[Physics] Fw: Occultations and eclipses

[Ruud Loeffen]

Carl and Tom.

Thank you for your efforts in this "head hurting" discussion. I hope we
will have more of these disputes.
It's rather quite lately around here.
And Arend: Still alive and searching?

Ruud Loeffen.

On Fri, Aug 4, 2017 at 2:38 AM, carmam at tiscali.co.uk <carmam at tiscali.co.uk>
wrote:

> Further to my previous posting, I was dealing with a static situation when
> calculating the visibility of the occultations of any two of the four
> Galilean moons of Jupiter from Earth. I stated that the only occasion when
> the occultation could not be seen from any where on Earth was when Europa
> occulted Io, and that is because the disc of visibility would be only some
> 3,000 Km across. I did not go into how long that occultation could be seen
> from any given point on Earth, so here it is. Because of the very high
> visual approach and recession velocity between the two moons, and the ratio
> of that distance and the distance from Jupiter to Earth, the zone of
> visibility would race across the Earth's surface at a tremendous speed.
> Carl mentioned an occultation time of just a few seconds, and I can readily
> believe that to be so, given that ratio.The visual approach and
> recession velocity between the two moons can be as high as 30Km/s, and the
> ratio of the distance is 600:1, which gives a speed of the disc of
> visibility across the Earth of 18,000Km/s, so a zone 3,000Km across would
> take 0.16 seconds to cross any point. That is at the maximum speed when the
> moons are on the opposite sides of Jupiter looking from the north, but on
> the same side when looking from Earth. When they are on the same side
> looking from the north and from Earth, the approach speed is far slower,
> and can be as low as 3.6Km/s . This gives a speed of the zone of one second
> to cross any point. This is lower than Carl's figure which was (from memory
> 8 or 9 seconds). I will leave to anybody who wants to go with it to work
> out how long a much larger zone would take to cross a given point.
> My head hurts!
>
> Tom Hollings.
>
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-- 
*Ruud Loeffen*
Paardestraat32
6131HC Sittard
http://www.human-DNA.org
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