The Earth might seem a big planet to the people that inhabit it, but compared to the Sun, it is approximately 109 times smaller. No matter how huge the Sun would look, it is tiny compared to the solar system, which seems small to the distance to the next star. In the Milky Way alone there are over 100 billion stars, but the existence of hundreds other galaxies is already confirmed. Cosmology is the science that studies the entire Universe. The word derives from the Greek cosmos-, meaning world or universe and –logos, which stands for logic, word or study.
One of the well known theories of the formation and evolution of cosmos is the Big Bang. It considered the universe to have formed at a single point in time, and increasingly evolving over a 13,8 billion years time span, to the present. The discovery of the microwave background radiation in 1965 generated the concept behind this theory.
At the beginning, the universe is considered to have expanded in a rapid scale, which generated starting conditions for many galaxies. A second evolutionary step is considered to be the nucleosynthesis process that released many elements into the cosmic space. When the first clusters of atoms started to attract one another, it created regions in space with higher mass density, becoming the earliest stars. The low density regions helped the organisation of the primitive galaxies, cluster of galaxies and superclusters. These are bound together by the gravitational forces, that leave gaps.
Right now, it is considered that dark matter and dark energy are the fundamental components of the Universe. This space that is poor in elements is the dominant 96% of the mass of the Universe. Now, many scientists put great efforts and time into studying and understanding the laws of physics behind these components.