Friday, October 17, 2014

Oct 10: Explosive Lighthouses

This week, Columbia Astronomy's 4th year graduate student, Maria Charisi, gave a talk on gamma-ray bursts, or GRB for short. Gamma-rays are a kind of electromagnetic wave, like optical light, but with very short wavelengths, even shorter that of X-rays.

Maria started by telling us the history of how GRBs were discovered. The first GRBs were found by detectors which were built to detect nuclear explosion on the Earth during the Cold War. However, scientists found no correlation between these events and any nuclear explosions on the Earth. So this problem was passed assigned to astronomers to find out if they were related to any astronomical events. At first theorists proposed many mechanisms for GRBs, from neutron star collisions to alien space wars. Astronomers also argued about the location of these events. Some believed they were galactic; others believed they were cosmological. The varieties of theories and beliefs were due to the fact that the location distribution and distance of the GRB events were still unknown. With the launch of the Compton Gamma-Ray Observatory in the mid 90's and the Swift Gamma-Ray Burst Mission in the early 21st century, and with the red-shifts measured from spectra, astronomers finally concluded that GRBs are extremely luminous events that happen all over the Universe. 

Maria then described findings from more recent studies on GRBs. GRBs only last for a short time in the gamma-ray band, but astronomers believed there should be afterglows in other wavelengths, just like charcoals will glow as a fire burns out. They did follow-up observations of GRBs in the optical and infrared bands and found evidence of these afterglows. From the duration distribution of the bursts, astronomers split the GRBs into two different categories: short bursts which lasts less than 100 seconds, and long bursts which last a few hundreds seconds. 

The physical image of GRBs is still not clear today. One of the most widely believed theories is that when two compact objects collide, for example a neutron star and a black hole, tremendous energy is produced and ejected from two jets. If we happened to be in the line of sight of these jets, we would detect a GRB.

After the lecture, graduate student Jingjing Chen showed the first half of a PBS movie called 'Alien Planets Revealed' which discussed transit method of detecting exoplanets used by the Kepler mission. Unfortunately, the weather was not good for stargazing, so graduate students Jeff Andrews and Aleksey Generozov gave tours of the Rutherfurd Observatory instead while undergraduate Erin Flowers and post-doc Robyn Sanderson presented a variety of astronomical phenomena with the 3D wall. 

-- Jingjing Chen (graduate student) 

Tuesday, October 7, 2014

Sept 26: The Inconstant Moon

This week Columbia Astronomy's own outreach director, Summer Ash, discussed the many ways in which the Moon, frequently taken for granted in our night sky, can exhibit surprising and complex dynamics due to its complicated relationship with the Earth. After reminding us of the most well-known variation, lunar phase, she described the months - all six types!

Moving on from illumination effects, Summer described the many ways the orbit of the Moon around the Earth affects how we see it. Since its distance varies, sometimes it seems larger and brighter in the sky that others; this is the origin of the "Super Moon." Additionally, its orbit makes a small angle with the plane of the Earth-Sun orbit, which is why we don't experience eclipses at every new moon. Speaking of eclipses, she reminded us that total eclipses, where the moon completely enters the shadow of the Earth, are the ones you really want to get out of bed and check out. The Moon's red color during such an eclipse is due to the Sun's light being scattered by the Earth's atmosphere, the same reason the Sun looks red-orange at sunset: only red light can make it straight through!

If you were unable to attend the talk, or would like to read more, Summer wrote a blog piece on this same topic which you can read on Starts With a Bang.

After the lecture, graduate student Yong Zheng lead a lively discussion of the Milky Way's gas dynamics while Pratishta Yerakala demonstrated a variety of astronomical phenomena at the 3D wall and Adrian Price-Whelan, Jose Zorrilla, Emily Sandford, Maria Charisi, and Aleksey Generozov ran stargazing from Rutherfurd Observatory atop Pupin Hall. Objects targeted included the Ring Nebula, the Andromeda Galaxy, the Double Cluster and the beautiful visual binary star Albiero

-- David Hendel (graduate student)