DaytonDailyNews.com

Comet 17P/Holmes is doing something of a return engagement in the night sky.

The comet that until Oct. 23 had to be found with a telescope suddenly began brightening and now can be seen with the naked eye.

The same thing happened 115 years ago in November 1892 when Edwin Holmes, an amateur astronomer in England, was the first to spot the comet.

"This kind of sudden ejection of dust and gas from a comet is not unusual," said Wittenberg University's Dan Fleisch, an associate professor of physics. "Our current understanding is that this occurs when solar heating warms the surface as the comet approaches the sun. That heating can vaporize icy material, sometimes explosively, and brightness flare-ups are the result."

Still, there is a difference with Comet Holmes.

"What's unusual about Holmes is that this flare-up is occurring as the comet moves away from the sun, well past the time of maximum solar heating. Why that's happening at this point in Holmes' orbit is a mystery."

For Fleisch, it's just another example of the wonder of the universe.

"'How much we don't know about the universe' is a fairly constant thought in astronomy circles," Fleisch said. "As is, 'Given that we're dealing with a universe of objects that are unimaginably distant and exotic, it's amazing how much we've been able to learn about these objects using only our brains and the tools we build to observe them.'"

Comet Holmes does appear different than other comets in that there is not a long tail.

"The thing to remember about comets' tails is that they point away from the sun, not necessarily behind the comet," Fleisch said. "So on the outbound leg of a comet's journey, the tail actually leads the comet.

"In this case, the Earth is roughly between Holmes and the sun, so any tail that forms will point away from us, and we'll be looking more or less along the tail. Hence it's not surprising that Holmes isn't showing a long tail, although the latest images suggest that one may be forming."

How to find the comet

Face northeast.

Look for the constellation Cassiopeia, which is shaped like a "W."

Look below the "W." The brightest star you can see is Mirfak in the constellation Perseus. Mirfak is the top star of a triangle. The triangle's lower-left corner is Comet Holmes. The later in the day you look, the higher Comet Holmes will be in the sky.