March 15, 2013 Comments Off on Comet PANSTARRS

Looking up in the heavens can provide inspiration this week. The appearance of Comet PANSTARRS is a once in a lifetime event that you might want to take advantage of given an opportunity on a clear night. This new comet was discovered in June of 2011 by the PANoramic Survey Telescope And Rapid Response System atop the Haleakala volcano in Hawaii, and is expected to have a complete orbit around the sun of 110,000 years- so take advantage now! It is expected to be visible for the next couple of weeks just after sunset in the western sky. For the folks out there who know their constellations it will be just below Pisces and left of Pegasus and close to the horizon. Regardless of whether you can see it comets are fascinating celestial events.


Figure from for Finding Panstarrs

Comets are often called “dirty snowballs” because they are masses of stuff left over from the creation of the universe and frozen together with ice and other frozen material and coated with dark organic matter. They range in size from several feet across to much larger. The well known periodic comet, Comet Halley which appears every 76 years is thought to be about 8 miles across. Comets with their individual stockpiles of water and organic matter may well have been a source for organic matter during the early phases of Earth’s development, and NASA scientists have documented that materials from meteorites can contain DNA and RNA component parts. Meteorites are often pieces of asteroids and comets.

The Comet Panstarrs is about 100 million miles from Earth, so we are in no danger at all of it hitting the Earth. It is thought to have originated in the Oort Cloud and followed a path that took millions of years to get within the inner solar system where we can now see it. The Oort Cloud is in the far reaches of our galaxy and consists of billions of comets in orbit around the sun in a round cloud that is roughly 50,000 times further from the sun than the Earth. The Oort Cloud usually produces comets that remain in huge orbits around the sun, so seeing them is not likely to happen again, these are called non-periodic comets.  The Kuiper Belt which is much closer than the Oort Cloud usually produces the comets that become periodic comets like Halley’s Comet which have orbits of less than 200 years.

Most comets have what seems to be a fairly mundane existence without a whole lot of change under normal circumstances, it’s only when they get close to the sun that things start to happen. A comet has a nucleus which is usually no bigger than a few kilometers in diameter. As a comet nears the sun they develop an atmosphere which is called a coma. These can be significantly larger than the nucleus, up to hundreds of thousands of kilometers across. Sunlight and solar wind traveling from the sun forces the coma around and behind the nucleus to form a tail always pointing away from the sun. Often dust materials break off of the comet as it gets farther away from the sun and this material becomes random leftovers floating in space. If Earth happens to travel through one of these piles of leftovers, we are treated to a meteor shower, which is really nothing more than leftover comet dust.

Scientists have a difficult time predicting exactly how comets will behave. We know they appear and that they develop distinctive features but it is difficult to predict for example exactly how bright they will be. Scientists have suggested that Comet Panstarrs could be as bright as the stars in the Big Dipper, and that this likely occurred when it was closest to the sun, a mere 28 million miles or so on March the 10th. For approximately 10 days beyond March the 10th it will appear a bit higher in the sky each day- but is also likely to lose brightness with each passing day. One source reported that as of January 2011, we know of approximately 4,185 comets. 484 of these are periodic or short period comets, 1,500 are known as sungrazers which pass so close to the sun that they frequently break up into smaller pieces or disintegrate altogether. The remainder are chance encounter comets likely originating from the Oort cloud, having those far reaching orbits that are unlikely to be seen again like Comet Panstarrs

In 2013, we are expecting to be treated to two more comet shows after Comet Panstarrs fades into the distance again. Comet Lemmon is expected in early April, but not expected to be very bright or easy to see. The main event could be Comet ISON which should appear in November. Some scientists have predicted that this could be as bright as a full moon in broad daylight. Others are more cautious and warn that nothing is ever certain with predicting what will happen with a comet, and say that such predictions are likely to be largely overblown. Only time will tell, so stay tuned for Comet Ison, and in the meantime, see if you are able to spot Comet Panstarrs! So far weather has frustrated my attempts at seeing it- but I will keep trying

These updates are made possible by a generous donation from David and Rosemary Good.