A Window into the Universe from Baja California. The Observatorio Astronómico Nacional at San Pedro Mártir

In the highlands of Baja California, 180 kilometers from the northern border of Mexico and 2800 meters above mean sea level is the National Astronomical Observatory at San Pedro Mártir. The observatory has 11 telescopes; seven of them are currently in routine operations and the other four are in their testing phase. The natural astroclimatic  conditions are amongst the best in the world ( Plauchu-Frayn et al. 2017 and 2020), particularly the dark  sky which, thanks to its remoteness from large sources of light pollution like cities, makes the observatory a privileged site for studies that use the scarce light coming from very distant astronomical sources and that require the least possible interference. The prevailing low cloud cover and very low humidity of the site make the Sierra de San Pedro Mártir a privileged place for astronomical observations. It is sad to note that the excess of illumination and its mismanagement are destroying the world’s dark skies, which are an important natural resource and a source of wonder [see UNAM International 3, p. 108]. 

The three oldest telescopes at the observatory are, respectively, two meters, 1.5 meters and 84 cm in aperture. They were installed during the 1970s. They are currently equipped with instrumentation that allows us to obtain images and spectra in visible and infrared light, and to even measure the polarization of light from astronomical objects. Significant research has been done with them on normal and active galaxies, stellar groups (called clusters), various types of stars representing their different evolutionary stages, and the gas clouds that sometimes surround them. These classical telescopes are currently used for studies of satellites around the Earth  and minor Solar System bodies; of stars in binary systems ; of planetary nebulae ; of young and old stellar clusters to study the evolution of stars, active, and non-active galaxies, and of the most energetic events in the Universe ( including light from gravitational wave emitting events , among others. 

The newer telescopes are the product of the work of the astronomical community in Mexico in collaboration with international partners, mainly with countries in Europe and Asia, and with the United States. The eight newer telescopes have been designed to perform robotic operations that do not require someone on site for acquiring astronomical observations at night. The BOOTES-5 telescope—with a diameter of 0.6 meters—was inaugurated in 2015 to study the behavior of the brightness coming from high-energy explosions known as gamma ray bursts. The 50-centimeter diameter COATLI telescope was installed in 2016, and its  goal is to obtain high spatial resolution images at the limit of what the telescope design allows, which is currently work in progress with the telescope supplier. The three 1.3-meter diameter telescopes of the TAOS-2 project were installed in 2017, and have the scientific goal of studying the Solar System through a census of the small bodies orbiting the Sun beyond the orbit of Neptune, using cameras that take twenty images per second. Thanks to its wide field, the DDOTI project looks for the sources of gamma-ray bursts and gravitational waves by using six small independent telescopes of 28 centimeters in diameter each (two installed in 2017 and four in 2019). In late 2018, the one-meter diameter SAINT-EX telescope was installed, the first and, so far, the only telescope in Mexico dedicated to the study of exoplanets (Gillon et al., 2024). Since then, its observations have helped identify more than five extrasolar planetary systems through the planet eclipsing while orbiting its  star. In 2024, the 1.3-meter COLIBRÍ telescope was installed, with the aim to understand gamma ray bursts and gravitational waves by observing their behavior over time. Both TAOS-2 and COLIBRÍ are expected to complete their testing phase and begin routine observations in 2025. 

All the great observatories of the world struggle constantly to protect themselves from light pollution and radio emissions. The observatory at San Pedro Mártir is no exception. Despite these efforts, it is with sadness and concern that we see many astronomical observatory sites are being increasingly affected by this type of interference. It is everyone’s duty and responsibility, not only of the astronomical community, to protect the dark skies and fight against climate change to guarantee this natural resource so that future generations can be amazed by the marvelous night sky.

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