CfA Release No: 2007-31

For Immediate Release: Monday, November 26, 2007

Note to editors: High-resolution photo is available online at

http://www.cfa.harvard.edu/press/2007/pr200731_images.html

A LAST LOOK AT COMET HOLMES

Cambridge, MA - Comet 17P/Holmes, which dazzled sky watchers with a dramatic

outburst that made it visible to the unaided eye, now is fading from sight.

However, before it returns to the obscurity from which it came, astronomers

at the MMT Observatory took a final look.

In late October, Holmes brightened by a factor of about one million times

when it ejected a vast cloud of dust and gas. That cloud expanded over time

and now spans more than 870,000 miles, making it larger than the Sun (which

is 865,000 miles in diameter).

On November 4, Smithsonian scientists snapped this photo of Comet Holmes

using an instrument called Megacam, which is one of the largest CCD cameras

in existence. Megacam holds 36 9-megapixel CCD chips, for a total of more

than 300 megapixels.

Separate exposures through three color filters were combined to make this

final, full-color image. Individual stars appear as a line of colored dots

because the photos were centered on the comet, which moved slightly across

the sky.

Currently, Comet Holmes has a total brightness of 3rd magnitude, however its

large size on the sky (and resulting low surface brightness) makes it

difficult to see without binoculars or a telescope. However, when it was

discovered in 1892 it underwent a second bright outburst five months after

the first. If Holmes repeats its historical performance, then this comet may

offer viewers one more chance to see the show before it bows from the stage.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for

Astrophysics (CfA) is a joint collaboration between the Smithsonian

Astrophysical Observatory and the Harvard College Observatory. CfA

scientists, organized into six research divisions, study the origin,

evolution and ultimate fate of the universe.