My first (blurry) image of Jupiter, zoomed in 6x!

[-Velocity-]

I would think that the main issue with spotting the Moons of Jupiter naked eye would be glare and scattered light. Both in the atmosphere and on your retina. Jupiter is so bright that it has a little aura of scattered light around it in the sky... and of course, the lens in your eye and your cornea scatters even more. I did some observing from West Texas a couple years ago when Jupiter crossed the summer Milky Way (was that 2010 or 2011? I forgot) and Jupiter was annoyingly bright, nearly bright enough to cast noticeable shadows like I'd seen before with Venus.

P.S.- the idea that from very dark sky sites the Milky Way is bright enough to cast shadows is mostly a myth. The sky is always capable of casting shadows, whether the brightest portions of the Milky Way are above the horizon or not. You're a more sensitive than I am if you can notice a very slightly darker shadow when the Milky Way is up as opposed to hours before or later when it is not. Sorry, but I digress...

[-Velocity-]

You guys are making me really miss my telescope now.

I've got a 25" dob, but between moving and just plain terrible weather and luck, I haven't gotten to use it, other than for public outreach, for over a year now

A couple weeks ago, the day after Thanksgiving, I finally had clear skies coincide with time off and a new Moon. Guess what? For the first time in over a year, I was sick. F*** my luck.

[vetrox]

You guys are making me really miss my telescope now.

I've been out once this year. And that was a few days ago just to take a peak at jupiter cos its my favourite object. I had 3 hours of spare time got the telescope out...forgot how to collimate...remembered how to collimate, collimated....then re collimated due to error. Got 20 minutes of viewing in before jupiter moved out of line of sight.

Didnt even get to look at saturn, lemon, meteor shower, mars and a load of other stuff i wanted to look at this year. I've either been too busy, working or poor weather. Makes me depressed My girlfriend bought me a camera last christmas. Took that photo of jupiter and havent been able to get out since.

[K^2]

Alright, so I did the simulation, and while Io is completely washed out, and Europa is barely there, Ganymede and Callisto stand out surprisingly well. This simulation only accounts for the diffraction (6mm aperture, 17mm focal length) of an ideal thin lens, everything I found about human vision says that for perfect eye sight, that accounts for about 90% of aberration strength.

This does not account for diffraction and scattering in atmosphere or sensitivity of human retina. So it's not proof that you can see these moons, but it does show that they are within limitations of optics. So a camera with perfectly manufactured lens, having same aperture and focal length as human eye, would definitely be able to image the outer two moons from orbit.

So I withdraw my objection that it's impossible from perspective of optics, substituting it with mild skepticism. It is definitely impossible to see Io or Europa, though. That I have no doubt of.

Here is the output of the simulation. Each pixel corresponds to 2.5μm, giving roughly the equivalent pixel density to density of rods or cones. (Turns out, their maximum densities are about the same, 150k/mm², but achieved in different parts of the eye.) Contrast is set to make the outer moons clearly visible. Actual sizes of all objects on this picture would be less than one pixel across. So disk in the center isn't Jupiter itself, but area of the sensor saturated by its light. Actual human eye has greater dynamic range, so you'd see a significantly smaller disk, but the only thing that matters here is contrast of the moons, and light from Jupiter significantly overpowers that of Io and mostly that of Europa.

Oh, one more detail. I've put all four at maximum elongation, alternating direction from Jupiter. That can actually happen for the inner 3 moons, but I'm not sure it's ever the case with Callisto. But since only the outer two moons end up visible anyhow, it's a moot point.

[ihtoit]

a simple experiment to demonstrate sensitive spots in your eye: locate M31, the Andromeda Galaxy. You should be able to do this even in the middle of a town (if you have a clear sky, that is). Look slightly away from it (go one degree south east and look directly at nu Andromedae), and you will perceive more detail and might even spot M32 and M110. The retina contains two types of photoreceptors, rods and cones. The rods are more numerous, some 120 million, and are more sensitive than the cones. However, they are not sensitive to color. The 6 to 7 million cones provide the eye's color sensitivity (The proportion of RGB sensors in the cones (each is sensitive to just one primary colour) is approximately 64:32:2 respectively) and they are much more concentrated in the central yellow spot known as the macula. In the center of that region is the " fovea centralis ", a 0.3 mm diameter rod-free area with very thin, densely packed red and green cones (there are no blue cones in this region). This arrangement of sensors allows you to perceive whatever you are focusing on in colour and objects in the periphery of your field of vision in monochrome. This principle is used in the best of the best cameras, which have a separate CCD for each primary colour feeding off a common split beam. This maximises sensitivity across the entire focal plane and across the entire bandwidth of sensitivity of each sensor.

(citation: http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html, http://en.wikipedia.org/wiki/Three-CCD_camera and own observations)

[K^2]

What's your point? We aren't even discussing sensitivity or density of the rods. They are both sufficient and aren't the problem.

[vetrox]

-snip-

I dont want to sound rude (but its going to sound rude anyway)

But jupiter looks nothing like that to the naked eye. Thats what it looks like through a telescope with some magnification behind it. I dont know if its intentional but you need to remove the magnification ( i have no idea how you woul do that thought) maybe just shrink the picture?

[-Velocity-]

I've never heard of anyone spotting M32 or M110 naked eye, I am 99.99% certain that they are much too faint to be seen. Someone with ridiculously good vision MIGHT claim a successful sighting of M32 (they would have to have almost unbelievably good vision), but M110, in particular, is low surface brightness too- and 9th magnitude IIRC. No one will see that.

As far as adverted or direct vision, you'd probably need direct or semi-direct. The problem with adverted vision is that it has very low spatial resolution. VERY low spatial resolution. So your adverted vision wouldn't be able to separate Callisto from Jupiter's glare. You could probably use semi-adverted vision though. Maybe some of these observing techniques though are particular to my own visual system, my adverted vision sweet spots are located very far from the center of my visual field, and in very low spatial resolution areas of my visual field. When observing DSOs, I frequently have to use semi-adverted vision to increase my spatial resolution at the cost of a little sensitivity.

Anyway, I doubt my vision is low enough scatter to spot any of Jupiter's moons naked eye anyway. At the darkest skies in North America, I can barely get below magnitude 6.5. My daytime vision is good, so the central 3 or 4 mm of my eye's lens is good, but the outer areas of my eye's lens might be a little astigmatic, as I definitely notice a little astigmatism when looking at stars and rotating my head- the astigmatism rotates with my head movement.

Edited December 18, 2013 by |Velocity|

[K^2]

But jupiter looks nothing like that to the naked eye. Thats what it looks like through a telescope with some magnification behind it. I dont know if its intentional but you need to remove the magnification ( i have no idea how you woul do that thought) maybe just shrink the picture?

I don't know if you missed the part about dynamic range, or if the implications didn't sink in. This is what the signal on your retina is going to look like. The difference is that your eye has a great dynamic range and is sensitive to local contrasts. The image is limited to 8 bits of depth. The part that's completely white in the center is saturated at that range. The actual light from Jupiter is 1,000 times brighter than that of the moons. So the central point of that circle is way brighter. Your brain will interpret it as a bright dot with a bit of a halo. But this rendering can only pick up the halo's diameter, and that's the white disk you see here. If I set the contrast to the level where you can see Jupiter as a bright dot with just a bit of halo, the moons wouldn't be visible at all.

I could play with gamma correction to try and fit the actual range of that image into the available depth to try and make it more believable-looking. But that wasn't the point. The point was to compare the light of the halo to the light from the moons to see if light from Jupiter prevents you from seeing the later. And this image is quite sufficient for that.

[Sun]

I got a telescope one day at Savers for $5, but the front lens was missing, and I imagine that a good telescope would cost less than a lens for my telescope. So, I returned it. Now, I'll just have to wait until Christmas and see if I get one.

[PakledHostage]

It was clear out this evening so I took my camera out to help put this discussion into perspective. Below are two pictures that I took through a 300 mm lens on a standard DSLR camera (no telescope was used). Both images were cropped to 800 x 600 and then resized to 50% of their original size to fit this page. The scale of both images are the same. From left to right in the bottom image are Ganymede, Jupiter, Io, Europa and Callisto.

Edited December 19, 2013 by PakledHostage

[K^2]

That got me to drag my telescope outside. I really should invest into something with a better stand at some point. So much shaking, I could barely see the moons. And then the Earth turns, and I have to re-train the scope again, which is horrible with this stand. And all of that in the snow.

[Tommygun]

This has me thinking, can you take any two hand held magnifying lenses and mount them to a stick at the right spacing and make a telescope out of them or do the lenses have to be a specific shape.

[K^2]

You can do precisely that. I used to demo that to students during optics labs at uni. Obviously, an expensive, high quality telescope is going to be more complicated, but your basic Galilean telescope is just two lenses with the right spacing. It works best if your objective is low power lens and your ocular is a high power lens. Large diameter of the objective also helps.

[Tommygun]

Hummm....well I have a 6 inch magnifying lens, a small high power inspection lens, several two by fours and duck tape.

I may have a redneck telescope in my future. Will see.

[K^2]

Sounds like a plan. The basic setup is to have your objective lens set up a virtual image for the ocular lens to look at. So you'd be using the inspection lens as if you are actually looking at a small object right next to it. The virtual image from an object that's "infinitely" far away is going to be right at the focal distance. So you'd set up the inspection lens just past the focal point of your 6" objective lens. The virtual image needs to end up just a bit under focal distance from inspection lens. That should give you a sharp image and maximum magnification.

[-Velocity-]

Hummm....well I have a 6 inch magnifying lens, a small high power inspection lens, several two by fours and duck tape.

I may have a redneck telescope in my future. Will see.

Well, magnifying glasses are pretty short in focal length, so get ready for the chromatic aberration from hell.

[Tommygun]

I have been playing around with it today and just by holding the two lens by hand I was able to see through them.

The distance between the two lenses is about 38 centimeters. The image is quite bright and I can see a nearby mountain well for the brief time I can keep my arms in position.

It's time for the wooden 2x4. I think I'll use a folding ladder for a tripod and then aim and hold the "telescope" like a scoped rifle.

If it works I'll also try my digital camera on it. Just hope the neighbors don't see me walking around in the dark with a 2x4 in my hands.

[JebidiahsBigSister]

It's optically impossible. You can say as much as you want that you have seen it, but even at maximum elongation, light from Jupiter proper is too strong to make it possible to see something that's 2x10^-3 away without some sort of an aid. Like lajoswinkler pointed out, you can use something to obstruct light from Jupiter and then just be able to see these, but there is absolutely no way to see them without doing something. Human eye can't do it. Period.

You are wrong. I have seen it and so have many others. It is most definitely not "optically impossible. That's just nonsense. Difficult yes because of the brightness but the brightness of Jupiter varies with distance from the earth /sun by an entire order of magnitude. All it takes is sharp vision and the right conditions (clear, dark skies away from light pollution, knowing where the moons will be at max elongation, jupiter at lowest magnitude) The magnitudes of both the planet and the moons (ganymede and callisto) as well as the separation (a third of our moon's diameter) make it optically possible. I know, I've seen them many times on a dark evening and pointed it out to others as well. Think what you will but I have the experience.

P.S. There are quite a few reports of visually observing jupiter's moons available on reputable astronomy blogs on the web. Just because you haven't seen or done something hardly makes it impossible. Period.

[GJames]

This thread is pretty well timed; just taken a few snaps through my telescope the other day. I used my iPod touch camera held up to the eyepiece. Hopefully the images will show up okay, still trying to figure out posting photos...

Here's Jupiter, the Moon and Venus:

I'm getting myself a camera adaptor for Christmas, and I've got a few videos of the Moon that I'll try to stack sometime, so this could be the start of something pretty cool...

Edited December 19, 2013 by GJames
Added BB codes.

[Motokid600]

To this day... this video still impresses me. I took this though my CPC11 with a simple point and shoot. It was a muggy, summer night ( best time to view the planets ) and along with the sounds in this video its my best shot of Jupiter to date. I have MUCH better equipment now, but ive been neglecting planetary observations for reasons im not sure off. We live in light polluted skies so planets should be a priority. Also managed to capture a transit at the same time.. hope you guys enjoy this. I know I did.. make sure you full screen it in 720p. And hell turn up your volume too..

Now if I look close.. I swear I can see the moons resolved into disks. ( its very possible to do )

Edited December 19, 2013 by Motokid600

[K^2]

Difficult yes because of the brightness but the brightness of Jupiter varies with distance from the earth /sun by an entire order of magnitude.

The moons are brightest when Jupiter is. In fact, their luminocity is always proportional. Magnitudes aren't, because of logarithmic scale, but if you convert these to luminosity, you'll see that they have the same range. So you are still going to have the best chance of seeing them when Jupiter is brightest.

P.S. There are quite a few reports of visually observing jupiter's moons available on reputable astronomy blogs on the web. Just because you haven't seen or done something hardly makes it impossible. Period.

My objection wasn't based on "I can't see them." I haven't had 20/20 since I was six. It was based on a rough estimate of dispersion of Jupiter's light, which has turned out to be too rough. I have seen ran the simulation, output of which you can find in this thread, which has demonstrated that only the inner two moons are impossible to see because of Jupiter's light. The outer two Galilean moons at maximum elongation might be visible with perfect eyesight.

By the way, right now seems to be a good time for it, based on PakledHostage's photograph and what I've been able to catch through the telescope. If your eye is sensitive and focused enough to see the moons of Jupiter, you should be able to see them now.

[GJames]

To this day... this video still impresses me. I took this though my CPC11 with a simple point and shoot. It was a muggy, summer night ( best time to view the planets ) and along with the sounds in this video its my best shot of Jupiter to date. I have MUCH better equipment now, but ive been neglecting planetary observations for reasons im not sure off. We live in light polluted skies so planets should be a priority. Also managed to capture a transit at the same time.. hope you guys enjoy this. I know I did.. make sure you full screen it in 720p. And hell turn up your volume too..

Now if I look close.. I swear I can see the moons resolved into disks. ( its very possible to do )

Have you tried separating out each frame from the video and stacking them? You can get pretty simple free software to do it that can give you a really sharp image; you might even see the moons as full discs...

[PakledHostage]

By the way, right now seems to be a good time for it, based on PakledHostage's photograph and what I've been able to catch through the telescope.

It does change quickly. Below are two screenshots from the astronomy app on my phone. The first shows how the moons were positioned at about the time I took the picture on the previous page of this tread. The image on the right shows how they are currently positioned.

[Motokid600]

Have you tried separating out each frame from the video and stacking them? You can get pretty simple free software to do it that can give you a really sharp image; you might even see the moons as full discs...

Registax er.. something I believe the program is called. I have it, but I've yet to learn it. Like I said ive been neglecting planetary imaging. But its time to switch to over from DSO's. My skies are on the border of yellow and red on the pollution scale.

Fyi everyone.. light pollution does NOT impact planetary views ( excluding Neptune and Uranus ). The light from planets is so bright and concentrated light pollution takes no effect. Infact the best ameture photos I've seen of Jupiter were takin from major cities on roof tops. Stable air is what makes for good planetary views. And apparently the air is more stable year round in a city then in a rural area. Believe it or not lol. I'm getting this information from both personal experience and a backyard astronomy text book. Where it also states its very possible to view Jupiters moons with the naked eye.