Last month I had the chance to observe at the Galileo National Telescope (TNG) at the Roque de los Muchachos Observatory on the island of La Palma. Working the night shift doesn’t leave much time for sunbathing, but it’s handy because the conditions needed for great observations are often the same as you’d find in a warm vacation destination. Located at an altitude of 2,370 meters on the edge of La Caldera de Taburiente, the TNG is home to five instruments: SiFAP2, Nics, Dolores, GIANO-B and HARPS-N. We mainly observed the HARPS-N instrument, or as it is officially called, the ” Hah aAccuracy RDistance Speed PLannet vinegarSearcher of noCalled the orth hemsphere because astronomers love acronyms, the instrument is designed to measure the star’s radial velocity signal, a technique that detects how much the star is “wobbling”, which allows it to determine the minimum mass of an orbiting object (if the mass is low enough, you’ve got a planet).
As there are no direct flights between Belfast and La Palma, we had to make a quick stop in Tenerife before arriving in La Palma the next morning. A short taxi ride over mountain roads brought us to the Residencia where we would be staying for the next nine days. Observations began the following evening, so we had plenty of time to watch the sunset. The image below shows the other three terrestrial planets in our solar system: Venus shining brightly near the horizon, Mercury (a rare sight!) slightly above and to the right of Venus, and Mars slightly above and to the left. As my phone camera is not as good as the 3.58m world-class telescope, I annotated the image to make sure it wasn’t just a smudge on the screen.
A typical “day” on an observing run (in summer when the nights are short) is as follows: wake up around 3:30pm, have a quick breakfast, head to the telescope at 5pm to start the calibration and schedule the target list. Depending on how early you can finish the calibration, you can eat dinner as late as possible and then kill a bit of time before returning to the telescope at sunset (around 9pm in our case). After watching the sun go below the horizon, go to the telescope control room to check the schedule for the night, check the weather forecast to make sure there are no pesky clouds approaching, and if necessary, find a backup target that can be observed even in bad weather. Scientific observations start at the end of nautical twilight when the horizon is no longer visible (so called because during this period sailors navigated using a bright guide star so they could see the horizon). If the weather is clear and there are no technical issues with the telescope, it is very easy to observe the target list and continue observing until the end of nautical night at around 6:30am. After filling out an overnight report detailing our observations and any issues that may have arisen, we return to the Residencia and go to bed around 7am to get as much sleep as possible before starting the same routine again.
The first three nights of observing went well, and the second night conditions were surprisingly good. Seeing (a measure of image quality due to atmospheric turbulence) reached 0.19 arcseconds. To show how good the conditions were, I’ve included a cartoon below.
We filled our time by doing other tasks as best we could while adapting to the night shift, but most of the time we played cards while making sure the observations were going well. During our free time during the day, we climbed to the top of Roque de los Muchachos, from where we had a great view of the caldera (the remains of a huge volcanic crater) and the island of La Palma. In the distance we could see the site of the Cumbre Vieja volcano, which erupted in 2021 and is still smoking.
The fourth night of the run marked the halfway point and the weather worsened considerably, with high clouds rolling in all night, hindering observations and forcing us to chase targets in gaps we found. This is a common situation on runs, where conditions are changeable and we spend time waiting for the clouds to pass, so it was a useful experience to learn how to deal with unfavourable weather.
The fifth night was expected to continue with the same weather as the previous night, but luckily the clouds disappeared before they reached us. The final two nights of observations also went smoothly, giving us the opportunity to talk a bit about the interesting history of the TNG design. The TNG design is derived from that of the New Technology Telescope (NTT) at La Silla Observatory in Chile. As the name suggests, NTT pioneered many technologies that are widely adopted in many of today’s best telescopes. NTT implements active optics, which compensate for atmospheric effects to maintain image quality. While most large telescopes have historically been built using spherical domes, NTT and TNG use octagonal housings, designed to reduce turbulence created as air passes over or through the telescope structure, which also improves image quality. These technological advances are most notably applied to the Very Large Telescope (VLT) at Paranal Observatory in Chile (just a few kilometers away from NGTS).
Finally, I’d like to thank the Royal Astronomical Society for kindly funding this trip. I had a fantastic time and learned a lot about how astronomy actually works – a skill that will no doubt be useful in my future career as an astronomer.
