Texas – an infrared journey

The following photo essay was part of the Kolari 2019 infrared photography competition, where I got into the finals (and subsequently an honourable mention) for that year’s international infrared photography awards.

Astronomy has a few perks, one of them being able to travel to far-away continents (depending on the perspective) and explore locations you can otherwise never access. My main scientific work is the hunt for extrasolar planets and in the context of this, I regularly travel into the mountains of Texas, to the McDonald observatory. Living close to a young mountain range, the Bavarian alps, I was amazed by the completely different look of the much older geology of the Texas mountain range. My observing run took place in summer 2018, during the local monsoon season, which led to things I never thought I would see: thunderstorms below the milky way, beautiful, multi-layered rainbows and huge forest fires that darkened the sky for days, to name a few. Armed with a full-spectrum camera and another one dedicated to infrared, I attempted to capture my experiences. The following essay is a condensed view of several observing runs, always taking place at the same time of the year.

Our flight took us over the UK and Greenland, with a particularly scenic moment over the Isle of Skye. The NDVI filter was perfectly suited for that with its combination of gold and blue. As it happens with airplanes, the edge of its wing was inside the photo so I had to remove it. Therefore, the geology of the island that is photographed here may not be 100% accurate.

Having arrived in Texas, our final trip was a drive through the mountainside. While taking photos out of the car is a challenge, the light through the clouds and the pale traces of plant life on the rocky hills made it worth a try.

: The first time we could see the observatory. The road divides the image and provides a nice visual cue as to the difference of the telescopes: the left one, called HET, is an experimental, modern 10 meter class telescope that however can only rotate and not tilt. The two telescopes on the right are much older with ages of 50 and 80 years, respectively, but thanks to modernizations they are still actively being used for science. The Harlan J Smith telecope, second from the right, was used to measure the distance to the moon by recording emitted laser beams that were reflected by mirror plates set up by the Apollo mission.

Having reached the top, weather got worse quickly. Here, one can see the HET, which is located on the opposite hill, in more detail. Infrared was able to pierce the fog while visibility was much worse in the visible.

The weather cleared (more or less) nicely for the first night of the observing run. However, several thunderstorms were still visible on the horizon, which led to a sight I never thought I could see: lightning arcs below the milky way. Taken in full spectrum, lightning changes its color into a golden hue due to the infrared excess.

Several days later, an astrophysicist’s worst nightmare happened! Forest fires several dozen kilometers away spread out and slowly crept closer towards the observatory. We had to close down the dome and enjoy the show while everthing smelled like barbecue. Thankfully, the fire department was successful in stopping it. Due to full spectrum, the glow and optical properties of the smoke particles turned them into a pinkish hue.

Our visibility was extremely poor in the following night, i.e. while we couldn’t detect a cloud with our sky surveillance camera, stars appeared to be much fainter than they should be. Since we wanted to do spectroscopy where every photon counts, this was a huge problem. I therefore went outside to take infrared images which is when we finally realized what was going on. Seen here, the pink glow in the sky is created by ash particles that were now spread evenly across almost the whole sky. The full moon provides illumination for the ground while the sky appeared utterly dark in the visible.

Everything looked more peaceful on the next day. Sadly, infrared revealed a suspicious „cloud“ in the sky, which is likely ash and not water. On the right, one can see how it slowly dissolves in the wind.

The next day, with an early end of the night due to the ash particles, we decided to take a walk and explore the surrounding area. The so-called red edge makes every plant appear very bright in the infrared and cacti are no exception – they look quite alien.

Finally, success! Clear, dark skies for science and also for photography. The milky way is fascinating both in the visible and the infrared, but I prefer the mix that is created by this filter and wavelength-sorted with blue corresponding to green, green to red and red to infrared. The H-alpha regions, where monomolecular hydrogen gets excited and emits light in very strong colours, appears golden.

Several days later, the weather got worse again. During the day, we got treated by a beautiful, sky-spanning rainbow. Infrared is a very useful tool to improve the detail of such an event since it shows a smaller wavelength range. Here, one can see the secondary rainbow, Alexander’s dark band to the right of the primary rainbow, and supernumaries (more on that in the following picture).

A more zoomed-in photo reveals supernumaries. Rainbows are created by water drops of equal size, where light gets reflected inside the drop and, depending on the wavelength, exits the drop at a certain angle. However, if there are several similar-sized types of water drops in the sky, one can see such supernumaries where each order corresponds to a different particle size.

Since the weather got worse again (and our working night therefore short), we decided to make a small road trip to Prada Marfa. While standing there, I photographed parts of the scenic landscape with an old windmill at the center.

With this photo, our observing run concludes. We collected data in sufficient amounts to keep ourselves busy until next year and enjoyed the scenic route back to the airport, the road leading up into the magnificient mountain pass below the clouds.

Travelling back, we were allowed an amazing look at the forming cumulus congestus and cumulonimbus clouds. Infrared enables a clarity that is not possible in the visible spectrum, free of haze. Looking at it through the viewfinder was amazing!