Omega Centauri lies at a distance of 17,090 ly and it is both the brightest and the largest globular cluster in the sky.  In fact, it's the only globular in the sky that can be seen with the naked eye.  It has an estimate mass of 4 million solar masses and its apparent size is about the same size as the moon.  It contains several million stars and it is estimated to be about 12 billion years old.  The center of the cluster is so dense that stars are only separated by 0.1 lys, which is about 100 times larger than our solar system.  One study analyzing observational data from Hubble and Gemini concluded that there is likely a 40,000 solar mass black hole at the center of this cluster.  Other studies have challenged that conclusion and limited the size of any possible black hole to be 12,000 solar masses.

As I've written about previously, my 20" scope has developed a number of problems and this image was the result of some testing that I did to look at some of the fixes I've recently implemented.  @Kevin Morefield  has kindly shared some of the excellent data that he has been collecting with his recently installed CDK17 and it emphasized just how poorly my scope was behaving.  His data also drove me crazy to get this scope tuned up to work as well as his.  So, the first thing that I did was to have the observatory techs help me to more carefully align the secondary mirror.  I have a copy of SkyWave and it was obvious that for some reason, my scope was showing field independent coma, which is the symptom of secondary mis-alignment.  We spent an hour under the sky and we were able to dial the rms coma contribution from a bit over 0.12 waves to below 0.06 waves.  The centering of the secondary is still off but that's something that I may address when I visit in April.  Since the secondary is spherical, the centering of the secondary only affects the quality of the spider diffraction pattern and not the image quality.  This scope was perfectly aligned when I shipped it to Chile but I believe that the techs may have messed with it when they first set it up.  I did only a cursory inspection of the alignment on my last visit so I may have missed the fact that the optical alignment was out of whack.  That's my bad.

Two days after aligning the secondary, the Atik Horizon II guide camera, which had developed a serious problem with excessive dark current finally died completely.  I could connect to it but it just transmitted a frame full of zeros.  This is the second Horizon II that has failed on this scope and both have only lasted about 6 months before failing.  That's not very good.  So, a few nights ago, I had the techs locate the repaired Horizon II and we spent about 2.5 hours mounting it and getting it refocused.  Felipe who helped me had never worked with an ONAG system but he did a great job and at the end of the process we both agreed that we could probably get the next camera replaced in about half the time.  The week before, Gaston had visited me in Tucson and we spent some quality time together looking at SkyWave and the the guiding performance of my scope.  He made a number of small changes to the SKG guiding parameters and after installing the new camera, I'm now seeing superb guiding performance.  When the seeing is really good I've seen rms guiding errors on the order of only 0.15", but more common numbers are around 0.25", which is still quite useable.  When I travel to Chile in April, I will take two ZWO ASI1600 uncooled guide cameras to replace the Horizon II cameras.  I don't know if they will be better; but it's hard to imagine that they could be worse.  Once I have the new cameras installed, I will also try to retune my mount.  Right now it is only tuned for a single position in the sky; but, that's a whole different story.

I'm still having trouble getting my main QHY600M-p to connect correctly.  It's like having a car that will only start every 12th try after a rest of 2 hours to 2 days between each attempt.   When the camera connects normally, it works just fine.  When it corrects incorrectly, there is extremely high noise in the lowest 8 bits.  You can see stars but faint data is completely gone.  The histogram of the data doesn't show a nice peak for the black regions.  Instead, it shows a very broad range of values at the dark end.  Once the camera connects properly, it has continued to work until it loses power so I've been leaving it powered on all the time.  Unfortunately, the observatory power isn't all that reliable and power gets lost every 2-7 days--always during the daytime.  And now I've begun to notice that the camera is beginning to jump into the failure mode even when it is powered.  That's not a good sign and it's an indication that the clock is ticking toward total failure.

Last November, I ordered a new Moravian camera to replace the QHY but they keep delaying the shipping date.  Now, I’m getting worried and I’ve sent them an email to see what’s going on but so far, they haven’t bothered to respond.  I also have another QHY camera that I can take but I’d rather jump to the Moravian.  If they don’t get it to me before I leave, it could be a long time before I head back down there to install it, which I’d really like to do on my own.  On top of that, there are a number of other fixes and improvements that I want to do while I'm down there but I'll chronicle those along with a future image.

Globular clusters aren’t really a prime target for me but with the moon out, I selected this cluster just to test out the quality of subs that I could get after all of this work on the scope.  The seeing monitor was down so I don't have an official number but I did get one sub in the Green that showed a 1.1" FWHM number.  About half of the data had FWHM below 1.8" and I believe that the distribution was driven primarily by seeing fluctuations.  Along the way, I've observed that the scope does seem to perform better with the fans off and that's how I took all of this data.  The fans are really useful for preventing dew and baffle plumbs but I don't think that they are well placed on my version of the CDK20.  There are just three fans on the rear back plane.

It has been a VERY long time since I produced an image from a single night of imaging!  I took LRGB data using 3-minute subs and this image used only the RGB data.  There wasn't much processing involved other than removing a sky gradient (probably from moonlight) and to use StarShrink to slightly shrink the star sizes.  I tried BXT but it was a complete failure.  This type of object appears to be well outside of the training parameters used to train the neural net and it produced gibberish.  My overall processing goal was to present the object as closely as possible to how it might look through an eyepiece--and that's always challenging.  Hopefully it's close.  Just to keep things reasonable, this image has been resampled to half the size of the original.  As usually, feel free to let me know what you think.  It's a quick effort but I kind of like how it turned out.

- John