Comets in the sky like diamonds

With not one but two bright comets visible in the next year, 2013 is projected to be an exciting year for stargazers.

About once every decade a comet comes along bright enough to be seen in the sky with the naked eye. This year proves to be an exception: 2013 has been dubbed “The Year of the Comet”.

Astronomers are predicting that at least two comets will be entering the inner solar system this year and have the potential to be “Great Comets”, or in layman’s terms, comets that are exceptionally bright and easily visible.

Etienne Rollin, a physics laboratory supervisor at Carleton University describes comets as “extremely dirty snowballs”. Comets are essentially large clusters of ice, snow and dirt. Rollin uses his fist to represent the Earth and his other hand to rotate in circles around it as he describes a comet’s orbit.

“They come from the outer solar system and enter the inner solar system where they get very close to us and the sun so their orbit is elliptical,” says Rollin. He notes that as the comet gets close to the sun, some of the water in the snow and ice gets transformed into gas and vapour so the visible tail  trailing the comet is actually a reflection of sunlight onto this vapour. However, this makes it difficult to predict which comets are going to, in turn be “Great Comets”.

“Sometimes the comet is dirtier than we thought and has less water so there is less to become vapour,” says Rollin.

A snapshot of the C/2011 L4 Pan-Starrs comet taken early evening on March 18, 2013 by Etienne Rollin. Though the comet is invisible to the naked eye it can be seen quite clearly using binoculars and can be observed in the evening for the remainder of March 2013.

One of these expected “Great Comets” is currently visible in the sky. Technically this comet is titled C/2011 L4 but has also been named Pan-Starrs after the Panoramic Survey Telescope and Rapid Response System, an array  of astronomical cameras and telescopes in Maui, which discovered the comet.

For those surfing the Internet, it’s currently swimming with pictures of the Pan-Starrs comet, vivid against either a day or night sky.  But for Rollin seeing the comet first hand has been lacklustre.

In addition to his academic duties, Rollin hosts astronomy nights using the Kessler Observatory atop Carleton’s Herzberg building. So far, he says that the Pan-Starrs comet has been “disappointing”. But he doesn’t feel that this means the predictions for this comet were wrong.

Sitting in his office surrounded by tacked-up  pictures of planets and the moon , he explains, “I’ve seen it but in the evening it gets cloudy so seeing the comet itself hasn’t been easy. It’s nothing compared to the Comet McNaught (C/2006 P1)  I saw in 2007.”

An image of Comet McNaught, visible to the naked eye, taken at Carleton University’s Kessler Observatory as it passed throughout the Ottawa sky just after sunset in early January 2007. It was the brightest comet seen since 1965.

He has higher hopes for the comet ISON (or C/2012 S1, named after the International Scientific Optical Network) which is projected to shine brighter than the moon. This comet is set to be visible in November and December of this year. Rollin says this is ISON’s first pass around the sun so astronomers are expecting it to be very bright, perhaps even the most impressive comet in the last 100 years.

“ISON would have been kicked out of the Oort cloud that surrounds our solar system, it’s where we think holds a lot of comets,” says Rollin. “Sometimes comets are kicked out of the cloud because of a collision or because of gravitational pull.” Either way, they can last several orbits and Rollin hopes that ISON proves to be a comet like that.

Comets usually melt or dissipate every time they pass the sun until they don’t exist anymore but there are more ways for a comet call it quits.

“Some survive for thousands of years before they are over,” Rollin explains. “Some of them will just crash into the sun if they have the correct orbit.”

Could a comet ever crash into Earth? Rollin says that it is possible all the water on Earth is a result of comets crashing into it billions of years ago. However he thinks it is not something that should be of concern yet.

“Comets? I don’t think we ever observed a comet crashing into any close planets … yet,” says Rollin. And with a smile adds, “That would be great, to see something like that.”