December 6: Comet of the Century?

In the year after Comet ISON's detection in September 2012, many predicted that its close encounter with the Sun would produce a show worthy of the title "comet of the century".  However, as graduate student Erika Hamden showed, Comet ISON's passage was less spectacular than predicted, though no less interesting.  The comet's orbit showed that it came from the Oort cloud, a sphere of small icy bodies surrounding the Solar System.  Objects in the Oort cloud probably spend most of their time around 0.75 lightyears from the Sun, but occasionally a nearby star can perturb the cloud and send comets into the inner solar system.  Since Comet ISON came from the Oort cloud, it hadn't interacted with the Sun before and so it could provide information about the composition of Oort cloud bodies.

Erika played movies like the one above from several space-based solar observatories (i.e., NASA's Solar Dynamics Observatory, NASA's Solar and Heliospheric Observatory, and NASA's Solar Terrestrial Relations Observatory) showing Comet ISON as it approached the Sun and after its closest encounter. Astronomers had predicted that, after it passed by the Sun, Comet ISON would be very bright and spectacular to see. However, the comet broke up when it got close to the Sun.  The movies showed that some bright debris reappeared after Comet ISON passed the Sun, but it faded rapidly, indicating that the comet had fallen apart. Comet ISON was probably a loose ball of ice that was destroyed by the Sun's heat, like a poorly-made snowball that falls apart before reaching its target.  Although it was not the "comet of the century", Comet ISON provided astronomers with plenty of information about Oort Cloud comets and provided everyone with a great show.

Clouds and rain prevented any roof activities, but undergraduate Claire Ding showed 3D movies on the 13th floor, and graduate student Andrew Weis gave a slideshow of highlights of the winter sky in the lecture hall.

--Steph Douglas (graduate student)