"Human"

When we humans feel very tired, we often say that we can fall asleep standing up, but this is just a description. In reality, it is impossible for humans to sleep standing up, but there are many animals in nature that have this such a skill that humans do not have, for example, horses can sleep standing up effortlessly.

The solar system is a system of celestial bodies kept in motion by the sun's gravity, which means that all bodies within the effective range of the sun's gravity are part of the solar system, so by this definition, how large is the solar system?

The reason we don't see time travelers is actually because they are not in our timeline

Of all the known rocky planets in the solar system, the one with the most similar natural environment to Earth is Mars, and exploration data show that Mars also has an atmosphere, four seasons of the year, and even a rotation period similar to that of Earth.

In orbit for longer and longer periods of time, we need to solve not only inorganic resupply problems such as food, water, oxygen and propellant, but also the various problems faced by astronauts flying in orbit for long periods of time

It is proposed that birds originated from dinosaurs, and that "ancestor birds" are a transitional species between birds and dinosaurs.

How long can humans survive on earth? This is a question that many of us want to know, and i believe that we do not want to wake up to a "Purgatory" Like venus, and hope that the earth can remain alive forever, so that we humans can continue and our generations can survive on earth forever. If the earth's environment were to change drastically and become an extremely hot planet like venus or mercury, then naturally everything in the world, including humans, would not be able to exist.

In theory, when a civilization develops into a civilization that can cross the stars, there is basically no risk of extinction

If mankind can master the method of extracting uranium from seawater in large quantities in the future, there will be enough uranium on the earth to last for tens of thousands of years, even hundreds of thousands of years!

In our solar system, there are 2 planets in the habitable zone of the solar system, one of which is our home planet Earth, and the other is Mars