The universe is the entire material world, diverse in the forms that matter and energy take, together with all galaxies, stars, planets and other astronomical objects.
Explanation of the term
The universe is so big that its dimensions are hard to imagine. The universe studied by astronomers is a part of the material world that can be studied by astronomical means that correspond to the achieved level of development of science (often this part of the universe is called a metagalaxy), stretches for 1.6·1024 km and no one knows how big it is beyond the visible parts
In the narrower sense, the universe is understood as the world of celestial bodies with the laws of their movement and development, their distribution in time and space. Matter in the universe is distributed extremely unevenly, a large part of it is concentrated in individual more or less dense cosmic bodies: galaxies, stars and nebulae. Distances between individual objects are usually measured in light years, i.e. the distance light travels in one year (it takes more than 4 years from the Sun to the star closest to us).
The science of astronomy studies the celestial bodies that make up the universe. Astrophysics tries to understand the phenomena and processes occurring in the universe. Theories of the evolution of the universe and hypotheses of its further development are developed within the framework of cosmology. The scientific study of the universe is based on the so-called cosmological principle, which states that the laws of nature are the same throughout the universe.
Structure of the Universe
Among the heavenly bodies, the stars stand out the most because of the light they emit. Stellar matter is in the state of plasma — an electrically conductive magnetized medium. In the bowels of the stars, the temperature reaches tens of millions of degrees. The evolution of stars includes the following phases: a protostar, the formation of a thermonuclear focus in the center of this formation, the main phase of hydrogen burning in thermonuclear reactions, the transformation of a star into a red giant, and then into a white dwarf (for stars similar to the Sun), the collapse of massive stars with the explosion of "supernovae" ” and the emergence of neutron stars and collapsers — “black holes”.
Some stars have satellites - planets or massive bodies similar to them and together with them form systems similar to our Solar System.