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Sky Sphere

The phenomenon of sky as mentioned above. Humans in different parts of the world have observed it for many ages. Although people in ancient times did not have equipment such as cameras, they often had enough free time and patience to observe. and remember the gradual change in the sky for a long time and finally came to a conclusion similar to ours: the sky appeared like a huge sphere. which covers the ground with one half above the horizon and the other half beneath the horizon The observer will be at the center of this sphere. no matter where he goes on the face of the earth In the case of an observer such as an astronaut that floats outside the spaceship far from Earth He will see the sky around him. It is a large sphere that wraps around him, and stars appear as bright spots attached to the inner surface of the sphere.

Today, we know that stars are enormous globular globules of gas that are scorching hot, scattered in vast air. Some were floating alone. some were grouped together from two or more up to a cluster There are tens of thousands of members living together in a large system. by natural attraction to each other. The sky is a big sphere and the star is a bright spot fixed on the inner surface of this sphere. Therefore, it is an incorrect concept. It has many benefits in the study of astronomy. because it is the foundation of determining the position of the stars that we can see in the sky

This concept is still in use. This large sphere is called The celestial sphere and has the properties we define as follows:

1. The celestial sphere has a very long radius. It is mathematically estimated that the radius of a celestial sphere is infinity.
2. No matter where the observer is going, it will be on the earth. in the center of the world? in outer space He would feel as though he was always at the center of the celestial sphere.
3. The stars, planets and sun are considered to be on the inner surface of this sphere for the planets, sun and moon. Moving on a sphere, the star may be considered static. and moving with the rotation of the celestial sphere
4. The celestial sphere revolves around itself every day. as already mentioned
5. Observers who live in different sub-districts If the telescope is pointed or aimed at the same star, the line pointed or aimed is a straight line that is parallel.
6. The distance between two objects (eg two stars) on the celestial sphere, measured by measuring the angle of which the radial line from the center. For example, the distance between Dubhe and Merak is 5°, or the diameter of the Sun as it appears on the celestial sphere is 1/. 2 ° etc.

The rotation of the celestial sphere

Let’s say an astronaut travels out and floats still. in a place far from the earth, moon, star or any planet As he looked around, the vast expanse of space contained stars. spreading far and wide until it was only seen as a bright spot would appear to him like a gigantic sphere enveloping him around the star that lit up. will appear brighter depending on the actual brightness and distance. The distance of that star is compounded if he is really still.

Without any movement or rotation, the sphere, the sky that appeared before him, would remain stationary forever. as shown in Fig. A and B.

If an astronaut swings a limb or body movement in a way that made him start to revolve around himself Principles of Relative Motion This will make him not feel that he is spinning. Instead, he would see, as if a celestial sphere with a star attached to it, revolved around him. in the opposite direction from where he was spinning. As shown in Figures C and D.

These criteria used to describe the appearance of the sky revolving around an observer at Standing on the surface of the earth because of the Earth’s rotation around itself. We already know that our Earth is almost spherical in shape. which has an average radius of 6,371 kilometers, humans and all living things arise and live on the surface of this sphere. an observer watching the sky By itself is located in the direction of the center of the Earth (vertical) as in the top picture.

The daily rotation of the Earth. will take the observer rotates around the axis of the earth as well Observers assume themselves and the ground on which they stand. no movement Because it is difficult to notice. and think directly He therefore saw that the sphere the sky revolves around him and the axis which passes through him and is parallel to the axis of rotation of the Earth. equal to the rate at the world revolve around oneself but in the opposite direction.