Returning Comet Holmes
Dazzles Sky Watchers
Locating Comet Holmes: First, find Cassiopeia in the northeast, then find Comet Holmes
Alittle-known comet is causing quite a stir during its visit to the inner solar system.
The dim comet, called Comet Holmes, brightened unexpectedly over just a few hours in mid-October 2007, catching astronomers by surprise. The comet’s sudden burst of light was almost as if someone had turned on a light switch. Comet Holmes is now visible in the night sky to the unaided eye. The comet, discovered in 1892, resembles a fuzzy tennis ball cruising in the constellation Perseus.
View from a backyard telescope
A comet is a ball of rock and ice, often referred to as a “dirty snowball.” It orbits the Sun and sometimes exhibits a coma, a cloud of gas and dust that forms around the comet’s nucleus.
Astronomers do not know why the comet has brightened so dramatically. One possible answer is that a crack the size of the Grand Canyon opened up, exposing chunks of ice beneath the comet's surface. Sunlight heated the ice, causing pieces to break off and form a large cloud of gas and dust around the comet. This cloud helps make the comet appear brighter.
Looking into the heart of the comet
The Hubble Space Telescope snapped an image of the comet's bright core. Although the nucleus is too small to see, the central portion of the image reveals the dust near the nucleus. Scientists hope to use this and other Hubble images to determine how big the nucleus is and how much of it was blasted away during the recent outburst.
Many comets lose ice particles when they travel close to the Sun. Comet Holmes, however, appears to have ejected its material when it was moving away from the Sun. The frozen wanderer made its closest approach to the Sun last spring, and even then, it did not travel that close to our star.
Comet Holmes is called a short-period comet. These comets orbit mainly in the inner solar system and travel around the Sun in less than 200 years. Comet Holmes swings by the Sun every seven years. It is a member of the Jupiter family of comets, which orbits between Jupiter and the Sun. Asteroids also follow a similar orbit.
Although this dramatic flare-up is surprising, it is not the first time Comet Holmes has had an explosive outburst. The comet had a flare-up in November 1892, when British amateur astronomer Edwin Holmes discovered it. Stargazers continued watching the comet’s return visits. They lost the icy object, however, after the 1906 visit.
For decades, Comet Holmes was out of the limelight. Then, in 1964, astronomers found it again with the help of computer predictions by astronomer Brian Marsden. Amateur and professional astronomers have been monitoring Comet Holmes every seven years during its return. Since its discovery, Comet Holmes has made 16 trips around the Sun.
The comet will remain bright for at least a few more weeks.