Comet Holmes orbits between Mars and Jupiter. It never comes very close to the Sun. Its position is shown here on October 24, 2007, when it suddenly brightened dramatically.
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Original Windows to the Universe artwork by Randy Russell using data from NASA/JPL.
News story originally written on October 29, 2007
In late October 2007 Comet Holmes suddenly grew dramatically brighter. In just a few hours between October 23rd and 24th, the comet became nearly 500,000 times brighter! Before that time the comet was extremely dim, having a magnitude of about 17, and could only be seen with large telescopes. After its sudden brightening, it became visible to the naked eye and is about as bright as Polaris (the North Star).
The comet now has a coma (the name of the "atmosphere" that forms around a comet when it heats up and emits gases), giving it the appearance of a fuzzy ball when viewed through even small binoculars or a telescope. The comet is still quite far from the Sun beyond the orbit of Mars, and does not have a noticeable tail.
Astronomers are not quite sure why Comet Holmes has brightened so suddenly. Perhaps some unusual event caused a large amount of ice in the comet's interior to be exposed to the warming effects of the Sun, turning the ice to gas and forming the suddenly large coma.
Comet Holmes was first discovered in 1892 by the British astronomer Edwin Holmes. It orbits the Sun once every 6.9 years, keeping between the orbits of Mars and Jupiter. It is usually very dim because it stays quite far from both Earth and from the Sun, so it is not heated much and therefore doesn't usually emit much gas and dust to form an easily visible tail. It went through a brightening phase around the time of its discovery in 1892 similar to the 2007 outburst. In 1892 it brightened to about magnitude 4 or 5, similar in brightness to some of the dimmer stars visible without a telescope.
The links below provide photos of Comet Holmes and sky charts to help you find it in the sky. It is currently (as of this writing in October 2007) in the constellation Perseus.
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