How are constellations formed?

The reason for the seasonal change of starry sky is related to the revolution of the earth. The stars outside the sun are far away from the earth, and the earth is very close to the sun. Therefore, when the earth revolves around the sun, from the earth's point of view, the sun seems to move between relatively stationary stars with a period of one year, which is called "solar annual apparent movement".

Because the atmospheric molecules of the earth scatter sunlight, we can't see half of the starry sky submerged by the sun's brilliance during the day, but only the other half in the opposite direction at night.

In this way, with the annual apparent movement of the sun, we see different starry sky in turn. In spring, the sun is not far from Pegasus, and in the middle of the night, Leo in the opposite direction hangs overhead.

In summer, the sun moves near Orion and Scorpio can be seen in the middle of the night; In autumn, the sun is in Leo, and Pegasus becomes the protagonist of the midnight starry sky; In winter, the sun moves to Scorpio, so Orion is in the sky at midnight, which is the change of the stars in the four seasons.

Of course, the change of the starry sky is not a sudden change of seasons, but a continuous process every night. Because the annual apparent movement of the sun is 360 degrees a year, which is equivalent to moving about 1 degree on the ecliptic every day, it takes about 4 minutes to turn this1.

So the same star rises 4 minutes early every day, 2 hours early in a month, 24 hours early in a year, and returns to the original time. The stars have shifted, and year after year, the starry sky always runs regularly like this.

There are bright stars in winter, and connecting Betelgeuse in Orion, Sirius in Canis Canis and Nanhesan in Canis with imaginary line segments just forms an equilateral triangle, which is the winter triangle. In addition to the triangle in winter, a diamond in winter is uniquely painted on the bright canvas in the starry sky in winter night.