How large should Saturn be?

[old glyn]

This question will display my ignorance I'm afraid, but I would like to know what sort of telescope would show Saturn the apparent size of a 2p coin held an arms length from the body.

[Moonshane]

I think that most scopes would do so. The thing that will determine magnification broadly is the atmosphere. Saturn is always quite small. I was looking last night at 228x and it was still small in the field of view but quite a lot of detail was visible. usually the best planetary magnifications are between 120x - 200x.

Around 250x is often the absolute max you'll get with any scope on planets in the UK. A 6" reflector (this is what I was using) is certainly capable of this if the seeing is good.

the moon allows more magnification.

[Nillchill]

try this link mate may help you decide

http://www.12dstring.me.uk/fov.htm

[reader34]

Thank you, an awesome website!

[old glyn]

How large might it appear in a 12" aperture jobbie? Or am I wrong in thinking wide apertures give larger images? Sorry to harp on but it appears that I might be missing something fundamental here.

[John]

The maximum magnification usable is mostly limited to around 200x - 250x by the seeing conditions although if you have a larger aperture scope it is occasionally possible to use more magnification than that.

You don't actually need mega-magnfication to see the maximum details that a scope can show. I was observing Saturn with my 10" scope last night and found that 180x was the optimum for a crisp image and nice contrast. More magnification was not leading to more detail - less in fact because the larger image was not so crisp and contrasty.

Another night, with different seeing conditions things might be different.

[Nexus 6]

Hi old glyn, I would definately agree with Moonshane, you'll get some very nice views at around the 200x mark and as comformation of that my best this year have been at 180x, 13mm Televue Nagler/fl scope 2350mm.

It has looked outstanding to me and size wise was not bad but not as big as a 2p coin, for views at that size using the 7mm BGO ep/fl scope giving 336x, the image was pretty poor and I stuggled to make out much detail

[leenewtoastro]

How large might it appear in a 12" aperture jobbie? Or am I wrong in thinking wide apertures give larger images? Sorry to harp on but it appears that I might be missing something fundamental here.

if i'm right aperture won't change the size of object in ep.

?

[great_bear]

Here's another one: Telescope Simulator

[Ad Astra]

if i'm right aperture won't change the size of object in ep.

?

You are quite correct. Aperture gives you more brightness, (more light down the optical path to your eye). Aperture also controls the amount of 'information' in the image, in other words, the best resolution of the scope (smallest detail that you can see on Saturn or the Moon, for instance) is a mathematical function of aperture.

All that optical theory works great if you have the Hubble or Webb space telescope at home - but the rest of us live at the bottom of an ocean of air, and the condition / stability / pollution level / stray light have a much greater affect on maximum magnification (with image clarity!) you can get on any given night.

Best seeing occurs after midnight. The earth cools off, air stabilizes, and many of the local shops and neighbors lights have turned off!

Hope that helps,

Dan

[Moonshane]

You are quite correct. Aperture gives you more brightness, (more light down the optical path to your eye). Aperture also controls the amount of 'information' in the image, in other words, the best resolution of the scope (smallest detail that you can see on Saturn or the Moon, for instance) is a mathematical function of aperture.

All that optical theory works great if you have the Hubble or Webb space telescope at home - but the rest of us live at the bottom of an ocean of air, and the condition / stability / pollution level / stray light have a much greater affect on maximum magnification (with image clarity!) you can get on any given night.

Best seeing occurs after midnight. The earth cools off, air stabilizes, and many of the local shops and neighbors lights have turned off!

Hope that helps,

Dan

just to add the this, the thing that does affect magnification is focal length of the telescope. e.g. a tube 500mm long will give an image half the size of one with a tube 1000mm long with the same eyepiece. in other words magnification = focal length of scope divided by focal length of eyepiece.

[Capricorn]

A 2p coin is 2.5 cm.

My little arm will just make 75cm from the rest of me.

So a 2p coin at arms length is 2.5/75 radians. = 0.03rad.

Saturn has a diameter of 120,000 (seems to be about the average value)

Saturn is 1,320,000,000,000 away (Again the general average is about this)

So Saturn subtends and angle of: (120,000)/(1320,000,000,000) Rad, or 0.00009 Rad, lets say 0.0001 for ease.

To increase the apparent size to the same as a 20 coin you would therefore need a magnification of 0.03/0.0001 = 300x

And the eye would play tricks and you would still think it looked small.

[Moonshane]

very interesting calculation! I had not thought to work is out like that

I agree that when observing the field of view can make a massive difference to how big an object looks i.e. in a wider field Radian Saturn is likely to appear smaller than in a narrow field ortho of the same focal length.

[great_bear]

Best seeing occurs after midnight. The earth cools off, air stabilizes, and many of the local shops and neighbors lights have turned off!

- and also the heat from their rooftops eases off a bit

So a 2p coin at arms length is 2.5/75 radians. = 0.03rad.

I had no idea that it was this simple.

Is this mathematically accurate - or just an approximation?

[old glyn]

Thank you, kind people, for taking the trouble to inform me. :-)

This site seems like an agreeable fellowship where members are keen to assist each other.

[Capricorn]

When using radians the tan of the angle (WHEN THE ANGLE IS SMALL) is very close to the angle itself. Makes the figures a lot easier to play with.

Used Radians as no point converting to degrees and then back again.

All that is wanted is the ratio with is dimensionless.

Pull up the calculator:

Put in 0.01, set the units to Rad and click Tan.

Tan 0.01 Rad = 0.0100003333.

So close enough for this.

Some of the O'Level maths did stick.

Does however make you realise how small Saturn really is.

[Davidv]

Saturn is always quite small. I was looking last night at 228x and it was still small

It's all relative really. I would be chuffed with Saturn at 228x compared to the 176x I'm used to. However, I would say 150x or less was a bit small. Dave

[John]

When we are looking at Saturn through the eyepiece we rarely have anything else in the field of view to give it any scale. I found the photo below of a lunar occultation of Saturn where the Lunar limb does give at least some sense of proportion to Saturns apparent size in the sky.

The other evening, when the moon was full, I held my index finger up, at arms length, and the full moon was about half the diameter of my finger tip. With that in mind, and looking at the picture, it really brings home to me the immense distance between us and Saturn and just how tiny it appears to us, even when magnified hundreds of times with a telescope.

[Key]

It should be a lot larger but as it's so far away we'll just have to make do with it being small!

Some of the pic's on here using quite small 'scopes and images captured through webcams make it clear that you can still get some very nice images - with a fair bit of skill, some luck and a lot of patience!

[ollypenrice]

Saturn will always be small but you would need a staggering lack of imagination not to be transported into a heaven of delight by seeing it in a decent amateur telescope. In fact a decent amateur telescope can give as much as is available in almost anything.

Olly

[wolfytom]

Before I got my scope, I was obsessed with asking "what size will Saturn be" in scope a, b or c?

I opted for as much aperture as I could afford (10") and the planet transports me to that 'heaven of delight' every single time I see it. (Brilliant,Olly) And I'm only using a 10mm ep.

Believe me, it's so beautiful I've barely looked at anything else yet!

[Nexus 6]

Saturn stuns I reakon, if there is one sight that can give us all that feeling of utter amazement , it has to be THE one.

[ollypenrice]

It's what got me hooked, for sure. I was travelling in the Andes and was offered a peep through a small refractor. Life has never been the same since, right down to a change of job and a change of country!! Beware...

Olly

[bcfcciderhead]

Was looking at Saturn Friday (my first night in the new house/garden) and yes about the size of a penny, using my 8" dob and 200x mag, small but the detail was very good.

Lots of WOW factor as always and also had a few neigbours over (now they no i'm not a perv), never seen so many people shocked at what they saw, they loved it, also never heared so many wives saying "no your not having one"

[Donkeiller]

I think this site

http://www.12dstring.me.uk/fov.htm

greatly undersells what you can actually see- certainly for planets.

I reckon I see Saturn and Jupiter at 2-3 times the size of what is illustrated on the

site for a given scope/eyepiece and magnification.

If I could only see in real life the kind of images that this site produces I would sell up and start a new hobby.