Confused about Saturn.

[LukeSkywatcher]

OK so i have just come in from a really good night outside. Progress on seeing Mars is coming along very nicely.

I turned my 130P on Saturn and man oh man was i nearly in tears with sorrow.

Last time i looked at Saturn was a couple of yrs ago and then i observed it with my 90EQ scope. Saturn was AMAZING. In the scope the disk of the planet was a very pleasing size. If memory serves me well (and it usually does), Saturns disk was about the size of a pea held at arms length (maybe a slight bit smaller). OK the rings were quite wide open at the time which was great but what i'm talking about here is just the actual planet size.

Tonight when i observed it.......it was tiny. Not a hell of a lot bigger then Mars.

I know Saturn is close to the moon (directly above it when i observed) and that would make things difficult for seeing detail etc but surely that would not have any effect on the actual size of the planet.

I include a couple of simulted images of Saturn in both a 3" scope and a 5" scope. I can honestly say that the image in the 3" scope is pretty much as Saturn appeared in my 3.5" scope, but the image of it in the 5" scope is NOT what i saw tonight in my 5" scope. It looked more like i was using a 1" scope to observe.

Any ideas on what i am doing wrong?

Scope is collimated as best i can get it. It was cooled down enough as i had been out for a couple of hours. I tried it with every EP i own and even a 2x Barlow. Nothing seemed to work. It remained tiny and as the magnification was increased the views got worse. I distinctly remember using a 9mm EP on it with the 90EQ scope.

Thanks in advance.

[DarkerSky]

Hi Paul. I wonder if Saturn's poor declination might be the difference? It being quite low down in the sky at the mo means more air turbulence and less clarity in the views. Not sure how high in the sky it would have been when you observed it in your 3"

[LukeSkywatcher]

Maybe the declination has something to do with it, but every time i have observed it it has been really high up (well above the "dirt" in the atmosphere).

I've been thinking about this for a few hrs now and here is what i have come up with:

a) Planets observed (Jupiter and Saturn and Mars) with my 90EQ scope looked great. I could see detail on them all. They were all quite big in this scope.

Planets observed (Mars and Saturn) with my 130P scope look terrible. Next to no detail and they are very very small.

c) The 90EQ scope has an apeture of 90mm and a focal length of 1000mm

d) The 130P scope has an apeture of 130mm and a focal length of 650mm

Conclusion

It seems to me that the smaller apeture scope with longer f/l is good for planetary observation but not much good for DSO observation, while the larger apeture scope with shorter f/l is good for DSO observation but not much good for planetary observation.

I may be way off the mark here but that is the only thing i can think of.........my new scope with its short f/l (650mm) is a bit pants for looking at planets.

I have included an image of Saturn i found online that shows roughly the size it appeared in my 5" scope. Its not exact but close enough.

[coxie]

that last image is how i saw saturn in my 130p too paul. I only had a 25mm eyepiece though as i didnt have much time left and have only observed it once, all i can say is i hope it gets better than that for me. I am yet to see any detail on mars yet just still looks like a star to me.

[dweller25]

Sorry if I'm teaching you how to suck eggs but a 9mm eyepiece in your 90mm scope will give x111, the same eyepiece in your 130mm scope wil give x72.

With the 9mm eyepiece and a barlow you will get x222 in the refractor and x144 in the reflector.

To achieve the same magnification as the 9mm gives in the refractor you would have to use a 6mm eyepiece in the relfector.

HTH

[brianb]

You need shorter eyepieces - or a stronger barlow - with a short focal ratio scope.

[LukeSkywatcher]

Sorry if I'm teaching you how to suck eggs but a 9mm eyepiece in your 90mm scope will give x111, the same eyepiece in your 130mm scope wil give x72.

With the 9mm eyepiece and a barlow tou will get x222 in the refractor and x144 in the reflector.

To achieve the same magnification as the 9mm gives in the refractor you would have to use a 6mm eyepiece in the relfector.

HTH

Thanks Dweller. I was/am aware of the numbers you stated. I did try the 6mm EP in the reflector but was frustrated and tired by then so didnt give it a fair go. Also not too easy to find saturn at that mag (even when stepping up/down from 32mm,20mm,10mm). Removing and replacing the EPs causes Saturn to go missing,LOL.

I will try it again next clear night.

[LukeSkywatcher]

You need shorter eyepieces - or a stronger barlow - with a short focal ratio scope.

I have two 2x Barlows. Would it be worth my while stacking them with say a 15mm EP?

[dweller25]

I wonder if it's a difference in the apparent field of view you are seeing ?

[LukeSkywatcher]

I wonder if it's a difference in the apparent field of view you are seeing ?

It would have to be a huge difference to show the results i saw earlier then what i saw 2 yrs ago.

[yeti monster]

Your first image is how I remember my first view of Saturn, many moons hence, through my 84mm newt using the 6mm EP. A view I haven't been able to repeat this time around, using the 114mm newt, and only just got close to with the 10" SNT, using a 4mm EP. I think now my problem is the quality of EPs that I currently have. Future purchasing, of good quality kit, will improve things I'm sure.

[Cornelius Varley]

Something to remember about the planets is that they are n ot stationary objects. In the intervening two years Saturn has moved, so the distance between the Earth and Saturn has also changed. Have you looks through your 90mm recently to compare the size of Saturn with what you remember from two years ago ?

Peter

[LukeSkywatcher]

Something to remember about the planets is that they are n ot stationary objects. In the intervening two years Saturn has moved, so the distance between the Earth and Saturn has also changed. Have you looks through your 90mm recently to compare the size of Saturn with what you remember from two years ago ?

Peter

I'd be stunned if Saturn has moved that far away in the last couple of yrs. I have yet to have another look through the 90EQ to see if it is as i remember. THAT will be a true test.

Typically though it is cloudy today and no sign of it going to be a clear night.

[brianb]

In the intervening two years Saturn has moved, so the distance between the Earth and Saturn has also changed.

Distance between Earth & Saturn only varies about 20% ... not 1000% like Mars.

[LukeSkywatcher]

Distance between Earth & Saturn only varies about 20% ... not 1000% like Mars.

Exactly. So you can see why i am wondering just why the difference in size appears. I think i can rule out the distance issue. The difference between the 1st image and the last image is a LOT more then 20%.

Also one thing to note that may shed light on it is that Mars,Saturn,Jupiter were all roughly (give or take) the same size as each other when viewed in 90EQ scope and they are also now roughly give or take the same size as each other when viewed in 130P(except Jupiter cuz i havent seen it in the 130P).

My apeture is bigger now but my f/l is just over half of what it was. I really cant help but think this is the cause.

Some scopes are better suited for planets then others.

My plan of action is to:

a) Observe Saturn with the 90EQ again.

Give more time with 6mm EP (with/without barlow) on the 130P

c) Stack both barlows and then observe with various EP's (i dont like the idea of adding yet another glass to the equation but it has to be tested)

I'm down but not out. There is an answer/solution to this.

Thanks so far for all your comments,suggestions.

[brianb]

Mars,Saturn,Jupiter were all roughly (give or take) the same size as each other when viewed in 90EQ scope

Eh?

The globe of Saturn is at the moment fairly similar in size to that of Mars (apparently!) but Jupiter is always at least twice as big. In fact Jupiter's equatorial diameter is (apparently!) about the same size as Saturn's ring span.

When Saturn's rings are well open, the planet as a whole does look larger, that's a visual illusion, eye & brain being confused by the ring system.

[LukeSkywatcher]

Eh?

The globe of Saturn is at the moment fairly similar in size to that of Mars (apparently!) but Jupiter is always at least twice as big. In fact Jupiter's equatorial diameter is (apparently!) about the same size as Saturn's ring span.

When Saturn's rings are well open, the planet as a whole does look larger, that's a visual illusion, eye & brain being confused by the ring system.

Well yeah i didnt REALLY mean Jupiter also. I just meant in the 90EQ it was a very nice size. Clear banding on the surface etc.

You are right about Saturn and its open rings. Obviously it does appear larger, but the planet disc size remains the same.

The globe of Saturn is at the moment fairly similar in size to that of Mars (apparently!)

Yep as i said earlier both appear about the same size right now. That really would explain it. I never thought that Saturn could appear that size.

Ahhhhh i dunno. I'm no planet expert. I just cant get over the difference in size between 2 yrs ago and now. Maybe Saturn was at opposition back in Feb 08?

All i know is that i saw Saturn as big as it is in the 1st image and last night it was as is in the last image. Granted different scopes but surely the size difference cant be THAT big.

Hence my confusion. Next clear night all my confusion will be laid to rest.

I HOPE.

[LukeSkywatcher]

I just had a look at Stellarium. Saturns apparent diameter is: +0 degrees 0'45.2"

Mars apparent diameter: +0 degrees 0'11.9"

So Saturn should appear about 4(ish) times as large as Mars does right now?????

But it is further away. It must be 4 times as far away because last night the diameter of both planets was roughly the same.

Think i'll go have a lie down and rest my tired brain.

[James]

I find perception plays a big part in this. My best view of Saturn ever as at Kelling at the Spring 2007 event. It was huge in my eyepiece and I was able to get to 400x easily etc etc...

Problem is, the next time I looked at it under the same circumstances (same mag, scope etc but worse seeing) it appeared much smaller than I remembered it. The next time I looked under the same circumstances it seemed smaller again and the next time and the next. In fact everytime I look at Saturn I think it's smaller than the last time but in reality it isn't and can't be. I've come to the conclusion that certainly in my case it's just a perception issue - my memory seems to boost the size of the view for me automatically.

James

[brianb]

Saturns apparent diameter is: +0 degrees 0'45.2"

Half the story. BAA Handbook gives (for 0h UT March 5th) equatorial diam 19"4, polar diam 17"5, ring major axis 44"1. Mars at its closest this year was 14"1. Jupiter will be 49"9 when at its closest in September.

[LukeSkywatcher]

Ok so lets put this one to bed. Am to to deduce from this that even though i was/am only talking about the actual planet size (equatorial diameter), when the rings are closed up as they are now that the brain plays dirty tricks on you and makes the equatorial diameter look smaller then it appears when the rings are open?.

So the planet diameter (eqautorial) is actually the very same as it was 2 yrs ago when the rings were open but now the rings are closed the brain is fooled into thinking the planet diameter is smaller..................which as we all know is impossible unless Saturn has shrunk and we dont know about it,LOL.

OK i can live with that. I dont like it but what can i do about it.

When do the rings open up again to what they were back in 2008?

Thanks all for being patient and understanding with me on this.

[brianb]

Saturn takes ~30 years to orbit the sun, during which the rings go from fully presented (north face) through edge on to fully presented (south face) and back through edge on to the starting point. So it goes about 12 degrees along the ecliptic per year ... taking 7.5 years to go from edge on to fully open, though they will be half open 2.5 years after ring crossing (which occurred in Sep 2009).

Next time the rings are fuilly open (around 2017) Saturn will be in Sagittarius, very badly placed for those of us un northern Europe. Make the most of the next year or two.

Edge on rings are excellent opportunities for seeing Saturn's fainter satellites, which get washed out by the glare from rthe ring system when it's well presented.

[LukeSkywatcher]

Last night i couldnt tell what were moons of Saturn or just background stars. Guess that will come with time and experience and learning.

Thanks for the info on the rings. Half open over the next couple of yrs is good for me.

[Chris H]

I have had the same problems identifying Saturn's moons, I have taken to sketching everything I can see in the ep and comparing it with the next sketch done on the next clear night. I now know which are the moons just not which moons they are.

[brianb]

I have taken to sketching everything I can see in the ep

If your sketch is reasonably accurate, and timed & dated, you should be able to run Stellarium, set the same time & date and map the positions of the satellites. Alternately run Stellarium first, print off a labelled image of the field & use that at the eyepiece.