[Chaos-l] Jovian moons

[Joseph Mack NA3T]

It came as a big surprise to me on observing the jupiter 
moon conjunction the other day to find that the line joining 
jupiter's moons is not straight. If you already knew this, 
then you don't need to read any further.

Jim from the Raleigh astronomyers (cc: 'ed here) 
straightened me out. He sent me this explanation from 
http://www.curtrenz.com/jupiter.html

" As viewed from Earth the tilt of Jupiter's equatorial 
plane at opposition appeared to be +3.0 which is not far 
from the maximum. The orbital planes of the four Galilean 
satellites lie close to that plane and mutual events 
(transits, occultations, eclipses) not involving Jupiter 
will not occur during the current apparition. In fact for 
now Callisto will always appear to pass north or south of 
Jupiter during conjunctions. Of course the events involving 
Jupiter and the inner three Galilean satellites and their 
shadows will still happen during every one of their orbital 
periods. Near the time of opposition the satellites will 
occult their own shadows. "

I have never given jupiter's moons more than a casual glance 
and whenever I have (ofter with binos), I've seen what I 
expected; the moons in a straight line. This has been over 
many decades. I thought this was to be expected; jupiter's 
inclination to the ecliptic is near enough to 0, and so is 
the inclination of the jovian moons (jupiter's equatorial 
bulge will handle that). As well the eccentricity of jupiter 
and its inclination to the ecliptic are nearly 0 too. 
Everything about Jupiter is simple right?

Well apparently not. The orbital radius of the jovian moons 
combined with the 2.9deg tilt of jupiter's poles means that 
the plane of the jovian moons (in the same way that saturn's 
rings are sometimes edge on, and sometimes facing us) puts 
Callisto jupiter crossings above and below jupiter, when 
jupiter's nodes are at right angles to our line of sight.

So every 3yrs Jupiter's moons will transition from orbiting 
in the apparent plane of jupiter's equator to the maximum 
distance above and below the equator.

Jim sent me these:

a js simulator for the Jovian moons.

http://www.shallowsky.com/jupiter/

click on "animate" to see it run. You'll see the line 
joining the moons is a dogleg. Now go to Nov/Dec 2014 and 
you'll see that the moons are pretty much in a straight 
line.

Here is a link showing 63 of Jupiter's 67 moons in motion:

http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/jupmoon.htm

(2nd frame)

Thanks Jim

Joe


-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
generator at http://www.wm7d.net/azproj.shtml
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