تعاريف ومصطلحات أساسية

We will know in this section some basic terminology which we will address in detail in the next door.
1. Earth and the solar system:

We live on the surface of the planet. And although this may seem strange at first sight, the planet's spherical shape already! There are several proofs of this simple example, note when the ship away on the horizon, we see first the disappearance of the lower part of them and then the upper part gradually disappears. This is clear evidence of the uneven ground. Also, the earth revolves around itself, and this is the reason for the difference of night and day, and why they may make us think that the sun is orbiting around the Earth! It is strange that although the Earth is orbiting the sun and not vice versa. And there are several indications that, although it is not simply evidence of a spherical earth. As human beings since ancient times knew that the earth is spherical, but they thought for centuries that the sun and other planets all revolve around the Earth. We shall confine ourselves in this section by saying that the rotation of the hypothesis we expected the sun around the earth in contrast and make the calculations extremely complex.

Star and the sun is no different in nature from the rest of the stars that you see at night. The only difference is the dimension. As the closest star to us after the sun is located at a distance of approximately 250,000 times the distance between us and the sun! And for this it during the day, sunlight dominates the light of the rest of the stars, and we can not enjoy seeing them only by the night and despite the fact that many of the brightest stars most of the sun.



And our planet belongs to a group other planets revolve around the sun. And this group, called the solar system, consisting of nine planets, including Earth. And are (from closest to furthest in relation to the sun): Mercury, Venus, Earth, Mars, Jupiter, Saturn, Auros, Neptune and Pluto. And some of these planets have moons or more spins around. The Earth has one moon, while Mars has two satellites. It also contains the solar system on several other objects eg planets and comets car ... And planets are different from the star through nature and through its movement in the virtual sky.

Definitions of key terms

2. Milky Way, our galaxy:



As we said earlier, the sun in nature like all other stars. And belong to all the stars that we see with the naked eye at night, including the sun, to collect a great star-shaped spiral galaxy, which is called Azm about 100 billion stars. It also contains the galaxy as well as objects other than stars, Calcdm example. And the universe contains countless galaxies that may be similar to our galaxy or not. And called our galaxy the "Milky Way" because of its arms spiral appears on the surface of the earth and as a way to structure! And the solar system does not occupy a central place in the galaxy.

1 س.ض. = 63000 و.ف.

Units of measurement dimensions and times:


Changed and the units of measure with the dimensions change our view of the universe. At the level of the solar scientists have known "astronomical unit" and is the medium distance between the Earth and the sun.

1,. P. = 150 million km.

Thus Vkkb Mercury spins at a distance of approximately 0.4 and. P. Pluto from the sun while going about 40 and. P. From the sun.

To calculate the dimensions of the stars closest to us, scientists have learned and unity "light year" and is the distance light travels in a year. Since the speed of light, the secret of 0 = 300000 km / s is:

1 hr. Z. = (300000 × 1000) × (365 × 24 × 60 × 60) = 9500 one billion km.

1 hr. Z. = 63 000 and. P.

The nearest star to us after the sun is just about 4.3 o. Z. From Earth.

And at the level of what the galaxy far, used unit Albarsk. And we will come back to talk about the origin of this unit and the cause of her coming in the doors.

1 b. O. Q = 3.26. Z.

And a radius of the Milky Way about 10,000 b. O. And about the solar system by 8000 b. O. From the center of the galaxy. The closest galaxies to our galaxy away from us by nearly 50,000. Q. And at the level of the universe, estimated dimensions that can be accessed through the monitoring of about 4000 million b. O.

For the units of measurement times are day and year. Today marks the time of the earth's rotation around itself. And the time of the year represents the rotation of the Earth around the Sun and is equal to about 365.25 days.

Thus the time of rotation of Mercury around the sun 88 days, while Pluto is in its 250 years! And a turnover time of the solar system around the center of the galaxy about 200 million years old. And is currently estimated age of our solar system some 5 billion years and the age of the universe about 14 billion years old.