- 2020-05-20 14:30:06
- 己被围观 次
The sun is an ordinary star, which has spent about half of its main sequence career on the H-R diagram. It is a hot gas (plasma) sphere with a mass of 19.91 billion tons (about 330000 times the mass of the earth) and a diameter of 1.392 million km (about 109 times the diameter of the earth). Its average density is 1.4 times that of water, but it implies a wide range of density, from the ultra-high density core to the thin outer layer.
As a star, the overall appearance of the sun is 38.3 billion watts in luminosity and 4.8 in absolute magnitude. It is a yellow G2 dwarf with an effective temperature equal to 5800 degrees Kelvin. The average distance between the sun and the earth in orbit is 149597870km (499.005 light seconds or 1 astronomical unit). By mass, it consists of 71% hydrogen, 26% helium and a small amount of heavy elements. The angular diameter of the solar circle in the sky is 32 minutes, which is very close to the angular diameter of the moon seen from the earth. It is a wonderful coincidence (the diameter of the sun is about 400 times the diameter of the moon and the distance from us is just 400 times the distance between the earth and the moon), which makes the solar eclipse look particularly spectacular.
As the sun is much closer to us than other stars, its apparent magnitude reaches - 26.8, making it the brightest object on earth. The sun rotates once every 25.4 days (average period; the equator rotates faster than high latitude), and once every 200 million years around the center of the galaxy. The sun is slightly flat due to rotation, 0.001% different from the perfect sphere, which is equivalent to 6km difference between the equatorial radius and the polar radius (the difference is 21km for the earth, 9km for the moon, 9000km for Jupiter and 5500km for Saturn).