The last decades have seen a proliferation of astronomical observatories all over the world. Since 2000 alone, some 80 new observatories have been built on land and several dozen telescopes have been launched into space. All this added to the hundreds of existing observatories that have seen their technology renewed. The United States dominates the account, accumulating around half of the world’s observatories, and in Spain alone we have almost two dozen . In addition, we currently have more than 30 telescopes observing the universe from beyond our atmosphere , with another ten planned to be launched in the next few years. But do you really need all these telescopes? Or could we get by with less?
You probably already imagine the answer we are going to give, although perhaps not the reasons. The answer is yes, of course, that they are needed and that building an astronomical observatory or a space telescope is not trivial. That you need the preparation of a detailed project with which to convince the institutions that are going to finance it of your need. Institutions that are usually quite conservative when it comes to delivering money. So why are they needed?
For two technical reasons and one human. The human problem is simply that not all countries or all observatories are willing to share their results with any scientist or organization that requests them, so sometimes it will be convenient to collect the data on your own. Furthermore, science requires a certain reproducibility . If your discoveries cannot be corroborated by another team, they will be of little use.
The technical reasons are more interesting. The first of these is quite obvious: a telescope , however large and sophisticated it may be, will only be able to observe a small part of the sky . A low-end telescope, the kind you can buy in a large commercial area, already has enough magnification to not be able to cover the diameter of the Moon in its viewfinder. In addition, deep sky objects , see incredibly distant nebulae or even more distant galaxies, are extremely faint from our position, so many times the telescope in question needs to collect their light for minutes or even hours to form an image in real time. the detector.
Therefore, if we intend to observe the entire night sky, we will need a large number of telescopes studying it. In addition, especially for telescopes on the ground but also for space telescopes with relatively low orbits, our planet limits their access to half the sky . Therefore we will need telescopes capable of pointing in all possible directions : north, south, east and west. That is why we have telescopes in New York, California and Hawaii (and in many other locations) within the United States, but also in Mexico, in Chile and Argentina, in South Africa, in Australia or New Zealand, in China or Japan and in the United Kingdom, Germany or Spain. Within Spain, the main observatories are in the Canary Islands and Andalusia , but there are also other important ones in Mallorca, Barcelona, Ávila or Valencia .
The second reason so many telescopes are needed is because none of them are capable of observing the sky in all its nuances . Different objects emit light in a different part of the electromagnetic spectrum . Stars like our Sun emit most of their light in the visible part of the spectrum , but cooler stars (such as Proxima Centauri ) will emit more in the infrared while much hotter stars (such as Gamma Velorum ) will also emit in the ultraviolet . But not only stars emit light.
Supernova explosions emit huge amounts of ultraviolet light and X-rays (which is light even more energetic than ultraviolet). X-rays are also emitted by the solar corona or intergalactic gas clouds that abound in galaxy clusters. Gamma rays , the most energetic possible electromagnetic radiation, are emitted around the most extreme objects in the universe, such as in the beams emitted by rapidly rotating neutron stars or in the accretion disks of supermassive black holes that dominate the nucleus of Earth. many galaxies.
In addition to cooler stars , planets orbiting any star also emit mostly infrared light. This is the light detected by night vision cameras, which is emitted by our body, for example, because it is at a temperature of about 36ºC. Microwave light can be found in the cosmic microwave background , but it can also be emitted in processes that take place in the atmosphere of some planets or even in comets . Radio waves have been detected coming from many different objects and even from the diffuse regions surrounding some galaxies. The famous photograph presented in April 2019 of the central black hole of the galaxy M87 was taken with radio telescopes, for example.
Also, not all of these frequencies can be detected from the earth’s surface. Our atmosphere is transparent at some frequencies, but completely opaque at others. For example, it allows visible light and radio waves to pass without much problem, but absorbs infrared light (hence global warming) and the ozone layer absorbs ultraviolet light (hence its disappearance was a problem). The atmosphere also quite successfully absorbs the most energetic frequencies, such as X-rays and gamma rays. For this reason, not only do we need a large number and variety of telescopes, but some may be located on the earth’s surface, but others must inevitably be located in space , outside the atmosphere.