Topic 2

16/08/2021

There are always stars on the celestial sphere or vault. A man who sits down and sees them, will always see that the stars are moving, will see that the stars start from the bottom and come up to the highest point, then let down the sun horizon. From this we deduce that the stars do not change each other's position, but their whole rotates from east to west around us. We will always notice that the same thing happens, so we will call: Diurnal motion what happens. The diurnal motion is the rotational motion of the Earth. Then we move on to the stars which are either planets or stars, but most likely stars, in any case they are celestial objects. It was discovered that there are stars circulating between the stars, the fact that they are not static, these stars were called: "planets". In the past, planets meant a wandering star. Maybe sometimes you look at the sky and see the stars. You see, some are at almost equal distances, no, it's not. The stars are far away and not so close! There are stars that are close and form constellations such as: Big Dipper, Little Bear, Hercules, etc. There are also stars that are very separated from each other and do not form anything. There are so many stars and you can't name them all. Then it was decided that bright stars like Sirius should have names, and the least bright ones, one letter from the Greek alphabet followed by the constellation in which it is, so we can say: Star "a" in the constellation Hercules. This used to happen, now the stars are sorted in catalogs according to its positions. However, the star does not change its position, but does the celestial vault do it? Think that you are going from west to east or vice versa and you see the same vault, but some stars or celestial objects disappear. The apparent celestial vaults that are seen from diphritic locations go into a single sphere or spherical surface on which all the constellations, stars and celestial objects are located and as we said above, the Earth is at its center. It is called as we have said before: The celestial sphere being an apparent sphere. This means that the celestial sphere makes a diurnal motion. If it does so from east to west, then in astronomy it is called: retrograde meaning. That is, in the negative trigometric sense => it has uniform motion.