions can be described analytically - that is, the motions at all times can be calculated by hand from basic theories.  When three or more massive objects interact gravitationally, the interactions become complicated and can only be modeled using computer simulations. Andreas showed the results of a few of his simulations - after the objects orbit chaotically around each other for a while, one object (usually the one with the lowest mass) is thrown out of the system with a very high velocity.  The remaining objects end up closer together, and this process, called scattering, is thought to be responsible for bringing massive objects like black holes and neutron stars close enough together that they can merge into an even more massive object. 

After the lecture, audiences were treated to a showing of LIGO: A Passion for Understanding, a 20 minute film about a project to detect gravitational waves coming from closely interacting massive objects.  After the film, graduate student Aleksey Generozov and I answered questions about gravitational waves and LIGO.   Graduate student Yong Zheng was the roof captain, sharing glimpses of the Moon, Albireo and the Ring Nebula while undergraduate Pratishta Yerakala took attendees on a 3D tour of the Universe with the 3D wall.

-- Steph Douglas (graduate student)