What are they and what are the differences between stars, suns and galaxies. How they were formed, what they are. Summary.The universe is a set of galaxies and celestial bodies. It originated about 20 billion years ago, due to the explosion of a primordial atom, which by bursting released into the universe many particles of protons and electrons, which by condensing formed all the various celestial bodies.
GALAXIES
All the stars in the universe are grouped together in galaxies, that is, groups of stars. The galaxy in which we live is the Milky Way , which has the sun as its point of reference, and is made up of about 100 billion stars. Galaxies have different shapes, the best known of which are: elliptical, spiral and barred spiral.
STARS
Stars are celestial bodies that shine with their own light. They are gaseous agglomerates and produce a large amount of energy. The distance between stars is measured in AU. The magnitude of a star allows us to see its brightness. The absolute brightness of a star is the amount of energy it emits, while the absolute magnitude is the unit of measurement of absolute brightness. The spectrometer is an instrument that allows us to see stellar spectra, that is, the radiation of stars and their colors that are divided into 7 main classes and are: O, B, A, F, G, K, M.
SOLAR SYSTEM
The solar system has the sun as its point of reference. It originated about 5 billion years ago, thanks to the explosion of a star very close to us.
This explosion released dust and gas into the universe that condensed toward the center, and gave birth to various celestial bodies, namely planets, comets, satellites, and meteoroids. Planets have a rocky surface and are located between Mars and Jupiter. Comets are stars with a tail that move along an elongated trajectory. Meteorites are bodies that leave a luminous trail when they come into contact with the Earth’s gravitational field.
THE SUN AND THE EARTH
The sun is an average yellow star. The innermost part of the sun is called the nucleus. Its temperature is very high. After the nucleus there is the radiative transport layer, in which energy propagates by radiation, then we have the convective transport layer in which energy propagates through convective motions. Finally we find the photosphere, which is the external part that we see, formed by the chromosphere and the solar corona.
The Earth is part of a group of celestial bodies called the solar system. They influence each other due to the force of gravity, that is, the force of attraction exerted by the bodies due to their mass. All the bodies of the solar system are subject to the gravitational attraction exerted by the sun. The Earth has a spherical shape flattened at the poles, and this is due to the centrifugal force. The figure that best represents our planet is the geoid, and this is because there are both reliefs and depressions.
THE CONSEQUENCES OF THE EARTH’S MOTIONS
As we have already mentioned previously, the Earth performs two movements: one of rotation, and one of revolution.
The rotation lasts 24 hours and determines day and night. The sun illuminates only half of the Earth’s surface . The boundary between the illuminated part and the dark part is marked by the circle of illumination .
The passage from the illuminated surface is not abrupt, and can be witnessed by dawn and dusk, that is, in the moments of the day in which the sun is not present in the sky, but we still see its light retained by the Earth’s atmosphere. The revolution lasts 365 days and determines the various seasons. We have two equinoxes : the spring equinox (March 21) and the autumn equinox (September 23). Finally, there are two solstices : the summer solstice (June 21) and the winter solstice (December 22).
