Talk:Kreutz Sungrazers

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This article was nominated for the March 2005 International writing contest.

Contents 1 A family tree image 2 Delightful! 3 Aphelion 4 Brightness of Sun from sungrazing comet 5 Nice article 6 Not a descendant of Aristotle's comet

[edit] A family tree image

I've had a bash at creating an image showing a 'family tree' of how the Kreutz group's major members have come to exist. I think a nicely-done graphic could really illustrate the article well, but I'm not sure what I've done is very good at all, so thought I would put it here first. Would appreciate comments, and if anyone can design a better-looking diagram that would be great! Worldtraveller 02:15, 25 Mar 2005 (UTC)

[edit] Delightful!

The images in particular, both of the sungrazer and the family tree above, make my heart sing. +sj + 05:56, 28 Mar 2005 (UTC)

Excellent, very pleased to hear it! In the hope that it might make more hearts sing I've now put the image on the article page. Worldtraveller 14:13, 28 Mar 2005 (UTC)

[edit] Aphelion

Does anyone have any info on the aphelion or eccentricity of these comets? Google doesn't seem to know. --P3d0 July 6, 2005 04:07 (UTC)

Marsden 1967 (ref 4 in the article) gives 200AU as a typical aphelion and 0.005AU as typical perihelion. where A and P are aphelion and perihelion distances, so that gives typical eccentricity as 0.99995 by my reckoning. Do you think this info should be in the article? Feel free to add it wherever you think best.

By the way, interesting addition of yours about the energy reaching the surface of a sungrazer at perihelion - was it your own calculation or does it come from somewhere we can add a link or reference for? Worldtraveller 6 July 2005 09:44 (UTC)

It was my own calculation, and I think it was wrong, so let me explain myself, and others can confirm. The angle comes from sinΘ / 2 = 1 / 1.3, giving 100°. The Sun subtends 0.53° from Earth, which is 192 times smaller, giving an area roughly 36,700 times smaller. I assume the sun's image in the sky is simply magnified by this factor (which isn't exactly right but should be close enough for first-order estimates). The Sun's radiation is 13600 kW/m² at the distance of the earth, so it should be 36,700 times larger on a Sungrazer, giving about 500 MW/m². --P3d0 01:45, July 11, 2005 (UTC)

I was confused by this section... "This comet was found to have passed just 200,000 km (0.0013 AU) above the sun's surface, equivalent to about half the distance between the Earth and the Moon. It thus became the first known sungrazing comet. Its perihelion distance was just 1.3 solar radii. "

Isn't perihelion the point of closest approach to the sun? How can that distance be both half the distance between Earth and Moon, and 1.3 solar radii? I must be reading it wrong... can someone clarify? Wordie 9 July 2005 04:14 (UTC)

The distance between the Earth and Moon is almost 400,000 km. 200,000 km is about half that. Meanwhile, the solar radius is 700,000, so 200,000 is about 0.3 of that. Does that answer your question? --P3d0 01:45, July 11, 2005 (UTC)

[edit] Brightness of Sun from sungrazing comet

I've recalculated the numbers in the section describing the brightness of the Sun as seen from a sungrazer - here's my thinking:

1. Earth is about 215 solar radii away from the Sun. The sungrazer in question was 1.3 solar radii away from the centre of the Sun. It was 165 times closer, so the Sun would have appeared 165 times wider than it does to us. It's about 0.5° across from here so over 80° across from there.
2. The angular area of the Sun from the comet would be (165)² times greater than it is from Earth; and the amount of light received would also be (165)² times greater (inverse square law).
3. The solar constant at Earth is 1.37kW/m². This also follows an inverse square law, so would be (165)² times greater at the Sungrazer: 37.3MW/m²

Does that make sense? Worldtraveller 09:29, 18 August 2005 (UTC)

[edit] Nice article

I randomly stumbled on this article while perusing a list of articles with "Great" in the name and arriving here from Great Comet of 1882. Really nice introduction to something I hadn't heard of before. Carcharoth 15:02, 20 January 2007 (UTC)

[edit] Not a descendant of Aristotle's comet

Per the Great Comet of 1882 article as cited there:

Current models do not support the frequent supposition in the prior literature that the famous comet of 372 BC is in fact the ultimate parent of the Sungrazers. The comet of 372 BC is often associated with Aristotle who, along with others from his time, described that comet in his writings. However, Aristotle was only twelve at the time of the comet's appearance and the historian, Callisthenes of Olynthus, who also wrote about it was born ten years after its appearance. Consequently, their reports should not be taken as eye-witness accounts. Further, there is no mention of the comet in Chinese literature of the time. Instead either the comet of February 423 or of February 467 with orbital periods of around 700 years is now considered the likely progenitor of the Sungrazers. The fragments of the Great Comet of 1882 will return in several hundred years time, spread out over perhaps two or three centuries.

I think this article needs to be updated to reflect this modern opinion. The diagram of the family tree would need to be updated.

WilliamKF 02:35, 19 October 2007 (UTC)