Math/astronomy problem...

[helen99]

Mercury's apparent retrograde motion lasts 2-3 weeks. Venus retrograde lasts one month or thereabouts. Mars retrograde lasts for about 3 months. These time differences are to be expected given the distances and positions with respect to the sun and earth. But look at all the other planets. Jupiter's, Saturn's, Uranus's, Neptune's and Pluto's all last around 5 months. I'm sure there's a mathematical explanation for why the apparent backwards orbit of the outer planets are the same length no matter how far away they are, but I'm not sure what it is.

Edit: Clearly I can't count. Jupiter's is four months. Saturn's is 4.5. Uranus's is 5.0. Neptune's is 5.0. Pluto's is 5.5. Still, the outer planets are puzzling, since they are at vastly different distances. Maybe their actual orbital speeds are different, but I'm not sure that accounts for it.

Here's the schedule:

Date	        Planetary station	 Exact degree

Dec 31, 2008	Saturn turns retrograde	 21Vir46
Jan 11, 2009	Mercury turns retrograde 07Aqu45
Feb 1, 2009	Mercury turns direct	 21Cap44
Mar 6, 2009	Venus turns retrograde	 15Ari27
Apr 4, 2009	Pluto turns retrograde	 03Cap18
Apr 17, 2009	Venus turns direct	 29Pis11
May 7, 2009	Mercury turns retrograde 01Gem44
May 17, 2009	Saturn turns direct	 14Vir54
May 29, 2009	Neptune turns retrograde 26Aqu28
May 30, 2009	Mercury turns direct	 22Tau52
Jun 15, 2009	Jupiter turns retrograde 27Aqu01
Jul 1, 2009	Uranus turns retrograde	 26Pis37
Sep 7, 2009	Mercury turns retrograde 06Lib13
Sep 11, 2009	Pluto turns direct	 00Cap39
Sep 29, 2009	Mercury turns direct	 21Vir36
Oct 13, 2009	Jupiter turns direct	 17Aqu09
Nov 4, 2009	Neptune turns direct	 23Aqu41
Dec 1, 2009	Uranus turns direct	 22Pis42
Dec 20, 2009	Mars turns retrograde	 19Leo41
Dec 26, 2009	Mercury turns retrograde 21Cap47
Jan 13, 2010	Saturn turns retrograde	 04Lib39
Jan 15, 2010	Mercury turns direct	 05Cap33
Mar 10, 2010	Mars turns direct	 00Leo17

Comments

[hummingwolf.insanejournal.com]

Maybe the explanation here (http://en.wikipedia.org/wiki/Retrograde_motion#Apparent_retrograde_motion) is vaguely helpful? I'm full of headache, so am not much use at all.

[helen99.insanejournal.com]

It's helpful in that it helps me to understand the basics of why it happens (planets passing each other), but those outer three still puzzle me - I wonder why their retrograde periods are so close in duration. In any case, this was a protest post more than anything else, so it's not imperative that I find out why. I'm sure it has something to do with velocity and the cosine of theta, but it's been too long since I've studied either astronomy or trigonometry to do the calculations.

I'm mostly protesting my own tendency to lend credence to the "Mercury retrograde" mythology. (Most of this journal so far has actually been in protest of my usual tendencies, come to think of it). All the planets exhibit apparent retrograde motion, not just Mercury, and all retrograde motion is apparent, and thus could not have an observable physical effect on the surrounding solar system.