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Jupiter's moons

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#1 philipdehazya

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Posted 06 August 2020 - 06:32 AM

All: A few nights ago, I had my telescope (14 in dob with 50mm Russell eyepiece; 32X with my scope) pointed at Jupiter. I live in a light polluted area (Long Island, NY). I "think" I was able to count at least 7 moons. Or, they looked like they could be moons and did not look like stars to me. I have viewed the 4 Galilean moons many times, but this was different. So my question, did I see a few of the smaller moons this time or was I looking at stars in the background?

Thanks-Phil



#2 Xilman

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Posted 06 August 2020 - 06:56 AM

All: A few nights ago, I had my telescope (14 in dob with 50mm Russell eyepiece; 32X with my scope) pointed at Jupiter. I live in a light polluted area (Long Island, NY). I "think" I was able to count at least 7 moons. Or, they looked like they could be moons and did not look like stars to me. I have viewed the 4 Galilean moons many times, but this was different. So my question, did I see a few of the smaller moons this time or was I looking at stars in the background?

Thanks-Phil

I think it extremely unlikely. The great majority of Jupiter's satellites are very faint --- well below 20th magnitude, and the remainder are either the Gallileans and few which lie in the 15-20 range. You would probably find it difficult to see very much below 15 with your telescope in a dark site.

 

You almost certainly saw background stars. Jupiter is now in a rich part of the Milky Way and there are plenty of faint stars in its vicinity.

 

FWIW, I have been imaging faint Jovian satellites on the last couple of observing sessions. All of them are fainter than magnitude 17.  A mug shot of Pasiphae was posted yesterday. With luck Carme, Ananke and Lysithea should make an appearance over the next few days.


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#3 Sandy Swede

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Posted 06 August 2020 - 07:00 AM

Maybe, maybe not.  Did you check with a planetarium program such as Stellarium?  This is why I need to have a notebook handy when observing.  I see something, but by the time I wonder about it, I can no longer recall the object or the arrangement.  A Homer moment - Doh!  As they say, "Don't feel like the Lone Ranger."


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#4 spereira

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Posted 06 August 2020 - 07:16 AM

Moving to Solar System Observing ...

 

smp



#5 philipdehazya

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Posted 06 August 2020 - 08:30 AM

Thanks to you both for you insights!



#6 Redbetter

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Posted 06 August 2020 - 05:12 PM

All: A few nights ago, I had my telescope (14 in dob with 50mm Russell eyepiece; 32X with my scope) pointed at Jupiter. I live in a light polluted area (Long Island, NY). I "think" I was able to count at least 7 moons. Or, they looked like they could be moons and did not look like stars to me. I have viewed the 4 Galilean moons many times, but this was different. So my question, did I see a few of the smaller moons this time or was I looking at stars in the background?

Thanks-Phil

Only 4 may have been the moons, and you would know which ones when using sufficient magnification because they are obviously disks in that aperture.  32x won't show that, but they are so bright and aligned in such a way right now that it is hard to mistake a star for one of them.

 

The others you saw were stars, especially in NYC metro.  The other Jovian moons all require darker sky, large aperture, and considerable effort to find/identify and observe.

 

p.s. A 50mm eyepiece is an unusual choice for a 14" f/4.5 Dob.  The exit pupil would be around 11mm. Some/many will have trouble with seeing the central obstruction or a considerably darker central field with such a large exit pupil, particularly on a bright target or in bright sky.   I can understand doing it if it provides your widest true field of view, even though effectively you were likely observing with 9" of aperture or less.  


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