Talk:C/2011 L4 (PanSTARRS)

Epoch 2050
Why is epoch 2050 used? The epoch (astronomy) article says "The equinox with equator/ecliptic of a given date defines which coordinate system is used. Most standard coordinates in use today refer to 2000 Jan 1.5". Bubba73 You talkin' to me? 00:35, 9 March 2013 (UTC)


 * Epoch 2000 (moment in time used as a reference point for the time-varying orbital elements) would be the past orbit. The future orbit is better expressed using a barycentric solution after the comet has left the planetary region of the Solar System (2050). -- Kheider (talk) 02:40, 9 March 2013 (UTC)


 * OK, that makes sense, since it will probably be observed for years. It seemed strange because we know the position of the stars in 2000 but don't exactly know their position in 2050.  But I suppose they are known well enough.  Bubba73 You talkin' to me? 02:49, 9 March 2013 (UTC)

Inconsistency?
Isn't an eccentricity of greater than one (1.000087) inconsistent with an orbital period (~106000 yr)? —S MALL JIM   10:11, 10 March 2013 (UTC)


 * Not if you are using different epochs to define them. The solar system is not a two-body problem and for an Oort cloud comet you really need to compute a barycentric solution (gravity of Sun+Jupiter) after the comet has left the planetary region to get a meaningful solution. In 2050 (after the comet is done being influenced by planetary encounters) the eccentricity of C/2011 L4 will be "EC= 9.998657427407123E-01" and the orbital period will be "PR= 3.871269770653494E+07" days. -- Kheider (talk) 10:34, 10 March 2013 (UTC)


 * Thanks - in view of the thread above, I guessed that the explanation was going to be something to do with different epochs. Shouldn't the article use the figures you've quoted, then? I can't be the only one with a little knowledge (a dangerous thing!) who's concerned about the apparent contradiction. —S MALL  JIM   17:27, 10 March 2013 (UTC)


 * Here in 2017, I still get PR= 3.889317025887299E+07 / 365.25 = 106483 years. -- Kheider (talk) 05:03, 2 December 2017 (UTC)