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Martian Moons

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#76 Jeff B1

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Posted 02 November 2020 - 06:35 AM

Mars is under 20" again! I'm a bit sad about that. Gonna be a while til we see it cross that threshold again.

If you have been observing Mars for much of the apparition then you will enjoy it eve after it gets half that apparent diameter.  You are acclimated now and the Red Planet is easier to see.  2022 Mars will be higher in the sky for you.


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#77 happylimpet

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Posted 02 November 2020 - 07:58 AM

If you have been observing Mars for much of the apparition then you will enjoy it eve after it gets half that apparent diameter.  You are acclimated now and the Red Planet is easier to see.  2022 Mars will be higher in the sky for you.

True. I was getting great views and images down to 6" last time (especially as by then it had crept north). Plenty to look forward to, just the beginning of the end!



#78 kb58

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Posted 02 November 2020 - 08:45 AM

I managed to see Phobos several weeks ago, so figured that it would be easy to see Deimos—hah. I hope that I don't have to wait 15 years for that.



#79 Jeff B1

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Posted 02 November 2020 - 09:20 AM

I had an old FORTRAM program listing for the ephemeris for Phobos and Deimos, but it was in a more modern version that I had no clue of the new functions and could never translate it to Visual Basic.  I can't even find the algorithms for the elongations or ephemeris.  It should be fairly easy to use the Jupiter moons program with the Mars moons stuff, but that never quite works.  Anyone know where I can find a program code listing  for the ephemeris of Phobos and Deimos?  



#80 kb58

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Posted 02 November 2020 - 02:12 PM

Speaking of programs, StarWalk II and Sky Safari disagree about where the moons are, but I got off on a technicality, not being able to see either last night. Both did save me from mistaking a star about five diameters from Mars for one of its moons, though.



#81 Jeff B1

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Posted 02 November 2020 - 02:51 PM

I gave Grischa Hahn (WinJUPOS) that old FORTRAN listing and he adopted to WinJUPOS. Guess he is up to date in FORTRAN speak.  The last time I did any programming in it was in the IV or between that a 77 version.   They added so many new functions I was completely lost.  Differentiating 5th order trigonometric equations is not the problem.



#82 Redbetter

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Posted 05 November 2020 - 05:34 AM

The first rain since May might actually finally make it in this weekend...or at least cloud since it will be headed toward 3rd quarter and new Moon of course, so I fit in some Mars observing with the 20" in the red zone backyard tonight.  (Hoping for the rain to finally put out the back country fires to the east of me that have wrecked DSO observing since August.)   Mars and its moons have dimmed about half a magnitude since the peak of the opposition.  It is 19.3 arc seconds across now, still quite large.  Seeing was decent, good enough for 278x unfiltered at the start, but declined somewhat over the next hour or two.  

 

Early in the session I searched for Deimos at 278x without any sort of occulting bar.  Deimos was nearing greatest elongation, and I eventually picked it up in averted vision where it could be consistently located..  I had to wait nearly 2 hours before Phobos was nearing elongation on the other side of the planet.  Whenever the seeing would sharpen I could detect Phobos on the edge of a diffraction ray, but there was enough fluttering to the seeing that I could not see it at 357x. 

 

The main reason for doing this again tonight was to get a feel for how much Mars and its moons will have to have shrunk and dimmed before I can no longer catch them with the 20" in decent seeing in bright skies.   It won't be nearly as close and large next time around at opposition in 2022, and it will be increasingly distant in 2025 and 2027 before it begins to slowly wend its way back in subsequent oppositions. 

 

If you want to be ready for seeing the moons in 2022 at close approach of ~17.2 arc seconds, start practicing now to get an appreciation of what it will take.  


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#83 Jeff B1

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Posted 07 November 2020 - 11:36 AM

Well, after wasting time on creating a realistic program to list the elongations of Deimos, that makes little sense, I found several tables for 2018 that do not match each other nor mine or JPL’s.  Mine appeared that Deimos had a fairly high elliptical orbit -- when the eccentricity is very close to zero (0.0002).  So, it is a complete waste of my time at my age to worry about two tiny rocks orbiting Mars. bow.gif


Edited by Jeff B1, 07 November 2020 - 11:37 AM.

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#84 luxo II

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Posted 09 November 2020 - 11:25 PM

Going to try tonight - the weather looks nice and Phobos will be at maximum elongation from Mars around 10pm local time, perfect.

It helps a lot to study Phobos’ orbit - when it’s close to Mars you have little to no chance.
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#85 Special Ed

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Posted 11 November 2020 - 12:15 PM

I tried for the moons again on November 9th between 0115 and 0145 UT using a chart from this source which I got from the Oct. S&T Mars issue.  

 

https://pds-rings.se...acker2_mar.html

 

I cross-checked the chart with WinJUPOS and SN Pro and all three agreed.  Phobos was going to be too close to Mars to realistically be able to detect but I though I'd have a shot at Deimos--it was close to greatest elongation at ~55".  I was using an occulting ep that I made from a piece of W32 filter gel that Jeff Beish was kind enough to give me inserted into a 23mm eyepiece.  Using a 2x barlow I could reach 340x with my C14.  I looked and looked but never saw Deimos (or Phobos).  I could see a 12.7 mag star about 5 arcminutes from Mars but nothing close in.  I'm beginning to wonder if Mars is getting too far away to see the moons.  Any thoughts?



#86 kb58

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Posted 11 November 2020 - 07:23 PM

That's what I'm afraid of. I managed to see Phobos first try, so couldn't understand what all the complaining was about. Well I do now, as I've been unable to see either at any time over the last few weeks. Really don't want to wait another 15 yrs, but the cosmos doesn't run by my schedule, haha.


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#87 Redbetter

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Posted 12 November 2020 - 12:57 AM

I tried for the moons again on November 9th between 0115 and 0145 UT using a chart from this source which I got from the Oct. S&T Mars issue.  

 

https://pds-rings.se...acker2_mar.html

 

I cross-checked the chart with WinJUPOS and SN Pro and all three agreed.  Phobos was going to be too close to Mars to realistically be able to detect but I though I'd have a shot at Deimos--it was close to greatest elongation at ~55".  I was using an occulting ep that I made from a piece of W32 filter gel that Jeff Beish was kind enough to give me inserted into a 23mm eyepiece.  Using a 2x barlow I could reach 340x with my C14.  I looked and looked but never saw Deimos (or Phobos).  I could see a 12.7 mag star about 5 arcminutes from Mars but nothing close in.  I'm beginning to wonder if Mars is getting too far away to see the moons.  Any thoughts?

Hard to say.  The key ingredient is still the seeing.  You have the aperture and combined with the occulting set up you should still have a good shot at it, but getting cooperative seeing has been the most important facet/obstacle when spotting either of the the moons near elongation.  Very good seeing is when Mars looks sharp enough in larger aperture that I am not wanting to quickly switch to a red filter at 278x.  That is when the moons become most accessible.  

 

If 12 mag stars are remaining sharp at 340x then you should have your best shot.  If not (e.g. only sharp at moments, drifting in and out of blur at best focus) then you might need to drop back a notch or two.  Unfortunately, that generally means the seeing is marginal or worse anyway.  Dialing back can be tricky when you only have a single occulting eyepiece, but you might be able to unscrew the Barlow element and attach it directly eyepiece to reduce the Barlow factor.

 

I've been pulling for you on this one.  Mars is still a bit closer/larger than it will peak for quite a few years, so this is still your best shot with your gear--assuming that you catch a very good patch of seeing to pull it all together.



#88 Special Ed

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Posted 12 November 2020 - 01:47 PM

Red,

Thanks for the input.  I reckoned the seeing that night at 6/10 Pickering (or about Antoniadi III) which must not have been good enough.  I could never get the 12th mag star to come into sharp focus.  I guess I won't give up yet--thanks for the encouragement.  smile.gif



#89 Pcbessa

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Posted 15 November 2020 - 01:58 PM

Here in Scotland I have at least 80% of clear nights with seeing not good enough for the Martian moons. When seeing is sharp I usually say wow at the fineness of detail on Mars.

Pickering 6 or 7 is good enough.

I also noticed that I only spotted Deimos twice or 3x this autumn, and all those nights were moon-free. I think sky darkness is also a factor. I live in a region with quite dark skies...

By the way I also noticed the impact that great seeing has in the moons of Uranus.

#90 Special Ed

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Posted 20 November 2020 - 11:44 PM

Well, I saw one of the moons of Mars--and the harder one to see at that.  Seeing was good but there was a six day old Moon.  I started seeing it with AV but by the time of greatest elongation I could see it with DV.  A full report is here.

Here is the sketch I made of the FOV.

 

202011-20-0030-MR-CM207-Mars-Phobos.jpg


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#91 Jeff B1

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Posted 21 November 2020 - 11:42 AM

Weird; I was making a fun list of times to see Deimos at max elongation and my times would not match with several other lists found on the evil Net.  It should be very easy to start with a known time then count out the  time it takes the rock to orbit Mars, like 109,123.2 seconds or sometime like that.. Huh. Deimos has a nearly perfect circular orbit and it should be a matter of simple athematic.

 

Reference:  Universe Today --  "Deimos’ orbit is nearly circular, ranging from 23455.5 km at periapsis (closest) to 23470.9 km at apoapsis (farthest) – which works out to an average distance (semi-major axis) of 23,463.2 km. With an average orbital speed of 1.3513 km/s, it takes 30 hours, 18 minutes and 43.2 seconds to complete a single orbit (or 1.263 days)." or 109,123.2 seconds.


Edited by Jeff B1, 21 November 2020 - 11:52 AM.


#92 Jeff B1

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Posted 22 November 2020 - 08:16 AM

Then I look in an old copy of the Astronomical Almanac (1999) to find Deimos orbits in 30h, 17m, 54.87s (109,074.87 seconds).  Weird.



#93 maroubra_boy

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Posted 22 November 2020 - 06:28 PM

I observed Phobos using a 9" Santel f/13 Maksutov with a 12mm orthoscopic eyepiece from my home in Sydney on the 12th of November.  Painstaking exercise.  Observation was confirmed by fellow CN'er Luxo II.  Keeping Mars just outside of the FOV was the only way to observe Phobos.

 

This was my first observation of Phobos.

 

Had a go at Deimos on the last New Moon Saturday, 15th of November, with my 17.5", but seeing conditions were too poor.

 

Alex.


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#94 Napp

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Posted 23 November 2020 - 12:17 AM

I finally observed Deimos the evening of November 3-4.  Both were to be at about maximum distance from Mars and on directly opposite sides of Mars helping with identification.  I set up my 10 inch DOB and 8 inch SCT.  I worked hard with my 10 inch DOB, a 10mm occulting eyepiece I made earlier that day, and a 2X focal extender.  Several times I thought I might have gotten a brief glimpse of Deimos with averted vision.  Suddenly it popped into direct vision for several seconds and then was gone.  I think I may have glimpsed it a couple more times with averted vision but that was it for visual.  I was not able to spot Phobos visually.  I took a few pictures with a dslr on the SCT using a 4X barlow.  I was able to photograph both Deimos and Phobos.

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#95 kb58

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Posted 23 November 2020 - 04:24 PM

Oh sure, rub it in. I thought Phobos was the "hard one" to see, and found it first try. I assumed then that Deimos would be easy. Hah, no one told the moon that.



#96 Jeff B1

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Posted 24 November 2020 - 01:37 PM

I give up trying to find the correct orbital period for Deimos.  So far I have found at least five different times.  The one I found that reflects a correct period is from a table from 2018 that yields 30.2 hours.  But my Astronomical Almanac yields 30.291075 hours.  Oh well, so much for 5th grade math.  lol.gif



#97 Redbetter

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Posted 24 November 2020 - 06:15 PM

I give up trying to find the correct orbital period for Deimos.  So far I have found at least five different times.  The one I found that reflects a correct period is from a table from 2018 that yields 30.2 hours.  But my Astronomical Almanac yields 30.291075 hours.  Oh well, so much for 5th grade math.  lol.gif

JPL's site gives the orbital elements for satellites, with Deimos listed as having a period of 1.2624 days.  Link  That value is somewhat lacking in precision;  exploring further there is an extra digit added elsewhere (link):  1.26244 days.  These are listed as sidereal days, so the day would be 23.9344696 hours if I understand correctly.  The net using the more precise value is 30.2158 hours or 1 day 6 hours 12 min 57 sec.

 

I suspect the difference you are seeing is in rounding differences depending on how values are expressed, as well as 24 hours vs. the somewhat shorter sidereal day.  That would explain the values you list above reasonably well. 


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#98 Jeff B1

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Posted 24 November 2020 - 06:44 PM

JPL's site gives the orbital elements for satellites, with Deimos listed as having a period of 1.2624 days.  Link  That value is somewhat lacking in precision;  exploring further there is an extra digit added elsewhere (link):  1.26244 days.  These are listed as sidereal days, so the day would be 23.9344696 hours if I understand correctly.  The net using the more precise value is 30.2158 hours or 1 day 6 hours 12 min 57 sec.

 

I suspect the difference you are seeing is in rounding differences depending on how values are expressed, as well as 24 hours vs. the somewhat shorter sidereal day.  That would explain the values you list above reasonably well. 

Of course. My problem is that so many sources are different and those tiny rock have been studied to death and everyone should agree on the numbers.  The high order equations shows me the truth.  It is just something to do to avoid TV. wink.gif  Thanks  for the interest.  


Edited by Jeff B1, 24 November 2020 - 06:45 PM.



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