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McDonald Observatory 5 – Starlight Serenade

Updated: Jun 3, 2022

2021.06.12 - On my second night of astrophotography in the Davis Mountains, the brilliant dome of stars was yet again marred by thick layers of clouds along the horizon. At first, I wondered if the Milky Way would be lost to the clouds for the entire night, but in the early morning hours it finally broke free of the Earth's glowing veil, and the race to capture the targets on my list began.


The Milky Way Galaxy over Fort Davis State Park
The orange haze of cloud cover that had been on the horizon the night before now extended almost above me

The clouds that had dominated the sky all day still stubbornly clung to the basin South of the mountain range. I was worried that the hours I had spent scouting and waiting on the exposed, wind-raked ridge of the mountain were all for not, but shortly after midnight the Milky Way finally broke through the golden veil of clouds that still lingered above Fort Davis.


I had spent the last three hours of daylight scouting the ridge from one end to the other looking at potential shots and shooting locations. In the end, I decided that the best place to start was at the highest point of Skyline Drive. I opened the rear hatch of the Subaru and started the process of setting up, leveling, and balancing the Skyguider Pro star tracker with my camera rig. While the Milky Way continued to rise, I aligned the star tracker to Polaris, and then started working on getting the autoguider set up so the tracking could be more accurate and I could take longer shots at lower ISO. Unfortunately, the computer never recognized the autoguider because the drivers from the manufacturer's website were no good. I would later discover through online forums that the manufacturer required you to contact them directly and they would email the correct drivers whenever they got around to it which is a completely ridiculous way to distribute software. Just more proof that it is always better to test new equipment before a trip. Without the autoguider to calibrate the rate of rotation, I was locked into a maximum shutter length of about 40 seconds at 200mm.


I used the information I gathered the previous night to guide me towards my first target, the Lagoon Nebula

While the exposed ridge left me vulnerable to the wind, and the nearby clouds blocked the stars, the summit provided an incredible feeling of openness and elevation that made me feel closer to the stars than I have ever felt before. A clear dome of stars slowly extended from the North and created a feeling of endless depth as I stared into the heart of the Milky Way Galaxy. That feeling was only accentuated as a large meteor stretched across the sky above my head. It extended across a third of the sky, and I could even see particles breaking up and burning away behind it. It was undoubtedly the best and closest meteor I have ever witnessed, and the experience is indelibly etched into my memory.


The Color Quandry - Milky Way shots at 20mm with landscape in the foreground and 80mm+ deep space images are two fundamentally different endeavors. Not only do they have different challenges to overcome from the standpoint of exposure and composition, but they also have distinctly different color palettes. The white balance for an image with landscape in it often needs to conform to the temperature of light as it bounces off terrestrial surfaces. Keeping the ground tones warm and natural generally forces the sky into a cooler palette. However, with an image taken solely of celestial objects, color becomes more subjective. White balance values closer to the temperature of daylight bring out warmer tones and more contrast in the dust clouds. The more I research about the nature of light, the limited spectrum visible to humans, and how wavelengths of light (experienced as color) are distorted by the atmosphere, speed, time, surfaces, etc, the more the relative subjectivity of the very notion of what color something "is" becomes strikingly evident.

Astronomical objects are generally hard to find, even with skies as dark as those in the Davis Mountains. The sheer number of visible stars can make it hard to pick out the once obvious constellations that I generally use as guides to direct my camera towards stellar objects. Moreover, many of the most interesting objects hide in the dark areas between the most luminous stars. On the previous night atop Mount Locke, I scouted the locations of the astronomical objects that I was interested in capturing. The Lagoon and Trifid Nebulae had been reasonably bright objects in the wide shots of the Milky Way, so they seemed like the perfect targets for my very first attempt at capturing deep space objects.


At 80mm I could see the telltale magenta glow of the Lagoon Nebula near the Galactic Center

It still took until 2 am for the Milky Way to rise high enough above the clouds for me to have a clear shot of the Galactic Center which lingered closer to the Southern horizon. The Galactic Center is slightly wider and brighter than the rest of the Milky Way and is only visible in the Spring and Summer in the Northern Hemisphere. I had a star chart for the Lagoon and Trifid Nebulae, so I began the arduous task of focusing the camera in the dark (using live view to tighten the stars into as small of a circle as possible using the manual focus ring), while also trying to aim the lens at the small section of the Milky Way where the Lagoon Nebula was hiding. I used a Nikkor 80-200mm f2.8 lens (one of the all-metal ones from the 90s before vibration reduction and polycarbonate were a thing), so I started off at 80mm to give me the best chance of finding and centering the Nebulae.


I used the hot-shoe of my camera and the middle of the lens to roughly aim the rig similar to a rifle (though now I use a red dot sight anchored to the hot shoe which is much more accurate). When looking at the sky, we generally reference objects via the dome of view created by the horizon. Rotating away from North gives us our azimuth, while the degrees above the horizon gives us our elevation. This method is more intuitive as it is based on how the sky looks from our perspective. However, our perspective is very askew from how the stars move in relation to the Earth's rotation, and it changes depending on where we are.


A quick sketch to describe the relative reference planes of an observer in Houston vs the rotation of the Earth

However, a German equatorial mount like the Skyguider Pro is aligned to the Earth's center of rotation which roughly aligns in the Northern Hemisphere with the star Polaris. Depending on the latitude of the observer (roughly 29.5 degrees North in Houston), the location of Polaris will either rise or fall. As you can see from my rough sketch, if you were on the equator, Polaris would effectively be on the horizon, and if you were on the center of rotation, Polaris would be directly overhead. From the latitude of my location in West Texas, Polaris was roughly 30.5 degrees above the horizon. Since the equatorial mount is aligned to Polaris, all of my movements on the mount are locked into that angled grid of rotation, coupled with the perpendicular axis of lens rotation from atop the declination bracket.


A comparison of the Equatorial (blue) vs Azimuthal (grey) reference grids looking at Polaris, (program: Stellarium)

In practice, all this really means is that while I view stellar objects on an Azimuthal Grid, I have to move my camera relative to the Equatorial Grid. It takes a while to get used to the zig-zag pattern of movement, especially when trying to center on an object and frame a shot. Larger, heavier, and more expensive mounts have methods to simplify or altogether automate around these limitations, but due to the very small, manual nature of my light, travel mount, I don't have that luxury.


After a few rounds of carefully moving the rig (which doesn't have finely-tuned adjustments) based on a few 40-second test shots, I finally felt pretty good about the orientation of the camera.


At 200mm, the color and detail of the nebulae really began to pop

I zoomed the lens to 200mm and took about 4 good shots of the Lagoon Nebula at around 40 seconds each. I actually took two additional shots, but I tried to increase the exposure to 77 seconds which caused the stars to elongate too much and thus made the shots unusable. I stacked the 4 good shots to create this final image which has less noise and more light detail than any single image. There is a complex relationship between how photons travel through space and how they impact the pixels on an image sensor. Stacking images is a process that uses algorithms to determine the difference between sensor noise and reliable light data which leads to a better image.


In hindsight, after reading multiple articles about the benefits of photo stacking deep space images, I should have taken at least 10-15 images in order to maximize the benefit of stacking. However, as I mentioned before, this impromptu trip precluded any in-depth research so I’ll have to try that next time. Per the recommendation of many accomplished astrophotographers, I used the fantastic, free stacking program Sequator (unfortunately it is only available on PC). I liked the program so much that I donated to the developer to hopefully help keep it up to date for many years to come.


I had originally planned to take the picture of the Lagoon Nebula with my 500mm lens, but with the lack of an autoguider limiting me to 40 second exposures on a 200mm f2.8 lens, I was pretty certain that swapping over to the 500mm f5.6mm would waste precious time as the longer focal length and reduced light input would certainly leave me with overly dark and noisy images. Instead, I decided to try and find the second deep sky object that I was actually the most interested in, the Eastern Veil Nebula. Little did I know that it would largely be an equally frivolous endeavor.


Cropped 200mm image of The Trifid (left) and Lagoon (center) Nebulae

The Veil Nebulae are an incredibly beautiful nebulaic object near the tip of Cygnus’ (the Swan’s) Eastern facing wing. Even with all the dense stars of the Milky Way surrounding it, the constellation was still easily recognizable. Deneb and Sadr were visible through the lens, but once I panned down to Epsilon and Zeta, it became much harder to gauge where I was. Even with a 40 second exposure, all I could see was a blank field of stars. As it turns out, the Veil Nebulae are exceedingly dim, so my limited focal length and exposure time made it all but impossible to capture fully.


The 80mm image as shot (left) and after post-processing (right) when the arcs of Veil Nebulae are only just visible

I was certain that I was looking in the right place, but time and time again I just couldn’t see if I was anywhere near where I needed to be on the small screen on the back of my camera. Little did I know that I was exactly on target, but the Veil Nebulae are just so dim that I needed my exposure to last multiple minutes to capture it (something my current rig just couldn’t do). I only took a couple photos because I wasn't at all certain that I was even looking in the right place, but after returning home and cranking the exposure of the terribly underexposed image, I found that my star navigation was good, I just didn’t have the setup to really capture the beauty of such faint nebulae.


I made this GIF to graphically explain what was hidden in the underexposed image

I didn't want to waste more time on an object I couldn't see, but since I was fairly certain that I had the right location, I took one last image at 200mm hoping that it would reveal its secrets in post-processing. Even with a considerable amount of post-processing, the image below only hints at the incredible color and whispy detail of the nebulae. Hopefully, I will have another opportunity to try again under dark skies in the future.


The first of what will likely be many attempts at capturing the Veil Nebulae

Frustrated with not getting the Veil Nebulae, I decided to search for the Andromeda galaxy because I was at least certain that I could navigate to it with the naked eye. Unfortunately though, that portion of the Milky Way was lost in the glowing haze of the clouds still lingering over Fort Bend, so multiple attempts at capturing the galaxy were largely unsuccessful. However, I still enjoy how the haze created an ethereal glow that accentuates the varying frequencies of light emitted by stars of different temperatures. That kind of information can be easily lost in a clear photo, so it was a happy accident.


I'm not sure if it was a satellite or a meteor that created the line just above Andromeda

At this point I was 1 for 3, so I decided to abandon deep space imaging from my windy post on the summit and head East to one of the stone viewing structures dotting the ridge. By this time, twilight had started to sneak in, and the brilliance of the Milky Way began to fade in the increased light. It was already 4 am, so I only had 20 minutes or so to commit to the shot. I was too tired to set up the star tracker again, so I just eye-balled the composition and manually focused the 20mm lens (which was frustratingly difficult for some reason), and used my headlamp to briefly illuminate the spiraling lookout. By the time I finally had the right focus and exposure, the galaxy had moved off-center. When aligning terrestrial objects with celestial objects, it becomes painfully clear exactly how quickly the Earth rotates to the East, making the stars appear to move rapidly to the West from the Earthen observer's relative field of view.



This was the second night I had spent awake into the twilight hours of the morning. My eyes were painfully dried out from the constant wind on the summit, and I knew that I had a long drive back to San Antonio the next day. I wearily packed up my gear, turned on my parking lights, and slowly crept down the mountain road in 1st gear to try and limit the noise and light caused by my trip back to my campsite.


Before retreating into my tent, I stared longingly at the glowing expanse of stars slowly fading into the coming twilight and contemplated how much I would miss them. Compared to the dark skies of West Texas where the universe feels within reach, returning to the glaring, featureless skies of the city can feel like being trapped in a cage of wasted, artificial light. Begrudgingly, I flopped onto the floor of my tent, and did my best to fall asleep in the fading darkness, whispering farewell to the stars between shallow, fleeting dreams.



Final Post: McDonald Observatory 6 - Flora & Fauna




© 2017-2022 Shaun C Tarpley Photography

 
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