The Milky Way Galaxy

[해설사 이상현]

Milky Way Galaxy

Do you sometimes see stars? When I was young, I could see countless stars in the summer sky. The sky we see is called the Milky Way Galaxy.
There are millions of stars in this galaxy. One of those stars is the Sun and the Earth. There are hundreds of billions of other galaxies in the unuverse besides the Milky Way. So how many stars are there in total in the universe?

Write the number 1 and add a zero(0) to it throughout one minute. Can you read this number? It is no exageration to say that there are as many stars in this universe as the numer you just wrote.
Many of those stars are actually breaking into pieces and scattering across the universe, and even at this very moment, numerous planets are being formed from the dust and gas coming out of them. However, while this is happening, there is a constant sound coming from the far corner of the universe.  These ultrasonic waves are the echo of the great explosion called the ‘Big Bang’ of creation. Well, some of the ultrasonic waves occurred as early as 1.8 billion years ago. For 1.8 billion years it came across the universe and now we can hear it.
The Solar System is the gravitationally bound system of the Sun and the objects that orbit it.The largest of these objects are the eight planets, which in order from the Sun are four terrestrial planets (Mercury, Venus, Earth and Mars수성, 금성, 지구,화성); two gas giants  (Jupiter and Saturn목성 ,토성); and two ice giants  (Uranus and Neptune천왕성,해왕성). The Solar System developed 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc.

Stars orbiting the sun do not orbit on different tracks on a flat surface, so they can collide with each other as shown in the picture.