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Astronomical Observatory: Cool Images

The Expanding Gas Cloud of Comet 17P/Holmes , L. Molnar

Gas Cloud
Gas Cloud
Gas Cloud
Gas cloud
Full color images of Comet Holmes taken October 27, 28, 29, and 30, 2007

The four images above were taken 3-6 days after the outburst of Comet 17P/Holmes began. The cyan color indicates emission from gas molecules such as CN, C3, C2 and NH2. Hence we are seeing the expansion of a cloud of gas. (The central portions of each image are saturated--this is the brightly reflecting dust from the comet.) The graph below shows the expansion of the outer edge of the cloud: a speed of 1500 m/s. By the last image, the dust cloud has a diameter 11 times that of Jupiter, the largest planet.

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).

Go back to our Comet Holmes home page or on to our Expanding Dust Cloud page.

Expansion of Comet Holmes Dust 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 times

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 31 October 2007, by L. Molnar



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