The Calar Alto Astronomical Observatory (CAHA) is located at an altitude of 2.168m in the Sierra de Los Filabres, in the north of the province of Almería. Founded in 1973 following an agreement between the German and Spanish governments, Calar Alto has several telescopes specializing in various research projects, such as the search for exoplanets.

We spoke with Jesús Aceituno, Director of the Observatory, who passionately shared with us some of the secrets of the center, and from whom we highlight an important phrase to raise awareness in the community:

Illuminating the domes at night with a simple cell phone or a flashlight can destroy hours of observation work…

What is special about this environment that it has one of the most important astronomical observatories in the world?

When the extinct Federal Republic of Germany decided to set up a professional observatory back in the 70s, several campaigns were carried out to test the quality of the sky in different locations on the Mediterranean coast and North Africa.

After 3 years of campaigning, the Sierra de los Filabres was chosen as the best location due to the number of clear nights, low turbulence values, good transparency and generally stable weather conditions, giving rise to the Hispano-German Astronomical Center. 50 years later, the mountain continues to provide conditions that make the Calar Alto sky the Sky of Europe.

What are the center’s main instruments and what research are they aimed at?

One of CAHA’s strengths is the instrumental equipment that its telescopes have. Every so often, we try to identify which niche is not covered in modern Astrophysics. To address this, a leading instrument is developed that distinguishes us from other observatories.

This is the case of the CARMENES instrument, a very high resolution double spectrograph that operates simultaneously in the visible and infrared range, making it unique in the world. The purpose of this instrument is the search and characterization of Earth-like rocky planets where the conditions for life as we know it can exist. To date, CARMENES has discovered more than 60 planets, of which about 15 are of this type so attractive to all fields and in some we have even detected molecular oxygen in their atmospheres.

Could you share with us some of CAHA’s most important milestones?

Throughout our history, many discoveries have been made from CAHA. Each year, around 110 impactful articles are published in peer-reviewed journals and this average has remained more or less constant over the past 25 years. This adds up to an average of about 2.750 discoveries in half of our history, so it is difficult to highlight just one or two.

But following the thread of the previous question, I would highlight the discovery of a double planetary system similar in a certain sense to the Venus-Earth system, in the star TeeGarden which is ten light years away from us. These are two twin planets to Earth that are in the habitable zone. Without a doubt, they could be the protagonists of the script of any science fiction movie of the moment.

We could see recently the Northern Lights and comet C/2023 A3 (Tsuchinshan-ATLAS) with the naked eye in this area, we would like to know how these special events are experienced within CAHA

Since childhood we have always thought that the Northern Lights are exclusive events of arctic latitudes, so the first time you see one from CAHA, your brain tries to associate it with any other different event and you do not believe what you see. This feeling is amazing and above all magical.

The same happens with comets, professional astronomers are used to working behind a screen and often forget the immeasurable beauty of looking at the universe with the naked eye or with simple binoculars. Fortunately, from time to time, we are visited by one of these comets and it makes us have to put aside our powerful telescopes to use binoculars and enjoy like a child who starts in this profession/hobby, regardless of the time some of us have been in this. It is simply magical, the feeling of observing something simply because it is beautiful.

Finally, some cyclists do this iconic area of the Badlands route at night. We always invite them to stop pedaling for a few minutes and look at the sky, what recommendation would you give to these people to immerse themselves in this environment?

The first thing is to enjoy it, unfortunately because of light pollution more than 80% of the world’s population does not know the sky. I still remember the first time my wife visited CAHA. We live near the coast where you only see a handful of stars. Arriving at CAHA at night, we got out of the car and I was talking non-stop, when I see that she was petrified pointing at the Milky Way asking what the hell that was. In fact, it was the first time she had seen the sky in its entirety.

There are still places where this feeling can be experienced, and CAHA is one of them. But there is a risk and you must be deeply respectful. CAHA is a temple of astronomy, we enjoy international prestige and therefore we invite everyone to visit us, but it should be done preferably during the day and if it is at night through the guided visits designated for that purpose and there is a reason for this.

Exposures in telescopes can last from 30 minutes to several hours. The largest telescope in the observatory is capable of detecting the glow of a lighter located on the promenade of Malaga!, imagine what flashlights, or vehicle lights in the vicinity of the domes can do. We often find tourists who, in the dark of night, turn on the car lights in the direction of the domes or simply point their mobile flashes to take a selfie. When we notice them, the excuse of “it was only a moment”, destroys hours of work.

That is why our advice is to either make these night visits through the company Azimuth which has been with us since 2015 and know perfectly well how to carry them out so as not to harm the observation, or to retreat about 500m from the summit. The sky there is just as good and we don’t get in each other’s way.