Talk:Comet Shoemaker-Levy 9

From Wikipedia, the free encyclopedia

	Comet Shoemaker-Levy 9 is a featured article; it (or a previous version of it) has been identified as one of the best articles produced by the Wikipedia community. If you can update or improve it, please do.
	This article appeared on Wikipedia's Main Page as Today's featured article on November 15, 2005.
Article Milestones Date Process Result April 20, 2005 Featured article candidate Promoted Current Status: Featured article

	Astronomy Portal This article is within the scope of WikiProject Astronomy, which collaborates on articles related to astronomy, and WikiProject Astronomical Objects, which collaborates on articles related to astronomical objects.
FA	This article has been rated as FA-Class on the assessment scale.
Help with this template This article has been rated but has no comments. If appropriate, please review the article and leave comments here to identify the strengths and weaknesses of the article and what work it will need.

	This article is within the scope of the Solar System WikiProject, a collaborative effort to improve Wikipedia's coverage of the Solar System.
FA	This article has been rated as FA-Class on the assessment scale.

This page has been selected for Version 0.5 and the release version of Wikipedia. It has been rated FA-Class on the assessment scale. It is in the category Natsci.

The spoken word version of this article is part of WikiProject Spoken Wikipedia, an attempt to produce recordings of Wikipedia articles. To participate, visit the project page.

Contents 1 Units 2 ...and terms 3 Clarification on Impact 4 picture mislabelled 5 Collision 6 What SL9 orbits 7 The Cure 8 Continuum? 9 Decreasing content 10 rate of cometary impacts?

[edit] Units

I see some of the ",000 km" have been turned into Mm.

Does anyone use the megametre in practice? MKS (meter-kilogram-second as referenced in the article International System of Units) astronomers tend to use "×10⁶ m" (or, for CGS, "×10⁸ cm"); others generally use "thousand km", in my experience. -- ALoan (Talk) 18:26, 19 Apr 2005 (UTC)

[edit] ...and terms

I think ,000km is more immediately comprehendible to the general public, and astronomers too - the refs pretty much universally use ,000 km in this context. Therefore, I've switched it back.

Also, the term perizene is not ever used by astronomers. Much used here on Wikipedia is the Wikipedia:Google test, but in astronomy you can also use the ADS test (ADS is the astrophysics data service, and has an extremely advanced search engine which covers references back to the 1850s), which in this case gives perijove an impressive 17,882-0 victory over perizene in the number of occurrences in the literature. So, I've changed that back as well. Worldtraveller 18:49, 19 Apr 2005 (UTC)

Oops, it's not quite such an emphatic win for perijove - I had the synonym replacement turned on so it was searching for Jupiter, Jovian etc as well as perijove - it's actually 41-0. Worldtraveller 19:19, 19 Apr 2005 (UTC)

Indeed - I was happy to read the apsis page, and see the "correct" term perizene, but from a google test it seem that no-one uses it apart from WP and its mirrors. -- ALoan (Talk) 20:00, 19 Apr 2005 (UTC)

[edit] Clarification on Impact

One thing I hope someone could clarify... the "Impact" section says that the comet impacted Jupiter on the side hidden from earth, but that Galileo was able to observe this even though it was on it's way to Jupiter. Wouldn't that mean Galileo would also be unable to see it? Could someone clarify this, either here or on the main page, as to the path of Galileo that allowed it to see the impacts?

The Galileo spacecraft had an interesting journey to Jupiter, with gravitational slingshots past Earth twice and Venus once - essentially it approached Jupiter from the side. In any event, approaching direct from Earth would be difficult, due to the spacecraft's angular momentum. See this illustration -- ALoan (Talk) 11:34, 3 November 2005 (UTC)

[edit] picture mislabelled

The picture with the caption "A sequence of Hubble Space Telescope images showing the appearance of the fireball of the largest impact, that of fragment G" was in fact not taken by the Hubble. I believe it was taken by the galileo. A picture of Jupiter showing a partial phase like that could never be taken from Earth, or Earth orbit.

Good spot. Changed. I also I think it was W rather than G - see this and this... -- ALoan (Talk) 11:34, 3 November 2005 (UTC)

But now there's a mismatch between the article and the description on the image's page. Bazza 16:06, 15 November 2005 (UTC)

[edit] Collision

This was not the first direct observation of two celestial bodies in collision. That was in 1178 when several people in Canteberry, England observed an object collide with the moon. A monk recorded the event. Not to nit pick. The overall article is great. Dr U 01:13, 15 November 2005 (UTC)

That's not what it says here http://unisci.com/stories/20012/0420014.htm! And do you mean "Canterbury"  :-)

[edit] What SL9 orbits

I removed the bogus third sentance on SL9 orbiting Jupiter rather then the Sun and the reference that caused the confused sentance. I then replaced it with a (week) sentance trying to focus on what made SL9 interesting, the fact that it might hit Jupiter!

In fact, it was orbiting Jupiter when discovered - you can easily verify this by checking the references. User:Worldtraveller

[edit] The Cure

As I do not have much time now and I do not know where to put this trivia bit, I ask the community: On the Wild Mood Swings album (1996) The Cure had a song called 'Jupiter Crash', which commented on the crash ('Was that it?' / 'Was that the Jupiter show?' / 'It wasn't quite what I'd hoped for you know'), which is used to comment on an unsuccessful love affair. Maybe someone can add a trivia section and check the exact text? Thanks!

Zement 08:56, 15 November 2005 (UTC)

Lyrics to the song can be found here: [Link to copyvio website removed]"

I added a trivia section today. As I am not a native speaker of English, I'd like to ask that someone checks it for errors. Thanks! Zement 09:52, 16 November 2005 (UTC)

User:Worldtraveller removed the Trivia-section for being "too tangential". Do you agree? I think hat, while the article explicitely mentions the huge media attention for the event, a trivia section should be allowed. Zement 17:40, 16 November 2005 (UTC)

[edit] Continuum?

- "Radio observations revealed a sharp increase in continuum emission at a wavelength of 21 cm after the largest impacts ..." -

"continuum" links to a disambiguation page, and none of the referral pages there seems to be relevant. Can anyone clarify this? -- 15 NOV 2005

I've linked continuum to Black body (radiation) as the best match I can find. -Wikibob 22:29, 15 November 2005 (UTC)

[edit] Decreasing content

WorldTraveller, would you care to explain why you felt compelled to decrease the article's content? Specifically:

• The comparison between Jupiter's Hill sphere radius and the comet's apoastron about Jupiter.
• The Jupiter-centric eccentricity of the orbit, compared to the heliocentric value.
• The fact that the comet's 1992 approach was well within Metis' orbit.

Urhixidur 03:58, 22 February 2006 (UTC)

Sure. I didn't actually feel compelled to 'decrease the article's content', I just felt compelled to ensure it was readable and understandable to an audience as wide as possible, and I removed those bits because

• I had no idea what a Hill sphere was, or why it was being compared to the comet's apojove. I am an astronomer so I thought that would certainly be even more confusing for a layman.
• Again, very confusing. I understand what was meant but I don't think most people would. I couldn't see any way of rewording it without making it overly lengthy. Also, I didn't think it was terribly important to talk about how the comet's orbit looked in the frame of reference of the Sun, as it doesn't really add anything to the reader's understanding of the comet.
• Its significance was unclear. I've added it back now with a mention that Metis is the innermost moon.

Among the other changes I made were changing Gm to million km - this is because I think the latter is immediately understandable to a far larger number of people. This is discussed at the top of this page as well. And I removed all the redlinks to astronomers because I really think most or all of them would not warrant an article. If they do, I do too for my paper cited in Cat's Eye Nebula, and I am sure I'm not notable. Worldtraveller 11:35, 22 February 2006 (UTC)

A Hill sphere (not heard of that one either) seems to be the same as the Roche sphere (related to the Roche limit, no doubt, within which tidal disruption can be expected) - this should be explained. I have no idea why eccentricity around the Sun or Jupiter is that interesting (this is a comet: its orbit is bound to be wildly eccentric, however one looks at it). The third point is clearly related to the first and looks interesting, though. -- ALoan (Talk) 12:20, 22 February 2006 (UTC)

« ...I have no idea why eccentricity around the Sun or Jupiter is that interesting (this is a comet: its orbit is bound to be wildly eccentric, however one looks at it... »

That was the whole point of the comparison: SL9's orbit was not wildly eccentric in heliocentric terms. As is typical of short-period comets, the eccentricity was mild (about 0.2). It became very accentuated (almost 1) for two reasons: 1) as a result of the capture process and 2) only in Jupiter's frame of reference.

Urhixidur 04:53, 23 February 2006 (UTC)

Ignorance about the Hill sphere is not going to be remedied by omitting any mentions of the concept, now is it? There is an article that describes it, so fresh knowledge is just a click away. (Sarcasm off) It is indeed closely related to Roche's work, and any considerations of orbital capture unavoidably deal with it. To speak of the comet being in orbit about Jupiter is just another way of saying it is wholly within Jupiter's Hill sphere. All right, I'll try adding a paragraph that explains these bits in better fashion. Not that it matters, but I also hold an M.Sc. in Astronomy.

Urhixidur 04:13, 23 February 2006 (UTC)

Okay, done. Interestingly, source 1 has SL9 be a Jupiter inner-grazer before the capture, whilst source 17 has it an outer-grazer after the capture. This may not be a contradiction (the swap may be part of the capture process), but until we can get our hands on a copy of source 1, I changed the paragraph so it gives a more geometry-neutral explanation.

Urhixidur 04:47, 23 February 2006 (UTC)

Fine - clearly I was displaying my ignorance of solar system astronomy ;) As you say, not that it matters, but if academic credentials are at all relevant, Worldtraveller and I both have doctorates in astronomy (mine, ahem, some time ago, before I started doing something less worthwhile...) Your fuller explanations are excellent. Well done. -- ALoan (Talk) 10:35, 23 February 2006 (UTC)

[edit] rate of cometary impacts?

I've changed this claim: rate of cometary impacts on Jupiter is thought to be between two and ten times higher than the rate on Earth [15] because it was contradicted by the source it cites: for Jupiter-interacting comets of greater than 1 km diameter, a Jupiter impact takes place every 500-1000 yr, and an Earth impact every 2-4 Myr. Now every 500 to 1000 years is a rate 2 to 8 thousand times higher than the rate on Earth. Even so, out of curiosity, is a two thousand times impact rate lower or higher than would be expected from Jupiter's greater mass and capture cross-section? It orbits at 13 km/sec, compared to Earth's 29 km/sec, has 121 Earth's area, so ignoring gravity it looks like Jupiter should sweep up 55 times more objects. I've no idea how to estimate the gravity effects, but suspect that the cited rate is somehow greater than would be expected. -Wikianon 13:04, 3 October 2006 (UTC)