Talk:List of non-periodic comets
|WikiProject Solar System||(Rated List-class, Mid-importance)|
|WikiProject Astronomy||(Rated List-class, Low-importance)|
Added another comet
Could you explain me what I did wrong, I Just modificate the table to include the predicted next perihelion and the Comet Lovejoy If I remove some valuable Information it was not my intention. (188.8.131.52 05:27, 6 June 2007 (UTC))
In the first pararaph the text "They are usually on near-parabolic orbits that will not return to the vicinity of the Sun for thousands of years, if ever" confuses me a little. My understanding is that an elliptical orbit will always return, a hyperbolic orbit will never return, and a parabolic orbit is the special case at the transition between the two which will "just never return", and which in practice is impossibly unlikely to arise. Therefore, should this text read something like: "They are on hyperbolic orbits that will never return to the vicinity of the Sun"? The suggestion of the possibility of returning in thousands of years contradicts the fact that they are "non-periodic". Is the point being made that we cannot measure some of these orbits accurately enough to know? Whatever, this needs clarification. Matt 03:08, 25 January 2007 (UTC).
- Actually, as an afterthought, the terms "parabolic orbit" and "hyperbolic orbit" probably don't make sense. Should be "trajectories" rather than "orbits"? Matt 03:10, 25 January 2007 (UTC).
- "Orbit" is what astronomers always call them, even parabolic orbits. As I understand it, parabolic orbits come in from infinity. And infinity is a very good approximation for the distance of the Ort cloud (50,000-100,000 AU or about 1 light-year) where astronomers think most comets come from. At discovery it takes a couple of days before a first-attempt parabolic orbit can be fitted to the observations of a new comet, and maybe a month or 3 before the difference between a parabloic orbit and an eliptical orbit can be determined. A hyperbolic orbit would require the comet to come from "beyond infinity" (or propelled into the solar system), instead of just falling into it from a very long ways away. Hope this helps. Reguards, GraL 15:41, 9 May 2007 (UTC)
one of only four comets known to have had a negative absolute magnitude ?
I count more then 4 on this list
Comet Hale-Bopp(C/1995 O1) -2.7
Comet McNaught (C/2006 P1, Great Comet of 2007)
C/1577 V1 (Great Comet of 1577) (1577 I) -1.8
Great Comet of 1729 (C/1729 P1, 1729, Comet Sarabat) -3.0
C/1746 P1 (1747, Comet de Chéseaux) -.5
Great September Comet of 1882 (C/1882 R1, 1882 II, 1882b)
Irate velociraptor 03:15, 6 April 2007 (UTC)
|Comet name||apparent mag||absolute mag|
|C/1729 P1 (Sarabat)||4.5||-4|
|C/1577 V1 (Brahe)||-7||-1.5|
|C/1995 O1 (Hale-Bopp)||-0.8||-1.5|
|C/1746 P1 (de Chéseaux)||~5||-0.5|
|C/1811 F1 (Flaugergues)||0|
|C/1743 Q1 (Klinkenberg)||0.5|
|C/1882 R1 (Great September Comet)||-17||1.0|
|C/1913 Y1 (Delavan)||1.1|
|C/1433 R1 (Great Comet)||1.2|
|C/2006 P1 (McNaught)||-5.5||4.5|
|1P/1982 U1 Halley (1986)||5.0|
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 184.108.40.206 (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)
- 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)
- 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/1980 E1, C/2009 R1, C/1956 R1, C/2007 F1 (LONEOS), C/2001 Q4 (NEAT), and C/1970 K1 are good candidates to be ejected from the Solar System outright. -- Kheider (talk) 09:21, 8 February 2011 (UTC)
- 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)
- 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)