On February 25, the National Radio and Television Administration recently announced that from February 25 to March 17, satellites used for broadcasting and television program transmission in China will enter the solar eclipse period. During this time, TV programs affected by the corresponding frequency bands may temporarily experience "snow" on the screen. If the satellite TV you are watching suddenly shows unclear images, snow, frozen frames, or even a black screen, do not worry, this may be caused by the solar eclipse phenomenon.
What is a solar eclipse?
A teacher from the Information and Communication Engineering Department of Harbin Institute of Technology explained that communication and broadcasting satellites, in addition to orbiting the Earth, also move with the Earth around the Sun. Every year during the spring and autumn equinoxes, the Earth, satellite, and Sun are on the same line. When the satellite is between the Earth and the Sun, the strong solar radiation can cause a brief interruption in communication signals for about ten minutes when the Earth receives signals from the satellite. This natural phenomenon is called a solar eclipse interruption. This interruption occurs twice a year, each time lasting about ten days. The solar eclipse interruption is an objective phenomenon. The impact of the interruption can be reduced through the design of communication frequencies, but it cannot be completely eliminated. The "solar eclipse" can affect the reception of satellite TV signals, causing unclear images, snow, and other phenomena, but it will not damage the TV. However, the "solar eclipse" does not affect the signals of mobile phones used in daily life.
When does the solar eclipse interruption occur?
The Earth is about 150 million kilometers from the Sun, and the satellite is about 36,000,000 meters above the ground. The Earth's radius is about 6,400,000 meters. The distance between the satellite and the Sun is more than 4,000 times greater than the distance to the Earth. The angle between different latitude ground stations, the satellite, and the line connecting the Sun and the ecliptic plane changes very little. Only around the spring and autumn equinoxes can the Earth, satellite, and Sun be aligned. China is located in the northern hemisphere. Due to latitude differences, a few days before the spring equinox during daytime, the angle between the Earth's equatorial plane of rotation and the ecliptic plane of orbit around the Sun gradually decreases from north to south, and the satellite is slightly above the ecliptic plane. The ground stations in the northern hemisphere, the satellite, and the Sun may sometimes be in a straight line. In other words, as the Sun moves from the southern hemisphere to the northern hemisphere, China experiences the "solar eclipse communication interruption" phenomenon from north to south successively. The higher the latitude, the earlier it occurs, but it always occurs before the spring equinox.A few days after the autumnal equinox, during the daytime, the angle between the Earth's rotational equatorial plane and its orbital ecliptic plane begins to increase from south to north. In other words, the Sun moves from the Northern Hemisphere to the Southern Hemisphere. At this time, ground stations, satellites, and the Sun in the Northern Hemisphere will align in a straight line. During this period, China begins to gradually experience the 'solar conjunction communication interruption' phenomenon from south to north. The lower the latitude, the earlier it occurs, but it always happens after the autumnal equinox. Of course, the condition for solar conjunction communication interruption is that the ground station, satellite, and Sun on Earth are aligned in a straight line. Due to the movements of the Earth, satellite, and Sun, the time they are in a straight line is very short. Also, because of differences in longitude, the time at which this 'solar conjunction communication interruption' occurs varies across locations. The same ground station will encounter the 'solar conjunction communication interruption' phenomenon twice a year. The duration of each occurrence and the daily interruption time vary depending on the geographic location of the ground station and the size of the antenna. Generally, it lasts at most one week, for 5–10 minutes each day, occurring around noon.