In ancient Egypt, the Milky Way was called "the Nile in the Heaven".

At that time, if you looked in the south from somewhere near a pyramid,
the Milky Way looked as if it had been connected to the Nile.
The Milky Way has been likened to a river all over the world.

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It was called "the River in the Heaven" in Japan, "the Ganges in the Heaven" in India,
and "the Silver River" in China.

A legendary of the Star Festival came from the sentiment to bright stars located on both
sides of the Milky Way in China.

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On the west side of the Milky Way, Orihime, a daughter of God of Heaven, was weaving at her loom.

Her father, who thought that Orihime would be happier if she married, went to find a bridegroom.
And, he met Hikoboshi, who was taking care of a cow on the east side of the Milky Way.
Father was pleased with Hikoboshi very much, and decided to join the two in marriage.

They happily married and Father delighted. However...
The couple did nothing but play and did not work at all.

Father got angry and said to them.
"You two should live separately on the east and west sides of the Milky Way as before!"
Water sprang out between the couple to be a river in just about no time.
The river was getting bigger and bigger to separate them.

Thus, the couple lived separately on the east and west sides of the Milky Way.
Father could not bear to see Orihime, who was crying every day, and said to her.
"If you work as hard as before, I will allow you to meet him once a year at the night on July 7th."

The couple came to work hard in expectation of meeting each other on July 7th.
And on July 7th, the couple had a once-a-year date crossing the Milky Way.
It seems that Chinese people do not have the custom of having Star Festival decoration.

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In English, it is called the Milky Way.
The origin is said to come from the Greek myths.
When Hero Hercules was still a baby, Hermes, God of messenger, who considered
making Hercules immortal, let the baby suck the nipples of sleeping Goddess Hera.

Hera, who was surprised and awaked, thrust the baby away.
But milk, gushing out from her breast Hercules sucked strongly, splashed to the sky.
And it is said that it became the Milky Way.

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Well, is the Milky Way really a river or a way in the sky?
At the beginning of 17th century, Galileo Galilei, an Italian astronomer, watched the Milky Way
through his own-made telescope, and found that the Milky Way is a cluster of many stars.

About 150 years after the discovery of Galileo, William Herschel, an English astronomer,
studied how stars are scattered by counting them sedulously.
As the result, he came to a conclusion that stars gather discoid to form a nebula.

Herschel could only count stars that he could see with his telescope.
Since he did not count those that could not be seen because they were too far,
the stars counted by Herschel were only part of the whole.

Afterwards, the efforts of astronomers and the progress in telescopes allowed us to view distant stars.

And it was revealed that the Milky Way is a view obtained when the Galaxy,
a large group of stars, is seen from the inside.

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There are many galaxies in the universe.
Famous ones include the Andromeda Galaxy and the Sombrero Galaxy.
The galaxy where our solar system belongs is called the Milky Way Galaxy or Our Galaxy
for the differentiation from other galaxies.

Well, let's go on an expedition to trace a secret of Our Galaxy!
First of all, let's get off from the earth at a dash!

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Now, we are in the distance of more than 10,000 light-years from the earth.

We are now seeing Our Galaxy. It is said that there are about 200 billion stars there.
We can find it is discoid as Herschel said.

Galaxies are classified into a Spiral galaxy, an Elliptical galaxy, a Lenticular galaxy,
a Barred spiral galaxy, and an Irregular galaxy depending on its shape.

Since it looks like swirling when seen from above, Our Galaxy is classified into a Spiral galaxy.

The entire Our Galaxy is rotating. The rate is about 220 km/sec in the vicinity of the sun.
The diameter of the Galactic disk is 100,000 light-years, which is the distance of 100,000 year
at the speed of light. The Solar System where our earth belongs is in the distance of about 26,000
light-years from the center of the Galaxy.

Next, let's have the edge-on view of the Galaxy. It looks like a convex lens in the edge-on view.
We can find that the Galaxy has the dilated part in the center and the discoid part when looked laterally.
The Solar System is in the slightly upper part of the rotation plane of the discoid part.

Well, let's see what is in the discoid part of Our Galaxy!
There are many celestial bodies, such as a Diffuse nebula, a Dark nebula, an Open cluster,
variable stars, and a Planetary nebula in the discoid part of Our Galaxy.

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We keep on going to the center of Our Galaxy and return to the Solar System where our earth belongs.
The center of Our Galaxy is in front of us. We are seeing the dense Milky Way. This is the summer Milky Way.
It looks like this because we see the center of Our Galaxy, where there are many stars.

Well then, let's look around! You can find some parts look dense or sparse in the Milky Way.
Now, we are looking in the opposite direction to the center of Our Galaxy.
The Milky Way looks sparse.

Now, we are seeing the winter Milky Way.
Since there are fewer stars in the outer part of Our Galaxy, the Milky Way is only seen vaguely.
Like this, the winter Milky Way and the summer Milky Way are connected.
Now, we are looking at the center of Our Galaxy.

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Let's go on an expedition to see what is in the heart of Our Galaxy!
We are more approaching to the heart of Our Galaxy, and now in the dilated part.

The dilated part in the center is a cluster of old stars aged more than 10 billion years
that were born with the birth of Our Galaxy.
It is said that there are about 10 billion stars in it.

Recently, it was observed with Chandra, X-ray observatory of NASA, that a strong X-ray is radiated
from somewhere around the central dilated part, namely, the center of Our Galaxy.

This x-ray seems to be radiated at the last minute before a substance is absorbed in a black hole.
And there is a greater possibility that a celestial body with high density in the vicinity of Our Galaxy
is a black hole.
It has been considered that in the vicinity of the center of Our Galaxy, a black hole absorbs stars nearby.

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We have been exploring Our Galaxy.
Presently, we cannot see the Milky Way unless we go to the mountains where the sky is unilluminated.
Even if we know what really the Milky Way is, its beauty will never change.

If you have a chance to go to a place where the sky is dark,
how about imaging a romantic story while looking at the Milky Way?