Astronomy Guide November 2023

Last month, I visited La Palma, the most northwesterly island of the Canary Islands, Spain, located in the Atlantic Ocean. Before going into details of my trip to its highest mountain, the Roque de los Muchachos (2’426 m or 7’959 ft), here some information on climate, geology and geography of the island. You’ll find a detailed map of the island here.

La Palma offers a diverse range of geological, geographical, climatic, and ecological features that make it a captivating destination for nature enthusiasts and stargazers. It is a volcanic island formed through volcanic eruptions over millions of years – the last one dating back to as recently as 2021, when the Cumbre Vieja volcanic ridge in the southern half of the island erupted between 19 September and 13 December 2021.

The island’s geology is characterized by steep cliffs, rugged terrain, and volcanic craters – the terrain is sometimes so steep, I needed an another, stronger rental car on the second day of my stay. La Palma offers a wide range of landscapes, from lush forests in the north to arid volcanic expanses in the south. It has a mild, subtropical climate. The north and west sides of the island receive more rainfall, resulting in lush vegetation, while the south and east are drier. Fauna and Flora are diverse, with unique species, such as the giant lizard (Gallotia simonyi). In the higher elevations and within the Caldera de Taburiente, there is a beautiful laurel forest, a relic of the Tertiary Period and a UNESCO World Heritage Site.

All Canary Islands are famous for their excellent astronomical quality of the sky – protected by law!

During my visit, I booked a guided tour at the Roque de los Muchachos Observatory (ORM). At ORM, on the rim of the Taburiente National Park, stands one of the largest arrays of telescopes in the world. Because of the excellent sky above La Palma, the observatory has exceptional conditions for astronomical research.

Together with the Observatorio del Teide (OT) on Tenerife, ORM is part of the Observatorios de Canarias (OOCC). Jointly, they contain the telescopes and instruments of around 60 institutions from over 20 countries – with optical and infrared astrophysics. The ORM site in La Palma currently (information from 2021) hosts the largest optical-infrared telescope in the world, along with 20 other telescopes and instruments for studies such as nocturnal observations, robotic observing, solar physics, and high energy astrophysics.

The site also hosts the twin telescopes MAGIC I and MAGIC II (MAGIC = Major Atmospheric Gamma Imaging Cherenkov Telescope), with a reflector diameter of 17 meters each. They are being operated at night and can detect very high energy gamma rays. High energy gamma rays can only be observed indirectly because the absorption process in the atmosphere proceeds by creation of a shower of high-energy secondary particles. Charged particles in the shower emit light, so called Cherenkov radiation. A Cherenkov telescope is sufficiently sensitive to observe this light on the surface of the earth. MAGIC I and MAGIC II measure these high-energy gamma rays from our Milky Way and distant galaxies, helping astrophysicists to advance in their studies of stellar explosions, pulsars, black holes and gamma-ray bursts.

As you can see on the picture above, there is a third Cherenkov Telescope (called Cherenkov Telescope Array (CTA)), the Large-Sized Telescope LST-1. It is a prototype that was inaugurated in 2018. The parabolic reflective surface is of 23 meters in diameter. It is 45 meters tall and weighs about 100 tons but is able to re-position within 20 seconds to capture brief, low-energy gamma-ray signals.

CTA is a global initiative with about 120 telescopes on two sites: one in the northern hemisphere at Roque de los Muchachos and the other in the southern hemisphere near the existing European Southern Observatory site at Paranal, Chile. During my visit at ORM I had the chance to see the Gran Telescopio CANARIAS (GTC). It is a reflecting telescope. The primary mirror is made up of 36 hexagonal segments, which, when put together, have a light-collecting surface of 75.7 m2, equivalent in size to a single, circular mirror with a diameter of 10.4 meters. The First Light Ceremony was celebrated on 14^th July, 2007. Scientific production of the telescope started in March 2009 with the first science instrument OSIRIS.

Don’t forget to visit the Roque de los Muchachos Visitor Centre and discover the entrails of the telescopes, delve into the depths of the cosmos with modern, interactive technology.

I highly recommend visiting La Palma, also called La Isla Bonita, with untouched nature away from mass tourism. It’s also safe to visit alone, crime is low. If you are planning to visit the Roque de los Muchachos Observatory, take into consideration enough time for the drive up there. Roads are generally well built but narrow, tight curved.

For astrophotography, beware that access to the observatory is closed starting 8 p.m. but you can drive sufficiently close. Don’t use full beam and in general: use as little light as possible. If you need light, best take a red headlamp. And enjoy the stars! In my case, I had the bad luck to visit during a meteorological phenomenon called “Calima” that occurs when fine sand and dust particles from the Sahara Desert are lifted into the atmosphere and transported by wind.

I recommend visiting the whole island. If in the west where the volcano broke out in 2021, support local businesses and communities by visiting museums, eating out and buying locally. Areas most hit are El Paso, Los Llanos de Aridane and Tazacorte. The courage and optimism of people living there are impressive and a true inspiration.

Make a stop at The Caños de Fuego (Fire ducts) Volcanic Caves Interpretation Center. It was created as a result of the discovery of a system of volcanic tubes in the Las Manchas area, formed by the solidification of lava emerging from the eruption of the San Juan Volcano in 1949. The centre aims to teach its visitors about the geological formations that develop during and after volcanic eruptions. Across the road, find a magnificent floating walkway that leads to the floating glass viewpoint and a view over the Cueva de Las Palomas Volcanic Tube. Access to this tube is currently not possible due to the new volcanic eruption in 2021 which also covered this area with a thick layer of volcanic ashes.

The capital, Santa Cruz de la Palma on the east coast of the island is well worth a visit. Santa Cruz de la Palma (Spanish for Holy Cross of La Palma) is a city and a municipality on the east coast of the island of La Palma in the province of Santa Cruz de Tenerife of the Canary Islands. Santa Cruz de la Palma old town with its cobblestone streets, colonial-style buildings with wooden balconies is also worth a visit. The fish at the Restaurante La Chalana is fresh, local and excellent! The tapas choices very nice as well.

Even by car, you’ll have to walk uphill/downhill a lot to get to see the best places and have the best views, so don’t forget your hiking shoes, and always take enough water with you.

Sources and further reading:

• del Fresno, C., Cesca, S., Klügel, A. et al. Magmatic plumbing and dynamic evolution of the 2021 La Palma eruption. Nat Commun 14, 358 (2023).
• GTC (Gran Telescopio Canarias), European Space Agency
• Instituto de Astrofísica de Canarias (IAC)
• MAGIC – Major Atmospheric Gamma Imaging Cherenkov Telescope
• The First Large-Sized Telescope of CTA Makes its Debut.
• ChatGPT