Come see this "fat moon" tonight!

This year's first "supermoon" will appear in the night sky in the early morning of August 20. Interested people in our country can look up at the sky in the evening of the 19th to admire this "fat moon".

On August 30, 2023, the "supermoon" rose over the Temple of Poseidon at Cape Sounion, Greece. Xinhua News Agency (Photo by Marios Rolos)

When the moon and the sun are on opposite sides of the earth and their ecliptic longitudes differ by 180 degrees, the moon seen from the earth is the roundest and is called a "full moon" or "wang". The 14th, 15th, 16th and even 17th day of each lunar month are all possible periods for a full moon to appear.

This is the "super moon" photographed in Lhasa, Tibet on March 10, 2020. (Photo by Xinhua News Agency reporter Pubu Zhaxi)

Xiu Lipeng, a member of the Chinese Astronomical Society and an expert in astronomy, said that the moon's orbit around the earth is an ellipse. Sometimes the moon is close to the earth, and sometimes it is far away from the earth. The closest point to the earth is called the perigee, and the opposite is called the apogee. From an astronomical perspective, a "supermoon" can be simply called a "perigee full moon", that is, the full moon appears exactly near the perigee, and at this time, the moon looks particularly large. This "supermoon" will be full at 2:26 on the 20th, and the moon will pass the perigee at 13:00 on the 21st.

This is the "supermoon" photographed in Beijing on April 8, 2020. (Photo by star photographer Wang Junfeng)

"Supermoons" are not rare phenomena, with one or two and three or four occurring in a year. This year, there are four "supermoons" that appear in sequence, and the next three appear on September 18, October 17 and November 16. Among them, the "supermoon" on September 18 is the largest full moon of the year.

This is the "supermoon" in the night sky of Sydney, Australia, taken on April 27, 2021. (Photo by Xinhua News Agency reporter Bai Xuefei)

How to enjoy this year’s first “ supermoon ”?

Since the full moon occurs in the early morning, the public who are interested can observe it in the evening of the 19th. At this time, the moon has just risen from the east. Due to the reference on the ground, the naked eye will feel relatively large, and the color of the full moon is slightly reddish; when the moon rises to a certain height, the naked eye will find it difficult to distinguish this difference, and the color of the moon will gradually turn white or white-yellow.

You don't need professional astronomical equipment to appreciate the full moon, just like appreciating a meteor shower, you can use your naked eyes. Of course, if you use a small astronomical telescope, you can observe the bright or dark details on the moon more clearly.

Supermoons , more and more ?

Supermoon is a term coined by American astrologer Richard Noelle in 1979. But it is not a professional term in astronomy. Supermoon is actually a perigee full moon. Because the moon is closer to the earth, the moon seen is 12%-14% larger than when it is at apogee.

In recent years, there have been more and more reports about "supermoons", which seem to appear every few months. Why is this? Isn't this "super" astronomical phenomenon rare?

Kou Wen, a senior engineer at the Beijing Planetarium, said that the supermoon itself is not a very rare phenomenon. People have the impression that there are more supermoons, mainly because there is no specific measurement standard for supermoons in astronomy. After all, supermoon is not an astronomical term, and there is no so-called strict definition of how close the moon is to the perigee and how close it has to be to occur a full moon to be called a supermoon.

Source: Science Popularization China Comprehensive Xinhua News Agency