Jupiter Moon Transit Question = Shadow or Actual Moon

[Bart]

Hello All

Just watched Io transit jupiter. Very distinct black dot. Was i watching the dark side of Io pass, or was i watching its shadow on the surface of Jupiter. Couldn't see a moon AND a shadow transit, there was some wispy stuff up there tonight. Thanks

Barry

[bus_ter]

Yes you would have seen the Moons shadow. If the Moon has gone just past Jupiter you can see the moon and it's shadow falling on the surface. I think it's a lot harder to see the moon if it's still in front of the planet.

[cotterless45]

Super, saw this at 2.15' nice and clear, no sign of the moon throwing the shadow though,

Nick.

[chiltonstar]

Io is more difficult to see - Ganymede is easier for example. When a moon passes in front of a darker area on Jupe it is usually more obvious.

Chris

[NGC 1502]

The shadows of Jupiter's moons are seen as very obvious inky black dots as they transit the disc of Jupiter. High power is not needed to observe this, 80 - 100x is enough, if the scope and the state of the atmosphere are ok, then of course you can go to a much higher mag.

The moons themselves are very much tougher to see as they transit. Your best chance is to catch the moon just after it is on the disc, or just prior to it leaving. The apparently darker edge that Jupiter has (called limb darkening) produces a greater contrast between the moon and Jupiter, making it easier to spot as a very tiny bright disc.

Last Weds ( 21st Nov) I saw the shadow of Ganymede very easily using my 70mm refractor. At 2010 hrs, using my 10" Dob I saw Ganymede itself just within Jupiter's SE limb, its shadow not far from the SW limb. At 2130 hrs, the shadow of Ganymede had left Jupiter's disc, but Ganymede was just inside the SW limb, and the Great Red spot was on the meridian, a cracking sight best view was at 150x.

Regards, Ed.

[michael.h.f.wilkinson]

I have seen many shadow transits, but only seen a moon crossing the surface once or twice. Two factors are important: seeing, and whether the moon crosses a dark region.

[Astro Imp]

Very interesting thread, I have seen several shadow transits but have as yet failed to see the actual moon in transit. Still I'll keep looking, never know one of these days I'll be lucky.

[chiltonstar]

I have seen many shadow transits, but only seen a moon crossing the surface once or twice. Two factors are important: seeing, and whether the moon crosses a dark region.

I have seen many actual moon transits and would say the darker background is important, but also the contrast of the scope, and of course knowing exactly where to look. It's easy in my ED80 and 102mm frac, more difficult with my 5" Mak. I think the same probably applies to the GRS.

Chris

[Johannes]

I agree with everybody I have seen a few transits but only seen the moons on rare occaions. John

[John]

The disk (as well as the shadow) of Europa was clearly visible at the beginning and end of last nights transit at the limbs of the planet the surface, where the surface contrast appears to darken slightly. As soon as the moon moved over the central 90% (estimated) of the surface it became very hard indeed to see against the surface tone which was a very close match for that of the moon.

[Bart]

thanks all, just going outside now to see if i can make out Io and its shadow/

[Bart]

Oh well, just got to where i could see Io against the very outer edge of the SEB and then clouds rolled in. It was as clear as a bell when my alarm went off. They stayed away just long enough for me to get up, make a coffee and then sit down to observe when, BAM, permanent cloud cover......

Barry

[Bluey]

I think there is a transit tonight , starting at 9.52, so I will try to catch my first ever view, clouds permitting of course!

[Dunkster]

I've only seen Io transit and only once...was scratching my head wondering what the dark spot was...then the planet started growing a pimple which then proceeded to separate. Then the penny dropped

[Astro Imp]

I think there is a transit tonight , starting at 9.52, so I will try to catch my first ever view, clouds permitting of course!

I was waiting for this, had some good views and then clouds.