Jupiter Transit

[supernova1965 (Warren)]

Hi everyone just want to check. I was checking out Jupiter at about 6.45pm and I saw the normal 4 moons stretched out but then I saw what looked like another moon transiting the center widest band it was smaller than other transits that I have seen was it a moon or something else hopefully a hit? I couldn't be so lucky but even a smaller moon would be great.

[Glenn Dawes]

Hi Warren,

It was Europa's shadow, the moon closest to Jupiter at the time.

Regards

Glenn

[ngcles]

Hi Warren & All,

On the subject of Jupiter's satellites, someone the other day (here or elsewhere, I can't recall) recommended this piece of freeware:

http://www.astrosurf.com/rondi/jupiter/

Jupiter 2 is excellent and only a small download.


Best,

Les D

[supernova1965 (Warren)]

Originally Posted by Glenn Dawes

Hi Warren,

It was Europa's shadow, the moon closest to Jupiter at the time.

Regards

Glenn

Thanks for the clarification was that the moon on the right while looking through the scope real close to Jupiter. I learned something great I thought that the moon also had to be in front of the Planet to leave a shadow.

[astro744]

It is all about triangles.

At opposition Jupiter-Earth-Sun angle is zero in one plane and a few degrees in another. Either side of opposition the Earth-Jupiter-Sun angle increases to a maximum determined by the size of the orbits and then shrinks back to zero at conjunction (Earth-Sun-Jupiter).

Draw a triangle with Earth, Jupiter and Sun at each apex. Then draw small circles around Jupiter representing the satellite orbits.

Just look at a single plane for the time being for simplicity. When a satellite is in line with Earth-Satellite-Jupiter the disk is seen to cross planet's surface for observers on Earth. When a satellite is in line with Sun-Satellite-Jupiter the satellite disk would be seen to cross the planet's surface from the Sun but its shadow would be seen to cross the surface from the Earth.

The geometry is a little more complex due to the inclined planes of Earth, Jupiter and all the satellites. Have a look at Jupiter2 software and look at the Polar view (bottom left). The Sun is represented as a yellow dot at the bottom of the picture and the direction toward Earth is the small vertical line. Note the other side of opposition would have the Sun on the left. (When Jupiter is in the pre dawn sky in the east).

[supernova1965 (Warren)]

Thanks for that I am making the brain work that is good this is exactly what I saw got the snapshot from Jupiter2 looks like a very good program thanks Les D for the link.

[Coen]

Jupiter 2 is an excellent little app however it does have an error. I have pointed it out in an email to the author of the app before the latest version came out but got no response. I see it is still present in the current app. Of course it may just be my installation.

If you enter a fractional time zone e.g. 10h 30m, click the "Now" button and see what you get. The click the real-time button, then go back to the now button (do these steps with little time between them). On my screen the positions of the moons skip by about 5 minutes or so - the "Now" skipping forward in time relative to "real-time". Which is right (i.e. the real-time or the "Now") I leave for you to determine.