Talk:List of non-periodic comets

Irate velociraptor 03:15, 6 April 2007 (UTC)[reply]

Do not confuse absolute magnitude with apparent magnitude! Chesnok 09:17, 6 April 2007 (UTC)[reply]

I came to the talk page because of two sets of trivial contradictions (this issue and the one already 'dealt with' in the next section about the intro paragraph... which, incidentally, has not been dealt with otherwise I wouldn't have considered mentioning it). It's not so much a matter of myself confusing the two, but that I saw the largely unexplained terminology (except for linking) to stop any casual reader from possibly being confused.

How to solve? One way would be a header/footer explanation to the tables to explain the two magnitudes (and thence the difference between the two) to prepare the casual reader about an important feature in the table without needing to move onwards. Alternately, if one can assign information of both absolute and apparent magnitude to separate columns in the table (or best guess, at least, where any such figure at all can be relied upon) then the distinction could be made explicit. It might even reduce the clutter from the repeated (if varied) information about the various magnitudes within the "Discoverer(s) or Namesake, Date of Discovery" field, to which it does not belong (nor does the information "Most hyperbolic comet known", technically, but...). The table (currently) below this comment-nesting could be the most handy source, to start off with, methinks. 31.86.130.216 (talk) 17:52, 12 August 2015 (UTC)[reply]

P.S. Please note this page: [1]. Chesnok 10:09, 6 April 2007 (UTC)[reply]

The article says that non-periodic comets are "defined as comets with orbital periods of 200 years or more". This appears not to make sense: if a comet has any orbital "period" at all -- even if thousands of years -- then it is necessarily periodic. My understanding is that "comets with orbital periods of 200 years or more" is the definition of long-period comets. Non-periodic comets are surely by definition comets that never return. I think, however, that some people (confusingly IMO) use the term "periodic comet" to refer exclusively to comets with periods of less than 200 years, and I wonder if, by extension, "non-periodic comets" is imagined to mean all comets that are not "periodic" according to that confusing definition.

Whatever, I think what we have right now doesn't make any sense to the ordinary reader: the introduction needs clarifying, and the article title possibly needs changing too. Matt 13:31, 25 December 2007 (UTC).

• This terminological issue affects several articles; please see the discussion at
  Talk:Comet/archive 1#Confusion/contradiction and comment here. Matt 03:06, 27 December 2007 (UTC). —Preceding unsigned comment added by 86.136.194.71 (talk
  )

• I have made some adjustments to the opening paragraph in an attempt to clarify this. Matt 20:41, 28 December 2007 (UTC). —Preceding unsigned comment added by 86.142.111.76 (talk)

"Small Bodies: Profile". NASA/JPL Planetary Data System. Retrieved 2009-04-26. mentions Single-apparition, but does not discuss the term "Non-periodic". Rule #3 explains periodic comets. -- Kheider (talk) 09:13, 7 February 2011 (UTC)[reply]

More correctly, comets are divided into short-period (periods smaller than 200 years or comet have been observed in more than 1 apparition) and long-period (periods bigger than 200 years). There are no "non-periodic" comets at all since all long-period comets belong to our Solar System and circulate around Solar System barycenter. Long-period comets may have eccentricities bigger than 1 while being in inner Solar System due to planet gravitational perturbations. There are few comets that escaped the Solar System. There were no comets that came from outside Solar System. Fjörgynn (talk) 06:27, 8 February 2011 (UTC)[reply]

Though it is somewhat of a misnomer, a "non-periodic" comet is any comet that's name starts with C/, D/, or X/. The only periodic comets are those with names that start with P/. Comets such as

C/1970 K1 are good candidates to be ejected from the Solar System outright. -- Kheider (talk) 09:21, 8 February 2011 (UTC)[reply

]

"D/" designations has been assigned only to periodic comets. Fjörgynn (talk) 10:25, 8 February 2011 (UTC)[reply]

"There are few comets that escaped the Solar System. There were no comets that came from outside Solar System." - I'm not sure those two statements can be simultaneously asserted. Comets (of which there are 'few') that leave the Solar System go 'somewhere', and may conceivably pass through (hyperbolically/non-periodically) other solar systems in the passage of time. By the same measure, we cannot rule out the possibility of (very rare?) comets skirting our Sun that have themselves arrived from some external star. Unless we can assert that the passage of time required would might mean sublimation or other erosion of all cometary material by interstellar starlight, etc.

But, please, someone sort out the "200 years" / "hundreds or thousands of years" thing for (effectively, in human lifetime/record-keeping time terms) non-period comets. I know it's a matter of varying "standard uses" for terms, yet surely someone with authority should have been able to sort it out over the intervening years since the issue was brought up... 31.86.130.216 (talk) 18:13, 12 August 2015 (UTC)[reply]

Kheider, it is probably more simple to look at origin and future 1/a values in orbital elements than to calculate barycentric orbital elements for distant epoch. These values can be found in Kazuo Kinoshita home page or in Nakano Notes. Fjörgynn (talk) 06:33, 8 February 2011 (UTC)[reply]

For comets with periods greater than ~10kyr, I still prefer barycentric coordinates since they do not fluctuate with the epoch as rapidly as heliocentric values. You just want to select an epoch when the comet is beyond the strong influence of the gas giants (esp. Jupiter). -- Kheider (talk) 09:21, 8 February 2011 (UTC)[reply]