The Milky Way is vast and endless, so how long is a galactic year?

According to foreign media(2021 hermes bags) reports, we have long been used to distinguishing the four seasons of the year by the position of the earth relative to the sun. However, although the earth's journey around the sun is very important for humans on earth, it is really insignificant compared to the epic journey of the sun-and our entire solar system-orbiting the center of the galaxy.

　　 Keith Hawkins, assistant professor of astronomy at the University of Texas at Austin, said that it takes about 220 to 230 million Earth years for the sun to revolve around the Milky Way in its orbit—that is, the time it takes for the earth to revolve around the sun once.

In other words, if we use the galactic "clock" to measure time, our earth has only existed for about 16 years (in galactic years or cosmic years), and the formation of the sun has only been 20 years, and even the entire universe will exist. For about 60 years.

　　 The process of the solar system revolving around the Milky Way is very similar to the process of the earth revolving around the sun. However, Hawkins explained that the solar system does not revolve around a certain star, but revolves around a super massive black hole located in the center of the Milky Way. Moreover, this super-mass black hole has a huge gravitational force on all matter in the Milky Way.

　　 "The sun's revolution speed is very fast-about 230 kilometers per second, which is equivalent to 500,000 miles per hour, and the sun keeps revolving around the center of the Milky Way," so that it will not be drawn to the black hole, Hawkins said.

　　Our position in the Milky Way

　　 Compared with the earth year, the galactic year represents a larger unit of time. But in the Milky Way, this time unit is not uniform. The Milky Way that we people on Earth call is relative to the position of the Earth in the Milky Way.

　　 "We can say that a galactic year is about 220 million or 230 million earth years. But on other planets in the galaxy, their galactic years are different," Hawkins said.

　　 The diameter of the Milky Way is about 100,000 light years, and our Earth is 28,000 light years away from the center of the Milky Way. "If you think of the Milky Way as a city, then our earth is probably in the suburbs," Hawkins explained. If it is a star whose orbit is close to the "city center" black hole, then a galactic year is relatively short. But in the "outskirts", where our solar system is located, "the Milky Way is a little bit longer," he said.

　　 Similar rules apply to different planetary year lengths. For example, Mercury is the innermost planet in the solar system. Mercury revolves around the sun in only 88 earth days. Uranus, the seventh planet in the solar system, orbits the sun in 84 earth years. The orbital period of the distant dwarf planet Pluto is 248 earth years.

　　 Although the physical mechanism of planetary orbits is similar to the mechanism that shapes the orbit of the solar system around the Milky Way, one question is worth mentioning: how do astronomers calculate the length of the Milky Way? Hawkins said that, in fact, this is a fairly basic science, already very clear in the early development of modern astronomy.

　　 "It is mainly to observe the motion of stars around the Milky Way," he said. "You can observe the motion of stars around the Milky Way, and then deduce the length of the Milky Way from the speed and direction of other stars."