Why does aurora produce color?

Aurora is a phenomenon that charged particles from the sun collide with the magnetic fields at the poles of the earth and discharge in the sky.

The sun is a huge and hot gas ball, and the nuclear reactions of various chemical elements are carried out inside and on its surface, resulting in a powerful stream of charged particles, which are emitted from the sun and shot into the surrounding space at a very high speed. When this charged particle stream shoots into the thin upper atmosphere around the earth, it collides violently with the molecules of the thin gas, resulting in a luminous phenomenon, which is aurora.

These colorful lights in the night sky are common in high latitudes near the north and south poles. On a clear summer night, you can sometimes see the aurora in low latitudes far away from the city lights. On the border between Canada and the United States, you can see the Northern Lights on many nights every year. The northern lights or the southern lights are as charming as fireworks. The colors of aurora vary from light green to deep red. Some of them are like colored paper ribbons, some are like bows, some are like curtains, and some are like shells. (Qiu Ya)

Color luminescence often occurs in the atmosphere above latitude near the geomagnetic pole. Generally, it is belt-shaped, arc-shaped, curtain-shaped or radial. These shapes are sometimes stable and sometimes constantly changing. Aurora is produced by the flow of charged high-energy particles (up to 10 kiloelectron volts) in the solar active region to excite or ionize molecules or atoms in the upper atmosphere. Due to the geomagnetic field, these high-energy particles turn to the polar regions, so aurora is very common in high magnetic latitudes. Aurora often appears in the range of about 25 ~ 30 from the magnetic pole, which is called aurora area. The area between 60 and 45 degrees of geomagnetic latitude is called weak auroral zone, and the area below 45 degrees of geomagnetic latitude is called micro auroral zone. The lower limit height of the aurora is less than 100 km from the ground, the maximum light height is about 1 100km, the normal maximum boundary is about 300 km, and in extreme cases it can reach more than 1000km. According to the research on the distribution of aurora in recent years, the shape of aurora is not a ring with the geomagnetic pole as the center, but more like an ellipse. The spectral range of aurora is about 3 100 ~ 6700 angstroms. One of the most important spectral lines is the atomic oxygen green line of 5577 angstroms, which is called the aurora green line. The appearance of aurora is related to magnetic storms, the earth's corona, solar wind and cosmic rays, so it is also related to solar activities. As early as more than 2,000 years ago, China began to observe the aurora, and since then, there have been abundant aurora records.