Extraterrestrial

In the Milky Way, the closest stars to the Sun are 4.22 light years away

The universe is so big, but man's range is so small that the furthest man has been so far is the moon, which is only 380,000 km away from earth on average. Of course, humans have also launched all kinds of probes, and if you include them, the range of human activities is much larger.

According to our knowledge of known life, liquid water is essential for life. In other words, if there is liquid water on a planet, there is a possibility of life, and it is for this reason that scientists always consider liquid water as the first requirement when assessing the possibility of life on a planet.

Below the solar system, there is a star system labeled "alpha Centauri".

The energy released by the sun's nuclear fusion reaction, in addition to making the sun shine and heat, there is an important role, that is, to resist its own gravity

The so-called gravitational equilibrium surface refers to the surface formed by the same point of gravity. On Earth, we call the gravitational equilibrium surface that coincides with the stationary ocean surface the "geodetic level", which is actually equivalent to what we often call sea level.

Harrison Schmitt is the world's twelfth human to set foot on the lunar surface and the only scientist to have landed on the moon. On the 50th anniversary of the first human landing on the moon in June 2019, he warns that many people may be allergic to the dust on the lunar surface

The milky way is a huge galaxy with hundreds of billions of stars, and the sun is just one of the less prominent stars that, along with many other stars in the galaxy, orbits the centre of the galaxy.

The moon is the closest planet to the earth and the brightest and most easily observed object in the earth's night sky. Because the moon is always facing the same way towards the earth, for us humans living on earth, we can only ever observe one fixed side of the moon.

So far, we have not found any trace of life on Mars. No one knows whether there is life on Mars. However, when we are exploring Mars, sometimes we will see some interesting scenes, even some garbage. It is strange that there is no one on Mars. Why is there garbage? Where does this rubbish come from?