According to Mr. Đặng Vũ Tuấn Sơn, Chairman of the Vietnam Astronomical and Cosmological Association (VACA), on May 21, a circle appeared around the Sun in several localities, which is an optical phenomenon known as the 22-degree halo of the Sun, and it is not a rare occurrence.
On the afternoon of May 21, many areas in the northern region, such as Quảng Ninh, Hải Phòng, Hà Nội, and Hải Dương, reported that numerous residents discovered a bright circle surrounding the Sun.
Mr. Đặng Vũ Tuấn Sơn explained that the phenomenon is called the 22-degree halo of the Sun or solar halo. Some places refer to this phenomenon by a different name, which is “aura.” However, according to Mr. Sơn, this is a subjective term and not entirely accurate.
The solar halo occurs under specific conditions, such as in the upper layers of the Earth’s atmosphere, where the weather is very dry, with low humidity but abundant ice crystals.
“Light from the Sun or Moon, when passing through ice crystals, is refracted, creating a halo around the Sun with a radius of 22 degrees from the Sun, hence the name 22-degree halo,” Mr. Sơn stated.
Solar halo appears in several localities.
Additionally, the Chairman of the Vietnam Astronomical and Cosmological Association mentioned that there is a folk saying: “A halo around the moon signifies dry weather, while a bright moon indicates rain,” which suggests that the appearance of halos around the moon can signal hot weather conditions, but this saying is not entirely accurate.
The solar halo is less common than the lunar halo but it is not an overly rare phenomenon and does not significantly affect daily life. However, this phenomenon can indicate a short period of prolonged heat with little rainfall to follow.
The solar halo only appears in certain localities, while it may not be visible in other areas. Experts explain that this is due to the specific atmospheric conditions needed, where dry air and a higher altitude with many ice crystals are required for it to occur. Areas with clouds and high humidity will not be able to see this phenomenon.
