Astronomy is the discipline that studies celestial bodies, their distribution, formation and evolution, and also aims to predict what will happen to them. Thus, for example, when studying the Sun, the astronomer describes its movements, the amount of energy it produces and the fuel it uses; he also analyzes how it was born -like the rest of the stars- inside a cloud of gas and dust and, not satisfied with this, he calculates that it will live another 4.5 billion years.

Modern astronomy is called astrophysics, because researchers use physics to study celestial bodies. Physics is a discipline that seeks to explain natural phenomena as simply as possible. For example, it predicts that when a meteorite falls on the surface of the Moon, it will produce a circular crater whose size will be larger in diameter, the larger the size of the impacting body. Physics can also predict the orbits of celestial bodies, so astronomers can study asteroids and know in advance if one will ever hit the Earth.

Unlike other sciences where experiments can be done, astronomy is observational: it has to wait for celestial bodies to "do things". Fortunately, there are billions of stars to be analyzed, so new events are observed every day, and what happens in them can eventually be applied to others.

Astronomy applies the physics that is known here and now to the rest of the universe. If you discover that bodies reflect light and that for that reason they shine and can be seen like the tip of our nose, then you will know that the Moon shines because it reflects the light of the Sun and that the part that looks dark during its phases corresponds to its night, that is, where the light of our star does not reach it.

Galaxies, such as Andromeda, are conglomerates of a hundred billion stars, gas and dust. The light from this galaxy takes two million years to reach the Earth.

Most of the study of the stars is done by analyzing the light they emit or absorb. Astronomers can take images of celestial bodies to know their shape and also to analyze how they interact with radiation and light. In this way, they can find out what temperature they are at, what they are made of, or how fast they are moving.

Thanks to remote observations and careful analysis, astronomers have been able to find out that stars are spheres of glowing gas, which are grouped into stellar clusters called galaxies. They have also discovered that the distances at which celestial objects are found are enormous compared to our dimensions. They calculate, for example, that along the Earth's equator, there would fit 40 023 890 men holding hands, that along the equator of the Sun, there would fit 109 Earths, that in the distance that separates our planet from the Sun, there would fit 108 suns and that the distance to the nearest star is 824 000 times greater.

Astronomers observe celestial bodies to obtain data, but these are of no use to them as long as they do not interpret them, that is, as long as they cannot understand their meaning. Little by little, researchers have learned to obtain information about the light coming from celestial bodies by means of telescopes, which are like enormous funnels that capture light because, as we mentioned before, celestial objects are so far away that the light that reaches us from them is, in general, extremely faint.

Astronomy is also concerned with naming and classifying celestial bodies. The International Astronomical Union is divided into commissions where researchers from all over the world agree on the units, the names of objects and their catalogs. So, for example, they may be in charge of defining the longitude of the year, naming new satellites, stars, nebulae and galaxies that are discovered, or deciding the boundaries between constellations.

Some of the most important problems facing modern astronomy

Astronomy has directly explored the nearest bodies of the Solar System This is a task that astronomy will continue to do, because knowing our nearest neighbors allows us to know better the Earth and the functioning of the Sun, this will help us to better preserve our planet.

Astronomy has proposed a theory about the formation of the Solar System and others similar to it. Based on it, it has found that all stars are born inside clouds of gas and dust. Planets, satellites, asteroids and comets are formed from a disk of matter that is left rotating around newborn stars.

Astronomy has managed to understand how stars evolve, that their life depends on the amount of matter they contain; the less matter they have, the longer their life span. Sun-like stars live about ten billion years. Near the end of their lives they become red giant stars. Stars with much greater mass live only a few million years and end their existence in an explosion.

Astronomy has cataloged thousands of objects, including galaxies and quasars, which are the most distant objects known to exist. It has discovered what is known as dark matter, a substance that exerts gravitational pull on other objects, but does not interact with radiation.

Astronomy has proposed a theory to explain the formation and evolution of the Universe, that is to say, of matter, space, energy and time. It is called the Big Bang Theory and suggests that fifteen billion years ago energy, matter and space were formed, which evolved to form all the bodies we know today, including life.

Like any other science, astronomy continually modifies knowledge and proposes models to try to explain the observations. New physics, as well as different observations, allow us to modify theories to get closer and closer to understanding the workings of nature. In science, there is no absolute truth, but models that pretend to know what surrounds us.

By Julieta Fierro