Saturn & Jupiter Observation Notes - 18th July 2017

[MarsG76]

Observation 18 July 2017

Date: 18th July 2017 @ 18:50 – 22:20AEST

Location: Backyard

Equipment: 14” Skywatcher GOTO Dobsonian, Televue 11mm Nagler T6, Celestron 5mm, LV 7mm, Televue 2X Powermate, Televue 2.5X Powermate, Televue 3X Barlow, Baader Neodymium, Baader Contrast Booster.

 

Jupiter: At 19:08 there was a dark mark on the Northern equatorial belt, initially I thought that it was a darker area within the cloud belt but later using the “Gas Giants” app I found out that it was the shadow of Io. On the right side of the planet Io was rising, slowly moving away from Jupiter while observing for the next 30 minutes or so, not often does one experience a moon rise on a different planet. Europa was on the opposite side moving closer to the planet.

Ganymede and Callisto are further away from Jupiter on the right, same side where Io was rising and opposite side of Europa.

There was a substantial amount of detail visible within Jupiter’s atmosphere. There was cloud band shading and visible different coloring, lines and irregularities in the atmosphere. The most details visible was in and above the NEB, different colouring, from brown to yellow to even a blueish tint just above the NEB. The northern cap was slightly shaded but the southern cap was distinctly darker than the norther cap and easy to see with tiny spots on it, very subtle but definitely made the cap look slightly textured. Southern cloud belt was visibly irregular across the planet.

The GRS was not facing toward us until later at 21:27 but at this time Jupiter was low in the west, 20-30 degrees, not far from mountains so it was not as crisp as at 19:00 but still quite a bit of details are visible and a lot better than last observing session. The best magnification to use tonight is 300X initially than 150X to 235X when lower in the horizon to look at the GRS.

 

Saturn: At 22:02 Saturn was as high as it’ll be tonight and it looked crisp and detailed. The Cloud band on the globe was clearly visible, the Cassini division was visible nearly all the way around in the rings, the innermost ring to Saturn looked a bit darker then the others and there was a tiny visible shadow on the rings behind Saturn with 5 moons, Titan Enceledus, Tethys, Dione and Rhea orbiting it.

Magnified 300X and 330X the views were sharp and clean, whereas at 375X and 470X was a near crisp view as Saturn was overhead near zenith. 660X was softer with hints of Cassini division within the rings but its impressive with how big it is in the FOV.

To get Saturn to look so sharp, I was fine adjusting the collimation using the primary mirror while defocussing Saturn and adjusting until Saturn defocussed symmetrically in both focus travel directions.

 

Neptune: Neptune was the last object for tonight observation but it was just a blueish fuzzy dot, it was low in the eastern horizon, and I guess the lightning activity out to sea coupled with the picking up wind didn’t help. I Magnified it 300X, might have been bit much for it in the current position, but no matter what, I doubt that less power would show any more detail.

 

Mirrors might not be as perfectly collimated as I thought since when defocussing on Jupiter’s moons to fine tune collimation, were defocussing into a ring with the central obstruction in the middle but not defocussing “round” but more to what appeared to be oval, defocussed symmetrically but oval.

I think that the 14" SW still hasn't shown me the best it can do and I will need to play and practice with the collimation some more. Newtonian collimation is definitely a fair bit more involved than SCT collimation.

Thanks for reading,

Clear skies.

 

[Charic]

On 22/07/2017 at 08:24, MarsG76 said:

I found out that it was the shadow of Io

My most memorable image of Jupiter was the same, observing the shadow of Io, but I don't recall seeing Io itself! need a bigger scope for that?

On 22/07/2017 at 08:24, MarsG76 said:

I think that the 14" SW still hasn't shown me the best it can do and I will need to play and practice with the collimation some more. Newtonian collimation is definitely a fair bit more involved than SCT collimation.

Keep playing and tweaking, it will come right eventually, and the more you get acquainted with the procedure, like they say, the easier it gets, practice makes perfect.
I can only imagine what the views will be like compared to my 8" baby scope!

[Stu]

On 22/07/2017 at 08:24, MarsG76 said:

but not defocussing “round” but more to what appeared to be oval, defocussed symmetrically but oval.

Isn't that a sign of astigmatism in the mirror? Does the oval change orientation by 90 degrees moving from inside to outside focus?

 

[John]

1 hour ago, Stu said:

Isn't that a sign of astigmatism in the mirror? Does the oval change orientation by 90 degrees moving from inside to outside focus?

 

I agree - this is worth looking into. Defocussed stars and their diffraction rings should appear round on both sides of focus. If they are oval and if astigmatism is the cause (pinched optics ?) the long dimension of the oval should reverse either side of focus.

There could be other causes of these oval star tests though I guess ?

But they might well be an indicator of an issue that is holding planetary performance back.

[jetstream]

On 2017-07-22 at 02:24, MarsG76 said:

I think that the 14" SW still hasn't shown me the best it can do

Are the primary mirror clips restraining the mirror? The primary should be able to "slide" around minutely when held by the clips IMHO.

[MarsG76]

On 7/24/2017 at 10:20, Charic said:

My most memorable image of Jupiter was the same, observing the shadow of Io, but I don't recall seeing Io itself! need a bigger scope for that?

Keep playing and tweaking, it will come right eventually, and the more you get acquainted with the procedure, like they say, the easier it gets, practice makes perfect.
I can only imagine what the views will be like compared to my 8" baby scope!

I think that your 200P will show shadows of moons on Jupiter is the sky is clear enough, I remember about a year and a bit ago I saw a shadow on Jupiter in my 8" SCT and remember thinking that perhaps it's another comet strike, until I checked out the Gas Giants app... No comet.. Io shadow.

Still the 8" SCT did show it.

 

[MarsG76]

On 7/24/2017 at 16:38, Stu said:

Isn't that a sign of astigmatism in the mirror? Does the oval change orientation by 90 degrees moving from inside to outside focus?

 

Good point.. next time I check that out. Thanks

 

[MarsG76]

On 7/24/2017 at 18:35, John said:

I agree - this is worth looking into. Defocussed stars and their diffraction rings should appear round on both sides of focus. If they are oval and if astigmatism is the cause (pinched optics ?) the long dimension of the oval should reverse either side of focus.

There could be other causes of these oval star tests though I guess ?

But they might well be an indicator of an issue that is holding planetary performance back.

 

18 hours ago, jetstream said:

Are the primary mirror clips restraining the mirror? The primary should be able to "slide" around minutely when held by the clips IMHO.

Perhaps your're right.. although the mirror has no clips and any real pinch point or deformable point on the collimation screws. The mirror is basically on a frame that's spring loaded and the collimation screw push on a 10mm thick and solid piece of metal holding the mirror, I doubt that it deforms because of that....

eventually it'll be sorted out... hanging to see Saturn, Jupiter and hopefully Mars next year at 600X magnification and crystal clear view.