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Apparent size of comets in images from the SOHO satellite

by Ostsol
Tags: apparent, comets, images, satellite, size, soho
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Oct29-12, 10:50 PM
P: 12
I've gotten into an amusing discussion with another individual on the topic of the apparent size of comets as seen in SOHO satellite images of Sungrazing or Sun-impacting comets. I won't go into the crackpot conspiracy theories I've heard, but will instead ask: why do these tiny comets appear so large in the images (relative to the Sun itself)?

My own thoughts have led to two potential answers, but I'm still a little unsure. Here they are:

1) The comets reflect a great deal of intense light as a result of their proximity to the Sun and this results in pixel-bleeding on the CCDs. Thus, they appear much larger than they really are.

2) The comets disintegrate as a result of receiving so much solar radiation and the cloud of debris around them can become very large.

I guess it could be a combination of both, too.

Am I on the right track?
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Oct29-12, 11:28 PM
Drakkith's Avatar
P: 12,013
I'd guess that both come into play. Plus some comets may enter the camera field of view while they are in between the camera and the Sun, and thus look larger.
Oct30-12, 05:06 PM
PF Gold
P: 519
Don't forget that the coma of a comet can balloon to larger than the size of a planet, despite its relatively tiny nucleus. The Great Comet of 1811 reputedly had a coma roughly the diameter of the Sun!


Oct30-12, 05:35 PM
P: 22,315
Apparent size of comets in images from the SOHO satellite

That's not the only one:
Comet Holmes (official designation: 17P/Holmes) is a periodic comet in the Solar System, discovered by the British amateur astronomer Edwin Holmes on November 6, 1892. Although normally a very faint object, Holmes became notable during its October 2007 return when it temporarily brightened by a factor of about half a million, in what was the largest known outburst by a comet, and became visible to the naked eye. It also briefly became the largest object in the solar system, as its coma (the thin dissipating dust ball around the comet) expanded to a diameter greater than that of the Sun (although its mass remained minuscule).

Oct30-12, 09:52 PM
P: 12
Very interesting and informative! Thank you, all!

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