97 replies to this topic

[Allan Wade]

Is anyone having any success observing Deimos and Phobos this season?

 

For one reason or another I just got my first look through the 32” last night at Mars for this year. Started of with the 10 Ethos for 310x. It was fine, but not my usual way to observe and enjoy the planets. So I slipped in the Denk bino and 18 Tak Abbes for 344x. Now, that was much better.

 

Spent quite some time enjoying Mars and soaking up all the detail. I knew where Deimos was, and it was ideally placed near maximum elongation from Mars. But I couldn’t see it. So I slowly inched Mars toward the edge of the field, and then just outside the field of view, and like switching on a light Deimos popped into view. It was a very bright and easy observation, and now when I moved Mars back into the field I could just see it through the glare.

 

Deimos is the easier moon to see, so start with that one and you need to either use an occulting bar eyepiece to block out the glare from Mars or sit it just outside the field of view like I did. Use simple glass eyepieces too if you have those available.

 

Phobos was ideally placed as it was diametrically opposite to Deimos, so I could use that as a guide to line up on. Initially I couldn’t see Phobos as it was still 90 minutes away from maximum elongation, so I spent the time looking at Mars, and every now and then I would move it out of the field of view and check again for Phobos. Typical of all these moons that are close to their planet and move fast, the session goes something like this. Nothing yet, nothing yet, nothing yet, oh there it is. And so it was with Phobos. Once it separated far enough from Mars to punch through the glare it was a relatively easy observation to see constantly. 
 

So with one month to opposition the prime moon observing window is now. The smallest scope I’ve used to see them is a 12”, and I recall they were quite easy to see at opposition, even Phobos which is the tougher of the two. So the chance to see them in smaller scopes is very short, perhaps a week or two either side of opposition. I’m always thrilled to see the Martian moons, so don’t waste the opportunity.

[sunnyday]

thank you for your sighting report, I liked it.
can you tell me at what telescope diameter we can see the moons of mars ? 

[slavicek]

Thanks for the report. That gives me hope. I will try Mar's moons next week, using occulting bar eyepiece made for this occasion.

[Allan Wade]

can you tell me at what telescope diameter we can see the moons of mars ? 

Like all challenging observations, the best advice is to use the largest telescope you can the first time you attempt seeing it. My own example is seeing the Horsehead Nebula in my TV76. There’s no way I could have ever achieved that without all the experience I gained seeing it in larger telescopes.

 

With the Martian moons I first saw them in my 12” dob leading up to opposition many years ago. By the time opposition arrived I had seen them many times and found them not particularly challenging to see. But to put an absolute value on what aperture is required to see them is very hard because there are so many variables. I would say experience in actually seeing them at least once in a larger scopes is the number one priority required to find them again in smaller scopes.

 

As a guide though, for a first attempt a 12” at opposition should easily pick up Deimos. I’m sure someone can jump in with reports of seeing them in smaller scopes. I’ve never tried, so I’ll give the TOA130 a try next month and let you know.

[Allan Wade]

Thanks for the report. That gives me hope. I will try Mar's moons next week, using occulting bar eyepiece made for this occasion.

You’ve got the perfect tool to make light work of the moons with that 22”.

[Allan Wade]

I saw Deimos and Phobos in the 16” last night. Again using the Denk bino at 234x and 305x. They were easier to see at 305x and only when I held Mars just outside the field of view. They were both in a diffraction spike at the time, but given these are generally observations for medium and bigger size dobs, everyone is going to be battling with the diffraction spikes. Especially trying to see Phobos which never gets more than about one Mars diameter away from the planet, so it is always in and around the spikes.

 

Fortunately we are right in the window now where the moons are bright enough to punch through the glare of the spikes, yet it’s still not an easy thing to see. I see it as a ‘lumpiness’ in the usually uniform brightness of the spike. It doesn’t look like a bright point source of light as it would when out in clear space, but rather a ‘dome’ of increased brightness in the spot where the moon is.

 

It’s subtle, but like all these observations, once you’ve seen it once and worked out what you are looking for it becomes very easy to repeat the observation. Obviously the easiest way to see them is when they are clear of the spikes, which is at least more of an option with Deimos, but for Phobos learning to see it through a spike gives the best chance of success.

[Special Ed]

Thanks for the reports, Allan, and congratulations on seeing the moons once again.  

 

I plan to try for them but right now am dealing with very poor transparency due to wildfire smoke coming from the fires out west.  I made an occulting type eyepiece using a piece of magenta filter gel that covers one half of the FOV.  I'm hoping this is the year I finally spot Phobos and Deimos.

[Allan Wade]

I hope you see them as well Michael, and give us report. I hope we have lots of people report seeing Phobos and Deimos.

[Redbetter]

Haven't seen them so far this opposition.  I have tried from the backyard with the 20" but the seeing in the backyard is poor during hot weather...and now we have smoke that is regularly rendering Saturn invisible naked eye.  On some nights it works like #23 filter so not too bad on Mars proper.  

 

I was able to see both moons in 2018 whenever the seeing was good at my dark site and they had good elongation, despite being below 30 degrees elevation.  I would like to try it with the 10" because that mirror is sharp, but I can't see bringing the 10" and 20" up the mountain when my son isn't with me.  

[Orion92]

Allan,

 

Is there a website or app you would recommend to see the positions of Phobos and Deimos? I’d like to give them a try in the coming weeks with my 12” if the clouds ever give me a break down here in FL. It’s always a thrill to see the moons of the planets I think, too.

 

Clear skies,

 

Kyle

[Redbetter]

Stellarium works pretty well for this.  You can zoom in and out some to find marker stars for relative orientation.

[Allan Wade]

Allan,

 

Is there a website or app you would recommend to see the positions of Phobos and Deimos? I’d like to give them a try in the coming weeks with my 12” if the clouds ever give me a break down here in FL. It’s always a thrill to see the moons of the planets I think, too.

 

Clear skies,

 

Kyle

I’ve always used Sky Safari on the iPad and found it very accurate and reliable. The only exception being Saturn’s moon Phoebe and then seven of Jupiter’s outer moons which were quite erroneous in Sky Safari, so I had to use the Minor Planet Centre ephemeris. I’ve found Sky Safari good because I use it as a planning tool to determine my observing windows and then I can use it again at the eyepiece. Once I’m orientated I put the iPad away to get my deep night vision back. Though that’s not a factor with Mars blasting your eyeballs. 

[Redbetter]

I got Deimos tonight.  I expected it to be hopeless, but the seeing was supporting 357x for planetary--wasn't stable, but it was usable seeing, slow enough to reveal some small planetary detail that has been missing in the backyard.   I had about 3 to 4 magnitude of smoke dimming, I could only vaguely detect a few bright stars naked eye.  However, I noticed that once I adapted at the eyepiece I could steadily hold an 11 mag star just north of the planet, and I knew that Deimos would be somewhere around 80 - 90 degrees offset at about the same distance trailing, and a magnitude dimmer.  The chase was on...

 

I had hints of it at 357x but couldn't get a lock or hold it sufficiently to be certain.  So I tried the 3-6 zoom, going progressively higher and moving the planet out of the field.  This started at 417x, then 500, 625, and finally 833x.  I had indications but was again having trouble pinning it down.  I was trying to remember if I still had my home made occulting bar on my 7.4 Plossl and went back inside to check.  Sure enough, it was still in place and it turned out that it was just the right width to turn to block one axis of broad diffraction spike and the planet at 338x.  Eventually my eye adapted a bit more and I became more certain about Deimos at moments.  I could hold it at times, and always in the same position.  That's what I was after.

 

I am surprised I could even reach ~12th magnitude in these conditions in town, let alone so close to Mars.  But seeing is king...and for once the king graced me with his presence.

[Allan Wade]

Great stuff, but old hat for you though. You did well to see Deimos given the conditions. I’ve had superb skies at my dark site lately, so not much of a challenge.

[Redbetter]

It mostly cleared last night so I was able to tag Deimos again.  Tonight was even clearer, but my DSO sites are closed due to fire and smoke, so it was backyard observing again with the 20".  Phobos was going to reach greatest elongation around 2:20 AM with Deimos well beyond and a 10.6 mag star almost in line several times more distant. 

 

The sky was surprisingly steady for the backyard, little air movement at ground level, and twinkle-free overhead (some twinkling lower.)  It wasn't quite as steady as it looked, good for 278 to 357x for Mars, showing Olympus Mons and the bright southern Tharsis volcanoes' orographic clouds.  I didn't have trouble finding Deimos, and searched for Phobos at 338x with my occulting bar eyepiece, but the seeing wasn't steady enough to easily boost magnification.  Occasionally cooler air would drift in and blow up the seeing for a time.

 

I decided to try to catch some good moments with the 3-6 zoom, putting Mars out of the field.  The TV 3-6 zoom is special for this purpose, because while the outer portions of the 6mm setting show some aberrations at the edge, the shorter focal length fields are increasingly sharp at their edges.    So at anything other than the 6mm setting, the field stop blocks the planet with a sharp edge of field and no lateral glow.

 

Having failed with the occulting bar at 338x with only a few unconfirmed glints, I used the 3-6mm TV zoom at the 5mm setting (for 500x), to move Mars just out of the field and hold it there just eclipsed by the field stop (all manually tracking...with grass binding azimuth movement somewhat.)  I finally searched the diffraction ray in the lower right quadrant and found Phobos just inside the upper portion of this ray, difficult but consistent and generally held in view once spotted.  I could hold it and Deimos at the same time.  Phobos was very close to the planet, less than 1 diameter away from the edge of the disk. 

[Allan Wade]

Mate that is awesome. The old school way too. I just cheat by pressing a button to get Mars outside the field stop and it stays there while I look for the moons. No where as hard as what you're doing.

[t.r.]

Allen...Do you think a C11 could accomplish this in country skies?

[Special Ed]

I made an attempt last night/early this morning but no joy.  By the time I got out, Phobos was probably too close to Mars but I should have been able to see Deimos--not sure what happened.  Mars is *really* bright.  I may not have been looking far enough away from Mars to see Deimos.  Good practice, even if it was a fail.

[Allan Wade]

Allen...Do you think a C11 could accomplish this in country skies?

Yes I’m very sure you could do it. But as Michael described, it's not that easy, and you will most likely not see them when you first try, but you learn so much from the failed attempts. I’ll relate how confidently I spent my first night trying to see Amalthea. I had no idea it would be 3 years later before I would actually see it. I would have spent perhaps 30 sessions and somewhere close to 100 hours at the eyepiece to finally see Amalthea for 15 minutes. I believe it took the knowledge from all those failed attempts for me to bring everything together to achieve that observation.

 

I would probably ignore Phobos completely until you have success with Deimos. Then use that experience to track down Phobos. Also, even in the 11” the chance of seeing Phobos is a very small window either side of opposition.

 

So definitely get cracking now on Deimos. Remember to either use an occulting eyepiece, or put Mars just, only just, outside the field stop. Plan ahead so you know when Deimos is at max elongation. Now I think of it, your absence of diffraction spikes is going to be a significant advantage for you. I think you’ll be fine.

[Redbetter]

As Allan says, start with Deimos, it is easier to catch well away from the strongest glare.  The problem with Phobos is proximity.  My suggestions, repeating some things Allan has already related:  

• Use planetarium software to estimate when elongation will be best for your location.  This will help you determine favorable observing windows.
• Use software to identify field stars and their relative positions to that you know what areas to concentrate on.  The moons are hard to see next to such an intensely bright planet if you don't have some sort of external reference point.  (Account for any left-right image flip with your scope type, diagonal rotation, and orientation with respect to the horizon.)  I am doing this without tracking, so I keep in mind preceding/following and whether or not the moon should be up/down relative to the planet.
• As Allan says, practice, even on some nights that don't look favorable.  This can help you work out kinks, or identify needs that you didn't realize you had.  Experiment to find which eyepieces have the sharpest resolution near the field stop for example.  I tried and failed many times over several oppositions with an 8" SCT, before I finally bagged Deimos then Phobos with a 20" during a favorable opposition.
• Use (probably have to fashion) an occulting bar or strip to reduce veiling glare.  Something very flat and thin with a clean edge can be taped to the field stop of some eyepieces.  Rough or thick occulting strips will create some out of focus diffraction effects.  You might also find your initial choice of material is too thin to fully cover Mars at very high magnification.
• Alternatively, use an eyepiece that has a very clean/sharp/undistorted field edge near the stop, and that does not show light leakage from the planet if placed ever-so-slightly out of the field.  Wide-field designs have too much lateral stretching and such--these don't matter within the central 2/3 or more of the field, but near the very edge they hurt the contrast too much.  I realized that my 3-6 TV planetary zoom was ideal for this when someone complained about the field edge at the lowest 6mm setting.  I confirmed some lateral color there, which I had overlooked because I almost always use it somewhere in the 3 to 5mm range.
• Getting to some rural sky should help because it will provide better contrast, even with Mars' veiling glare in the vicinity.  Of course for the next two weeks the Moon is not helping...
• Seeing is the biggest variable and is difficult to predict.  The smaller the aperture, the better the seeing will need to be.  So try often during periods that the elongation is favorable.
• Be ready to try different magnifications (eyepieces and/or Barlows) to find the sweet spot for the seeing on a given night.  Over magnifying for the seeing results in the faintest stellar objects being out of focus much of the time, and the faintest ones disappear.  Under magnifying often results in inadequate separation from the planet's glare, so if the seeing supports more, use it.

I don't know if I ever caught Phobos or Deimos with the 8" SCT even in excellent seeing when set up next to the 20" that was showing them without any occulting devices.  If I did, I neglected to write it down.  

 

I have tried a few times with my son's Z10 in town, but haven't had the seeing I expect it will take.  If I can get the smoke to clear from my dark sky sites, I will take it to one of them since they are many times darker and they have better seeing on average.  I am certain the scope is capable of it, but it hasn't had a good opportunity so far.

[Ittaku]

Stellarium works pretty well for this.  You can zoom in and out some to find marker stars for relative orientation.

I've found this quite unreliable for Saturn's moons and the much simpler "Sun, moon, and planets" app actually correct when stellarium isn't. No idea why, but neither Stellarium nor skyportal/skysafari seem to have Saturn's moons in the right places, so I end up using a combination of apps.

[Redbetter]

I've found this quite unreliable for Saturn's moons and the much simpler "Sun, moon, and planets" app actually correct when stellarium isn't. No idea why, but neither Stellarium nor skyportal/skysafari seem to have Saturn's moons in the right places, so I end up using a combination of apps.

Which doesn't apply to Mars...where I can confirm it is sufficiently accurate based on recent visual sightings.  

 

Which moons of Saturn?  I have found Stellarium reliable enough for Saturn's moons Mimas through Hyperion based on observations--typically seeing the moons first, then confirming later.  Where it and others have trouble is Phoebe, as well as with Jupiter's similar outer moons.  These are distant enough that their orbits are somewhat irregular and different, but I don't know how they are modeled specifically.  For these far outer moons, I use the Minor Planet Center's ephemeris service and plot as needed.    

 

The main limitation with the faint irregular outer satellites is being able to plot field stars down to the 16+ magnitude.  Stellarium does some of that, although from what I have seen the catalogs are pretty poor at this level and beyond.  That is why I have hand plotted vs. the DSS images at times.  I am looking forward to the gas giants moving out of these busier star fields down in the mucky seeing low in the sky (which happens to be the light polluted portion of my dark sights as well.  I haven't bothered with these irregular outer ones for several years because of their location.  

[Ittaku]

Which moons of Saturn?  I have found Stellarium reliable enough for Saturn's moons Mimas through Hyperion based on observations--typically seeing the moons first, then confirming later.  Where it and others have trouble is Phoebe, as well as with Jupiter's similar outer moons. 

Can't remember exactly but I usually try to pinpoint which moons I'm imaging and usually the inner ones are off by a variable amount, enough to make me wonder what I'm looking at.

I think in this one Tethys and Mimas were off from memory for example:

https://www.cloudyni...44-drizzle30wg/

[Redbetter]

Caught Phobos again (not Deimos), easily tonight with the 20".  I have been seeing Deimos regularly, but Phobos has been elusive.  I had set the scope up early expecting some steady sky when Mars was high enough.  It is the same pattern I have had for several nights:  stagnant jet stream, smoke suppressing temps some in the day, and keeping the air from cooling off much until after midnight.  Initially I could only see Capella, the Moon, and Mars naked eye due to the smoke and full Moon in town. 

 

I put in an eyepiece for 357x and focused, Mars was looking sharp without any filter.  And there next to Mars was Phobos less than a diameter away and trailing roughly on a line with Mars' equator.  I didn't use an occulting bar or even really look for it, it was just there, plain as day.  Seeing makes ALL the difference with this one.

 

I thought,"Shoot...I should have set out the 10 inch!"  I ran into the house and hauled the Z10 out, hooked up its fan and did a collimation check, only to find I had loosened something on the focuser and spent too much time fiddling with it, before confirming the primary was still spot on and the secondary hadn't move either.  Then I had some trouble with altitude tension allowing drift because I didn't have it balanced without finder and with light eyepieces, not good for 350x.  By the time the scope had cooled somewhat and I had everything dialed in, Phobos had moved and the seeing was slipping away.  No joy in the 10".  I could still catch it some in the 20", but not like before.

[Redbetter]

Woohoo!  Success, but not with the 10" as I planned.  Nope...I was able to catch both Phobos and Deimos a few minutes ago with 8" of clear aperture, using an off-axis mask on the 20".  (Okay, it was actually about 8-1/16" of clear aperture which is what was left after cutting/clean up/sanding to make it uniform.)

 

Conditions:  shirt sleeve weather, 90% illuminated Moon, decent seeing, suburbs, some light smoke...  Unfortunately, the clearer sky also resulted in less stable conditions than I have been experiencing, so while the seeing was decent, it was not nearly as steady as it has been on previous smokey nights.  Still, I could see stars down to ~4th magnitude tonight and in previous nights it has mostly been only Mars, Jupiter (sometimes) and the Moon naked eye.

 

The reduced stability was immediately apparent at the eyepiece, even in the 110ED refractor at 193x.  Full aperture in the 20" was requiring the #25 filter to get reasonable focus and maximize surface detail at 357x--and that was mostly too much.  It did somewhat better at 278x, but even filtered this was pushing it.  

 

Knowing roughly where to look early tonight (Phobos preceding, Deimos following the planet) I turned the 20" on the red planet at 357x without a filter.  I was not seeing either this way.  I then tried with my 7.4 Plossl with occulting bar for 338x.  This allowed me to identify Deimos and hold it, but Phobos was elusive with so much glare close to the planet, along with the thick diffuse diffraction artifacts of the vanes. 

 

I decided the best way to tighten the focus and minimize glare was by employing my 8" off-axis mask.  This did much as I hoped, although the seeing fluctuation was still readily apparent, albeit in a reduced state.  I then moved Mars behind the thin occulting bar.  I didn't have much luck with Deimos early on, just too dim for conditions with 8", so I tried for Phobos very close to the planet.  After a time I realized I was catching a faint glint at moments in the same spot.   At first I thought it might be an internal reflection but by moving Mars up and down along the bar I was able to rule that out.  Eventually, it reached a point that I could hold Phobos at moments when the seeing was better.  The separation and position fit.  

 

I went back after Deimos and eventually was able to find it and hold it in averted vision.  I then re-targeted Phobos and again found it, somewhat more quickly this time.   In the interim between earlier observation of Phobos, its movement relative to the planet's orientation was apparent.  

 

Note:  I also tried the 10" some during this, unsuccessfully. I was finding it easier to work the 20."

Edited by Redbetter, 05 October 2020 - 01:28 PM.