Is the Vernal Equinox the Earth’s exclusive right?

Xinhua News Agency, Tianjin, March 19 (Reporter Zhou Runjian) On March 20, we ushered in the Spring Equinox, one of the 24 solar terms, marking the beginning of spring in the northern hemisphere of the earth. Did you know that in addition to the earth, Mars and Saturn also have Spring Equinoxes? What does the Spring Equinox mean to these two planets?

Xiu Lipeng, a member of the Chinese Astronomical Society and an expert in astronomy, said that according to our definition of the Earth's vernal equinox, all planets that revolve around the sun and have a spherical shape and a stable rotation axis can have a vernal equinox. But in fact, among the eight planets in the solar system, only Mars and Saturn have obvious four seasons like the Earth, and naturally have the vernal equinox, summer solstice, autumnal equinox and winter solstice. The other five planets, either because of the small inclination of their rotation axis or because they are too far away from the sun, do not have obvious four seasons.

For Mars, the spring equinox marks the beginning of spring in the northern hemisphere and autumn in the southern hemisphere, and the dust storm season that has spread across the planet ends. With the arrival of early spring, a new cycle begins, so the spring equinox is the new year for Mars.

"Similar to the calendar on Earth, we have also developed a calendar for Martian activities, which is the Martian calendar, which stipulates that each Martian New Year begins with the vernal equinox. Since the first Martian New Year began on April 11, 1955 Earth time, it is now the 38th Martian New Year. The next Martian New Year is September 30, 2026 Earth time." Xiu Lipeng said.

For Saturn, the spring equinox means a change in the shape of Saturn's rings. A circle of rings surrounds Saturn's equatorial plane, which is very eye-catching under the sunlight. Because the direction of Saturn's rotation axis is relatively close to that of the Earth, when Saturn is near the spring and autumn equinoxes, Saturn's rings are facing the Earth sideways and seem to disappear; and when Saturn is near the summer and winter solstices, Saturn's rings have the largest inclination and are most complete when observed from Earth.

Xiu Lipeng said that when the spring equinox arrives, the sun will shine directly on the equator of Saturn and also shine vertically on the rings of Saturn. With this opportunity, we can find some "details" that are difficult to see normally. For example, when the rings of Saturn turn completely sideways, some small satellites hidden in them will be exposed to the field of view of human probes.

Although the Earth, Mars and Saturn all have spring equinoxes, the "scenery" is unique on Earth. "There is no 'birdsong' on Mars, and no 'flower fragrance' on Saturn, only the daunting cold environment. On the other hand, on Earth, flowers are red, willows are green, grass is lush, and birds are flying, full of vitality everywhere," said Xiu Lipeng.