Skip to Navigation | Skip to Content

Astronomical Observatory: Cool Images

Comet 17P/Holmes , L. Molnar

Content on this page requires a newer version of Adobe Flash Player.

Get Adobe Flash player

Content on this page requires a newer version of Adobe Flash Player.

Get Adobe Flash player

The two movies above show the evolution in the appearance of Comet 17P/Holmes from October 27-30, 2007. To play a movie again, press the stop button (the square) followed by the play button (the triangle).

Both movies are representations of the same data. The upper one has the brightness enhanced to the point that the center is saturated, allowing one to see how the cyan colored outer gas cloud extends far beyond the much brighter yellow dust cloud. The lower one has the maximum brightness pegged to the brightness of the bright spot near the center. This movie shows details in the dust cloud such as the extension to the lower right (southwest).

Comet 17P/Holmes was discovered in November 1892 during a bright outburst (Kronk 2007). Since that time it has remained very faint, orbiting the sun in an eccentric orbit every 7 years (one of the Jupiter family of comets). On 24 October it brightened by a factor of 400,000, increasing by 0.5 magnitudes an hour until it peaked at just brighter than 3rd magnitude (Green 2007a).

On the 27th, the comet was 150 million miles from Earth. The physical size of the solid nucleus (likely a dark object) is estimated to be no more than 10 km across (about the size of the city of Grand Rapids). The field of view in the movies is 21 by 15 arcminutes. (For comparison, the Moon is 30 arcminutes across.) As the comet fills the field of view in the last image, it has reached a linear size 11 times that of the planet Jupiter.

For further analysis of the expansion rates (and the individual images), see expansion of the dust cloud and the expansion of the gas cloud.

Right Ascension (J2000) 03h 51m 51s (the first night)
Declination (J2000) +50 13' 42" (the first night)
Dates observed
  1. 27 October 2007, 05:52
  2. 28 October 2007, 03:31
  3. 29 October 2007, 02:32
  4. 30 October 2007, 03:45

(All times Universal Time = EST + 5 h)

Filter used Red, green and blue (RVB)
Exposure time

Average of 30 images, each 1 second the first night, 2 seconds the second and third nights, and 5 seconds the last night.


Daniel W. E. Green, 2007a October 24, International Astronomical Union Circular No. 8886. "Comet 17P/Holmes" [Official announcement of the discovery of the 2007 outburst]

Daniel W. E. Green, 2007b October 26, International Astronomical Union Circular No. 8887. "Comet 17P/Holmes" [First measurements of the comet's light spectrum]

Gary W. Kronk. updated October 2007. "17P/Holmes" [A page within a cometography website with both historical information and current images.]

Seiichi Yoshida. "17P/Holmes (2007)" [A plot of the comet brightness with time.]

Content posted 26 October 2007, updated 1 November, by L. Molnar

The animations were produced by Joe Girolamo of the Calvin Information Technology Digital Studio.


Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Nulla ut nibh.


Lorem ipsum dolor sitamet, consectetuer adipiscing elit. Nulla ut nibh.