Mixed fortunes

[Jimtheslim]

Took the 10" dob out last night and has some brilliant quality viewing of Jupiter. I can really understand now how much difference 'good seeing' can make. This time I could not only see the two main equatorial belts, but I could make out the lighter coloured line within the southern equatorial belt as well as dark, possibly stormy areas in the northern belt. The polar regions were also clearly defined and at times I could make out small belts above these, possibly the temperate belts. I was absolutely blown away, so much so that I decided to stay up until Mars became visible, low on the horizon at just after 1am.

Now not only was this rather comical, having to kneel on the patio to get my eye down to the eyepiece, but the view of Mars was terrible. It looked elongated with CA on one side and no detail at all other than it's red colour. such was my disappointment that I called it a day and succumbed to a few hours sleep without waiting for Saturn. And yes I was definitely in as good a focus as possible!

Could this have simply been down to the fact Mars is so low in on the horizon and hence more atmosphere to look through? If so will Saturn always be out of focus? I really hope not. As I say, seeing was superb for Jupiter, much clearer and crisp with far more detail than I have seen any other night

[Stu]

Excellent stuff Jim, Jupiter does look fabulous when the seeing is good. I'm afraid the other planets are not very well positioned at the moment, and will actually get worse before they get better!

The poor views you were getting were down to the thick atmosphere you were looking through to see Mars at such low altitude. The CA is caused by the atmospheric turbulence and refraction.

Saturn is always a little easier than Mars as its features are higher contrast, so it's well worth trying to see. Wait until it's at its highest for the night though for best views.

[John]

Low altitude (height above the horizon) adversely effects the views of practically all astronomical objects and the planets particuarly because you tend to use higher magnifications to view them (which also magnifies the atmospheric effects too !).

When planets are viewed relatively low down, apart from a lack of contrast and sharpness, they will appear unsteady and an effect called atmospheric diffraction causes false colours at the limbs of the planet.

Saturn and Mars, despite the latters favourable opposition this year, are rather lower than is ideal. Planetary observers are going to need to be patient !

At least Jupiter has been rewarding over the past few months.

 

 

[estwing]

try to put your scope on a table if viewing low....makes for easier observing!

[Jimtheslim]

Thanks. Unfortunately I don't have a table big enough for my new scope. Although I am currently debating whether to invest in a water butt stand or an adjustable stool.

As for it being low down I understand the atmosphere can play havoc, it's just that I have had some very rewarding views of Saturn with my 90mm refractor and with Mars being at a similar altitude I just wondered if a larger reflector would always suffer badly with the amount of turbulence it is looking through. I guess time will tell. I actually like looking at planets at twilight so rather looking forward to seeing it later in the summer when it continues to rise earlier

[John]

I think that refractors do tend to "cut through" poor seeing conditions better than larger aperture scopes. When the conditions are better (and / or the target is higher in the sky) the larger aperture gains and then takes the lead in the amount of detail that can be seen. I have 4" and 4.7" refractors and a 12" dobsonian. Under good conditions the 12" (unsurprisingly) shows more detailed views of the Moon and planets but the smaller aperture refractors often do better than their much smaller aperture might suggest.

Personally I tend to wait until objects are someway above the horizon whereever possible although occasionally thats just not going to happen so then I make the best of it to at least get a peek at something

On deep sky objects the larger aperture scope runs away with it practically all the time of course.

 

[mikeDnight]

Try to observe Mars when its close to the south meridian as it will then be at its highest point and less affected by atmospheric  turbulence  and dispersion. 

Mike 

[alan potts]

Good advice Mike but I saw it this morning from here and it was not much above Antares and I have about 11 degrees on anyone in the UK. Sadly it is just not going to be very well placed, even for me. I have split Antares a couple of times but I find it more difficult than Sirius which gets higher for all of us.

[Size9Hex]

Nice one Jim, sounds like you had a good view of Jupiter. I've got a 10" Dob too, and have had the same experience as you. Jupiter has been excellent, but Mars/Saturn less so. I can't offer as much experience as the folks above, but I have found Saturn and Mars are still a bit lacking in detail even when they're highest in the sky directly south. My next tactic is based on advice I read in another post, and will head off to a site that has grassy fields stretching for a few miles to the south, rather than tarmaced streets, heated buildings and city pollution (I live north of a large town). My understanding is that the atmosphere is more likely to be more stable under these conditions (and I can see the difference myself when targets reach a certain point over my neighbours roof). This may or may not be a factor for you, but thought I'd mention it in case it helps.

[Jimtheslim]

I have mostly fields to the south of me. Last Summer I had some great twilight views with my refractor, on one night it was tolerating 280x fairly well and at 140x it was absolutely crystal clear. I was just hoping to get somewhere near this with my dob. 

[Linda]

Now with the full moon, take a look at the shape of the moon when it get just above the horizon. It is ovally shaped. The atmosphere is making planets look rubbish.

I am looking forward to seeing Saturn once high(er) above the horizon. So far it hasn't been pretty, just recognizable.

[mikeDnight]

9 hours ago, alan potts said:

Good advice Mike but I saw it this morning from here and it was not much above Antares and I have about 11 degrees on anyone in the UK. Sadly it is just not going to be very well placed, even for me. I have split Antares a couple of times but I find it more difficult than Sirius which gets higher for all of us.

Hi Alan,

The low angle of Mars is certainly a problem as you say and at the moment at a little over 13 seconds of arc it's certainly a challenge. Jim's ten inch dob  may have better success if he stopped it down somewhat, which may have the effect of dulling the bright disc and increasing contrast and definition. Anything's worth a go I suppose!

Mike