Phobos & Deimos

[Tropo-Bob]

I have never seen Mars's moons and since this year is the best for another 15 years, I feel that its time for me to have a serious look for them!

Phobos, the inner moon is about a magnitude brighter than the more distant Deimos.

For those who have applied themselves successfully to the task of finding these Moons, I have some questions, namely:

What size and type of telescope did U use?
What magnification was used?
Did U use an occulting bar or disc?
Did U manage to see both moons? (over time)
How difficult were they to see?
Were they only viewed at their greatest distance from Mars?
Do U think they can be viewed with an 8" SCT?


Any hints or other advice that U can provide will be appreciated.

[bigjoe]

This is going to be some challenge all right Bob..as even with less bright Primaries, as in doubles with faint secondaries , or with big Magnitude deltas , if the conditions are just not right , the glare of the Primary nearly always wins out.
I think Phobos will be brighter than Mag 11.8 ?..will need to check .Separation from Mars at a given time...an occulting bar, or keeping Mars out of the FOV etc ... could be the difference; and a large enough aperture will be needed away from the Cities.
bigjoe.

[Tinderboxsky]

Definitely a big challenge. Sky Safari is suggesting magnitudes 11.3 (max separation 25”) and 12.4 (maximum separation 64”) in July.
I had a “half hearted attempt" last opposition and was unsuccessful. I was attempting to see Phobos when at maximum distance from Mars by placing Mars just outside the field of view. I have tried this technique with a few other faint objects I have chased over the last year or so. From my experience I am not convinced this method provides the best observing opportunity even if one is using eyepieces with good near to edge resolution.
I am planning to make an occulting bar for this opposition. I will place the edge of the bar just away from the centre line of the eyepiece FOV so that Phobos can be positioned near the centre of the FOV.
The other challenge I found is the rapid rotation times of the two moons (Phobos is just under 8 hours and Diemos is 30 hours) which means there is only a narrow window of opportunity to find the moon when near maximum distance from Mars. Everything needs to line up - scope at equilibrium, excellent seeing and transparency, Mars as close to culmination as possible, cooperative weather and clouds, time free of other commitments etc ... Definitely needs some careful planning and putting time aside in one’s diary for the best target times.
I am not sure about the aperture needed. I am going to try for Phobos with my 140mm refractor first and then move onto some bigger yard cannons if unsuccessful. I plan on trying the Astronomical Society of Tasmania’s C9.25 first and then the Society’s C14. We’ll see what happens.
I am looking forward to the challenge..

[bigjoe]

Look forward to your reports with the big scopes Steve..Ill probably try in a larger refractor of at least 120mm , and a larger reflector of 10 inches as well
The timings of the moons separations will be crucial..as far away from Mars as possible is best..not to mention their faint Magnitudes...And Mars high in the sky.
PS: Agreed..The occulting bar WILL be a must here.
bigjoe

[tonybarry]

Howdy Bob,

Bill Hanna (formerly of Alice Springs) observed an occultation of Deimos on the 24th June 2014. He used a Meade LX90-8" with a f/3.3 focal reducer and a Point Grey Grasshopper Express 28S4M running at 30 fps. The target star was mag.8.9 and Deimos was just 20 arc-sec from its primary (Mars).

The image of the target and Deimos's light curve is attached.

Note this is not an imaging of Deimos, but the special case where Deimos obscures a bright star (well, in the occ world, mag.8.9 is insanely bright - most stars are around mag.13).

Regards,
Tony Barry
WSAAG

[Dennis]

I just managed to record a scraping of photons for Phobos back in 2016.:)

http://www.iceinspace.com.au/forum/showthread.php?t=145831

Cheers

Dennis

[Tropo-Bob]

Thanks Dennis, this is a sober reminder about how challenging the task or seeing these moons may be!

[Allan]

I used my old 12” with a good Zambuto mirror last opposition to see Deimos. It was invisible in my widefields like my Delos, they show too much scatter for that sort of task. My best quality Abbe Orthos were needed to spy the little moon in the glare of Mars. I didn’t use an occulting bar, but experimented with placing Mars outside the field of view. Phobos was a no show.

Plus, you need a night of good seeing. I will have another go for Phobos this time around now I have the big dob, but I’m not holding my breathe.

[bigjoe]

Indeed Allan.
These objects orbit the equatorial plane of Mars and that may help location and thus detection.

At 27km(Phobos) and Deimos 15km diameters max and that faint, its a wonder we can see them in the glare at all.
Was going to try in a Refractor of 120mm 130mm..
But that looks like too much of a challenge, without keeping Mars out of the field at least...

I think I'll use the 10inch reflector first.

PS: Regarding less elements; Ive always found this the case on dim objects..An old Japanese Kellner from a 4" Unitron scope I had , serves this purpose.

bigjoe.