Time is an abstract concept. In order to describe the passage of time, we need to use very regular natural phenomena to define the unit of time. For example, the time when the earth revolves around the sun, we define it as one year.
However, this definition only applies to the earth. After all, in the solar system, the orbital periods of different planets are also different. In order to facilitate distinction, we can call it the "Year of the Earth".
What you need to know is that while the earth revolves around the sun, the sun is actually "leading" the many celestial bodies in the solar system orbiting around the center of the Milky Way galaxy.
We call the orbital plane of the earth's orbit around the sun " ecliptic plane ", and the disc-shaped plane where the main mass of the Milky Way is called the "galaxy plane". Because these two planes have an angle of about 60 degrees, the sun basically always revolves on the "galaxy plane".
Therefore, the actual motion of the solar system should be: relative to the plane where the sun's orbit is located, the orbits of many celestial bodies in the solar system will basically have a significant inclination angle.
Since the sun's revolution around the center of the Milky Way is also very regular, we can also define the time it takes for the sun to circle the Milky Way to be a " Milky Way Year ". So how long is a "Milky Year"? How many "earth years" are equivalent to? In fact, we only need two data to get the answer.
One data is the average revolution speed of the sun around the center of the Milky Way. Observation data shows that the sun is currently moving towards Cygnus , with a speed of about 220 kilometers per second. Considering that the resistance in the universe can be negligible, we can directly regard it as the average revolution speed of the sun.
Another data is the distance the sun revolves around the center of the Milky Way, which is impossible to obtain directly through observation data. After all, this takes too long, but we can still estimate it through known observation data.
Observation data show that the sun is located at the edge of a structural edge in the Milky Way called " Orion spiral arm ", and its distance from the center of the Milky Way is about 26,000 light-years. Here we can make a rough assumption that the sun orbits around the center of the Milky Way along a circular orbit.
Based on this, we can calculate that the distance between the sun around the center of the Milky Way is about 163,280 light years, which is about 15.45 billion kilometers (1 light year is equivalent to 946,073,0472,580 kilometers). We divide this number by the average revolution speed of the sun, that is, 220 kilometers per second, and we can draw that it takes about 223 million earth years to rotate around the center of the Milky Way.
That is to say, a "Galaxy Year" is about 223 million Earth years. It has to be said that a "Galaxy Year" is too long. You should know that the sun was born about 4.6 billion years ago, and dinosaurs first appeared in the Triassic period about 230 million years ago. This means that according to this calculation result, starting from the birth of the sun, the solar system is currently in the 21st "Galaxy Year", and in the last "Galaxy Year", dinosaurs just appeared on Earth.
It should be noted that the above calculation results are just a rough estimate. In fact, the orbit of the sun around the center of the Milky Way cannot be a standard circle.
In addition, astronomers have also found that during the sun's revolution, the sun does not always move on the plane of the "Military Way", but will regularly travel "above" and "below" in a similar way, which will undoubtedly increase the distance the sun rotates around the center of the Milky Way.
These uncertainties have led to the "Galaxy Year" being only a general range. Usually, astronomers value this range from 225 million to 250 million Earth years.
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