NTRODUCTORY TEXT / Astronomical Observatories

The oldest astronomical observatories were built around 2300 BCE as simple platforms that allowed an unobstructed view of the sky. The Alexandria Observatory—which was created in 300 BCE and existed for over 500 years—had already been equipped with instruments to measure the position of the stars. But the invention of the telescope dates back to 1608. From this date on, several observatories equipped with these devices were built, such as the Paris Observatory (1667) or the Royal Observatory, Greenwich (1675), which can be considered the first observatories in modern astronomy.

Astronomical observatories today are technological infrastructures designed to contain telescopes and other instruments for astronomical observations. Ground-based observatories—those we have built on the surface of the planet—are usually located in high places with little light pollution, low humidity, lack of wind, and clear skies. The growth of cities has pushed these large infrastructures to remote sites precisely to guarantee these conditions. An example of this can be found at UNAM: the observatory founded in 1867 in the facilities of what would soon become the National Preparatory School, had to be relocated due to the growth of the city, first to the Chapultepec Castle in 1878 and then to the Palace of the Archbishop in Tacubaya in 1908—the Tacubaya Observatory, near where the Observatorio station of Mexico City’s Metro is located today. This exodus of observatories happened all over the world, leaving only historical memories within the cities.

Relocating observatories to dark places is not sufficient to obtain the necessary astronomical observations because we want to measure electromagnetic radiation in all wavelengths—not just in visible light—to have a more complete knowledge of the emitting source. However, life on Earth is sustained because our atmosphere protects us from some of this radiation. Therefore, what is a benefit for the existence of life becomes an impediment to make astronomical observations in certain ranges of the electromagnetic spectrum. Nonetheless, as we know, humankind transforms difficulties into challenges. In this case, we have developed space observatories consisting of infrastructures that rotate around the Sun, outside our own atmosphere. Moreover, observations from space do not suffer from the distortions that our own atmosphere cause, providing sharper images even when using telescopes of the same size. Finally, observatories with intermediate qualities are the so-called airborne observatories, devices like airplanes or probes that make observations at a high altitude, above a part of the atmosphere.

Observatories are also historically differentiated by the type of telescopes they use: nighttime, daytime, and radio telescopes. Nighttime telescopes are only used when the Sun does not illuminate the sky; their purpose is to study other stars. Daytime telescopes are intended precisely to the study of the Sun, the closest example we have of a star. Radio waves are captured with huge antennas like the ones used in terrestrial telecommunications, known as radio telescopes. Moreover, the new era of knowledge makes remarkable advances requiring new observation techniques such as the detection of gravitational waves.

The following includes a detailed description of astronomical infrastructure in which UNAM has a key role. Of course, these large and expensive modern infrastructures require international consortia for their financing and proper functioning. This need, among others, makes astronomy a science that thrives on international collaboration as the only way to guarantee scientific progress.

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