Everybody knows that Earth rotates around itself and around the Sun, but times ago, nobody thought that. Even more, nobody accepted this fact that’s because we cannot feel it, despite the fact that the linear speed is 350 m/s. The first time talked about the Earth rotation was in Ancient Greece, but this opinion wasn’t accepted. For centuries and centuries this idea has remained in silence. The one who accepted and supported this idea based on his theory was Nicholas Copernicus, the founder of heliocentric system (1543). Despite the fact that he supported this idea, he didn’t have facts to prove it. The most convincing evidence was given by French physicist L. Fuko (1851), using a pendulum. It is known that the pendulum retains its shaking plan, so using the centrifugal we rotate the pendulum. We will see that it continues to shake in the same plan.
Fuko founded that the pendulum shaking plan has been rotated depending on Earth surface, which proves that Earth rotates based on the pendulum shaking plan. If you are on poles, this rotating period lasts one day and night, but going toward the Equator, the period lasts more. Another fact which proves the Earth rotation is the avoidance from the vertical of the objects that are falling. There are lots of sample proves that you have learned on geography. The portrayed axis around which it is thought that the Earth rotates is called Earth Axis. It spikes Earth in two points, which are the Earth poles. Today these poles are in Frozen Ocean (Nord Pole) and the other one, in Antarctica ( South Pole).
The rotation period of Earth lasts one day (one day and night). It rotates from West to East. The sky looks like a middle sphere which surrounds the Earth. It easy understood that it does exists another half, so the sky seems like a sphere, that means that the stars seems like have the same distance. This comes from the fact that we cannot understand which star is nearer. Even for the Sun and the Moon we think that they are in the same sky, despite the fact that we know they are nearer the stars. But which is nearer, the Sun or the Moon? How could you understand this? Do you have any sign? Even the clouds are in the same sky as Sun or Moon, but we understand that those are nearer.
If we see the sky at night we see so many stars putted there without any rule. There are not too much stars seen with free eyes. In a night without Moon we can see with our eyes 2500-3000 stars, pretending that this is the number of the stars seen in the other half of sky, we can say that there are not more than 6000 stars seen with eyes. The stars doesn’t look the same, some of them bright too much, some no. Those look like little white, red, azure and yellow lights. You have to know also, that stars may not look the same if you see it next night.
It usually seems like the star changes its color, its bright, even its place. All of these are called “glimmering”. This is caused because the star light before arriving in our eye perception has to pass through the atmosphere. The planets do not blink, those look like little discs. Even during the day there are stars in atmosphere, but we cannot see those because their light is disappeared from the sun lights on Earth atmosphere. If there was no atmosphere we may see the stars even during the day and the sky we be black. It is learned since old times that the stars do not move. To facilitate the orientation, the stars are stacked in Constellations.
The Constellations are named to facilitate recognition of the stellar sky. There exist maps so it may be possible to learn the Constellation positions and orientations. Most of their names have remained from ancient Greeks. Homer mentions most of them as: Andromeda, Orion, Twins etc. Those Constellations are seen from our countries. But there are lots of Constellations that cannot be seen by us, which are called : Indian, Pomp, Microscope etc.
Today we call Constellation not only a given group of stars which create a given figure but we call also a given part of the sky with everything that is into it. The entire sky is divided in 88 Constellations. There are used some astronomic notes about Constellation’s names which are known in all over the world. For example, UMa is used for Ursa Major. Inside the constellation the stars are signed with Greek letters, beginning from the most shining star till the less one. So, the Polar Star is the “a” of Ursa Minor (a UMi). There are also exceptions from this rule.
Lots of stars have specific names, for the weakest stars are used Latin letters, numbers, etc. In those parts of astronomy which study the positions, doesn’t matter the distance between Earth and other celestial body, but the direction it is seen from. It also, doesn’t matter the real distance between two celestial bodies, but the angle created between them. That’s why we will think that the celestial bodies are placed in the same sphere.
Attention!! It is not true, we will only assume that they are placed in a sphere. The sphere which has as a center, the observer eye, ands with an indefinite range where are reflected all the celestial bodies, is called celestial sphere. This visualized sphere is just the sky in daily life. The Earth is smaller, compared with the sky, that’s why we paint it as a point.