Monday, September 17, 2018

#161 - Saturday, September 15, 2018 - The Comet and the Supernova

Sometimes, going out to the observatory on a particular night is a bad idea.  And sometimes I do it anyway, despite my better judgment.  And sometimes it turns out to be a really good idea anyway!  On Saturday, I ran a 10k race early that morning, getting up at 5 AM.  The race started at 7:30 AM, and it was already in the lower 70s.  It stayed overcast during the race, but it was also muggy, so I was roasting hot by the end.  Despite my water-drinking efforts of the prior 24 hours, I still managed to become dehydrated, and I threw up in my friend's front yard, on her stairs, and then finally in her toilet.  Exhausted and sick, I made it home and took two 1-hour naps broken up by drinking water and eating some toast.

"Normal" people might have said, "Y'know, I probably shouldn't be out late tonight.  I should just go to bed."  But being normal is boring, so you bet your derriere I still went out to the observatory!

I was already still set up from Thursday night, so at least I didn't have to haul any gear around.  Just my DSLR, tripod, and bag with warm clothes, bug spray, and extra water and Gatorade.  I still had some hydrating to do.

I got out there around 8 PM, uncovered my Celestron AVX, Borg 76mm apochromatic refractor, and ZWO ASI1600MM Pro from underneath the TeleGizmos 365 cover I'd placed over the whole thing on Thursday night.  Once it got dark enough, I re-polar aligned (the setup is so lightweight, I was fairly certain that putting on and taking off the cover had moved it slightly) and then re-aligned.  However, while my western sky stars were showing up in the mount's initial guess easily, the eastern stars were not.  So I shut it off, re-polar aligned again, and then tried again.  The western stars were good, and the eastern ones were still a little ways off, and I had to use my finderscope to place them in the camera's FOV.  My target for the evening was continuing the Eastern Veil Nebula, NGC 6992.  I acquired the luminance frames on Thursday, so it was time for color frames.  I tried to use AstroTortilla to plate solve, but it was having trouble, so I gave up and tried to center the nebula myself.  I ended up a decent ways off of the luminance frames, unfortunately, although I still had the whole thing in the field.

Guiding was no better Saturday night than it was Thursday, unfortunately.  I tried guiding in just one direction again, and it helped a little, but not much, and then the dec axis took off and never came back.  As the night wore on, it just kept getting worse.  I did eventually re-focus the guide camera and re-calibrate guiding, but to no avail.

Finally, fellow club member John and I decided to pop open the dec casing to take a peak inside.  Sometimes, plastic shavings from the casing can get caught up in the gears.  We didn't see anything unusual though in the gears attached to the motor, but the worm gear was deeper inside the mount and would've required taking off a bunch of stuff to get to, so we ended up just putting it back together.  Further research is required.

In addition to that, I was having issues with my Hotech self-centering field flattener.  The 2-inch barrel at the end is just a little too fat to easily get into a 2-inch eyepiece holder, so I have to jam it into the one that screws into the Borg, and then take the Borg out of its ring clamps in order to screw the field flattener, filter wheel, and camera on as one piece because the filter wheel otherwise hits the dovetail bar and I can't actually screw it on.  Despite how hard it is to get into the eyepiece holder, it was still wiggling around, even though I had it tightened down.  Unfortunately, I didn't realize it was flopping around until much later in the evening.  

I'm starting to get suuuuuper frustrated with my gear.  I've put too much effort into this to be dealing with this crap!

Anyway, despite the problems, and the field flattener not flattening very well because it's too far from the camera with the filter wheel in between (I'm working on finding a male or female T-thread to 2-inch eyepiece holder so I can put it the correct distance from the camera), I managed to get at least a couple of color frames per channel that didn't have absolutely craptacular guiding.  I just reset the guide star about every 10 minutes, and was able to get some usable subframes.  

While processing the Veil Nebula on Sunday afternoon and seeing how bad my luminance frames really were, I decided to try something new to me - using my RGB frames together to create a synthetic luminance frame.  It's actually super easy, and the result was pretty good.

For this image, since I'm still practicing on better data with PixInsight, I used DeepSkyStacker to register and stack the RGB frames, and then I pulled each stacked R, G, and B frame into Photoshop and stretched and denoised them (using Deep Space Noise Reduction in Carboni's Tools).  I then combined them into one image (done by creating a new image, and copying and pasting each color image into the reg, green, and blue channels of the new image, respectively), and created a copy.  Next, I went to Image -> Mode -> Lab Color on the copy, clicked the Channels tab in Layers, and copied and pasted the Lightness channel into its down new document.  This is your synthetic luminance.  Then I copied that image on top of the RGB combined image, and set the blend mode as Luminosity, like I normally would for applying an L image.  Then I just went about processing from there, adjusting color balance and curves and saturation and the like.  (See this tutorial for a full walkthrough of my normal LRGB stacking and processing process with DeepSkyStacker and Photoshop).  It came out pretty well!  Plus I didn't have to worry about cropping out the big offset between my L image and the RGB images.  
Date: 15 September 2018
Object: NGC 6992 Eastern Veil Nebula
Camera: ZWO ASI1600MM Pro
Telescope: Borg 76ED
Accessories: Hotech SCA field flattener, Astronomik LRGB Type 2c 1.25" filters
Mount: Celestron AVX
Guide scope: Orion 50mm mini-guider
Guide camera: QHY5L-II 
Subframes: R: 8x180s (24m)
   G: 5x180s (15m)
   B: 6x180s (24m)
Gain/ISO: 139
Stacking program: 1: DeepSkyStacker
Stacking method (lights): Median kappa-sigma clipping (2,5)
Darks: 20
Biases: 20
Flats: 0
Temperature: -20C (chip), 66F (ambient)

Even though my Borg is an apo, which means it's supposed to not have chromatic aberration, I was getting some blue halos around the brighter stars.  They weren't nearly as pronounced as the ones I get on one of the club's telescopes, a Vixen 140mm neo-achromat refractor, and were easily correctable using Noel Carboni's Reduce Small/Large Blue Halos routines.  I also don't have any flat frames for this setup yet, since I have to pull out the drawtube on the Borg a little bit to reach focus, and it rotates freely, and I haven't really settled on the way I connect all the parts and pieces together to be able to draw reference marks so I can use the same flat frames every time.  So there's a bit of a glow in the middle.  But still, not bad for an hour's worth of data from a light-polluted location!  It's almost as good as the one I took of it on my DSLR from the Green Bank Star Quest last year, and that was doing 7-minute subframes from a very dark location!

The Eastern Veil Nebula is part of the larger Veil Nebula, or Cygnus Loop.  It's the remnant of a supernova that exploded 8,000 years ago, and now the nebula is 50 lightyears across!  It's approximately 1,470 lightyears away in the constellation Cygnus, the Swan, which is high overhead in the summer and early fall.  The original star was 20 times the mass of our sun.

By the time I got through all of the RGB frames, it was nearly 3 AM.  This was a lot later than I'd planned on staying out, but it's a lot easier to stay out late when you have friends there!  Fellow club member Bob was there as well, and my minion Miqaela, who had her Orion ST-80 on her Celestron AVX and was imaging the Heart Nebula and the Silver Dollar (Sculptor) Galaxy with her Nikon D5300.  John reminded us that Comet 21P/Giacobini-Zinner was rising by about that time, and I decided that I had to take this opportunity to catch it!  So I slewed over to its current location at the feet of Gemini, the Twins, just above star Propus.  Getting RGB images on a comet with a monochrome camera is not impossible, but is very difficult, especially with a manual filter wheel, so I decided just to take luminance monochrome images instead.  Because my guiding was so bad, I just took a bunch of 30-second frames, which were plenty to see this magnitude +7 comet.  In fact, I even aimed a pair of handheld binoculars that direction, and was just barely able to see its smudge!

Comets move with regard to the background stars, and move fairly quickly.  Thus, DeepSkyStacker has a few different comet stacking modes: align on the stars but streak the comet (standard stacking mode), align on the comet and streak the stars, or run registration and stacking twice and align both.  I did all three, but the align on the comet and the stars made for some really weird streaking artifacts in the background of the image, so I just went with the streaked stars, steady comet version.  Now, for added fun, DSS can't detect where the comet is located, so you have to do it yourself.  I had 50 frames, so I painstakingly selected the comet in every frame.  Luckily, it saves that information to the text file that contains the registration info for each frame, so you only have to do it once.  Using median kappa-sigma clipping made the stars get all weird and fuzzy and dim, but they looked much better when I used auto-adaptive weighted average as the stacking mode instead.
 Date: 15 September 2018
Object: Comet 21P/Giacobini-Zinner
Camera: ZWO ASI1600MM Pro
Telescope: Borg 76ED
Accessories: Astronomik L Type 2c 1.25" filter
Mount: Celestron AVX
Guide scope: Orion 50mm mini-guider
Guide camera: QHY5L-II
Subframes: 50x30s (25m)
Gain/ISO: 139
Stacking program: DeepSkyStacker
Stacking method (lights): Auto-adaptive weighted average
Darks: 20
Biases: 20
Flats: 0
Temperature: -20C (chip)

The gaps are a result of the many bad frames I had to delete.  I originally took 70.  Stupid mount and its tracking problems.

But anyways, you can see the tail!!  That is star Propus at the bottom.
Comet 21P was discovered by Michael Giacobini in December 1900 at the Nice Observatory in France, and Ernst Zinner observed its return 6.5 years later.  When I imaged it on Saturday night, it was 0.4 AU (astronomical units, or the Earth-Sun distance) from Earth, or 36.9 million miles.  

In addition to the above image, I also wanted to make a video.  To do that, I realized I could use PixInsight to apply the same processing to every image, and convert them all from FITS to JPEG after so I could make the video.  FITS is a special astronomy format that most everyday image editing programs don't support.

First, I needed to calibrate - subtract dark and bias frames to reduce noise.  I used the BathPreProcessing script for this, and saved out each file as a new image.  Next, I registered each frame to the frame the DeepSkyStacker gave the highest score to when I was processing the stacked image above so that the stars would be steady, and you could see the comet move through them without the jitter of the mount's crappy tracking.  Each of those aligned images were saved out.  Next, I imported one of the frames and applied a screen stretch using ScreenTransferFunction, and then applied that to HistogramTransformation to actually stretch the image.  I minimized that process and opened up a MultiScaleLinearTransform process to apply noise reduction (following the settings in the Light Vortex Astronomy tutorial I used recently on an Andromeda Galaxy image of mine), and then minimized that too.  After some Googling, I right-clicked on the background screen and clicked ImageContainer, and then opened all of my light frames in it.  I could only figure out how to apply one step at a time, so first I applied the HistogramTransformation process to stretch, and then re-imported all of the stretched images I saved out, and then applied the MultiScaleLinearTransform noise reduction.  Then I used the BatchFormatConversion script and converted all of the PixInsight-format images to 8-bit JPGs.  Finally, I used Time Lapse Movie Monkey to generate the video.  The slowest it would do was 10 frames per second, but that turned out to be fine.  So the video is only 5 seconds long (I need to make a repeating version next), but it's super cool!  
The video spans 33 minutes of real time.

Aaaaaaggghhhhhhh soooooo cooooooollllll!!!!!!!!

All the while I was imaging the Eastern Veil Nebula and Comet 21P, I had my DSLR on a tripod taking a series of 30s images facing north to make a star trails image.  They're super easy to create - I've got a tutorial in this post.  This is the longest one I think I've done, 5 hours and 20 minutes.  What you're seeing here is the rotation of the Earth on its axis that creates our day-night cycle.  The bright streak near the center of the vortex is Polaris, the North Star.  As you can see, it's not exactly on the North Celestial Pole, the center of that rotation, but it's quite close.  The pole is at the same altitude as your latitude, so if you live on the 40 N parallel, it will be 40 degrees above the horizon.  From the North Pole, it would be straight overhead.  From the equator, on the horizon.  In the southern hemisphere, they can see the South Celestial Pole, and use it for polar alignment instead.
Nikon D5300, 18-55mm lens at 18mm, f/3.5, ISO-800, 580x30s frames

There are several other interesting things going on here as well!  The long red streaks are airplanes.  The brightest one you can see made a few course corrections, hence the wobbliness.  The dome is lit up by red light from people arriving and leaving the observatory with their car lights on, and opening their cars to get stuff.  If you look closely a little ways above the dome, you can see a dimmer, shorter streak - this is a satellite.  In particular, it's an Iridium flare.  The Iridium constellation of communications satellites have orbits that cause them to glint the sun over to the darkened part of the Earth, and that glint lasts about two minutes as they move across the sky.  In this case, there are actually two streaks, since the aging satellites in that constellation are being replaced.  The second streak is the replacement.  I created another image with just the five frames that show the flare.

Satellites usually brighten and then darken as they move across the sky into the Earth's shadow, but Iridiums are far brighter, and for a shorter stretch of sky.  If you've ever looked up and happened to catch a bright light briefly appear in the sky and then fade out, it was probably an Iridium flare!  You can use the free cell phone app Heavens Above to track them.

I finally called it quits and packed up, and got home at 5 AM.  I realized that I had been awake for 24 hours!  (With the exception of the two hour-long naps I took that afternoon).  Whoopsie!  But I got such awesome images, it was totally worth it!

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