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Jupiter and Mars - visual factors coming together, for once!


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The weather forecast showed a clear spell this evening between 17:00 and 18:30 and a chance to get in some planetary observation.  My southern aspect sits directly under a streetlight, so normally I never take the dob out there.  I read a thread recently where @vlaiv advocated avoiding dark adaptation with bright planets and using your more densely packed retinal cone receptors to get more detail and, perhaps, some colour vision.

I think this and some other factors helped me got some of my most detailed views of Jupiter tonight. Using BST Starguider EPs, I found x180 was a bit mushy but at x140 maximised contrast:  the GRS was clearly visible and I was able to distinguish S Polar Region, S and N Equatorial Belts as well as the N Temperate Belt. 

Mars was subtle, as always, but Syrtis Major Planum and Meridiani Planum were easily distinguishable but I could not pick out the Polar Ice Cap.

Several other things helped, IMHO:

1.  Good seeing and transparency.

2. Relatively high visual altitude

3. Wind of 10mph - normally this a problem but I think it served to disperse heat shimmer rising from rooftops under the field of view.  Also, by causing an occasional tremor in the FOV, it improved perceptions of detail - a bit like the effect you get when you are struggling to perceive a DSO and the movement from a slight tap on the scope makes it pop into view.

4. A stable position of the target in the field of view.  In this case, an equatorial platform but any equatorial mount drive allows you the time to exploit moments of good seeing and tease out detail without constantly having to reacquire the target. 

5. Aperture - this seems to be controversial for planets but having looked through a number of refractors and SCTs, I am convinced that a large aperture scope enhances detail even in bright objects.

All in all, a very satisfying opportunity snatched before the clouds rolled in.



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Nice report! As far as Mars goes and for what it’s worth - don’t want to tell you how to duck eggs, your certainly more experienced than me - here’s what I’ve found since observing it this year, from the summer until now.

The EQ platform, which I’ve made following your instructions on here, has been great for the reasons you give. Especially later in the night when Mars is high. I find nudging my Don near zenith difficult at times. But once you have it in the centre of the FOV the platform does the work. After a while there’s some drift, but just tapping the end of the OTA is enough at high magnification to centre it again. And of course the higher something is then generally the better the seeing.

Being familiar with a target helps. The more you look the more you see.

On Mars I’ve used a blue filter - #82A. Now I don’t like the view that it gives and I don’t find it helps at all with albedo features. But it does bring out any white - eg clouds and ice over the poles. I’ve used it to try and see clouds/ice and then removed it. Once I’ve seen it using the filter I find it easier to see without - once seen it difficult to un-see.

For my 8” Dob (I think this will vary depending on the telescope) I find a variable polarising filter really helps, especially with small details. For other planets, eg Jupiter and Saturn I don’t think it helps at all, but on Mars, which will always be small and very bright, it does.

Making sure I DON’T get my eyes use to the dark really helps me with colour contrast on Mars. I’ll look at my phone screen for a while and then go back to the eyepiece. Or go back inside for a coffee and then immediately back to the eyepiece. When I’ve done this sometimes the difference on what I can see has been amazing. 

Another pair of eyes. My daughter has better eyesight than me, although that’s not what it’s about. Eg I’ll ask her “what can you see?” Occasionally she has spotted something (can be a tiny detail) I’ve missed/overlooked. After she’s told me what she’s seen I can then sometimes see it too.

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Hi Peter,

hadn’t thought of a filter but might try it when we get another clear night. If I’m honest, Mars wasn’t high enough really but the clouds were rolling in so I chanced my arm. 

I could certainly benefit from another pair of eyes!  Probably too late now for Santa’s list. 

Have a good Xmas. 🎅


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Happy Christmas John!

I also have a 2” to 1.25 adapter/extension tube that has a filter thread on the end. Can’t remember where I got it from but it saves taking the filter off/on when changing eyepieces.

For the variable polarising filter I adjust it until any diffraction spikes from Mars are almost gone. That seems to be roughly the optimum position and cuts out any glare. 

I have a few Starguiders. The 12mm and 5mm are the ones I use on Mars the most. The 12mm seems to have good contrast, better than the 5mm. I’ve used a 2x Barlow on the 12mm to give 200x and very occasional and in good seeing, a 3x Barlow for 300x. It’s certainly worth trying different eyepiece options to see which works best. 

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