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McDonald Observatory 2 – Starry Night Reprieve

Updated: Jun 3, 2022

2021.06.11 - As the sun finally released it tortuous hold on the desert, the cool, dark reprieve of a moonless night slowly settled upon the summit of Mount Locke. The clouds that had once dotted the sky receded to the horizon, and for a few short hours the Milky Way glowed brilliantly above our serene mountain top location. After little sleep and hours of travel I was tired, but I could hardly feel it due to the excitement of such a beautiful night.

The Milky Way Galaxy over Fort Davis State Park

I’m inclined to wing the small, insignificant decisions in life, but it has always been in my nature to plan complex events, especially those where timing and execution are paramount. However, for this impromptu photographic opportunity, the burdens of work and parent life left me with very little time to plan what I wanted to shoot, how I would shoot it, and how to set up my equipment to maximize success. In short, I was winging it all, including using some equipment for the first time.

Our host had mentioned the potential for getting start trails behind the Harlan J Smith telescope during the familiarization tour, and since I know these sort of shots take a long time and monopolize a camera, I decided that it was a perfect job for the older Nikon D750 and the manual focus 14mm to do while I worked on setting up the main rig.

The moonless night made using the viewfinder very difficult, so I composed the shot using 30 second exposures and making small adjustments until it looked the way I wanted. My cheap intervalometer was not working, so I just used the timer on my phone and manually released the exposure roughly every 20 minutes. Unfortunately this meant I was stuck babysitting the camera for the night and wasn't able to be as mobile as I had originally intended.

The 20 min exposures at 100 ISO had low noise but developed extensive artifacts and telescope blur

With the D750 chugging along, I began setting up the D850 on the iOptron Skyguider Pro. Unfortunately this was only my second time setting up the star tracker, so setting up in the dark was a challenge. Additionally, the location that was good for the star trails shot meant that Polaris (the star needed to align the star tracker) has hidden behind the telescope. I attempted to align the tracker manually, but one negative of the iPolar camera that I use with a computer to set up polar alignment (to the precision needed for deep sky objects), is that the permanently affixed unit fills the space that is otherwise the manual scope. The 20mm, wide angle shot shouldn't have needed exact alignment, but I soon found that the misalignment was causing more problems than it was worth on the long shots. In the end I had to try alternative methods as my time on Mount Locke quickly dwindled.

The night was pitch black, so it was very hard to see anything, including the outstretched legs of our tripods. The Observatory hosts gave us some glow-in-the-dark tape to place on the bottom of the legs to keep us from tripping over each other’s equipment, but I have to admit I was still nervous about shattering a lens or damaging a camera in such a big and active group, so I ended up being much more stationary than I had intended.

The yellow/green gradient at the bottom of the image is a result of artificial light reflecting off the clouds

Since I was having trouble keeping the stars from elongating, and I didn’t want to leave my D750 both because of the need to manually take each image, and fear of it getting knocked over (the 14mm has a domed exterior element that would certainly shatter if dropped), I began looking for alternative solutions. I overheard someone mention how well 6400 ISO worked for the Milky Way, so I decided to give it a try as I was hitting a shutter speed limit of about 25 seconds with the misaligned star tracker. I cranked the ISO up to 6400 and modified the shutter speed to around 27 seconds which balanced the detail of the Milky Way and didn't blow out the lights along the horizon.

The 500 Rule - If you research astrophotography at all, you will quickly run across the infamous 500 Rule. It simply states that if you divide 500 by the focal length of your lens, you will get a rough maximum shutter speed that will keep stars from elongating. As is obvious by the equation, the longer the focal length, the shorter the shutter speed you can use. It is not an absolute rule, and its value is dependent on the focal length you are using, but it's a good rule of thumb to give yourself a useful starting point.

The higher ISO did well to bring out detail, but the tradeoff was much more noise than I would have preferred. In hindsight, I think it would have been better if I had taken the risk and moved the mount to where I could align to Polaris, and then taken multiple exposures at closer to a minute to create a stack in post. The pitch black ground already meant that I would need to make a composite anyway, so a stack would have been manageable.

The pitch black ground required a much longer exposure to pull out detail, so when I noticed considerable traffic along the road down the mountain, I modified the exposure to about 6 minutes at 800 ISO which looked good enough on the back of my camera. After working on the image in post, I think closer to 20 minutes at 200 ISO would have been better for sharpness, but the city lights were hard to balance as overexposure in those regions would bleed into the dark landscape. It's a challenging shot to balance no matter how you look at it.

I used Photoshop to carefully merge the images of the night sky and ground manually because the automated methods in Photoshop and other programs couldn't manage all the artificial light pollution. It took a long time, but I am happy with the results (the composite image is the first one in this post).

Between exposures, I spent some of my time surveying the sky for the next night's deep space targets

There was a considerable amount of discussion about light pollution while we photographed the basin. The host that stayed with us on the lower road was Stephen Hummel who, in addition to taking amazing photos and hosting deep space live feeds from the 36" telescope, is also actively involved in advocating for Dark Skies in the region via the Dark Skies Initiative. In fact, the very next morning he was scheduled to hold a round table in the City of Alpine just a few miles South. I ended up joining him and some of the others in the group down there, and it resonated with me both from my photographic and architectural experience. Limiting light pollution has always been an interest of mine, especially while designing in San Antonio with all its Military Overlay Districts, but my foray into night photography has only reinforced the importance of limiting wasted light. There are so many lights in a modern city that needlessly project light up into the atmosphere which is not only wasting light energy, but that excess light brightens the sky and reduces our ability to see the stars. It can also cause glare to observers both on the ground and flying in the sky. Light pollution is the perfect name for this form of environmental destruction.

To help illustrate this point, I took the image I shot of the Milky Way and labeled all the glowing light sources that added an unnatural yellow/green tinge to the image. Looking to the South, the biggest offender is clearly the small College town of Alpine over 40 miles away, but when facing North it is very clearly the Permian Basin oil fields that are brighter even though they are over 150 miles away. Light pollution has no benefits, only detrimental effects on our environment and the health of both people and wildlife. It also puts a completely unnecessary load on our overloaded electrical grid, and Texas already found out during the freeze of 2021 how badly that can impact the state.

The best part of choosing to reduce lighting pollution is that every effort we take has an immediate effect on our environment (unlike global climate change which is precipitous and will take centuries to truly fix the damage we have already done). I fully support the Dark Sky Initiative and I hope to incorporate the principles of dark sky lighting design whenever I can in my architectural projects. The area around the McDonald Observatory is one of the darkest in the country, but we can still do better. If you are wondering how your location compares, see the dark skies map here. For comparison, I live in Houston which is about as bad as you can get in Texas.

Update 2.9.22 - After talking with Stephen Hummel of the McDonald Observatory on Instagram, I made a number of updates to the above image to better label the light sources. While the contrast of the light sources with the dark sky makes it seem extreme, the light pollution in this region is actually an order of magnitude less than it is in big cities, and they are getting better every year. Even since this image was taken, locations such as the Village Farm LP have dramatically reduced their impact by changing to warmer, less intense, and shielded light fixtures. The Greater Big Bend International Dark Sky Reserve is a glowing example of what the rest of Texas could be (ironic pun intended).

As our time on the mountain drew to a close, it was finally time to pack up my equipment and head up the steep, narrow, metal staircase back up to the top of the mountain. I unlocked the remote shutter release for one last time on the D750 and glanced at the final photo. I had no idea what the final composite image would look like, or the challenges it would provide. In the end, the long shutter method (as opposed to thousands of rapid shots merged into a single image) was successful and didn’t have an insurmountable amount of noise or artifacts, and it certainly took less hard drive space, but I never expected how complex it would be to resolve how much the telescope moved over the 4 hours of shooting. The irregular shapes along the top of the dome gave me endless trouble in post-processing as I tried to resolve the blur and lost star information. I'm pretty sure that I spent the most time creating this star trail image from the 12 approximately 20 minute exposures (a total of about 4 hours of exposure time), but I think it was well worth the effort.

The Harlan J Smith Telescope (center) and 0.9-meter (36") Telescope (right)

I was actually very lucky that my long shots facing the telescope weren’t mired by planes or satellites streaking across the image. However, I couldn’t say the same about the effects of my compatriots moving around the area. We used red lights to limit night blindness and our effect on each other's images (including the work being conducted by the HJST), but sometimes it was hard to avoid the path of an image, especially one like mine that looked across the road. Even though this meant that I had to spend extra time modifying the individual photos stacked into the main composite image, I think the unusable portion of some of the images were still rather fun. I’m accustomed to photographing alone, particularly in the dark, so I think the image below encapsulates rather well the inherent chaos of photographing in a group, especially on a pitch-black night where we could barely see our hands in front of our faces, much less where each other's mostly-black cameras were pointing.

As usual, I was the last person taking photos, and thankfully our hosts were patient with me. I waited for the D850 to take the last dark image (through Nikon’s long exposure noise reduction setting), and then packed everything up for the hike back up to the summit. Over the night, I had made a few trips to my car to bring more gear, so hauling it all back up in one trip was a bit of an undertaking. It’s easily 80lb of gear spread out through my bag, a pelican case, and two tripods. With all that weight, and the elevation that I had only just arrived at, I was gasping for air by the time we made it up three flights of stairs to the summit roadway on the Southeast side of the Harlan J Smith Telescope.

I was quite happy when the host offered to stop momentarily at the base of the HJST for a quick picture of the Milky Way behind the dome. It was actually an image I had hoped to get that evening, but I chose to stay and maximize the star trails images instead. If I had the time, I would have swapped the 14mm from the D750 over the D850 and composed the shot better, but unfortunately I had packed the D750 away and didn't have the time to pull it back out. It was pitch black, and I could barely see anything through the lens, so I just had to guess at my composition. I had just enough time to take a 45 second shot that was too high and to the right, and a 115 second photo that was too high and had elongated stars. Moreover, by this point the sensor was overworked and very noisy, so any exposure likely would have been messy. It took a little time in post to create a workable image from both shots, but I still enjoy the final product even if it isn’t perfect.

The Harlan J Smith Telescope looking North as I looked to the South

With those final shots the evening atop Mount Locke was officially over. I hauled my gear over the summit and back down to the parking lot with the rattling of my Pelican case announcing my location in the nearly-lightless evening. I hastily dumped everything in Sube, said goodbye to our hosts, and headed back down the mountain using only my parking lights as a guide to limit glare on the telescopes that were hard at work.

I arrived back at the Davis Mountain State Park around 1am and began the process of unpacking and assembling my camping gear. I’ve had my camping gear for so long now that I know it all by heart, so hanging my hammock and pitching my tent in the dark was easy enough. The hard part was trying not to make too much noise while doing it.

I stayed up a little longer just absorbing the incredible view of the Milky Way from the base of the shielded valley of the park. I had hoped to see Andromeda rise on the East side of the Milky Way, but I didn’t have any luck seeing it with all the mountains around. I finally gave up around 3am and headed to bed for the few hours of darkness left before sunrise. I had agreed to join a few of the people I met that evening in Alpine for an early morning photography exhibit/symposium put on by the Texas Photographic Society, so I finally relented and closed my weary eyes beneath the stars.

© 2017-2021 Shaun C Tarpley

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