July 27th: Interesting Comets

Date: July 27, 2010

Title: Interesting Comets


Podcaster: Ted Judah

Description: Ted talks about comets.

Bio: Ted Judah is an amateur astronomer in Northern California.

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Interesting Comets
IYA 365 Days of Astronomy for July 27, 2010

I’m going to try to photograph a comet.

Every once in a while a fuzzy object appears in the night sky. It may look like a smudged star. If we are lucky it may grow bright enough to see with the unaided eye over a period of days to months and may it form a tail. This tail may become so long that that it extends across much of the sky. These bodies are called comets, large icy snowballs in orbit around the sun. Each comet we see began as one of the hundreds of billions of snowballs in a great cloud of icy objects surrounding our solar system far beyond the outermost planets called the Oort Cloud or in a disk of icy bodies beyond Neptune known as the Kuiper Belt. A gravitation nudge from a passing star will cause one of these bodies to move closer to the sun. As it gets closer solar energy heats it and it sheds gas and dust that forms a tail. The gas is pushed away from the comet by the solar wind. and dust from the comet is left behind in the comets orbit by solar radiation pressure. Thus comets often have two visible tails – a sunlight reflecting, yellowish dust tail and a bluish gas emission tail that reveals irregularities in the gusts of solar wind.

And so I was off to my observatory to try to photograph a comet I had read about: Comet McNaught C/2009 R1. I’ll explain the name. The name McNaught comes from the discoverer, Robert McNaught. The ‘C’ designation means that it has an orbital period greater than 200 years and has only been seen once, otherwise, it would get a ‘P’ designation for periodic. 2009 is, of course, the year it was discovered. The R1 at the end means that it was the first comet discovered in the first half of September. Had it been the second comet discovered in that period it would have gotten the designation R2. If it was the first comet discovered in the first half of January it would have been given the designation: A1. If it had been the first discovered in the second half of January it would have been B1. First comet in the first half of February, then: C1. And so-on through the alphabet except that the skip the letter I and they don’t use Z. Really, this is true – I’m not making this up.

A dozen or more comets can be detected in the sky at any given time, but most are so faint they can be seen with only large telescopes. Every few years acomet appears that can be seen with the naked eye. Bright comets that reach 1st or 2nd magnitude come along about every decade or so.

But one never knows what comets may do. They may suddenly brighten. Case in point: in 2007, on the night of November 3rd, I was casually scanning the sky with binoculars from my backyard when I spotted a ‘fuzzy star’ in Perseus. It didn’t look familiar and a quick check of my sky atlas showed that there were no object in that area. I ran inside and excitedly told my wife that I just might have discovered a comet. But after a quick internet search it became apparent that this particular comet had already been discovered by a guy named Holmes – in 1892! So much for comet Judah! Comet Holmes 2007 visit was interesting in how it dramatically and rapidly brightened nearly a millionfold in less than 24 hours. To me, it resembled a giant space jellyfish. It briefly became the largest single object in the solar system. I’ll repeat that – Comet Holmes briefly was the largest single object in the solar system, as its coma (the thin dissipating dust ball around the comet) expanded to a diameter greater than that of the Sun although the nucleus was only 2 miles across. 17P Holmes will next reach Periheliion in March of 2014.

Most of you likely remember Hale Bopp in 1997. I remember clearly seeing it over the bright city I was living in at the time. There was an especially memorable warm, summer night when we had a bloody red, total lunar eclipse sharing the sky with this bluish, double-tailed comet. Some claimed that there was a UFO following the comet and later, the Heaven’s Gate cult members committed mass-suicide allegedly as a way of hitching a ride on the comet to there next lives.

Comet hysteria is nothing new. In 1910, Haley’s Comet made a reappearance during it’s 75.3 year orbit and the new science of spectroscopy detected cyanogen gas in the tail of the comet. Earth, it was incorrectly reported, was supposed to pass right through the Haley’s tail. A few careless astronomers of the day were quoted by the New York Times as saying, “This could be the end of life on our planet.” A portion of the public was convinced the Earth would be bathed in a cloud of poison and many gas-masks were bought and sold that year. Haley’s comet returned in 1986 and we sent a spacecraft to greet it. It will return again in July of 2061. I hope my eyesight is still good when I’m 92!

Comets on rare occasion strike planets. In 1994 Comet Shoemaker-Levy 9 broke apart and it’s pieces slammed into Jupiter. This type of event possibly less rare than we thought as an impact scar like the ones left after Shoemaker-Levy 9 appeared on Jupiter again in July 2009.

With advanced robotic telescopes regularly making comet discoveries it seems to be becoming increasingly more difficult for an individual astronomer to discover a new comet. But that doesn’t mean you shouldn’t try. A standard method of searching for comets is to sweep the sky with large binoculars and note any fuzzy objects you find. Check them against a star chart to make sure it is not a mere galaxy or nebula and then keep track of it to see if it moves. If you think you have found a comet send the information to the
Bureau for Astronomical Telegrams of the International Astronomical Union. If they decide you have found a comet, they will give it your name!

Happy Hunting!

End of podcast:

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One Response to July 27th: Interesting Comets

  1. Keith July 27, 2010 at 6:32 pm #

    Not bad information about comets, but unfortunately hit one of my pet astronomical peeves. The most famous comet of all is Halley’s Comet, named after Sir Edmund Halley, not Hailey’s comet, named after Bill Hailey and the Comets. The pronunciation should be more like “Hall – ee’s” or “Hal -ee’s”. A major outreach such as this podcast needs to get the correct word out to the public!

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