Halos around the Sun appear in many localities in Vietnam

This afternoon, May 21, in Hanoi, Quang Ninh and some other localities, solar halos are simultaneously appearing.

The appearance of the Sun accompanied by a halo is attracting the attention of many people this afternoon. This phenomenon is easy to observe in clear and cloudless conditions. Many people think that this is a rare phenomenon.

The solar halo phenomenon appears most clearly from 11:00 a.m. today (May 21).

Halos are rings of light surrounding the Sun or Moon. They often appear when a thin layer of cirrus clouds appears in the sky. The combination of chemistry, physics and geometry is the main cause of the sun's halo. The atmosphere mixes many gases, including oxygen, nitrogen and water vapor.

At high enough altitudes, water vapor condenses and then freezes into ice crystals. When sunlight shines through ice crystals, the crystal's geometry causes the light to refract, similar to what happens when light shines through a prism.

Sun or moon halos are often a sign of impending rain . Because haloes require ice crystals to form, ice crystals often appear in tiny clouds at high altitudes. These clouds can arrive days before a warm or cold air mass brings rain. However, not all clouds come with storms. Some haloes are simply signals of increased water in the upper atmosphere. This phenomenon can also happen with the Moon.

Most recently, the Sun with a halo around it appeared near noon on May 8, lasting for 10 minutes, making many people curious.