Five planets and a Jupiter transit

[mike.brightmore]

Just had a long night in the Solar System. The waning gibbous moon was so bright that I thought I would just stick with that, and Jupiter of course. The moon was exceptionally clear though lacking in depth due to it being almost full. Plenty of detail around the rim and along the terminator though and the craterlets in Plato were very clear.

Jupiter was magnificent as ever but no-one told me there was going to be a transit of Callisto. Europa and Callisto were on one side and Gannymede and Io the other - with Callisto very close to the planet.

Uranus was close to the moon, below and to the left, but I went for it anyway. It showed a distinct, milky white disc which took all the magnification I could throw at it - but no surface detail of course. After a bit more lunar and a look at Herschel's crater, seeing as he discovered Uranus didn't he - but it wasn't very clear - I went back to Jupiter about 1.00 a.m. and Callisto was transiting in front of the planet. Now this is the bit I cannot understand. I watched this transit until about 4.00 a.m. until I lost Jupiter in the murk and there were definitely two distinct black spots moving across the face of the planet (southern belt) from the direction of Europa towards Ganymede and Io. These black spots were about a quater of the width of the planet apart. I would expect to see one spot i.e. Callisto's shadow on the surface, but not two. Presumably one must have been Callisto and the other its shadow, but being illuminated I would not have expected to see Callisto as a black spot. Did anyone else see this???

Then winkled out Neptune which was very close to Jupiter. This was very small and faint and I couldn't detect any of its familiar blue colour. After Jupiter had sunk into the murk I had a look at Mars - not impressive as it is small and distant and it was getting light. Then finished off the night with the lovely gibbous Venus - but still puzzled about the two black spots on Jupiter though. During all that time I only saw two Perseid meteors. Doesn't bode well for Wednesday does it?

[Izar]

Mike

I started observing Jupiter late last night, and the seeing was fantastic. I've never seen so much detail before, white/black spots,

the NEB appeared split in places, SEB cleary split in two,even managed to see the STB as two separate bands, Numerous

faint bands from the NTB upwards to the darker pole and activity in the Equatorial Zone.

Then spotted the impact scare in the south, just superb.

As the night night went on, I spotted the jet black shadow of Callisto bite a notch out of the side of Jupiter. I thought this will be interesting, will my Takahashi scope be able to see the Moon transit the globe as a very bright white/silver disk. Then to my surprise, it

appeared as a dark spot on the face of the gas giant.

To me, the colour looked slightly less intense than the shadow.

The shadow was jet black (darkest feature on the planet) and the moon did not have the same intensity of blackness, but was still a dark feature that was easily seen.

It was quite a sight, with the shadow and Callisto both running along the edges of the two separate belts of the SEB.

I had read before about the moons appearing dark in transit (some old Victorian book), but this was the first time that I've actually seen such an event. I wonder if it was some type of contrast effect?

[yeti monster]

I would image that it is to do with the amount of light being reflected directly towards us, obviously the planet is reflecting far more than Callisto, so yes it will be a case of sharp contrast between the two.

[brianb]

I would not have expected to see Callisto as a black spot. Did anyone else see this???

Yes. It's normal; Callisto's surface is much darker material than the bright clouds of Jupiter, or the surfaces of the other moons. What surprises me is that Callisto's shadow appears so much bigger than the satellite itself - you'd expect the converse; we're obviously seeing the penumbra as near black.

[mike.brightmore]

Which spot was the moon and and which was its shadow. Did the moon appear first on the face of Jupiter and then the shadow or vice versa. From the timings it would make more sense to me if the shadow preceded the moon.

[mike.brightmore]

Thought I would include a couple of snapshots (would love to see some proper ones if anyone imaged this transit). The first was taken with a Watec video cam at 0255 hrs (35 sec AVI at 25 fps stacked in Registax). The second with a Canon 350D DSLR at 0336 hrs. (1 sec exp at ISO 400). Ganymede and Io are bottom right and the two small dark shadows were moving towards them.

[seiko]

Thanks for posting Mike, Managed to see Callistos shadow myself through a little 5i.

[brianb]

Did the moon appear first on the face of Jupiter and then the shadow or vice versa. From the timings it would make more sense to me if the shadow preceded the moon.

The shadow - which appeared larger & darker - appeared first.

One rough image follows (work in progress), taken at 0127 UT 9th August 2009. North is up. Callisto's shadow is close to the centre of Jupiter's globe, and Callisto is just inside the eastern limb slightly south of centre.

[mike.brightmore]

Thanks ever so much for that Brian. I understand it all now. Looking forward to the next transit.