On a spectacular plateau in the heart of the alpine massif, at an altitude of 2550m, 12 of the most precise parabolic antennas on the planet are located. This is NOEMA, the most powerful set of radio telescopes in the northern hemisphere working in millimeter waves. This large scientific facility is the fruit of 40 years of cooperation between CNRS (France), Max-Planck-Gesellschaft (MPG, Germany) and IGN (Mitma, Spain). Built and operated by the Institute of Millimeter Radio Astronomy (IRAM), this array of radio telescopes, working in coordination with the large 30-m radio telescope at the IRAM-IGN station at Pico Veleta (near Granada), has already been the source of important discoveries, and is now poised to make observations that will continue to revolutionize the study of the universe, in particular studies of the formation of planets such as the Earth. See.

Black holes are on the crest of the wave, and it is largely thanks to them that astrophysics remains at the centre of the scientific news. Three years ago, while the 2017 Nobel Prize was rewarding the detection of gravitational waves that betray the collisions of stellar-mass black holes, the Event Horizon Telescope (EHT) was making the groundbreaking observations that would lead to the first image of the proximity of a supermassive black hole, a result that has already received numerous international awards. And we had not finished celebrating these achievements when the Nobel Prize in Physics 2020 was awarded to three scholars of these objects that we are all so passionate about. The National Geographic Institute has been at the forefront of several of these events. See.

The many visitors to the Real Observatorio de Madrid are usually impressed by its amazing historical and artistic heritage. But few are aware that, in this marvellous site of the National Astronomical Observatory, as well as in other infrastructures of the Observatory, world-class astrophysics research is carried out. With studies ranging from the formation of stars and planets to the properties of black holes, the Observatory today combines a fascinating historical-artistic tradition with pioneering astrophysics. See.

Since the first civilizations, the humankind has been fascinated about observing the night sky. This fascination suffered a first shock with the invention of the telescope by Galileo in 1609, and it has been continuously developed by further enhancement of observing capabilities. These have nowadays led to the construction of giant ground-based telescopes and space laboratories. Every day brings new discoveries about the cosmos which confirm that astronomy, in addition to being one of the most ancient sciences, is one of the most forward-looking as well.

The National Astronomical Observatory (OAN), since its establishment in 1790, has been participating in the great scientific adventure of astronomical research, not only by performing observations, calculations and studies to better understand the Universe, but also contributing to the outreach of this science that we are so passionate about..

This little book constitutes a new effort of the Observatory, to spread knowledge of general interest in astronomy. This edition was developed between March and May of 2020, during the grisly days of the COVID-19 pandemic, when all the Observatory staff were in home-office mode. See.

How was the distance to the Sun determined? How was Mercury’s orbit anomaly, which was the first phenomenon explained using Einstein’s general theory of relativity, discovered? How were most of the planets’ orbits which rotate around other stars discovered and characterized? The answer to these three questions is the same: by means of transits.

The measurement of the long distance from the Earth to the Sun was a real challenge for the ancient astronomers, only achieved in the modern age through the combination of Halley’s ingenuity, new instruments and the enthusiastic participation of hundreds of professional and amateur astronomers in the observation of Venus’ transits. This constituted the first scientific collaboration performed on a worldwide scale which was not exempt from adventures and tragedies. For its part, the observation of Mercury’s transits revealed an anomalous behavior of its orbit. This behavior would be the first of these phenomena explained using the new general theory of relativity. Nowadays, the planets’ transits facing stars around which they rotate, represent the most effective approach to discover and characterize them. See.

Selection of outreach articles of the Madrid Royal Observatory’s Almanac published between 2006 and 2016. It is available in electronic format to increase a new visibility and to keep it cost-free. These were selected to cover several theme areas that show some of the many aspects of the current research in Astronomy. See.