A first and a century

I finally had my 100th observing session last night, and it was quite a treat too.

Early in the evening the skies were looking pretty clear (just some thin cloud and haze around, the Moon had a bit of a halo) but still very bright. However, I noticed that Jupiter was placed such that I'd be able to see it from my back garden (it's mostly been out of view for me this apparition because it never rises about my house and it's very difficult to observe from the front of the house). Given that not a lot else was going to be visible at a reasonable hour I decided to get the 905 out and have a look at Jupiter.

At first the image was pretty awful but, as the 'scope cooled, things improved. I could see three Jovian moons, two some distance either side of the planet and one quite close. As I watched and waited for steadier moments I kept noticing a very clear, dark and well defined spot near the north pole of the planet. Given that I was unsure if I was seeing things I swapped eyes, rotated the eyepiece, shifted the 'scope around a bit — anything to eliminate some artifact from something. The image of a dark spot persisted.

I then came into the office and fired up Starry Night Enthusiast 4.5 and zoomed in on Jupiter and, sure enough, there it was: the dark spot I was seeing was the shadow of Ganymede! Not just my first ever sight of a shadow transit but a totally accidental find too.

I first noted it in my log at 21:58UT (I estimate it was just over ½ way through the transit — I've not checked the times anywhere yet) and last caught sight of it at around 22:15 (when I finished making a rough sketch of what I was seeing so I could check things later on). After that some cloud got in the way and by the time it had cleared (around 22:50UT) I couldn't make the shadow out any more.

It was a really enjoyable experience. Not only had I seen a transit, I'd "discovered" it by accident — that sort of made it all the more special.

Edit: I've now published the observing session notes.

File Under: Jupiter, Shadow Transit, Ganymede.


Jeff Stevens said...

Well done Dave, that's a fine observation. I've tried for one of these on several occasions but I have yet to witness one. The 905 must be giving some very clear views.

Dave Pearson said...

I was impressed that I could see it in the 905. It's a shame that it was such a hurried little session — if I'd have more time and conditions had been a little better it would have been interesting to get the 130M out and compare them side-by-side for something like this.

Ian Musgrave said...

Wow, that's great Dave. As Jeff says, I've tried for some time without success to see a shodow transit, congratulations.

Dave Pearson said...

Thanks Ian. Chances are I probably wouldn't have managed it if I'd actually tried to observe it knowing it was going to happen. Seeing it totally by accident was really nice.