Quite suddenly, in the northeastern skies, a fuzzy star has appeared. It isn't often that we get to see a comet without using binoculars or even a telescope, only once or twice every ten years, but we have a chance right now with the sudden brightening of Comet Holmes.
Comet Holmes is actually an old astronomical friend, having been discovered in 1892 by Britain Edwin Holmes. Since then, the comet has made sixteen trips around the Sun, but has never been so bright since its discovery. Right now, the comet is out beyond the orbit of Mars, moving away from the Sun and astronomers expected the comet to simply fade away. Comets usually brighten when they near the Sun, and outgassing begins, creating the comet's tail.
But that's not what happened with Holmes. On October 23, the comet had a major outburst and in only a day increased in brightness almost a million times! The comet never developed the traditional tail, making it look different from the naked eye comets of last decade. Rather, Comet Holmes just looks like a yellow-white fuzzball.
Astronomers are still trying to understand what caused Comet Holmes' outburst. One other outburst has been recorded when the comet was originally discovered. One theory for the outburst is that a vein of volatile ices in the comet's nucleus was suddenly exposed to sunlight.
So many trips around the Sun, and the subsequent outgassing which takes place on these trips, could have created an unstable nucleus with lots of pockets. A sudden collapse of one of these pockets could have created a tremendous amount of dust, seen as the outburst. And there could be another outburst in the near future.
Just as in any terrestrial structure collapse, there is always an attempt to reach stability, and one collapse is often followed by another in the quest for that stability. Indeed, after Comet Holme's initial outburst in 1892, there was a second only 75 days later.
The tail of a comet is one of its most recognizable features. Comte form tails as they near the Sun. Pressure from sunlight causes ices to evaporate and flow backwards away from the Sun.
But Comet Holmes has never formed a tail, or so astronomers thought. Then they studied the comet using infrared imaging. A faint tail-like structure was detected, but it was not pointing away from the Sun as astronomers would have expected.
Comet Holmes just seems determined to break all the rules!
Comet Holmes is easy to spot, even if you are troubled by some light pollution, though obviously the best views are from dark skies. The comet is now around magnitude 2.5, around the same brightness as the stars in the Big Dipper.
Viewers in the northern hemisphere can spot Comet Holmes during most of the night. The comet is in the northeast skies, between the constellations of Cassiopeia and Perseus. See our skymap for help. First, locate the distinctive "w" formed by stars in Cassiopeia and then look below that. Cassiopeia is high in the northeast sky during mid-evening. The comet will look like a fuzzy whitish-yellow tennis ball.
Binoculars will show a small yellowish haze of light around the comet. A small telescope will bring out more details.
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Kathy Miles, Author, and Chuck Peters, Systems Administrator