[Chaos-l] Jovian moons

[Robert Nielsen]

Cool stuff Joe!  I must admit I knew the Jovian moons weren't in a perfect straight line, because I've seen two of the inner ones side by side ...

Robert

On Feb 3, 2013, at 2:01 PM, Joseph Mack NA3T <jmack at wm7d.net> wrote:

> 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
> Homepage http://www.austintek.com/ It's GNU/Linux!
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