Why can't I see Jupiter

[jasperace]

Forgive my ignorance but I am a newcomer to astronomy. I have a small ETX refactor which I can use to see Jupiter as a bright point object with its Galilean moons. I have also recently obtained a second hand 8" Dobsonian scope of ebay. It provides great views of stars and the moon but when I try to look at Jupiter I just don't seam to be able to see a thing. Any suggestions.

[brianmc]

Probably not the same thing, but last night on my first go with my new 8" Dob I got a small black disc on a bright white disc when looking at Jupiter. It was a focus thing, I just had to move the focusser a lot further than I thought I'd have to.

What do you actually see when pointing at Jupiter?

[Alan_B]

What focal length eyepiece are you using ?

[jasperace]

Thanks for the reply. To be honest not a lot. When viewing the open sky faint stars become beautifully bright and reasonably sharp points of light. Observation of the moon reveals excellent detail and a real sense of surface relief. But Jupiter is just impossible to resolve into anything other than a blur. The focuser is not great and it easily slips from any position. Even so I have moved it through its entire length of travel to no avail.

[jasperace]

Thanks Alan 26mm

[sunshine185]

If using the dob, i would check for collimation. Even with a 25mm ep, jupiter and its bands are clearly visible and also its so bright at this mag it will give off glare.purist than this you got me stumped.

[jimmyjamjoejoe]

Focus on something else then move to jupiter without adjusting. At higher mags it gets blurry, so try it with lower mags first then try other eyepieces.

Try your lowest mag first, even if you see nothing more than a large yellowish "star" with 4 little pinpricks next to it.

Edit: yeah, 26mm in an 8ich dob should not be a blur, if you can't achieve focus anywhere in the range then something is up. Is the blur perfectly round or stretched out? sounds like collimation.

[Alan_B]

I agree with '185 about the collimation , especially as its second hand. it's a straightforward process to adjust and you will find lots of advice on here as to how to go about it

[sunshine185]

Do you have any sort of finder on the dob? if you say the stars are clear and pinpoint, the only thing i can think of is that you are not getting jupiter in the fov.

[perrin6]

Detail on the planets varies a lot due to the atmosphere. The moon is a lot more contrasty and detail shoes up more easily but the planets's details are more subtle and need steady atmosphere and patience. Ensure the scope is at the same temperature as the surrounding air by leaving it for about 40 minutes for the 8 inch dobsonian and keep looking because sometimes the air will vary between steady and still, sometimes it will eventually steady and other times it will not steady all night. Keep watching and if not good try again at different times through the night. Try different eyepieces as different objects have different ideal ranges of magnification - mars & saturn tend take high magnifications well, jupiter needs a little less.

[sunshine185]

Sry, just re-read your post, i think the first thing you need to do is get yourself a cheshire, if funds are tight, then a simple collimating cap will do, you can use an old 35mm film canister for this. Collimating will make a world of difference to the dob, if you get stuck, theres loads of people on here who will give you step by step instructions to collimate it. Good luck and let us know how you get on.

[Moonshane]

I seriously doubt this is collimation at 46x magnification, especially if he's getting sharp stars and lunar images which are at worst half decent.

I hesitate to ask this but are you pointing at the right object? Even with your small refractor, I'd expect it to be more than a 'bright point'. I would certainly expect you to see the main two bands even with dodgy collimation in an 8" dob at 46x.

try aligning your finderscope on Polaris - this will not move and then try again.

[MarkbPlym]

Hello

I have a Celestron Travelscope with 2x barlow lens. Last night was the first clear sky evening for a very long time. When looking at Jupiter, it appeared as a small blob in the 25mm eyepiece with 3 moons the size of pin pricks orbiting the planet. (Could not possibly tell which ones!)

I would have expected to see at least some cloud bands on Jupiter, is this because of the time of year when Jupiter is furthest away??

Time and date of my observations 11.50pm 10th February 2013 Plymouth, UK

Stars appear sharp, the moon looks excellent (when it is in view)

Can anyone suggest why, i was rather dissapointed last nights viewings.

Mark Bowles

[E621Keith]

Hello

I have a Celestron Travelscope with 2x barlow lens. Last night was the first clear sky evening for a very long time. When looking at Jupiter, it appeared as a small blob in the 25mm eyepiece with 3 moons the size of pin pricks orbiting the planet. (Could not possibly tell which ones!)

I would have expected to see at least some cloud bands on Jupiter, is this because of the time of year when Jupiter is furthest away??

Time and date of my observations 11.50pm 10th February 2013 Plymouth, UK

Stars appear sharp, the moon looks excellent (when it is in view)

Can anyone suggest why, i was rather dissapointed last nights viewings.

Mark Bowles

I think you are using too little magnification. If you have a travel scope 70 with a barlow lens and a 25mm, it will give you a magnification of 32x. Depending on your eyesight, I'd think you need at least 40-60x to see the bands.

PS. Next time it would be better to start a new thread rather than digging up an very old one

[cotterless45]

You'll need at least x100 to start to tease out detail . At x150 we've seen tears in the belts, gaps around the GRS, further belts to the equator and to the perimeter of the main belts. A lot of detail may be seen, but only with the very best seeing conditions,

Nick.

[MarkbPlym]

Thanks for the info, after some searching around I have come to a similar conclusion as you.

Mark Bowles

[watersblue]

If you were in Wales, I'd blame it on clouds.

[Obi Wan Ken00bi]

Funny question, most of the night I can only see Jupiter

[astronymonkey]

Id agree with Moonshane that this is unlikely to be collimation given the sharp views of background stars and the moon. One possibility is that you are not directly pointing at Jupiter but are seeing some of the internal off axis glare which Jupiter can produce when its just outside of the field of view. This can give some visual artefacts which can sometimes look like you are on the object but out of focus....the moon can also do the same but to a greater extent.

Id start by realigning the finder then searching again, but if you don't see Jupiter in the eyepiece an old fashioned "eyepiece field" to "eyepiece field" sweep around the area should find it.

On a separate note if there is slop in the focuser then this can usually be taken up by either tightening the thumbscrews (or screws on more basic units) which hold the focuser wheel shaft to the drawtube.....by the way, what scope is it (manufacturer, f ratio etc)?

Cheers,

Astronymonkey

[moogoomonkey]

Because of these damned clouds!