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Can anyone help with a question about the moons around Jupiter?

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#1 Galaxy Michael

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Posted 14 September 2021 - 12:57 AM

My daughter asked me a question about the moons around Jupiter and it got me wondering because I don’t know the answer.  Google didn’t help much, other than Google says 79 moons, not 68.

 

She asked, "If there are 68 moons around Jupiter, why do I only see 4 of them with the telescope?"

 

The quick answer here is we were using my Edmund Astroscan at home.  What I can’t find any information on is if we can see more than 4 moons around Jupiter with a bigger telescope.

 

If I bring my Obsession 15" dob to my high desert NM observing site, can I see more than 4 moons around Jupiter?

Unfortunately I am unable to transport my Obsession 15 for several more months.  I had to get a new vehicle and I need a camper shell before I can transport it. Like everything else these days, a camper shell for a pickup truck is on backorder due to supply shortages.

 

Thank you if anyone knows the answer.


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#2 Tapio

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Posted 14 September 2021 - 01:28 AM

Well, Amalthea is about mag 14 so could be detected with a larger scope. Only that Jupiter is so bright that it makes it really difficult.

How about moons of Saturn ?



#3 Galaxy Michael

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Posted 14 September 2021 - 01:43 AM

Well, Amalthea is about mag 14 so could be detected with a larger scope. Only that Jupiter is so bright that it makes it really difficult.

How about moons of Saturn ?

This is a really good comment about Jupiter being so bright.  I didn't think about this.

 

A mag 14 object can be an easy target with a 15" reflector, but next to a super bright Jupiter changes things a lot.

 

Thanks for sharing the name of the moon Amalthea.  I'll do a search on it.



#4 rkinnett

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Posted 14 September 2021 - 01:45 AM

You can find a list of Jupiter's moons here:

https://en.wikipedia...oons_of_Jupiter

 

That table doesn't list apparent visual magnitude as viewed from Earth, but you can get a feel for relative sizes by looking at diameter or mass.  The 4 classic Galilean moons are huge!  And the rest are tiny.  Also check out those discovery dates.  Ten moons were discovered between the Galilean moons and those discovered by the first spacecraft to flyby Jupiter.  Those ten discoveries were credited to five astronomers.  Starting with the earliest post-Galileo discovery, Edward Barnard discovered Amalthea in 1892.  Per various sources, Amalthea was the last of Jupiter's moons to be discovered by visual observation.  This discovery was made at Lick Observatory on a 36" or 39" reflector at Lick Observatory.  This article describes spotting Amalthea with 24" aperture under excellent conditions.  A few non-Galilean moons are larger than Amalthea and I assume would be similarly detectable, so long as their albedos are not substantially worse.

 

Unrelated story.. I once tried to name one of Jupiter's moons after my daughter, Chloe.  In 2018, the Carnegie Institute held a public contest to name 12 newly discovered moons, with a rule that proposed names must be of Greek and Roman goddesses who were either lovers or descendants of Jupiter or Zeus.  Turns out Greek goddess Demeter, also known as Chloe, was a sister of Zeus but also had a child with him.  Demeter/Chloe is known in mythology as the goddess of fertility.  I submitted the name Chloe along with a cheesy line about these new moons of Jupiter revealing the fertility of the early solar system.  They didn't go for it, but I'll tell the story every chance I get anyway. 


Edited by rkinnett, 14 September 2021 - 01:58 AM.

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#5 astrokeith

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Posted 14 September 2021 - 01:55 AM

The fifth moon visible is usually reckoned to be Himalia, since it is a reasonable distance from the bright planet, but needs a good planetarium program to locate it against the background stars.

 

Amalthea is really difficult, requires an occulting bar, perfectly clean optics, and a brilliant night.


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#6 Galaxy Michael

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Posted 14 September 2021 - 02:23 AM

rkinnett, Thanks for the information.  The wikipedia link is really helpful.  Looking at the orbits and positions image of the moons is fascinating.  I can only imagine how difficult it must be to identify them all individually.

 

Cool story about your submission for naming one of the moons.  It's too bad they didn't pick the name you suggested.


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#7 Galaxy Michael

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Posted 14 September 2021 - 02:34 AM

The fifth moon visible is usually reckoned to be Himalia, since it is a reasonable distance from the bright planet, but needs a good planetarium program to locate it against the background stars.

 

Amalthea is really difficult, requires an occulting bar, perfectly clean optics, and a brilliant night.

 

 

Thanks.  I'll see if I can get an accurate chart for Himalia and Amalthea when I'm able to transport my big telescope.  We will give them a try at the eyepiece.

 

It will be a fun project for us since my daughter asked about seeing more than 4 moons of Jupiter.



#8 Redbetter

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Posted 14 September 2021 - 03:22 AM

Glare from Jupiter makes Amalthea incredibly difficult, requiring excellent epic seeing and large aperture.  Aperture isn't really the problem nowadays since very large scopes are available to amateurs, but seeing is a huge problem. 

 

I have seen Himalia and Elara.  Himalia is dimmer than most sources list from what I recall (somewhere in the 15's.)  Glare from Jupiter was still a problem with these outer moons as it produces some far off axis reflections well outside of the field. I had to generate ephemerides from the Minor Planet center for the times I planned to observe, and plot these against images of the sky--planetarium programs are unreliable at these magnitudes, often showing non-stellar objects or missing stars.  Planetarium programs also often plot the positions of outer moons incorrectly.  


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#9 happylimpet

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Posted 14 September 2021 - 03:48 AM

Thanks.  I'll see if I can get an accurate chart for Himalia and Amalthea when I'm able to transport my big telescope.  We will give them a try at the eyepiece.

 

It will be a fun project for us since my daughter asked about seeing more than 4 moons of Jupiter.

That would be a brilliant project, and you can hold your head up high if you succeed as not many people have seen more than the bright four.


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#10 Allan Wade

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Posted 14 September 2021 - 06:40 AM

Himalia is by far the easiest Jovian moon to see after the big 4. It’s well in range of a vast number of amateur scopes, including your 15”. The biggest challenge is positively locating it. I’ve had success plotting the ephemeris data from the Minor Planet Centre into Sky Safari 6 with the extended star data base past magnitude 17. I’ve always found it easy to get orientated at the eyepiece with stars going that deep and locating the fainter moons hasn’t been a very difficult task in the 32”.

 

Next up in difficulty is Elara and then Pasiphae. That’s 7 moons so far, and those are all within reach once you start heading into the 20” class dobs.

 

Next is the group of Sinope, Carme and Lysithea. They peak at around magnitude 18 when Jupiter is at opposition, and they were a bit of a challenge even for the 32”.

 

Then there’s Ananke. I observed it on the night of Jupiter’s opposition last year. Going through the ephemeris data it reached magnitude 18.3 for a 6 hour period before beginning to fade again. It wasn’t long before it was back in the magnitude 19’s. 
 

Finally there’s Amalthea. I rate it tougher than the previous 11 moons I’ve observed. I have read in a few places they suspect as few as 20 people have ever seen Amalthea. Though that number might have grown a few by now. Though I would think it likely far less than 20 people have seen Ananke. But I spent 2 years and 3 oppositions and close to 100 hours trying for Amalthea before seeing it for a 15 minute window. It was worth the effort.


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#11 james7ca

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Posted 14 September 2021 - 09:45 AM

There are a few threads here on CN about visually detecting some of these fainter moons around Jupiter (and the other gas giant planets). Also, I know that I can image Amalthea clearly with my 5" refractor. In fact, on the best nights I can actually see Amalthea in the single exposure previews that are offered in programs like SharpCap or Firecapture (a realtime preview within the second or two that it takes to capture the image).

 

I've also captured Himalia and Elara with the 5" scope and recently I imaged Pasiphae with a 9.25" EdgeHD. All of these captures were done from my light-polluted location (Bortle 7) using CMOS cameras.

 

Here is the link of where I imaged Pasiphae and one where I imaged Amalthea with the 5" scope.

 

https://www.cloudyni.../#entry11329763

 

https://www.cloudyni...r/#entry7137356

 

One issue with all of these faint moons is that you need to be pretty careful that what you are identifying is actually the moon and NOT a background star. There are a LOT of stars that are magnitude 17 and fainter.


Edited by james7ca, 14 September 2021 - 09:47 AM.

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#12 btschumy

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Posted 14 September 2021 - 09:17 PM

Here is an image from SkySafari showing the orbits of all the minor moons.  For scale you can just see Callisto up and to the left of Jupiter at the far reach of its orbit.

 

 

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#13 Galaxy Michael

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Posted 15 September 2021 - 12:32 AM

Himalia is by far the easiest Jovian moon to see after the big 4. It’s well in range of a vast number of amateur scopes, including your 15”. The biggest challenge is positively locating it. I’ve had success plotting the ephemeris data from the Minor Planet Centre into Sky Safari 6 with the extended star data base past magnitude 17. I’ve always found it easy to get orientated at the eyepiece with stars going that deep and locating the fainter moons hasn’t been a very difficult task in the 32”.

 

Next up in difficulty is Elara and then Pasiphae. That’s 7 moons so far, and those are all within reach once you start heading into the 20” class dobs.

 

Next is the group of Sinope, Carme and Lysithea. They peak at around magnitude 18 when Jupiter is at opposition, and they were a bit of a challenge even for the 32”.

 

Then there’s Ananke. I observed it on the night of Jupiter’s opposition last year. Going through the ephemeris data it reached magnitude 18.3 for a 6 hour period before beginning to fade again. It wasn’t long before it was back in the magnitude 19’s. 
 

Finally there’s Amalthea. I rate it tougher than the previous 11 moons I’ve observed. I have read in a few places they suspect as few as 20 people have ever seen Amalthea. Though that number might have grown a few by now. Though I would think it likely far less than 20 people have seen Ananke. But I spent 2 years and 3 oppositions and close to 100 hours trying for Amalthea before seeing it for a 15 minute window. It was worth the effort.

I appreciate you sharing all of this information about your experience observing 12 minor moons of Jupiter.  I learned that it takes more than a big telescope... it takes a lot of effort.  I'm sure it was a rewarding experience as you observed them one by one.  Very cool about your successful effort to finally get Amalthea.

 

Since I can't even transport my 15" for a few more months, I'll have some time to work on this for next summer.  I'll get observing data for Himalia and put that one on as my goal.  My observing location is in a remote area of New Mexico.  The high desert dark sky out here is a good as it gets.


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#14 Galaxy Michael

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Posted 15 September 2021 - 12:42 AM

There are a few threads here on CN about visually detecting some of these fainter moons around Jupiter (and the other gas giant planets). Also, I know that I can image Amalthea clearly with my 5" refractor. In fact, on the best nights I can actually see Amalthea in the single exposure previews that are offered in programs like SharpCap or Firecapture (a realtime preview within the second or two that it takes to capture the image).

 

I've also captured Himalia and Elara with the 5" scope and recently I imaged Pasiphae with a 9.25" EdgeHD. All of these captures were done from my light-polluted location (Bortle 7) using CMOS cameras.

 

Here is the link of where I imaged Pasiphae and one where I imaged Amalthea with the 5" scope.

 

https://www.cloudyni.../#entry11329763

 

https://www.cloudyni...r/#entry7137356

 

One issue with all of these faint moons is that you need to be pretty careful that what you are identifying is actually the moon and NOT a background star. There are a LOT of stars that are magnitude 17 and fainter.

Very cool.  Thanks for sharing the links to your photos.  Your photos of the minor moons is helpful to me to get an idea of the glow of Jupiter in the path of the moons.  Nice one capturing Amalthea.



#15 Galaxy Michael

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Posted 15 September 2021 - 12:50 AM

Here is an image from SkySafari showing the orbits of all the minor moons.  For scale you can just see Callisto up and to the left of Jupiter at the far reach of its orbit.

Looking at this image of all of the minor moons is very cool.  It has to be a difficult task to individually identify this many moons while trying to find more.

 

I have SkySafari 6 Pro on my phone.

 

Which expansion pack do I need?  I see the "GAIA Extension Database" to add 90 million stars (1.64GB).  I'm guessing this is the one I need to get..  I need to free up some storage space on my phone.  I don't have room for it.  I should be able to remove enough stuff to free up the storage space needed.


Edited by Galaxy Michael, 15 September 2021 - 01:56 AM.


#16 Galaxy Michael

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Posted 15 September 2021 - 01:10 AM

Thanks for all of the information everyone shared for my question about Jupiter's moons.

 

My daughter is turning 4 years old this month so she is still very young.  She is the one who got me to post this question.  She was watching a kids program about Jupiter with my wife and they mentioned 68 moons of Jupiter.  She wanted to know why we only see 4 moons at the eyepiece.

 

I bring her outside every night to look at the sky.

 

Some of my daughters questions about the universe are easy for me to answer.  She is now asking me complicated questions about the universe that I don't know the answers to.  I like it, and I make all efforts needed to find the answers.  This question about seeing Jupiter's minor moons needed the experience from the CN forum since a Google search didn't help.

 

Tonight I brought her outside for our nightly observing session and the topic was Jupiter.  I summarized what I learned on this thread from all of you.  She is happy that we will try to observe the minor moon Himalia when the time is right.

 

Thank you!


Edited by Galaxy Michael, 15 September 2021 - 01:17 AM.

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#17 james7ca

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Posted 15 September 2021 - 02:17 AM

Do NOT use SkySafari to try and determine the locations of the outer moons of Jupiter, it won't give the correct locations. I know this from experience and I talked about this issue in the posts I made earlier about photographing Himalia, Elara, and Pasiphae.

 

If you need to locate any of these moons you'll have to use NASA's Horizons website (or similar) where you can enter the moon by name to generate accurate ephemerides.

 

Here is the link you need:

 

  https://ssd.jpl.nasa...orizons.cgi#top

 

After you get the correct location (and SkySafari can be off by degrees) you can then plot the location in SkySafari or (better) on a site like WikiSky.org. On WikiSky.org you can just enter an object's coordinates in RA and Dec as a series of six numbers (hh mm ss dd mm ss) and then WikiSky will display a very deep image that is centered on those coordinates with a small box indicating where the object should appear. Once you have this image it should be fairly easy to locate the correct star field in whatever app you like (for example, with SkySafari).

 

By the way, here are some threads that talk about visually detecting a few of the minor moons of Jupiter (found using Google search):

 

  https://www.cloudyni...rs-faint-moons/

 

  https://www.cloudyni...nd-maybe-elara/

 

  https://www.cloudyni...around-jupiter/


Edited by james7ca, 15 September 2021 - 02:26 AM.

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#18 Allan Wade

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Posted 15 September 2021 - 04:26 AM

James makes a good point. I wasted a couple of nights trying to find the minor moons using SkySafari. The location data for the moons in SkySafari is way off. The Minor Planet Centre ephemeris has been 100% accurate for every moon I’ve observed. 
 

The thing about these moons is they move across the sky quite fast, all of them, even the outer ones. So it’s a great confirmation factor. In every case I needed as little as 30 or 40 minutes to see them move against the background star field.


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#19 btschumy

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Posted 15 September 2021 - 07:46 AM

This is the first I’ve heard that the minor moon positions were significantly off.  I no longer work on SkySafari but will report this to the current developers.

 

You don’t need any expansion packs to see these, just the Pro version.  Go to Solar System settings and turn on “Minor Moons” and “Moon Orbits”.  Even if the positions are currently incorrect, it is still a nice visual to see how far out their orbits go.


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#20 Galaxy Michael

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Posted 15 September 2021 - 10:40 AM

Do NOT use SkySafari to try and determine the locations of the outer moons of Jupiter, it won't give the correct locations. I know this from experience and I talked about this issue in the posts I made earlier about photographing Himalia, Elara, and Pasiphae.

 

If you need to locate any of these moons you'll have to use NASA's Horizons website (or similar) where you can enter the moon by name to generate accurate ephemerides.

 

Here is the link you need:

 

  https://ssd.jpl.nasa...orizons.cgi#top

 

After you get the correct location (and SkySafari can be off by degrees) you can then plot the location in SkySafari or (better) on a site like WikiSky.org. On WikiSky.org you can just enter an object's coordinates in RA and Dec as a series of six numbers (hh mm ss dd mm ss) and then WikiSky will display a very deep image that is centered on those coordinates with a small box indicating where the object should appear. Once you have this image it should be fairly easy to locate the correct star field in whatever app you like (for example, with SkySafari).

 

By the way, here are some threads that talk about visually detecting a few of the minor moons of Jupiter (found using Google search):

 

  https://www.cloudyni...rs-faint-moons/

 

  https://www.cloudyni...nd-maybe-elara/

 

  https://www.cloudyni...around-jupiter/

Thank you for this.  I tested the NASA horizons link and captured the location data for Himalia.  I'll have to experiment with plotting the data to get it marked on a map.  All of my telescope gear is manually moved for observing.  I don't use auto tracking equipment.



#21 Galaxy Michael

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Posted 15 September 2021 - 10:46 AM

This is the first I’ve heard that the minor moon positions were significantly off.  I no longer work on SkySafari but will report this to the current developers.

 

You don’t need any expansion packs to see these, just the Pro version.  Go to Solar System settings and turn on “Minor Moons” and “Moon Orbits”.  Even if the positions are currently incorrect, it is still a nice visual to see how far out their orbits go.

Thank you if you can report this to the SkySafari developers.  It would be nice if I could use SkySafari when I have an opportunity to try to observer one of the minor moons.

 

Also, thanks for letting me know how to see the minor moons in Sky Safari Pro.  It worked.  I guess I need to dig through the settings to see what else I might be missing.  

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#22 gmiller123456

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Posted 15 September 2021 - 11:34 AM

Thank you if you can report this to the SkySafari developers.  It would be nice if I could use SkySafari when I have an opportunity to try to observer one of the minor moons.

 

Also, thanks for letting me know how to see the minor moons in Sky Safari Pro.  It worked.  I guess I need to dig through the settings to see what else I might be missing.  

Odds are they know and were just hoping people wouldn't notice.  The minor moons of Jupiter cannot be predicted with the normal Kelperian elements.  There is a kernal for NASA's SPICE toolkit that predicts many of them called JUP365, but it's about 1Gb in size.


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#23 Redbetter

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Posted 15 September 2021 - 05:57 PM

Odds are they know and were just hoping people wouldn't notice.  The minor moons of Jupiter cannot be predicted with the normal Kelperian elements.  There is a kernal for NASA's SPICE toolkit that predicts many of them called JUP365, but it's about 1Gb in size.

I have wondered how they were handled.  My understanding is that these distant moons have considerable perturbation of their orbits by other solar system bodies, so their orbits cannot be fully defined by traditional parameters.



#24 gmiller123456

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Posted 15 September 2021 - 08:12 PM

I have wondered how they were handled.  My understanding is that these distant moons have considerable perturbation of their orbits by other solar system bodies, so their orbits cannot be fully defined by traditional parameters.

Unfortunately none of the solar system bodies obey Kepler's laws well enough to compute accurate positions over a long period of time.  JPL's Development Ephemeris for the planets are several hundred MB in size, less accurate versions like VSOP87 are still a few MB in size.  JPL has computed a least squares fit of Kelperian elements, but they have errors of about half a degree and require some non-keplerian corrections (https://ssd.jpl.nasa...t/p_elem_t1.txt and https://ssd.jpl.nasa.gov/txt/p_elem_t2.txt ).

 

The link below is a paper by the authors of the ephemeris JPL Horizons uses to compute the positions and explains a lot about their orbits.  They do provide Keplerian elements, but they say it's only to describe the orbits for identification later.  I imagine that's what Sky Safari is using.

https://iopscience.i...538-3881/aa5e4d


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