Airy Disk??

[steady12]

Hi all..

Just got my telescope out properly for the first time and tried viewing jupiter( after spending a while today alinging finderscope, and focusing etc)... however all I am seeing is an airy disk? (or atleast this is what I am led to believe I am seeing after some goog'ling) Can anyone help explain what this is and why I am seeing one? Totally confused and a complete beginner! Any help much appreciated! Cheers.

SkyWatcher Skymax 127 SynScan Az GOTO (211) 25mm lense.

[John]

If you are seeing true airy disk you are possibly looking at a star rather than Jupiter. Can you see the dark shadow of your secondary mirror on this disk ?.

You will need to allow your scope good time to cool if bought out from a house - 40 mins or so is needed in winter conditions.

[Mr Spock]

An airy disk is what you see viewing a star at high power. It's usually surrounded by one or more diffraction rings. Why you get this when a star is a point scource has to do with the resolution of the telescope: the higher the resolution, the smaller the airy disk.

You will not see an airy disk on Jupiter as it isn't a point source. What you are seeing is Jupiter as a small disk because you are using a low power eyepiece - x60 with your telescope. You need a much higher power eyepiece to see detail, probably a 10mm or 8mm.

[faulksy]

as mr spock probably not enough power so you wont see any detail. with the 25mm can you see the moons floating around jupiter could be 4 depends were they are but should see 2-3 probably about 2 jupiter diameters away from main planet

[Capricorn]

Hate to disagree but I have seen banding on Jupiter at 29x, at 60x I would expect reasonable detail to be apparent. Especially on a Mak.

Is what you are seeing a disk (solid) or a ring (Doughnut like).

If the latter then you may simply be way out of focus, have seen the same on a few SCT's when the focus has been out.

How sure are you it was Jupiter in the view?

The 127 will have a fairly narrow field of view.

[angusb1]

You might need the diagonal (looks like a right angle with a mirror in) in to get it to focus. If you haven't then Jupiter could appear as a big white blob with no detail and the secondary will appear as a dark disc in the centre of that.

[steady12]

Thanks for all the responses... been a great help, atleast I can eliminate the airy disk idea (feel slightly daft now).

I spent earlier today aligning the finderscope with telescope and am certain that it is jupiter- but I think as you have all suggested this is probably way out of focus (and also I didnt give it time outside to cool after bringing out from indoors)... It is doughnut shaped, so I will have to spend some time tomorrow focusing my telescope properly, as I've no idea where to begin at night haha. I should mention that I have used it once before and managed to view jupiter with the 25mm with some success- could see 4 moons and jupiter, and then with a 10mm briefly before the clouds came and ruined it... however tonight it was just a doughnut shaped blur of nothing!

Too eager as a beginner to just point it at something and view things straight away- going to have to do a bit more reading and have some patience i think!

Thanks again for all your help!

[John]

You need to focus your scope as you are viewing something you want to look at. Astro objects focus at a completely different position from terrestrial objects. By all means find out how to adjust the focus in daylight but when using the scope it's something thats done "on the fly".

I assume the object you were looking at was not far from the Moon, as Jupiter is at the moment. There was a brighter object visible in the west in the early evening which was Venus - that would be an oval "blur" through an un-cooled scope probably.