المجرات أكبر المجموعات النجمية .. كتاب في سبيل موسوعة علمية .. الدكتور أحمد ذكي

Galaxies are the largest star clusters

The largest star groups are galaxies.
They are worlds apart.
And each of its worlds is composed of enormous numbers of stars. We will limit the statement and go into describing a galaxy from it. Who is more deserving of mention than our own galaxy, where we live, our earth lives, and our star lives, the sun? You will see that, like our galaxy, all other galaxies are.

- Our galaxy:

They called it the Milky Way.
The Greeks thought that one of their gods was breastfeeding while she was sleeping, and the milk flowed from her breast onto the patch of sky, while it was black at night, and it became the galaxy. Imagination and what imagination!!

As for the Arabs, they called it the Milky Way. Al-Tabban is a fig seller. They were empty, as if the Milky Way had carried their tree above the sky
Some of them fell until they filled the road, and thus the galaxy was created. Our galaxy is the stars that fill our eyes at night, and the sky is covered with it just as a judge wraps his scarf when he sits on the bench.

You ask: Where are the other galaxies? .
The answer: It is from the distance in the sky, and from the smallness
In the image thrown onto the net, the eye of the beholder even ignores its existence.

We go back and say: The stars in the sky that fill your eyes at night are the stars of our galaxy. As for the rest of the galaxies, they are the most, and in terms of global existence they are the most and the most numerous, to the point that we can almost say that they are all. These galaxies do not attract the attention of the observer. The observer can only see three of them with the naked eye.

Our galaxy, the Milky Way, consists of various groups of stars with a mass of about 100,000 million suns.

As for the shape of our galaxy, it is the shape of a loaf, round and dome. Some people liken it to two fried eggs, placing the back of one on top of the other. In its middle is a thick core, and it rotates with its stars around an axis perpendicular to the middle of the core, so it takes the shape of a spiral with two wings.

The length of our galaxy from end to end is about 100,000 light-years, or in miles it is about 6 million million x 100,000 miles, and its thickness is 20,000 light-years, or one-fifth of that length.

Our sun is located in this galaxy, about 25,000 light-years from its center. Therefore, the galaxy completely surrounds our sun and our Earth, so if you look from the surface of the Earth to the sky, on a dark night, you do not see any of the stars in the galaxy, except some of the stars in the sky. Others are on the other side of the earth. While you are in the north of the earth, you do not see stars from the sky that people who live in the south of the earth see.

- Maps and maps:

Geographers are accustomed to drawing maps of the Earth showing the locations of people, seas, mountains, rivers, and deserts.

They made a ball representing the Earth, and drew a circle on it
They called it the circle of the equator, and they made two poles on the sphere, a north and a south, and connected them to an axis that is the axis of the Earth, and it rotates on it.

Astronomy has revealed where this axis would point if we shot it to the sky, to the north. We knew that it meets the sky near the well-known polar star, and for this reason it is called Polar, and it is a star in the constellation (Ursa Minor). Just as we set the Earth's axis north, we set it south, so it met a point in the sky in the south. Since we have taken these two points, in the north and south of the sky, as the poles of the sky, in imitation of the Earth’s poles, we have come to the circle of the Earth’s equator, so we extended its surface from its edges until it met the sky on its sides, cutting it into a circle that we called the Celestial Equator.

Since we have a sphere in the sky that has two poles and an equator, we have called it the Celestial Sphere. We also called the globe the Earth, and the two spheres are united by one axis whose vertex meets approximately at the pole star, as we mentioned.

And we came to the galaxy, our galaxy, the Milky Way, and we saw it in the form of a domed disk with a central dome, with flaring edges, so we took the level of the disk as a level, and extended it from its edges, so it met the edges of the sky in a circle that we imagined and called the galactic equatorial circle after the galaxy.

It is a circle whose plane intersects the plane of the aforementioned celestial equatorial circle at an angle between them of 62 degrees.

Since the galaxy had an equator, it now had two poles, and they connected the poles with lines of longitude, so they made lines of latitude with the lines of longitude. In this exaggerated ball, they placed every star in the galaxy, every group of stars, and every constellation.

Astronomers have drawn a comprehensive map of our galaxy, including its equator, and its longitude and latitude lines, and they compiled it by including photographs they took of the galaxy, so it is as if it was viewed by an observer from the sky outside of it.

(Part of our galaxy, the Milky Way, contains about 100,000 million stars)