Unstripey Jupiter

[PSALM19.1 (Shaun)]

Hi...going back about 6 or so months, I had a 60mm refractor which provided smallish, but crisp and sharp views of Jupiter, where I could see clear dark bands running around it....anyway, I have had an 8" dob for a couple of months now and have looked at Jupiter a few times (3:15am and around 5:00am a couple of times); I guess I was expecting to see a lot more detail with an 8" scope than with a 60mm? Also, I thought the crispness would be better with larger apeture as well? Could it be that Jupiter is not in a good spot for viewing at present? Is Spring a bad time for planets? And the Great Red Spot - should I be able to see it and shadow transits of moons as well?

Any wisdom would be valued!

[Wavytone]

Originally Posted by PSALM19.1

the Great Red Spot - should I be able to see it and shadow transits of moons as well?

Bear in mind Jupiter is rotating so the red spot may or may not be visible depending when you look at it, unlike our moon which always shows more-or-less the same side. Similarly the Galilean moons orbit it and their motion is easily demonstrated over an hour or two.

Consult an ephemeris or a good smartphone astro app, if you want to know what to expect when.

I'll leave it as an exercise for you to find one for yourself.

[Poita (Peter)]

Check the collimation on your dob, if it is out you will really lose that fine detail. A dob will take a while to cool down as well and settle in to get good views.

Also, where you view Jupiter will make quite a difference, if it is just above the horizon it usually is hard to make out any detail, if it is high in the sky then it is usually a lot clearer/more detailed.

On any given night the seeing can vary greatly as well, with an 8" on a good night you should be able to see the bands pretty clearly, sometimes a coloured filter can help bring them out if the image is too bright.

There is a calculator and a printable guide to GRS viewing here:
http://www.skyandtelescope.com/obser...tml?page=1&c=y

[rustigsmed (Russell)]

also the app Gas Giants (on iphone etc) is an awesome tool for seeing GRS, moons, transits etc. I got it for free the other day.

planetary is very much dependant on the 'seeing' if the jetstream is unsteady it will 'blur' the view more.

[PSALM19.1 (Shaun)]

Thanks all; yes, collimation seems spot on (my eye-ball is smack dab centred when looking through the eye-piece) and thanks for the tip about using a filter - I have a set of them but thought it was only good for moon viewing! From where I am, Jupiter is certainly not high in the sky and that may be the problem....thanks again!

[PSALM19.1 (Shaun)]

One more thing...thanks Peter for mentioning a Dob needs to cool down: I have heard/read a few differring views on just how long it is supposed to take to cool - I generally don't use the cooling fan at the moment because here on the south coast of NSW it's still relatively cool at night; so how long would it take to cool generally? And does it make a big difference in what you can see?

Thanks again....

[Poita (Peter)]

If it is cool at night then it is more reason to run the fan!

You need to get the glass down to close to the same temp as the air, so if it has been a hot day and is a cold night, then the cool-down can take ages.

I take the scope outside as soon as the sun has gone down, that way when I am ready to view, it should be close to ambient temperature.

[PSALM19.1 (Shaun)]

Thanks again Peter; it didn't occur to me that a cool down would take longer after hot day and then cool night! Makes sense...now...

[barx1963 (Malcolm)]

All good advice, but as I have mentioned in another post, newts have a noticeable diminishing of contrast due to the obstruction. That may be contributing.
Also a larger image (as I am assuming you are getting with the dob) will also magnify the atmospheric distortions.
Planets are really a case of patience. On most nights you have to observe for a while to get those fleeting moments of clarity.

Cheers

Malcolm

[PSALM19.1 (Shaun)]

Originally Posted by barx1963

All good advice, but as I have mentioned in another post, newts have a noticeable diminishing of contrast "due to the obstruction. "That may be contributing.
Also a larger image (as I am assuming you are getting with the dob) will also magnify the atmospheric distortions.
Planets are really a case of patience. On most nights you have to observe for a while to get those fleeting moments of clarity.

Cheers

Malcolm

Sorry Malcolm, what do you mean by "the obstruction"?

[PSALM19.1 (Shaun)]

Okjust read your other post and now know what the obstruction is! Thanks!