Starry Messenger

The other night, Alec called from school. He has been pretty much incommunicado this semester, so a phone call was an occasion for some concern. Turns out he was headed back to his dorm after Marching Band practice after dark, when he happened upon the school’s astronomy club. He stopped by to chat, and was shown Comet Holmes. The club members pointed out the location for naked eye viewing and gave him a look through a telescope. He was excited and his first impulse, like ET, was to phone home.

Comet Holmes was discovered in November 1892 by (you guessed it) Mr. Edwin Holmes, a British astronomer. His namesake comet orbits the Sun once every seven years at a distance of about 200 million miles (a little over twice Earth's 93-million-mile orbit). It was re-observed in 1899 and 1906 before being lost for nearly six decades. Based on a prediction from calculations, the comet was found again in 1964.

It is a local (relatively speaking) object, reaching its farthest distance from the sun somewhere between the orbits of Mars and Jupiter. Every seven years it makes the round trip, and has been doing so for who knows how long. What makes this comet remarkable; a once in a lifetime viewing as some authorities have dubbed it, is that it periodically “erupts”. Normally a magnitude 17 object, only visible with a pretty powerful scope, it blossoms to a magnitude 3 object every 100 years or so. Magnitude 3 means it becomes as bright any star and is easily visible to the naked eye. On October 20, in less than 24 hours, it brightened by a factor of nearly 400,000 and has now up to a factor of over a million times what it was before the outburst. This is a change "absolutely unprecedented in the annals of cometary astronomy." The comet is now rivaling some of the brighter stars in the sky. When it first cooked off, some observers thought they were witnessing a super nova – an exploding star. A super nova was last seen in the galactic neighborhood around the time of Keppler and Tycho Brahe.

Theories abound as to why Holmes brightened up ("elementary Watson"--sorry, I couldn't resist), but as yet, no one has come up with anything definitive or remotely plausible. For all we know, Scottie just turned on the warp drive engines. What is amazing is that Holmes made its closest approach to the sun last May and came no closer than 190 million miles to the sun. The comet is now moving away from the sun, boggieing its way back to Jupiter. Not exactly a recipe for the typical show-off Great (notice the initial caps) comet. None the less, there it is, in the constellation Perseus.

You can see Holmes' comet almost any time this fall until it fades, when that will be is anybody's guess since we don't know how it got bright to start with. Some astronomers predict it will grow to rival the full moon in size. Go outside and find the constellation Cassiopeia. That’s the one in the North-east sky that looks like the number “3” as drawn by a first grader. (Tilt you head right and it looks like an “M”, tilt left and it’s a “W”). Find the bottom star in the group and look at about 5 o’clock. You will see a bright star in the Perseus, with a somewhat brighter star about 5 o’clock from it. This star is the top of a triangle. The bottom left star of the triangle is Comet Holmes. Look at it carefully and you will notice it is fuzzy around the edges. Binoculars bring this out even better. I set up my 20x spotting scope on the back deck and even with this relatively puny optics, I was able to see a star shining through the fuzz and the hint of a denser area in the center; the nucleus itself. Way cool.

A well-known astronomer once remarked: “Comets are like cats; they both have tails and they both go where they please.” If that is the case, then Comet 17P/Holmes must be of the Manx variety. Unlike some the so-called Great Comets (Haley on most occasions in the past thousand years, or Halle-Bop from a few years ago), Holmes does not possess a tail to speak of. Most comets can be described as “dirty snowballs,” consisting mostly of ice with chunks of rock embedded in. It may be that Holmes, with its seven-year run, has had most of the ice already ablated off the nucleus and is pretty much solid rock…or not. Like cats, comets are pretty much inscrutable.