At a family reunion Saturday night outside of Bastrop, I took a break from the festivities to step outside and spend some time with our dog, Ginger, who unfortunately was not invited inside.
It was a clear night, and where we were, the skies were relatively free of light pollution, so my eyes naturally went up to the sky. The most open view was towards the north, so I found myself staring at the familiar stars of the constellation Perseus. I've been intimately familiar with the star patterns of the night sky since I was a little kid, so I quickly recognized what I was looking at. For us northern hemisphere residents, Perseus is a dramatic constellation, in the plane of the Milky Way galaxy, and thus populated with numerous relatively bright stars.
Something was bit amiss, that night, however. Just outside of the familiar pattern was a bright fuzzy "star" that was not familiar to me. It was just about as bright as the stars in the main constellation, so I was puzzled why I had not noticed it before. I've not paid nearly as much attention to the night sky and other astronomical phenomena in recent years -- perhaps my memory was playing tricks on me? Its distinct fuzziness also made me think my contacts were not focusing properly. But other stars seemed fairly crisp, so that couldn't be the issue.
Could this be one of Perseus' bright clusters, thus explaining its fuzziness? If so, it was brighter than others that I remembered well, and I would be extremely embarrassed to forget about so bright a cluster. I'm not that old yet.
I stared at the fuzzy unfamiliar "star" for several minutes, pluging the depths of my memory, but just could not dig up anything. I then decided to retrieve my binoculars from the car. That would settle once and for all the question of the stars' blurred appearance.
Sure enough, in the binoculars, the fuzzy star appeared even fuzzier, even as the uncountable number of other stars appeared as sharp as ever. Something was up. I knew there was no cluster in this spot, certainly not one anywhere near this bright. That would be one of the brightest clusters in the sky and would be impossible to forget. By process of elimination, I determined that this had to be some sort of comet.
There was no hint of a tail, but that wasn't that unusual, in my experience -- comet tails can be much fainter than the head. Quite an exciting find, given that I had no prior clue of its presence, thanks to my lack of attention to events in our neighborhood of the Solar System.
Sure enough, after we returned home to San Antonio, when I looked up 'comet' in Google News -- figuring that any comet as bright as the one I saw would be big news -- here is an example of what came up (from New Scientist):
Dazzling comet outburst continues to mystify
The comet that suddenly became about a million times brighter nearly two weeks ago continues to "shine" with abnormal luminosity, leaving observers puzzled over what caused the outburst and whether the comet will perform an encore in the coming months.
Comet 17P/Holmes is normally an invisible runt of a comet, about 3.3 kilometres across and about 25,000 times too faint to be seen with the naked eye.
But following its sudden brightening on 23 October, the comet's coma, a surrounding shell of gas and dust, has been expanding at a rate of about 0.5 kilometres per second, making the comet appear as a fuzzy "star" that can be seen with the naked eye in the constellation Perseus (see image at right and watch a video of dust streaming off the comet's icy body, or nucleus).
The comet was actually discovered during a similar, but less spectacular, brightening event in November 1892. It faded after a few weeks, only to dramatically brighten again in January 1893.
The comet orbits the Sun every seven years on a path that takes it from the distance of Jupiter's orbit to about twice that of Earth's. Interestingly, in both the 1892 event and the recent one, the comet initially brightened about five months after reaching perihelion – its closest approach to the Sun.
"It's curious that the outburst came in the same period of orbit," says Brian Marsden, former director of the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics in Massachusetts, US. "It will be interesting to see if it behaves in the same general way [this time as before]."
The common timing of the two mega-outbursts following perihelion suggests that the intensity of the Sun's radiation is a key factor in the brightening. But that alone is not enough, as the comet reaches perihelion every seven years and hasn't produced such an outburst in 115 years. There are also plenty of comets that make closer approaches to the Sun than Comet 17P/Holmes without brightening nearly as much.
So go out on a clear night soon, look to the northeast and you, too, can see the new, and very unusual, comet. It's the brightest one we've had since Hale-Bopp back in 1997, but very different.
UPDATE: Predictably, Sky and Telescope has an excellent account of this comet and how to see it.