[Physics] Solar eclipses on Galilean moons

[Thomas Goodey]

On 21 Jul 2017 at 12:00, physics-request at tuks.nl wrote:

> I was intrigued by the fact that very rarely during
> history, it had been noticed by astronomers that one of
> the four Galilean Moons of Jupiter "suddenly disappeared"
> for a few seconds.  It was thought that that only
> happened when the Earth was in a rare orbital plane of
> the Galilean Moons, where the Sun's light to get to one
> of the moons got blocked by one of the other moons. 

The above cannot be right. You mean, the SUN was in that 
orbital plane. The position of the Earth would be 
irrelevant.

If the light FROM the moon in question got blocked by one 
of the other moons (on its way to you), then there wouldn't 
be a sudden disappearance of the former moon. It would 
appear to coalesce briefly with the latter moon, since both 
of them would be visible objects.

>  People (then) had realized that can only happen for
> a few seconds, but, astoundingly, no one had ever done the
> math to predict the event. 

The phenomenon you are describing is a total solar eclipse 
as seen from the surface of one of the Galilean moons, in 
which another Galilean moon blocks the Sun's light.

Calculations of this phenomenon are nowadays routine. I 
have seen them described on the Solar Eclipse mailing list.

> So I decided to spend about six
> months in calculating the VSOP87 millions of terms to
> calculate the exact orbits.  After about six months of
> calculating, I arrived at a prediction of about four such
> events, several years later (which no one had ever predicted
> prior to that). 

Are you sure about that?

> The events were only visible in desolate
> locations, and I did not see any of them. 

You are making some fundamental error here. Such events are 
visible from anywhere on Earth, or rather, from anywhere on 
the side of the Earth facing Jupiter at the time, and where 
it is night and not cloudy of course.

> Later, some other
> people did similalr calculations.

Yes, I have seen them discussing the results.

Thomas Goodey

*****************************
Anne's search for security 
holes in the localizer network 
software was close to 
impossible. Every year her 
zipheads pushed back their 
deadline for certainty another 
year or two. But the quagmire 
of Qeng Ho fleet software 
was almost eight thousand 
years deep.
--------- Vernor Vinge
----------'A Deepness in the Sky'