UNIVERSE:
MAN’S HOME. THE OBSERVATION OF THE SKY THROUGH THE CENTURIES

Through the centuries the sky sight, as well as the mentality and technological evolution, has been extended: if once it concerned everything we could see with the naked eye, now it can reach the furthest borders of the universe. In the earliest time people observed the sky in order to measure time, orient themselves and because of religious reasons. Watching the skyline they saw the Sun, the Moon, the fixed stars and some planets.
THE SUN was seen as a big, burning and shining ball which crosses the sky bringing light and heat. Often associated with the god of life, the Sun beat day and night and, with astronomical observatories you could know fiom his position in the sky, the exact day and month.
THE MOON the brightest celestial body in the night sky caused a lot of discussions about his nature: someone thought it was made of the same elements as the Earth and that life was possible there; according to the Aristotle’s theory, instead, it was the border between the sub lunar world (the Earth and the internal planets) and the super lunar world (the fixed planets and the external planets).
THE PLANETS. Thanks to the careful observation of the sky, the ancient astronomers were able to distinguish in then night sky, bright points which moved faster than the fixed stars and always on the same level. Those bright points were defined planets, orbiting round the Earth -according to Aristotle’s geocentric theory- on a level called ecliptic; at those times you could see: the internal planets (Mercury, Venus, Mars, and among the external one, thanks to their great brightness, Jupiter and Saturn. The identification of their satellites or the observation of their characteristic was impossible because of the inadequacy of men’s instruments, simply the human eyes.
THE STARS in those times, as nowadays, appeared like bright points, incredibly far and with different intensity. According to the ancient astronomers they were “hanged” on a crystalline sphere, as for the planets, which represented the border of the universe. The European culture received the Aristotle’s model by inheritance; it was based above all on three principal items:

1)The sky is immutable
2)The stars have been and will always be fixed
3)The celestial bodies move with a uniform rotary motion.

This model was accepted for one thousand and five hundred years, even though some changes were made by ToIomeo in the III century A.D. In his opera “The Almagesto” he gave, a detailed model of the universe pccording to a geocentric vision and was the first one who was able to explain the
retrograde motion through the epicycles theory.
The scientific revolution was necessary to change the way to observe the space around us. If Copernico, Kepler, Brahe, GaIiIeo and Newton changed the attitude towards universe, new technologies allowed new discoveries.
From that time on the instruments improved very much allowing the astronomers to find answers and new questions about the origin, the evolution and the fiinctioning of the universe; new branches of astronomy, such as cosmology, radio-astronomy, astrophysics, spectroscopy, were opened, and the sky vision is very different from the ancients’ one. As regards the distance, we can notice that the ancients’ universe was very small in comparison with our current knowledge; men’s house is extending continuously.
THE SUN AND THE STARS the sun was recognised the centre of the Solar System; it was anything but a normal star, medium sized, round which the planets orbit. The stars were defined like the nuclear power plant which transform their mass in energy, according to Einstein’s relativity law, through the reaction ofnuclear tusion. That reaction begins as soon as the core reaches very elevated temperatures and pressures, because of the contraction of a cloud of dusts and gas, due to the force of gravity.
The stars can be classified not only according to their brightness (Tolmeo inserted them in magnitude ranges) but also according to their chemical and physical composition; thanks to
spectroscopes and radio-scopes we can distinguish: main series stars, red giants and super giants, white and dark dwarf neutron stars, variable stars, pulsar, quasar, black holes. GALAXIES this word is completely new for the ancient astronomy: the stars, in reality, aren’t diffised uniformly in all the universe, but they are concentrated in some areas. Galaxies are then star clusters round which other planets can orbit in systems similar to the Solar one. THE MOON it’s the only extra-terrestrial ground visited by a man. The careful astronomical observation allowed us to state that the lunar material is similar to the Earth one and that there’s no life on our satellite. The motion and the lunar cycles analysis allowed us to understand phenomenon like tides.
THE PLANETS the new equipment for observation and the artificial satellites allowed us to find other new planets such as Uranus, Neptune, Pluto and other satellites, and to study their chemical composition.
Among the most important new branches of science started in the last century, we can underline:
-SPECTROSCOPY has helped astronomers to define the object that can be observed. With the spectroscope, discovered by Kirchoff and Bunsen, the light was seen to be divided as a prism.
The discoverers understood which elements a star consisted of and that there were some emissions that weren’t visible by human eyes.
-COSMOLOGY started in the 20h century in order to study the origin and the evolution of the universe. Hubble’s theory says that all the matter was concentrated on a single, hot and dense point fì-om which explosion universe took place.
-RADIOASTRONOMY started in 1953 when Jansky discovered a cosmic basic radiation: quasar.
Quasars are the farthest and the oldest objects that anybody as never had news of
-ASTRONAUTICS has allowed men to go to the Moon in 1968. After that satellites had been launched on the S u i on the Moon and on other planets.
Satellites have sent photos on and dates on to the Earth. Ail those steps have allowed us to better know the universe, our largest house.