Why do auroras only appear in the north and south poles?

Aurora only appears in the north and south poles because the gaseous substances in the polar regions are thin.

Aurora needs to meet three conditions: atmosphere, magnetic field and high-energy charged particles. The earth itself is a natural strong magnetic field, and the magnetic field in polar regions is the strongest. Therefore, the earth's magnetic field plays a key role in the production of aurora.

Gaseous substances in the polar regions are very thin. This atmospheric condition is helpful for high-energy charged particles to collide with atmospheric molecules, so that atmospheric molecules are excited or ionized to produce aurora. If the atmosphere is too dense, high-energy charged particles will collide with atmospheric molecules many times during their propagation, resulting in their energy gradually weakening and unable to form aurora.

Aurora is a stream of charged particles from the sun (solar wind), which enters the earth's magnetic field and appears in the sky near the north and south poles of the earth at night. The solar wind is charged particles ejected by the sun, and it is a powerful stream of charged subatomic particles, which can cover the earth. The solar wind flows around the earth over the earth and hits the earth's magnetic field at a speed of about 400 kilometers per second. The earth's magnetic field is shaped like a funnel, with its tip facing the north and south poles of the earth, so charged particles emitted by the sun settle along the funnel of the earth's magnetic field and enter the polar regions of the earth.

Characteristics of aurora

Aurora is most likely to appear before the vernal equinox and autumnal equinox, and it appears more frequently in spring and autumn than in Xia Dong. In addition, when there are more sunspots, or the solar cycle is in the stage of increasing coronal mass ejection and increasing solar wind intensity, the frequency and brightness of aurora will also increase.

Aurora mostly appears in high latitudes, especially in polar regions, and rarely appears in middle and low latitudes, especially near the equator. This is because the plasma emitted by the sun will appear when it blows near the earth, enter the polar regions of the earth under the action of the earth's magnetic field, and then bombard the upper atmosphere.

The change of aurora movement is characterized by a wonderful drama of nature, the magic master, on the stage in the sky, with hundreds of kilometers up and down and even nearly 10 thousand kilometers of aurora belt. This magnificent natural scene, as if touched with a little fairy, is quite mysterious. What is amazing is that the color of the aurora can no longer be described by colorful colors.

The above contents refer to Baidu Encyclopedia-Aurora