Transition of Callisto

[David55]

Strange weather this. Most days are cloudy and wet and yet most early evenings have clear periods which then getting increasingly hazy ready to rain the following day. Perhaps it is a local climate effect. For these conditions I usually use my Meade ETX80 'desktop' scope which is deployable in seconds and doesn't really need to cool down at all. But last night I dragged out the 200p dobsonian from its Christmas storage as the wind seemed to be making for some particularly clear views.

At this time of year I use the Pleiades as a sort of calibration check to see how good the seeing is and at least to be able to say I saw something before the haze/cloud develops. I was really after M50, which, although bright, is rarely far above the roof of the house next door, but the haze in that direction was already developing so where to go?

Jupiter obviously- my favourite object because it is always changing. It was taking magnification well, so, having centred it with my 32mm Panaview, I swapped to my 6mm Williams Optics SPL eyepiece. The main bands were fairly clear but there was a frustrating piece of dust on the lens just over the planet. So I changed to my 12.5 mm Meade Plossl. The smaller view was crystal clear but the dust remained. OK, you've guessed it, not dust but a moon transiting across the surface of the planet.

Forgive my ignorance, but it was late and I've never witnessed a transition before. And I've seen plenty of things that turn out to be optical errors- nebulosity around the Pleiades due to haze or poor focus being my favourite.

In fact, once I had my eye 'in', I could see the moon's shadow using just about every eyepiece (Barlowed or not) I have, the best view coming from the 9.6mm Plossl which came with my Meade.

And to confirm that my observation of a transition was correct, I turned to the free Jupiter Guide app I have on my iPhone- get it if you like like Jupiter. The app provided confirmation and told me that the moon in question was Callisto. It also told me that I was hours away from being able to see the Great Red Spot.

So that was me done for the evening. Happy with another 'discovery'. Super hobby isn't it?

[Moonshane]

Great report David. I think this is a classic example of learning from things that go wrong. Seeing a moon/shadow transit across Jupiter's disc is one of my favourite things to observe. next time, try to spot the moon on the disk too. They are harder to spot but it gets easier the closer to the edge of the disc the moon gets.

[estwing]

caught it myself,well done.

[cotterless45]

Neat ! Nothing beats a good transition, caught two moons right on the edge of the disc. It was like watching a space ballet !

Nick.

[Astro Imp]

Great report David, I've managed to see shadow transits but as yet have not been able to observe the moons themselves.