How big should Jupiter be ?

[Kevdan]

Hi all,

Last night was my first night with scope, I had some great views of the moon but when I tried to look at jupiter, it just looked like a big dot with dots around it, and even changing from a 26mm plossl to a 9mm plossl didnt make much difference, even using a 2x barlow didnt help much, I got a Skywatcher 150 with 750 focal length so using the 9mm plossl should have given me 83x and 166x with barlow.

I even tried to look at the orion nebular but could only make out the stars and the nebula itself was very faint.

Could this be down to collimation or the lack of it ? or would I need other EP's or even a 3x barlow

Kev.

[brianb]

Jupiter is small compared with the moon - at the moment you need about x50 to make Jupiter look as big as the moon does to the naked eye.

Nebulae are faint, you need 1/2 hour dark adaptation before your eyes will register them properly & even then they will not look like thne photos. Collimation makes very little difference to low magnification views, at high magnification it causes loss of contrast & resolution but not brightness of extended objects.

[smudgeball]

Hi

To give a very crude example.

Last night my 6" SCT with a 9mm Eyepiece and 2 x barlow looking at Jupiter was like this smiley relative to about half the size of this message box.

It was very clear and you could see the moons around it.

There are lots of factors that determine what you can see as I'm finding out.

Think there is a website where you can put details in and it shows you what to expect, but can't think of the name.

Sure someone will

Regards

Neil

[Kevdan]

Jupiter is small compared with the moon - at the moment you need about x50 to make Jupiter look as big as the moon does to the naked eye.

It was nowhere near that size it was probably 1.5mm - 2mm at most and certainly no coloured band visible, I could see 3 of the moons but couldnt make out which was which. I dont expect to see detail on the moons at all.

When you say "at the moment" could it be due to its position and does it get bigger ? if so when ?

Thanks for the replies

Kev.

Here's a picture sharpened up of the moon

[brianb]

When you say "at the moment" could it be due to its position and does it get bigger ? if so when ?

Jupiter is biggest (nearest) when close to opposition, ATM it's about 2/3 of the size it was in September. It will be even better placed (for those of us in the northern hemisphere) when it comes to opposition again in the autumn.

[RascalUK]

I saw the Orion Nebula for the first time about five days ago and again last night. It was much fainter last night so I put it down to atmospherics.

In Manchester, even though it was a "clear night", there was a paper thin layer of cloud knocking about.

[John]

The moons apparent size is about 1800 arc seconds. Jupiter's current apparent size is around 35 arc seconds so it appears 51.42 times smaller when viewed at the same magnification. So magnify Jupiter by 50x and it will indeed appear the same apparent size that the moon does to the naked eye, although there a lots of factors that won't make it seem that way to our brains !.

This opposition was one of the best for a while and at it's maximum size, Jupiter appeared around 50 arc seconds in apparent diameter, so larger but not hugely so.

To put this in perspective when viewing though a scope, the 9mm plossl eyepiece (no barlow) gives you 83x with your scope and shows .6 a degree of sky (total width of the field of view) which is 2160 arc seconds. So Jupiter, at 35 arc seconds, will currently appear to "take up" 1/62nd of the width of the field of view. (hope I've got that about right ).

On the Orion Nebula - use low power to see the whole nebula. Any light pollution in the sky (whether moon-made or man-made) will drastically reduce how much of the nebula you can see.

[spacebloke]

This is a image I took last night with my neximage. I think neximage give the equivalent of a 6mm ep

Obviously it looks sharper though the eyepiece

Jupiter 12th feb 2011.jpg

[Kevdan]

Thats made it a little clearer , I think, So let me get this right, to the naked eye the moon looks about 10-20mm and to jupiter to look this big I need to magnify by around 50x, but I used the 9mm which is 83x and it didnt look that big or am I not getting it.

Im not expecting to see hubble telescope type views, far from it, and considering this is my first scope which is second hand and last night was my first time using a scope of any description, I was pleased to even make out jupiter and three moons. Would It be better to use a 4-6mm EP for maginfication or go for a 15-20mm EP so as to increase brightnes.

Also would it be sensible to use a light polution filter to help with things?

Kev.

[tbird]

I have just bought the same scope as you and had my first night's viewing last night.

Using the 10mm eyepiece and a x2 Barlow supplied with the telescope Jupiter appeared slightly larger than this O but did show good detail with the cloud bands visible. As the evening progressed and Jupiter got lower the detail disappeared.

By the time Saturn had risen, a thin veil of cloud had stretched across the sky. I could see Saturn, but it was very blurred, only a hint of the rings and about the size of this o .

[John]

I'm not sure the analogy with the size of the moon helps to be honest. Jupiter is well past it's best now as brianb said.

You might want to get a decent quality 5mm eyepiece (150x) like a TMB Planetary. This would be good for Saturn and the moon as well.

The stock 10mm eyepiece and barlow lens are not great quality and won't be helping your scope to give of it's best.

[Neilius]

I think a big factor is atmosphere. I am using a 130mm and on a good night last week, I could (just) make out a division in the rings of Saturn - and then only breifly.

All objects will appear small, even (I guess) if your aperture is 12" at the same magnification. I think using a filter on Jupiter would resolve some detail, as it has always appeared as a very bright disk in my scope. Furthermore, as it moves away from us now, its not on my list of observing objects until next autumn

[Kevdan]

This is a image I took last night with my neximage. I think neximage give the equivalent of a 6mm ep

Obviously it looks sharper though the eyepiece

Jupiter 12th feb 2011.jpg

Hi,

I would have been really impressed if I had an image of this quality.

Nice pic.

Kev.