I Thought They Said Jupiter Was Big?

[Mr Spock]

It's meant to be viewed on a computer

[popeye85]

You ain't gonna see what some telescope boxes display.

tell me about it-on the box it shows a family all smiles looking through a scope into the sky, well when I drag my wife out of bed at 3am to look at, in her words-'another *insert curse here* star!' it really is not the same  as pictured on the box-I have a good mind to sue for false advertising!!

[LukeSkywatcher]

tell me about it-on the box it shows a family all smiles looking through a scope into the sky, well when I drag my wife out of bed at 3am to look at, in her words-'another *insert curse here* star!' it really is not the same  as pictured on the box-I have a good mind to sue for false advertising!!

I bought my 1st scope ( 90mm eq frac) partly because of the amazing images on the box and the promise that i'd see the same through the scope and partly because it was the perfect scope for me being in a wheelchair.

Wrong on all counts. I saw nice things but not as seen on the box. When fully assembled and ready to move around the garden the whole thing weighed in at 40Lbs and i can barely stand on my 2 legs let alone do a hand-stand to be able to observe with the scope and the silly positions the scope gets into while on an EQ mount.

I really enjoy observing Jupiter at 100-150x (with my 8Se). Its small but for me it seems to make the subtle details clearer and sharper. My first viewing of the planet lasted a full 10 hrs (a whole day on Jupiter). I loved watching the moons dance around and change position, vanish behind the planet and re-emerge.

Its a very dynamic planet unlike the rest of them which are pretty static.

[Chipela]

A magnification of 100x wiill make Jupiter much larger than the full Moon seen with the naked eye. Try looking at the full Moon through an empty tube and see how small the Moon then looks.

At the beginning I was very surprised how small the planets looked like in the eyepiece. I had made the math that a jupiter with ~30" diameter is 2.5x the size of the moon with 167x magnification. And yet it looked so small.

I came to the conclusion that for some reason the objects 'seem smaller than they really are' in the eyepiece. Or that the moon is not as large as one first thinks it is.

[geministar]

At the beginning I was very surprised how small the planets looked like in the eyepiece. I had made the math that a jupiter with ~30" diameter is 2.5x the size of the moon with 167x magnification. And yet it looked so small.

I came to the conclusion that for some reason the objects 'seem smaller than they really are' in the eyepiece. Or that the moon is not as large as one first thinks it is.

Say Jupiter is about 40" (arcsec) on average.

The Moon is about 0.5 degrees, that is 30' (arcmin) or 1800".

So at the same mag (or with the naked eye), the Moon appears about 1800/40 = 45 times bigger than Jupiter.

At a mag of x167, your true FOV might be 1/3 of a degree (depending on focal length), i.e. 1200".  So in the eyepiece, you would see about 2/3 of the Moon, but Jupiter would occupy 1/30 of the view.  

Whichever way you look at it, the Moon will always appear to be about 45 times the size of Jupiter (through the same EP).

This has nothing to do with real size.  It is just angular size - the angle that the object subtends at the eye, which depends on real size and how far away the object is.

(If I've made any mistakes in all this, I look forward to being corrected!)

[acey]

Say Jupiter is about 40" (arcsec) on average.

The Moon is about 0.5 degrees, that is 30' (arcmin) or 1800".

So at the same mag (or with the naked eye), the Moon appears about 1800/40 = 45 times bigger than Jupiter.

At a mag of x167, your true FOV might be 1/3 of a degree (depending on focal length), i.e. 1200".  So in the eyepiece, you would see about 2/3 of the Moon, but Jupiter would occupy 1/30 of the view.  

Whichever way you look at it, the Moon will always appear to be about 45 times the size of Jupiter (through the same EP).

This has nothing to do with real size.  It is just angular size - the angle that the object subtends at the eye, which depends on real size and how far away the object is.

(If I've made any mistakes in all this, I look forward to being corrected!)

Chipela is not suggesting that Jupiter in a telescope looks bigger than the Moon in a telescope, but that Jupiter in a telescope can have larger angular diameter than the Moon with the naked eye, yet we have a sense that the naked-eye Moon is large while the  enlarged Jupiter is small. It's a matter of visual perception. When we see a naked-eye full Moon near the horizon we perceive it as unusually large - an illusion that has been explained in various ways, but seems to be connected with our intuitive judgement of its distance in relation to terrestrial objects.

I wonder what impression the following would give. Print a silhouette horizon (trees, hills, roofs etc) on a very small piece of transparent acetate. Fix it on the field stop of a plossl so that it appears in focus when viewed through the eyepiece. Then look at Jupiter "rising" over this artificial horizon. Perhaps this would make Jupiter look bigger, though of course its angular size in the eyepiece would be unaltered.

When we look through an eyepiece we have a tendency to focus our own eye for near rather than distance vision. This could contribute to the pea-effect. I've tried relaxing the eye as if viewing at infinity, but since I'm astigmatic it gives a poorer view. People with better eyesight might find it gives the impression of a larger object.

[Chipela]

Chipela is not suggesting that Jupiter in a telescope looks bigger than the Moon in a telescope, but that Jupiter in a telescope can have larger angular diameter than the Moon with the naked eye, yet we have a sense that the naked-eye Moon is large while the  enlarged Jupiter is small. It's a matter of visual perception. When we see a naked-eye full Moon near the horizon we perceive it as unusually large - an illusion that has been explained in various ways, but seems to be connected with our intuitive judgement of its distance in relation to terrestrial objects.

Exactly! Thanks for clarifying my words, I forgot to mention that I meant moon with naked eye.

[geministar]

Chipela is not suggesting that Jupiter in a telescope looks bigger than the Moon in a telescope, but that Jupiter in a telescope can have larger angular diameter than the Moon with the naked eye, yet we have a sense that the naked-eye Moon is large while the  enlarged Jupiter is small. It's a matter of visual perception. When we see a naked-eye full Moon near the horizon we perceive it as unusually large - an illusion that has been explained in various ways, but seems to be connected with our intuitive judgement of its distance in relation to terrestrial objects.

I wonder what impression the following would give. Print a silhouette horizon (trees, hills, roofs etc) on a very small piece of transparent acetate. Fix it on the field stop of a plossl so that it appears in focus when viewed through the eyepiece. Then look at Jupiter "rising" over this artificial horizon. Perhaps this would make Jupiter look bigger, though of course its angular size in the eyepiece would be unaltered.

When we look through an eyepiece we have a tendency to focus our own eye for near rather than distance vision. This could contribute to the pea-effect. I've tried relaxing the eye as if viewing at infinity, but since I'm astigmatic it gives a poorer view. People with better eyesight might find it gives the impression of a larger object.

Thanks for the clarification.

Kindly disregard my posting!

[rockystar]

I believe this is the illusion you are referring to. The circles in the middle are the same size. It's all to do with what is around it and how the brain interprets the image.

The same effect can be seen in the eyepiece which is focused and have the same effect as the large outer circles, making it (Jupiter) look small, but when [the moon] viewed in the vast open night sky, it looks much large, even though relatively speaking, they are the same size.

[Yearofthegoat]

I put my 3.2mm EP in my 90 Mak last night to take a look at Jupiter, and it was enormous in the eyepiece. It wasn't clear most of the time but - and this might have been my imagination - there seemed to be brief moments of clarity. It certainly kept me at the eyepiece for a good half an hour or so until I had to turn in. When I get my 150P-DS pointed at Jupiter it's a lot smaller of course but the detail is (seems) much better.

[Re. the Jupiter rising thing, for a bit of fun if you set your location in Stellarium to Europa or Io, you can see Jupiter rising over your usual landscape. Jump to Mimas and do the same for Saturn. Great fun, especially on a 100" home theatre screen ]

[Mafisen]

On 2016-01-17 at 13:10, Feral Rabbit said:

Looking at it another way the 4 Galilean moons you saw have diameters are between 5,260km (Ganymede the largest) which is about as wide as the USA, and the smallest at 3,121km (Europa).  They are between 629 million Km and  928 million km away. Surely when you look at it like that then that is an amazing sight?.

In the grand scheme of things you will be in a very small minority of people to have seen those live and anything else you look at through your scope. Most people will never look up at night and see anything more than the stars and the moon.

Many years ago when I first saw Jupiter and it's moons through an old 4" refractor with diabolically dusty optics I was blown away with Jupiter and the red spot but I was more overcome with excitement at seeing the moons. I dragged my long suffering girlfriend out into the cold to show her...... She was completely underwhelmed as I had probably raised her expectations too high. Today when I look up with my scope I am always amazed even seeing the extra number of stars through the scope amazes me.

When you sit down and realise that in astronomy nothing is on the doorstep and that the distances you see things, apart from our moon, are in millions of miles, light years, millions of light years away then you realise that whatever you look up there is mind blowingly amazing.  Well that's how I feel when I look up.

A word of warning; when you move onto nebula don't expect big colourful clouds.

Lovely post this. I am very new to this as I only got a small 3 inch refractor for Christmas and started out having too high expectations. But then this morning, I saw Jupiter's moons very clearly (although no detail on Jupiter) and was blown away. I went inside to get my 7- year old son and it was a mighty feeling to show him the planet and its moons. 

Your post puts everything in perspective and when you really think about what you see and the vastness of it all, it's mind-boggling, the size and detail at hand notwithstanding. I've only done this for a month, but I already know that I will keep doing it for years and I know that my current telescope will be handed down to my kids when I buy a new one.

[Mak the Night]

I think it is because Jupiter's albedo is high, 0.52 I believe, although Venus is higher at 0.65 and the brightest is Saturn's moon Enceladus at 0.99. Venus and Saturn are often seen better in twilight conditions. The best viewing I've had of Jupiter this year was during its recent conjunction with the Moon. It may be because being only a few degrees apart the brightness was offset by the Moon itself.

[Beefybean]

13 hours ago, Mafisen said:

Lovely post this. I am very new to this as I only got a small 3 inch refractor for Christmas and started out having too high expectations. But then this morning, I saw Jupiter's moons very clearly (although no detail on Jupiter) and was blown away. I went inside to get my 7- year old son and it was a mighty feeling to show him the planet and its moons. 

Your post puts everything in perspective and when you really think about what you see and the vastness of it all, it's mind-boggling, the size and detail at hand notwithstanding. I've only done this for a month, but I already know that I will keep doing it for years and I know that my current telescope will be handed down to my kids when I buy a new one.

 

13 hours ago, Mafisen said:

Lovely post this. I am very new to this as I only got a small 3 inch refractor for Christmas and started out having too high expectations. But then this morning, I saw Jupiter's moons very clearly (although no detail on Jupiter) and was blown away. I went inside to get my 7- year old son and it was a mighty feeling to show him the planet and its moons. 

Your post puts everything in perspective and when you really think about what you see and the vastness of it all, it's mind-boggling, the size and detail at hand notwithstanding. I've only done this for a month, but I already know that I will keep doing it for years and I know that my current telescope will be handed down to my kids when I buy a new one.

Could'nt agree more with you, i got my first scope for christmas, 5 inch reflector and when i first saw Jupiter i was amazed at what i was seeing. I had a clear detail of the 2 central dark bands, 3 moons at the start of viewing 3 hours later 4 moons and the red spot. Like you 4 weeks in and already know i will looking at the stars and planets for years to come

[Ruud]

In this google image search you see lots of Jupiter images close to or halfway behind the Moon. Jupiter appears about as big as a large Moon crater. You need a good night with a stable atmosphere to see its true beauty. Just be patient and view it often. You will get lucky one day!

[rockystar]

11 hours ago, Ruud said:

In this google image search you see lots of Jupiter images close to or halfway behind the Moon. Jupiter appears about as big as a large Moon crater. You need a good night with a stable atmosphere to see its true beauty. Just be patient and view it often. You will get lucky one day!

that's a really good comparison of the relative sizes.

[Mafisen]

Had another great experience with Jupiter last night. Although the viewing conditions were appalling, with the full moon shining almost blindingly bright, Jupiter in close proximity of it and observing directly over a sodium streetlight, I saw the two main cloudbands on Jupiter for the first time and two moons. Only stayed out for 15 minutes or so, since I had to get up early, but it was an exciting sight. And it left me encouraged to see even more in the future. If I can see that kind of detail under those circumstances, I have high hopes of having some more spine tingling views in the future.

[John]

On 05/02/2016 at 14:10, rockystar said:

that's a really good comparison of the relative sizes.

Here is another one (the planets are shown here at their maximum apparent diameter compared with the Moon):

 

 

[Stub Mandrel]

Got some video of Jupiter last night but left my laptop out - it's defrosting now...

The moons close to Jupiter last night were Ganymede and Io (Io closest).

[glennbech]

Another advertising "trick" is to focus on magnification. This is often done on the cheap, low end scopes. You will see the usual family, holding hands around a scope, galaxies and huge planets in the background and the text will say "200x magnification" or something silly like that. 

I went into astronomy with pretty realistic expectations in 2007 with a 8" Newtonian. But I had no clue that many of the interesting DSO's were larger than the moon in size, only faint. I thought I had to hunt them down in a tiny piece of sky and that the magnification power of my newt would some how bring them into view

This belief also extended to planets for me when I started out. I had noe Idea that many of the planets are naked eye objects.