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Jupiter Satellites

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Old Tuesday 16th July 2019, 00:30   #1
eronald
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Jupiter Satellites

So Jupiter is now on our side of the sun. When you point your bins at it do you see the satellites?

I can see what looks like 2 satellites on the left with my 8x25 Zeiss Victory , and also less distinctly with my 7x42 UV, although I would have assumed the opposite. Btw, I know what's supposed to be visible at the moment of observation :)

Edmund
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Old Tuesday 16th July 2019, 01:30   #2
Pinewood
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Hello Edmund,

I like to observe and then check for what is supposed to be visible. If you go to this web site, then click on interactive tool, you can see the positions of the moons by time and date. With a binocular you need "direct view."

In your case, the higher magnification may have allowed for greater separation of the moons from the planet and from each other. On a cold and clear night, I once saw two moons with a 6x30 but higher magnification is better, if the optics are stable. My most useful binocular is a 12x50 on a monopod.

Clear skies,
Arthur Pinewood
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Old Tuesday 16th July 2019, 01:45   #3
eronald
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Hello Edmund,

I like to observe and then check for what is supposed to be visible. If you go to this web site, then click on interactive tool, you can see the positions of the moons by time and date. With a binocular you need "direct view."

In your case, the higher magnification may have allowed for greater separation of the moons from the planet and from each other. On a cold and clear night, I once saw two moons with a 6x30 but higher magnification is better, if the optics are stable. My most useful binocular is a 12x50 on a monopod.

Clear skies,
Arthur Pinewood

Hi Arthur,
Yes, I observed and then checked. I wonder what other people are seeing :)

In my case what looked like 2 moons was actually 3, the bins couldn't resolve a smaller separation between two of them, and Io was supposed to be on the right but even after reading that I couldn't see it.

This was tonight, viewing conditions are favorable due to distance. I wonder what other people are seeing.

Some people -or their kids- may be able to resolve the moons with unaided vision.

Edmund
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Old Tuesday 16th July 2019, 02:17   #4
Pinewood
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Hi Arthur,

Some people -or their kids- may be able to resolve the moons with unaided vision.

Edmund
Hello Edmund,

I have read that. As the moons are 6th magnitude, they are at the limit of visibility, if the separation from Jupiter were great enough, and the viewing excellent a child might see the moons.

There is an apocryphal story of a child visiting an observatory asking, "Why does the telescope show the moons on the wrong side from what I see?" I still think it rather unlikely.

Clear skies,
Arthur
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Old Tuesday 16th July 2019, 08:28   #5
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...and also less distinctly with my 7x42 UV, although I would have assumed the opposite.
That might be because a 6mm exit pupil is at the upper limit for stargazing. In any but the darkest skies, this large an exit pupil will lead to brightened up background which makes faint objects harder to see.

Plus like a photo lens, your eyes are not at their best performance wide open - any astigmatism will be quite visible and might be hidden at smaller pupil sizes.

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Old Tuesday 16th July 2019, 14:52   #6
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Jupiter's moons are magnitude 4.6 to 5.6.
Rather easy in a dark sky if Jupiter didn't overwhelm them.

Io is more difficult because it is nearer the planet. It also moves more quickly.

The moons vary constantly although some have periodic connections to each other.

There can be no set rule as to how easy they are.
They constantly move.
They vary in separation between each other and from Jupiter's limb.

The Canon 18x50 IS usually shows them where ever they are unless almost touching the limb.

A telescope is needed to show them crossing Jupiter and their shadows crossing the disc.

Eyesight varies. Also whether people see spikes or not. Most people see spikes.
Light pollution varies.
Transparency varies and so on.

They are interesting to watch.
I can identify them without reference, but I have been following them for 60 years and more.

There are quite a lot of confirmed cases of unaided views of Jupiter's moons.
Usually children, but some adults with very fine eyesight.

Saturn's moons are actually more interesting, but need a rather large scope.
There are more moons visible. 7 or 8 in large scopes.
And their interactions with the rings, particularly the edge on rings when multiple strange effects occur.

There are numerous photos in magazines and newspapers claiming to be Jupiter and Saturn's moons, when in fact they are displaying stars and moons.
I have got fed up correcting these erroneous manifestations.
It even occurs in astro magazines.
The reason is that most astronomers are now photographers, and have little actual visual knowledge of the moons.
And digital manipulation means that the images are actually fake.

Regards.
B.
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Old Wednesday 17th July 2019, 01:11   #7
eronald
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That might be because a 6mm exit pupil is at the upper limit for stargazing. In any but the darkest skies, this large an exit pupil will lead to brightened up background which makes faint objects harder to see.

Plus like a photo lens, your eyes are not at their best performance wide open - any astigmatism will be quite visible and might be hidden at smaller pupil sizes.

Joachim
Paradoxically, tonight the 7x42 shows a satellite better than the 8x25. Which may agree with your remark - the earth moon is further away in the sky from Jupiter whereas yesterday it was dazzling close.

Edmund
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Old Wednesday 17th July 2019, 02:40   #8
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In good conditions I can see all four Galilean moons with something like some 8X50/54s. Better than one might think. 12X50s do a little better.
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Old Friday 19th July 2019, 02:13   #9
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Thanks for posting. I attempted to view the moons of Jupiter using binoculars for the first time tonight. The Canon 14x32 showed four distinct moons without much effort. Using the Kowa Genesis 8x33 it took a little effort to resolve the separation between Io and Europa due to their current close proximity. However, the Genesis does such a wonderful job displaying stars as a tight sharply defined point that the experience was more pleasing than with the Canon.
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Old Friday 19th July 2019, 03:15   #10
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It depends on your skies (dark, with little turbulence). I regularly view all four Galilean moons with "regular" (not astronomic) binoculars. My nine year old can see them without binoculars.
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Old Friday 19th July 2019, 07:24   #11
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Hi Binastro,

Quote:
Originally Posted by Binastro View Post
Eyesight varies. Also whether people see spikes or not. Most people see spikes.
Hm, what are "spikes"? My eyes are far from perfect, but at least, with my 8x42, I could pick up four Jupiter moons fairly easily.

Regards,

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Old Friday 19th July 2019, 13:46   #12
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Hi Henning,
Perfect eyes would show a bright star as a small disc.
Most eyes show spikes coming out of the bright small disc.

The depiction of a star is say a 5 sided spiked object, it shouldn't be this.

The spikes are caused by eye imperfections.
Young eyes usually have less imperfections.

There are fairly numerous reports of unaided eyes sighting of up to 4 Jupiter moons.
They usually have to be at elongation, i.e. furthest from Jupiter.

Sometimes older but experienced observers are surprised to see one or more moons. Sometimes on having new very well computed glasses or with no glasses but a transparent favourable night.

The mean opposition Jupiter moon magnitudes are 4.5 to 5.5.
Favourable oppositions brighter than mag 4.4 to 5.4.

Regards,
B.

P.S.
It seems that all eyes show some spikes because the eye contains linear variable structure.
This causes diffraction.

How good the best young eyes are, I don't know, but certainly better than mine.

Presumably, young eyes and very good older eyes handle glare better than most people's eyes.
Glare may be the main factor stopping most from discerning the faint moons from Jupiter's brightness.

Last edited by Binastro : Friday 19th July 2019 at 16:46.
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Old Friday 19th July 2019, 14:08   #13
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Hi dusty roads,

It is wonderful your nine year old can see Jupiter's moons with unaided eyes.

My eyes were probably never good enough.
One problem is that nearly all my observing has been from towns, with only rare visits to dark places.
Up to age 40 I usually saw 11 Pleiads from towns, where I could see magnitude 5.9 stars.
From dark locations I saw mag 6.7 or 6.8 stars, even from Lyme Regis town centre with street lights.
On La Palma I was seeing down to mag 7.2 at the zenith at 7,900 feet on not the best night according to locals.
I saw 15 or 16 Pleiads there and M33 easily with direct vision.

I easily saw the double star epsilon Lyrae as double when young from towns.

My right eye saw 0.5 magnitude fainter than my left and green grass was slightly different with each eye.

However, I consider my eyesight to have been rather mediocre or at least average.
My cousin in his forties read car number plates at fully double my best distance and I was ten years younger.
I was stunned actually as I had to walk quite a long way to confirm the numbers and letters.
I have also been amazed at friends who can see tiny details close up that are completely invisible to me.

Amongst very well regarded astronomers, Denning the meteor specialist, Ricard Baum and Paul Doherty the planetary specialists all saw Jupiter's moons without optical aid even when older. There are probably quite a few others.

Regards,
B.

P.S.
Away from opposition Jupiter and its moons are fainter.

In addition, atmospheric extinction is large at low elevations above the horizon.
At 12.5 degree elevation this is about 1.28 magnitudes compared to 0.28 magnitudes at the zenith, in perfectly clear conditions. So Jupiter's moons are 1.0 magnitude fainter.
In poorer conditions it is worse.
Mountain top observatories lose less.

As Jupiter is only at about 15 degrees or less in England and still less in Scotland, I would not expect any unaided eye sightings of Jupiter's moons now from the U.K.
Things are better in the U.S., especially the southern States.

Last edited by Binastro : Friday 19th July 2019 at 16:06.
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Old Saturday 20th July 2019, 01:46   #14
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Perfect eyes would show a bright star as a small disc.
Most eyes show spikes coming out of the bright small disc.
The depiction of a star is say a 5 sided spiked object, it shouldn't be this.
As obvious as this seems now, it never occurred to me because I (still) don't see spikes myself. I thought the points of stars in art were cartoonish or figurative. Of course one sees this effect in photography, but it's intentionally generated by a special filter.

Quote:
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My right eye saw 0.5 magnitude fainter than my left and green grass was slightly different with each eye.
It makes sense that acuity isn't the only variation between one's eyes. I have noticed these differences, and would bet they're common. Best explored when no one is watching... :)
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