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Mars 3rd October 2018 10hrs 10min UT

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About this observation
Observer
Peter Anderson
Time of observation
03/10/2018 - 01:10
Object
Mars
Observing location
Brisbane, Australia
Equipment
150mm F8 achromat refractor 3X Barlow ZWO ASI 120 MC-S camera
Exposure
1/100 second - 300 frames - Gain set midway at 50
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I have been most frustrated. First Mars has had its  (almost to be expected) perihelic opposition dust storm which was virtually planet wide.  After this cleared around early to mid September, and Mars was already drawing rapidly  away,  the ‘seeing conditions’ I  continued to encounter were miserable for very high resolution work.  Even my new ZWO camera that I am engaged in a serious test of wills and  learning curve with, was not able to resolve much detail .  Finally tonight, when the disc has shrunk from  over 24” to 15.5” (very close to the size of the disc of Saturn and no more than 40% of its maximum area at opposition), I decided to stop trying with the C14 and instead go with the 150mm F8  refractor with a 3X barlow.

 

The rationale is that a smaller column of air is used by a smaller aperture (15cm instead of 35.5cm) and so you are more likely to be looking through one ‘cell’ of air at a time.  Okay, I could have tried an intermediate aperture, but I wanted a much smaller aperture to test the theory properly.  It seemed to work. Looking at the movies taken tonight, a percentage of the frames are reasonably sharp, unlike the three useful frames out of 500 that I had obtained with the C14.  Of course the image scale is much smaller – and so also is Mars. (A double blow.)

 

The attached image is taken at 10hrs 10min UT on 3rd October 2018.  Diameter 15.5”  This is the first quick processing but it shows the shrinking polar cap after the recent perihelion. Then above and to the right, the bright oval of the Hellas region, a germination area for some dust storms, is plainly visible.  Above it is the dark wedge shaped Syrtis Major.  The Syrtis Major was one of the first features to be recognised on Mars as far back at the mid 17th century.  You can easily identify these features from looking at a map of Mars and  you will see that it is the south polar cap you are looking at.  The disc is quite a gibbous phase as Mars is drawing away, and the opposing limb is quite bright, a phenomena that is commonly observed. There are other features that can be traced from a map, but be careful in tracing them because it can get to the stage of wishful thinking.

 

Still, I am happy that using a smaller aperture actually worked well. Of course I took  a ‘hit’ in the image size (2 X Barlow on the C14 is 2 X3910 = 7,820mm for F22 against 1200 X 3 = 3600mm or F24 for the 150mm refractor) but I did this so I could retain around the same brightness  and frame rate to minimise movement in individual frames. The results are measurably superior and the problem for the previous poorer past images has been mainly the ‘seeing’.   (I had even tried with the DSLR and didn’t do any better.)

Finally for UK observers, at 27.5 degrees south, Mars was virtually overhead in my sky at the time of the observation. (Do I hear a faint throaty growl?) Having smugly said that, it didn't really improve the 'seeing' though as I have described.

 

Well, we are expecting increasing cloud and then rain locally, and as Mars continues to shrink in size I am delighted to have finally got something tonight, at least. Nothing like what I had originally hoped, and famous lunar and planetary astrophotographer Damian Peach is certainly not under any threat whatsoever from me!

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