Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Observing the fainter moons of the solar system

  • Please log in to reply
16 replies to this topic

#1 Pcbessa

Pcbessa

    Messenger

  • -----
  • topic starter
  • Posts: 417
  • Joined: 26 Jan 2019
  • Loc: Forres, NE Scotland, UK

Posted 04 August 2020 - 05:21 PM

Hello,

 

I have a 10" Dob and so far I have seen the 4 Galileo moons; Titan, Rhea, Japetus, Dione and Tethys (in Saturn); Titania and Oberon in Uranus; and Triton in Neptune. All are relatively easy although Tethys, Titania and Oberon are often a bit difficult.

 

So far I have failed spotting Enceladus (which shouldn't be that super hard), Ariel and Umbriel seem to be very hard to see, and I haven't tried to see Phobos and Deimos (I will in soon as Mars reaches opposition)

 

I guess I would rank the moons by difficult like this:

 

Super easy to see:

4 Galileo moons

Titan mag 8

Easy:

Rhea mag 10

Japetus mag 10-12

 

Somewhat easy:

Dione mag 10.5

 

Less easy:

Triton mag 13 (a fainter moon but the advantage is that Neptune is also fainter, at 15")

Tethys mag 11 (for me Tethys is always a bit more difficult to see than Dione)

 

Slightly challenging but seen under good conditions with a 10":

Oberon mag 14 (around 40" from Uranus)

Titania mag 13.5 (around 25" from Uranus)

Deimos mag 11 (around 50" from Mars) I have not seen it yet

Pluto mag 14.5 (it has no glare, so it is easier to see)

 

Challenging/ requires good seeing (I have not seen these ones with my 10" Dob):

Enceladus mag 12 but around 20" from Saturn

 

Even more challenging: 

Phobos mag 11 but around 15" from Mars

Ariel (mag 14.5, around 15" from Uranus) I might have glimpsed this moon in one instance, but that was an unconfirmed case

Umbriel (mag 15, around 15" from Uranus) I have not seen it despite trying

 

Probably very difficult but still within the technical limits of a 10" under perfect seeing conditions:

Himalia (mag 14.5 and not too close to Jupiter but probably hard to spot in Jupiter's glare, max separation is 50')

Mimas (mag 13 but very close to Saturn, usually about 5" but max separation is 15")

 

Only reachable with much larger apertures

Charon (mag 16 and 1" away from Pluto - it would require very dark skies and perfect seeing)

Miranda (mag 16 and close to Uranus at 9") 

Phoebe (mag 16.5 but about half degree from Saturn)

Amalthea, mag14 but too close to the very bright Jupiter at 30"

Nereid, mag 18 (3' away from Neptune) probably too faint for most

Any other moons?

 

Would you agree with this ranking? Any comments on moons that can be seen with a 10" or 12" aperture under perfect conditions?


Edited by Pcbessa, 04 August 2020 - 05:41 PM.

  • Ittaku likes this

#2 Rich V.

Rich V.

    Fly Me to the Moon

  • *****
  • Posts: 7,248
  • Joined: 02 Jan 2005
  • Loc: Lake Tahoe area, Nevada

Posted 04 August 2020 - 05:42 PM

I've seen the five Saturnian moons you list in my 80mm refractor and my 100mm bino telescope.  Iapetus can be tricky depending of which face is illuminated; it has a light side and dark side approx. 2 magnitudes darker when seen on the east of the planet.  Seeing and transparency cooperating with a favorable positioning, I'd expect Enecladus to be easy enough in a 10"; a 4" refractor can show it.  I've had no luck yet with the 80mm.

 

Kudos to you for your other moon observations.  bow.gif

 

Rich



#3 Allan Wade

Allan Wade

    Aurora

  • *****
  • Posts: 4,732
  • Joined: 27 Jan 2013
  • Loc: Newcastle, Australia

Posted 04 August 2020 - 07:23 PM

That's a great list. Don't forget Lunar at the top as well, that will give you 13 moons which is excellent going in a 10".

 

I would make the following observations about your list.

 

If you have the capability to see Pluto, then you will be able to see Himalia and Hyperion. They are similiar magnitudes around oppostion and separated enough from the planet that glare doesn't affect the observation.

 

Umbriel is a very challenging moon to see. Beyond a 10", so would slide down your list.

 

Most people probably underestimate how difficult it is to see Mimas. It's harder than Phobos, which is how you've correctly ranked them in your list. Even in my 16" with Saturn near zenith, Mimas has been a challenge recently. With the rings wide open as they are, the extra brightness of Saturn would push Mimas beyond a 10".

 

 

 

Slightly challenging but seen under good conditions with a 10":

Oberon mag 14 (around 40" from Uranus)

Titania mag 13.5 (around 25" from Uranus)

Deimos mag 11 (around 50" from Mars) I have not seen it yet

Pluto mag 14.5 (it has no glare, so it is easier to see)

 

Challenging/ requires good seeing (I have not seen these ones with my 10" Dob):

Enceladus mag 12 but around 20" from Saturn

 

Even more challenging: 

Phobos mag 11 but around 15" from Mars

Ariel (mag 14.5, around 15" from Uranus) I might have glimpsed this moon in one instance, but that was an unconfirmed case

Umbriel (mag 15, around 15" from Uranus) I have not seen it despite trying

 

Probably very difficult but still within the technical limits of a 10" under perfect seeing conditions:

Himalia (mag 14.5 and not too close to Jupiter but probably hard to spot in Jupiter's glare, max separation is 50')

Mimas (mag 13 but very close to Saturn, usually about 5" but max separation is 15")



#4 Allan Wade

Allan Wade

    Aurora

  • *****
  • Posts: 4,732
  • Joined: 27 Jan 2013
  • Loc: Newcastle, Australia

Posted 04 August 2020 - 07:33 PM

Only reachable with much larger apertures

Charon (mag 16 and 1" away from Pluto - it would require very dark skies and perfect seeing)

Miranda (mag 16 and close to Uranus at 9") 

Phoebe (mag 16.5 but about half degree from Saturn)

Amalthea, mag14 but too close to the very bright Jupiter at 30"

Nereid, mag 18 (3' away from Neptune) probably too faint for most

 

I would rank these-

 

1. Phoebe is not difficult in semi large scopes.

 

2. Miranda is very tough. I haven't put the proper effort into seeing it yet, and have it targeted in a couple of months.

 

3. Amalthea has been observed by around 20 people since it was discovered by Edward Barnard. I spent two years trying to see it in the 32" before I finally had success for a 15 minute window. It needs everything to be perfect and is beyond difficult.

 

4. Charon is one I've been trying for for two years as well and still haven't seen it. So I would have to rate it beyond Amalthea.

 

5. Nereid is in the magnitude 19's. I haven't even tried for it and will need a much larger scope. There wouldn't have ever been a visual observation of Nereid.


  • Paul Morow likes this

#5 Allan Wade

Allan Wade

    Aurora

  • *****
  • Posts: 4,732
  • Joined: 27 Jan 2013
  • Loc: Newcastle, Australia

Posted 04 August 2020 - 07:54 PM

Any other moons?

For larger scopes there are several moons of Jupiter that are possible.

 

Elara and Pasiphae are in the magnitude 16's right now and well separated from Jupiter, so availaable to semi large scopes.

 

Then there's the next group of four I recently observed, which I believe is the first time they've been visually seen. Carme and Sinope were not too tough, being direct vision targets in the 32". Lysithea was a bit tougher and generally my observation was mostly averted vision. Ananke peaked at magnitude 18.2 for only six hours on opposition night before starting to fade quickly. I got it while it was around 18.3. As faint as these four are, they were not that challenging to find and observe, they just need a big enough scope. Where as I found Amalthea ridiculously difficult by comparison.

 

I'm sitting at 29 Solar System moons now. I want to catch Miranda and that will likely end what is possible in my 32".  


  • Rick Kapela likes this

#6 Pcbessa

Pcbessa

    Messenger

  • -----
  • topic starter
  • Posts: 417
  • Joined: 26 Jan 2019
  • Loc: Forres, NE Scotland, UK

Posted 05 August 2020 - 04:41 AM

I will then rank the hardest moons as such:

Challenges for a 10" aperture:
Pluto m14.5
Himalia Jup m14.5
Hyperion Sat m145
Deimos m12
Enceladus m12
Ariel m14.5
Phobos m11

Very difficult for a 10"
Umbriel m15
Mimas 13

Technically wirhin the limits of 10-14"
Elara Jup m16
Pasiphae Jup m16
Phoebe Sat m16.5

Need larger apertures,maybe around 20"
Carme Jup
Sinope Jup
Lysithea Jup
Ananke Jup m18.3

Too difficult for even most large apertures of 30"
Amalthea
Charon
Miranda
Nereid

Any comments?
  • Allan Wade likes this

#7 Allan Wade

Allan Wade

    Aurora

  • *****
  • Posts: 4,732
  • Joined: 27 Jan 2013
  • Loc: Newcastle, Australia

Posted 05 August 2020 - 08:56 AM

The Carme, Sinope, Lysithea and Ananke grouping are possible with a 30" plus size scope under pristine skies with them at very high altitude in the sky.

 

Miranda is likely in 20" size scopes with very good seeing.

 

Nereid is probably not possible in any amateur size scope.



#8 Allan Wade

Allan Wade

    Aurora

  • *****
  • Posts: 4,732
  • Joined: 27 Jan 2013
  • Loc: Newcastle, Australia

Posted 05 August 2020 - 09:57 AM

I will give it a try to rank the moons by progressive difficulty given what I've experienced over the years. To avoid too many variables we should assume dark skies and good seeing and transparency with targets at least 40 to 50 degrees altitude.

 

Binocular

 

Lunar, Ganymede, Io, Europa, Callisto, Titan.

 

3" to 4"

 

Rhea, Tethys, Dione, Iapetus.

 

8" to 10"

 

Deimos, Enceladus, Triton, Titania, Oberon.

 

10" to 12"

 

Phobos, Himalia, Hyperion, Ariel.

 

14" to 16"

 

Mimas, Umbriel.

 

18" to 20"

 

Phoebe, Elara, Pasiphae.

 

20" +

 

Miranda.

 

30" +

 

Carme, Sinope, Lysithea, Ananke.

 

Amalthea.

 

Charon.

 

50" +

 

Nereid


  • Magellanico likes this

#9 Pcbessa

Pcbessa

    Messenger

  • -----
  • topic starter
  • Posts: 417
  • Joined: 26 Jan 2019
  • Loc: Forres, NE Scotland, UK

Posted 05 August 2020 - 01:14 PM

Because I only have a 10" Dob, I do not expect to see many of these moons. But I am still looking forward to see Phobos and Deimos in soon, whilst Enceladus, Himalia and Hyperion should be rather straightforward challenges and my next targets.

 

Himalia and Hyperion at mag 14.5 are quite faint but should be observable under good conditions and good mapping of background stars.

 

Mimas should be observable when the rings cross the plane of Earth, not now.

 

I need to confirm a glimpse from Ariel, and Umbriel is less likely to be within the realm of my scope, but still a possibility. I found all moons of Uranus quite hard, but Oberon is the easiest. Ariel and Umbriel are likely to be the limit of my 10" Dob.

 

However, Phoebe could be another remote possibility for my aperture, only under excellent condition (at magnitude 16.4 it should be observable under Bortle 1 or 2 skies with Saturn high on the sky - not anytime soon.). I observed stars down to 16-16.5 under Bortle 2 skies at zenith and good seeing, so it would have been a question of mapping stars around Saturn and choosing a time of great orbital separation.

 

Anyways these moons are the list of what can be seen with a Dob under 20".


  • Allan Wade likes this

#10 Xilman

Xilman

    Mariner 2

  • -----
  • Posts: 257
  • Joined: 26 Feb 2018
  • Loc: Cambridge UK & La Palma

Posted 05 August 2020 - 02:22 PM

Would you agree with this ranking? Any comments on moons that can be seen with a 10" or 12" aperture under perfect conditions?

I draw a distinction between "observing" and "seeing". Professional astronomers do a great deal of observing. They hardly ever see any of their targets through a telescope eyepiece.

 

Iapetus is the faintest planetary satellite I have seen, and that through a 27.5cm Maksutov-Cassegrain, though that many years ago because I hardly ever use an eyepiece for anything serious these days.

 

Caliban, at mag 22.2, is the faintest I have observed.

 

Curiously enough, I was observing Carme (J-XI) and Pasiphae (J-VII) less than 20 hours ago. The presence of brilliantly moon-lit Saharan dust suggests that the attempted observation of Lysithea (J-X) was probably unsuccessful but I still have faint hopes that it will show up in the data taken last night.



#11 Allan Wade

Allan Wade

    Aurora

  • *****
  • Posts: 4,732
  • Joined: 27 Jan 2013
  • Loc: Newcastle, Australia

Posted 05 August 2020 - 11:36 PM

I draw a distinction between "observing" and "seeing". Professional astronomers do a great deal of observing. They hardly ever see any of their targets through a telescope eyepiece.

 

Iapetus is the faintest planetary satellite I have seen, and that through a 27.5cm Maksutov-Cassegrain, though that many years ago because I hardly ever use an eyepiece for anything serious these days.

 

Caliban, at mag 22.2, is the faintest I have observed.

 

Curiously enough, I was observing Carme (J-XI) and Pasiphae (J-VII) less than 20 hours ago. The presence of brilliantly moon-lit Saharan dust suggests that the attempted observation of Lysithea (J-X) was probably unsuccessful but I still have faint hopes that it will show up in the data taken last night.

I've always considered astronomical observing to be looking with your own eyes at targets in the sky, whether naked eye or through an eyepiece. Sitting at a computer screen while your equipment collects photons is imaging not observing. Just like the pros use equipment to gather data and then use that data to do science. I don't see any observing happening in that sequence.

 

I think it's great though that you are collecting images of these fainter moons.


  • Redbetter likes this

#12 Redbetter

Redbetter

    Cosmos

  • *****
  • Posts: 9,511
  • Joined: 16 Feb 2016
  • Loc: Central Valley, CA

Posted 06 August 2020 - 03:56 AM

Observing is actually looking at objects through the eyepiece as Allan notes.  I see all sorts of things in images without leaving the comfort of the house.  Frequently I use images to confirm things I have seen, and sometimes I use my visual observations to help imagers identify what they have actually imaged and sometimes were unaware were in the frame.

 

Saturn's retinue has been among the most variable.  For those at northerly latitudes many of the fainter moons are more challenging now due to low elevation and seeing.  And for the next several years I won't bother with Phoebe because of the rich Milky Way star fields making the search impractical for me.   However, it hasn't always been this way. Back in the first few months that I had my first scope, Saturn was in the midst of a ring plane crossing and Saturn was better placed.  With some effort and a number of attempts, I was able to observe  Mimas once near greatest elongation with the rings not being an issue.  That was with an 8" SCT and in a location that frequently had excellent seeing.   But with the rings in the way and Saturn low in the sky, seeing Mimas in the 20" is primarily about the seeing.  It can be easily found without knowing where to look on a good night. 

 

Iapetus is visible in my suburban backyard with a 60mm scope, when it's bright side is facing us.   I imagine a 40mm will show it in dark sky when it is well separated and that bright side is in view.

 

Hyperion should be a reasonable target for an 8".  It is one I remember chasing down with the SCT many years ago.  

 

Enceladus is one I can catch with 4-5" scope in the backyard on steadier nights.  I can't recall if I have caught it with the 80ED or not.  

 

Phobos and Deimos visibility depends very much on the opposition, elevation in the sky, and seeing quality.  I don't know what the minimum apertures are.  I remember trying for them with the 8" SCT several oppositions.  One was a close one when the 20" was new.  I might have nabbed one of them in the 8" then because I was under very steady sky and doing side-by-sides.  Unfortunately, I was too busy sketching and being wowed by the big scope to record whether or not any of my 8" attempts turned up either moon. I need to take a crack at it with the 10" this year, it is considerably sharper than the SCT. 

 

I suspect that Triton is within reach of a 5 or 6" scope on a steady night in dark sky.  However, I have not tried either aperture on it.  It is straightforward with an 8" SCT.  I have failed on it with a 110ED in poor seeing in dark sky, I would like to try this on a night of good seeing.  

 

Surprisingly, I was able to detect both Ariel and Umbriel with an 8" off axis aperture mask in the 20" under dark sky.   Seeing was 5/10 Pickering for the 8" aperture that night, and I used 357x.  Of course there was no spider diffraction or central obstruction with the off axis mask, so this isn't quite the same as doing it with an 8" Dob where there would be more diffraction/scatter from the planet to deal with.  But it wasn't great seeing either.  I had already seen all 4 with full aperture so I was able to check positions with high confidence.  Only Titania and Oberon were seen at 278x.  At 357x, Umbriel was seen about 50% of the time once I finally detected it.

 

I haven't tried for Titania or Oberon with only 6" of aperture, but I suspect they are possible in dark and steady sky at around 225 to 250x.  They were good targets for the 8" SCT in dark and steady sky at closer to 300x from what I recall.

 

I have seen Elara and Himalia with the 20".  Glare from Jupiter in the focuser was a big problem, so I ended up trying several times until they were oriented best, keeping them at odd places in the field from what I recall to prevent off axis glare.


  • Paul Morow and Allan Wade like this

#13 Xilman

Xilman

    Mariner 2

  • -----
  • Posts: 257
  • Joined: 26 Feb 2018
  • Loc: Cambridge UK & La Palma

Posted 06 August 2020 - 06:16 AM

I've always considered astronomical observing to be looking with your own eyes at targets in the sky, whether naked eye or through an eyepiece. Sitting at a computer screen while your equipment collects photons is imaging not observing. Just like the pros use equipment to gather data and then use that data to do science. I don't see any observing happening in that sequence.

 

I think it's great though that you are collecting images of these fainter moons.

We have to agree to disagree.  In my defence, all I can say is that professional astronomers consider themselves to be observing when they are collecting data and to be analysing when they subsequently process that data.

 

Whatever terminology we use, the important thing is that astronomers continue to get derive enjoyment from their activity.


Edited by Xilman, 06 August 2020 - 06:43 AM.


#14 Redbetter

Redbetter

    Cosmos

  • *****
  • Posts: 9,511
  • Joined: 16 Feb 2016
  • Loc: Central Valley, CA

Posted 06 August 2020 - 07:03 AM

We have to agree to disagree.  In my defence, all I can say is that professional astronomers consider themselves to be observing when they are collecting data and to be analysing when they subsequently process that data.

 

Whatever terminology we use, the important thing is that astronomers continue to get satisfaction from their activity.

That is very strange terminology to say the least.  It certainly doesn't apply to their historical predecessors.  They observed visually.  And with regard to observation in general, when I have observed experiments I have been physically present, watching or participating in the collection of the data to identify problems or recognize success in real time.  Typically I have done this to make early corrections to the method or sampling if something was discovered to be amiss, or if the methodology was not yet fully developed.   If I was not involved in any way other than setting up collection by some instrument or operator, then I was merely collecting data, NOT observing.   That was the difference between me conducting a plant test, and some duffer who was unaware of the actual conditions, instruments, and procedures used to conduct an actual test. Ask them a question about how the sampling was done or other conditions at the time and they had no clue...and they had no useful answers when things didn't turn out as expected. 

 

Data processing and analysis is a wholly separate process not to be confused with observing in real time.  It rather sounds like what you consider observing is a misnomer.  I have watched/listened to others taking images of Jupiter while I observed it live (and gave them what proved to be on-the-mark pointers about culling to improve their image detail and processing speed based on the number of frames they collected and the seeing I was experiencing at the time, without ever having imaged.)  I was observing and seeing.  They were waiting to collect data, then processing it to get an image they could see.  Their more detailed resultant image had its merits, but I wouldn't call what they were doing observing.  They were imaging.



#15 Xilman

Xilman

    Mariner 2

  • -----
  • Posts: 257
  • Joined: 26 Feb 2018
  • Loc: Cambridge UK & La Palma

Posted 06 August 2020 - 07:18 AM

That is very strange terminology to say the least.

 

... It rather sounds like what you consider observing is a misnomer.

If so, I am in very good company.

 

I am on first name terms with a number of professionals who consider themselves observers. The professional literature is full of references to "observing sessions", "observations", and the like.  I could but won't, out of consideration to most people here who (I believe) don't care that much about the minutiae, provide any number of documented statements made by present-day professional astronomers. If you would like a list of URLs, please PM me.

 

As I said, we have to agree to disagree. I am not going to put any great effort into trying to change people's minds on this topic.



#16 Redbetter

Redbetter

    Cosmos

  • *****
  • Posts: 9,511
  • Joined: 16 Feb 2016
  • Loc: Central Valley, CA

Posted 06 August 2020 - 08:40 AM

Whatever you want to believe, maybe you have convinced yourself.  How actually observing something visually and seeing it that way wouldn't qualify as "observing"...well...I submit it takes a special kind of cognitive dissonance to arrive at such a conclusion.  This is an observing forum, not an imaging forum.  It is not titled as a "seeing forum" as your initial post on the subject attempts to define observing.  I think most of us recognize that collecting data for scientific purposes or an image is not the same as actually observing something.  Some folks can't seem to tell the difference between the two things, but those who don't understand the distinction rarely seem to have done much in the way of actual observing

 

Case in point:

Iapetus is the faintest planetary satellite I have seen, and that through a 27.5cm Maksutov-Cassegrain, though that many years ago because I hardly ever use an eyepiece for anything serious these days.

 

Rather than continue the distraction you started, perhaps you might consider how your series of posts in this thread has in any way helped to answer the OP's original question:  "Any comments on moons that can be seen with a 10" or 12" aperture under perfect conditions?"  


Edited by Redbetter, 06 August 2020 - 03:48 PM.


#17 Xilman

Xilman

    Mariner 2

  • -----
  • Posts: 257
  • Joined: 26 Feb 2018
  • Loc: Cambridge UK & La Palma

Posted 06 August 2020 - 09:13 AM

How actually observing something visually and seeing it that way wouldn't qualify as "observing ...well...I submit it takes a special kind of cognitive dissonance to arrive at such a conclusion".

In my view, "seeing" and "imaging" are two special cases of "observing". You are putting words into my mouth.

 

Enough.  This has discussion gone on for too long.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics