Our Universe is formed by approximately 200 billion stars similar to the Sun, known as the Milky Way Galaxy. The shape of the Milky Way resembles a double-sided disk, with a diameter of about 100,000 light-years and a thickness of approximately 15,000 light-years in the middle.
A light-year is the distance light travels in one year, moving at a speed of 300,000 kilometers per second. Therefore, if light were to travel from one edge of the Galaxy through the center to the opposite edge, it would take 100,000 years.
So, if we go beyond this Galaxy, where do we go next? Outside the Milky Way, there are countless other galaxies known as nebulae. Close to our Milky Way is a group of stars called the Andromeda constellation. This is a galaxy similar to ours, with a shape and size akin to the Milky Way, but it contains about 200 billion stars.
If we could draw a sphere with a diameter of 2 billion light-years, it could encompass about 30 nebula systems. All these nebula systems combine to form the Great Universe (or the Great Galaxy). Can we see the edge of this Great Galaxy?
Our Earth belongs to the Solar System.
For humanity, Earth is like a home, and the Solar System is like the entire neighborhood.
In this neighborhood, there are some neighboring houses that have yet to be civilized.
Venus, Mars, the Moon…
Recent scientific explorations suggest that these celestial bodies may have once been the “neighboring civilizations” of Earth.
On these celestial bodies, remnants of past civilizations can still be found.
Some speculate that the Solar System was once a “civilization neighborhood”; after its decline, a new talent emerged, leading to the civilization of Earth. If this is true, beyond Earth, we might discover the existence of civilization and intelligence, perhaps even within our own Solar System. Although Earth seems to have been visited by a very distant messenger from outside the Solar System.
Next: Exploring the Moon
T.H
