Transit

[hickny (Peter)]

Is it possible to see the shadow of Jupiter's moons through an 8" dob? I have tried many times since May when I got my scope to witness a transit and haven't seen a shadow. Io's shadow is supposed to be visible at 6:46pm tonight. I can't see it. Is my scope the problem?

[erick (Eric)]

Peter, I've seen the moons' shadows in my 8" GSO dob. Questions/suggestions - are you well collimated? Do you see some banding on the planet's disc? Has the seeing been satisfactory each time you have tried? Is it too bright? Are you up to as high a magnification as seems reasonable - perhaps 200x or more?

Try your moon filter if it is too bright for your eyes.

Know where the shadow will be from your software so you know where to look.

If seeing is not great, the shadow will come and go in your view.
Just watch continuously as you track the dob.

If you are not seeing at least one band across the planet, I suspect you won't see the shadows and you might wish to check your collimation.

Good luck! Tell us how it goes.

Eric

[hickny (Peter)]

Originally Posted by erick

Peter, I've seen the moons' shadows in my 8" GSO dob. Questions/suggestions - are you well collimated? Do you see some banding on the planet's disc? Has the seeing been satisfactory each time you have tried? Is it too bright? Are you up to as high a magnification as seems reasonable - perhaps 200x or more?

Try your moon filter if it is too bright for your eyes.

Know where the shadow will be from your software so you know where to look.

If seeing is not great, the shadow will come and go in your view.
Just watch continuously as you track the dob.

If you are not seeing at least one band across the planet, I suspect you won't see the shadows and you might wish to check your collimation.

Good luck! Tell us how it goes.

Eric

Eric,
Thanks for the info. Yeah my scope is as collimated as I can get it. Jupiter is very bright. I see the pinkish bands more clearly in the late afternoon. In the dark of night they are hearder to see. I have been using my 9mm eyepiece and occasionally the barlow as well. I'm not impressed with the view through the barlow. I am viewing from my backyard in Sydney so I suppose the viewing is not as good as a dark sky location. One day I hope to go to a dark sky and observe.

[erick (Eric)]

Hmmmm. 9mm in a well collimated scope should be fine - depending on seeing conditions.

Also you don't need dark skies. Jupiter swamps skyglow!

My only comment then is are you sure you are looking at the time the shadow is on the planet, and not just a time when the moon is in front of the planet? The shadow trails the moon a reasonable amount at the moment. Perhaps use the software Jupiter2:-

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

Several people say this is the best Jupiter software. Make sure you have the orientation right and aren't looking for a shadow towards the bottom of your image when it's actually at the top!

OK, I've just checked. I make it Europa's shadow at 6:46pm. Perhaps look for an Io shadow transit (around 9pm 17 August, I think). It's closer to the equator - might be easier to see?

You'll get it, I'm sure. I saw a double transit and the seeing was average, so the shadow would come and go in visibility. As Jupiter drifted across my field of view it would snap into place, then vanish again.

Here's the thread where I and others discuss this - and some photos:-

http://www.iceinspace.com.au/forum/s...ad.php?t=21110

[hickny (Peter)]

Eric,
A minor point but Jupiter2 indicated Io? Or am I using it incorrectly. I'll try with the green filter I was given when I bought the scope.I had the adjustment for UTC at 2 hours instead of 10. Have only had the new PC for 1 day and am progressively adding and configuring more software. Silly me

[erick (Eric)]

Yes Peter, you had a UTC timing error. But you made me go and check Jupiter 2. At home I didn't have Jupiter 2 installed, so I used Sky View Cafe ( http://www.skyviewcafe.com/index.php ) when I replied last night. Yes, Jupiter 2 also shows the 6:46pm transit as Europa. Of course, Europa's shadow transits at a different latitude on the planet - you might have been concentrating elsewhere?

One thing is to get the orientation (N/S, E/W) of the software display the same as you see through your eyepiece. I use the positions of the Moons to clarify that - look for a time when you have a clearly unique distribution, both E/W (say three on one side and one on the other) and N/S (Ganymede is useful for this - it moves clearly from N to S as it orbits).

I think you should also put your moon filter on, to reduce the light. That's probably the green filter?

Everyone else, am I missing any suggestions for Peter to help him see these shadows?

[Blue Skies (Jacquie)]

I think seeing conditions should be taken into account and also the observers experience.

I've seen shadow transits a few times in my 8" too, and while Io is fairly easy to see, Europa can be a bit harder. Occasionally I've also been able to follow Io itself as it crosses the disc, but Europa is a bit small again for that in an 8".

If the seeing conditions aren't good you're going to struggle. I usually tell people that they have to be patient viewing the planets - depending on the night, you might get a period of 'wobbliness' then one to two seconds of steadiness where the shadow should pop out, then back to wobbliness for a while. Because of this it's best if you're sitting down and viewing to that you can put your full concentrating on looking at Jupiter and not have to worry about holding your body upright.