As one of the thousands of species living on earth, the biggest difference between humans and other species is that humans look up at the starry sky, and the starry sky is where the universe is.
According to astronomers' statistics, there are more than 7,000 stars in the Earth's celestial region that can be directly seen by humans with the naked eye, but because the Earth is rotating, the average person sees only more than 3,000 stars in half a sky area, including planets such as Mars Jupiter in the solar system, as well as many stars outside the solar system, such as Cowherd and Vega, and the Big Dipper, in high latitudes without light pollution, and even directly see clusters and neighboring galaxies.
The Andromeda Galaxy is 2.54 million light-years away from Earth, 200,000 light-years in diameter, and has as many as 1 trillion stars inside, which means that what we see now is actually the Andromeda Galaxy 2.54 million years ago.
Most of the remaining 7,000 stars are like the Sun, which can use the energy of nuclear fusion to emit light and heat spontaneously, but there is a very disappointing fact, that is, these more than 7,000 stars are all located in the Milky Way, strictly speaking, within 1500 light years.
The yellow circle you see now is only a small part of the Orion spiral arm of the Milky Way, but it has encircled all the stars that the human eye can see, and the maximum extent of the Kepler telescope search plan is only a sector area with a maximum distance of 3,000 light years.
The latest diameter of the entire Milky Way is 180,000 light-years, the center thickness is 26,000 light-years, the edge thickness is 3,000 light-years, there are 100 billion to 400 billion stars, the solar system and the Earth in the solar system, is just a grain of sand in the Milky Way, as for human beings themselves, perhaps just bacteria.
The ancients once thought that the brilliant starry sky they saw at night was the whole universe, but now we know that the starry sky above our heads at night is only a small part of the universe.
From Earth, flying at the speed of 300,000 kilometers per second for a year, we can only leave the solar system, and Voyager One, launched in 1977, will fly for a full 30,000 years.
4.22 years after leaving the solar system, we reach the famous Proxima Centauri, one of the legendary Three Centauri stars, the home of the Trisolarans.
After 160,000 years of flying at the speed of light, we are roughly freed from the shackles of the Milky Way and enter the Great Magellanic Cloud, from which to fly for another 40,000 years, which is the Magellanic Galaxy.
And celestial systems that are truly on par with the Milky Way, such as the Andromeda galaxy and the Triangular galaxy, will require us to fly 2.54 million years at the speed of light to arrive, but do you think that's the end?
The Milky Way, together with the above galaxies and nebulae, forms a 10 million light-year diameter local galaxy group, and several local galaxy groups form a 110 million light-year diameter local galaxy cluster, which contains about 3,000 Milky Way-like galaxies, each galaxy has hundreds of billions of stars.
Above this cluster are the Virgo Supercluster and the Raniacea Supercluster, the latter of which is roughly outlined like a goose feather in the universe, consisting of 500 galaxy clusters.
Like the solar system orbiting the center of the Milky Way, the vast Ranyakea supercluster is also moving in the direction of the giant source at the moment, but it is not the largest structure in the universe, and the largest monolithic structure in the universe is the "Great Wall of Wuxian-Coronal Constellation", with a diameter of 10 billion light-years.
According to current Hubble observations, the radius of the observable universe is 46.5 billion light-years, and there are about 100 billion to 200 billion galaxies inside, but these galaxies account for only 4.9% of the total mass energy of the entire universe.
The rest of the mass-energy distribution, all occupied by dark matter and dark energy, makes up a hollow structure throughout the universe, and dark matter that gathers galaxies that are not dispersed and provide additional gravity.
The size of the universe is difficult for human beings to imagine, in most people's minds, one light year and 100 light years are not fundamentally different, really want to let all mankind realize the vastness of the universe, perhaps only until the future era of interstellar navigation.