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Twentieth century astronomy and cosmology

Today’s image of the universe and knowledge of its components owe a great deal to quantum mechanics and the theory of relativity, the two fundamental physical theories that were formulated early in the twentieth century.

Astronomers, or rather astrophysicists, discovered the source of the stars’ energy and began to understand the process of their evolution. Cooperation between observers and theorists has led to the identification of an unusual stellar menagerie which is formed not only by stars similar to the Sun, but also by supergiants of a diameter that may even be equal to the size of the Solar System, or such exotic objects as white dwarfs, neutron stars and black holes which constitute the last stages of the life of stars.

Einstein’s theory of gravity, applied to the entire universe, allowed the construction of models of the expanding universe, which were confirmed by observations of the escaping galaxies, and later by the discovery of cosmic microwave background radiation which homogeneously fills space. Thus the Big Bang model was created, thanks to which we can now understand what the evolution of the universe has looked like during 14 billion years of its existence. This model, together with the theory of stellar evolution, provides an answer to yet another very important question: where the chemical elements, which are parts of the bodies of the inhabitants of Earth, came from.

The twentieth century brought an unprecedented development of methods of observational astronomy. First of all, man learned to understand and interpret the universe in the whole range of the electromagnetic spectrum. Optical telescopes are still very important research tools, but they are now accompanied by radio telescopes. Infrared and ultraviolet astronomy, as well as X-ray and gamma ray astronomy are becoming more and more advanced. Thanks to these new methods it could be established, for example, that our Milky Way is in fact a spiral galaxy, one of many in an expanding universe.

Astronomers of the twentieth century did not stop studying the nearest cosmic backyard, namely the Solar System. Very important results were obtained by using automated space probes, some of which even managed to land on the surface of such celestial bodies of the Solar System as the Moon, Venus, Mars, Jupiter, and Titan – one of the moons of Saturn. Studies of the Solar System gained an interesting perspective since astronomers started finding planets orbiting around other stars.

Today’s image of the universe emerged thanks to the discoveries made by many eminent scholars, astronomers, physicists, and cosmologists, who are too many to list even partially in this short essay. It should be noted, however, that the basis for current studies of space is a common assumption: that the Earth together with its star, the Sun, situated in the borders of a certain spiral galaxy, which is constantly growing away from billions of other galaxies in the expanding universe, does not hold a privileged place in the universe and that another observer who would be orbiting around another star, which would even be a part of yet another galaxy, would perceive the universe in the same or a similar way as we do. This assumption is called the Copernican principle.

Jarosław Włodarczyk
Institute for the History of Science
Polish Academy of Sciences

Further reading

  1. D. Leverington, A History of Astronomy from 1890 to the Present (London, 1995).
  2. M. S. Longair, The Cosmic Century: A History of Astrophysics and Cosmology (Cambridge, 2006).
  3. O. Struve, and V. Zebergs, Astronomy of the 20th Century (New York and London, 1962).