A double rainbow appeared in the sky of Hanoi during the national mourning, a rare phenomenon

On the afternoon of July 22, many people in Hanoi witnessed an amazing natural phenomenon when a bright and clear double rainbow appeared in the sky. Double rainbows are not only rare but also one of the extraordinary phenomena that nature brings.

Normally, rainbows appear when sunlight hits raindrops, causing refraction and dispersion. Long wavelengths (red) are bent more than short wavelengths (blue), creating a brilliant rainbow in the sky.

The double rainbow phenomenon, also known as a "twin" rainbow, occurs when the sun's rays reflect "a second time" with raindrops, forming a second curve on the same plane as the raindrops. main rainbow. Light that enters the raindrop and refracts at the surface does not escape after hitting the back of the raindrop, but is instead refracted a second time, creating a secondary rainbow.

The characteristic of the second rainbow is that the colors are inverted compared to the first rainbow. The light from the second rainbow is also dimmer and harder to see because the amount of light refracted the second time is much less. The shape and position of the secondary rainbow is also different, about 10 degrees away from the main rainbow and radiating at an angle of 50 degrees.

Double rainbows occur very rarely, so those who have the opportunity to witness this phenomenon are considered extremely lucky. In some Eastern cultures, double rainbows also represent luck and happiness.

The above images quickly received tens of thousands of likes, comments and shares. Many netizens were curious about this phenomenon when observing it for the first time. Besides, many people compete to share rainbow photos they see.

One account commented: "Yesterday afternoon, I also saw this rainbow appear for a long time. But I didn't bring my phone to take pictures on the road." Sharing on the media, Ms. Maia Nguyen (living in Hanoi) said that around 6:15 p.m. last night, while preparing dinner, the sky outside turned yellow. Because she thought there was going to be bad weather, Maia went to her balcony to check it out and suddenly saw a double rainbow.

"This was the first time I saw this phenomenon, so I took out my phone to take a photo. Yesterday, the sky in Hanoi was overcast, there was no sunshine," she said. Ms. Phan Trang also shared a photo of a double rainbow in Nam Tu Liem (Hanoi) and was impressed with the image above.

As for Ngoc Thao, she also shared the image of a double rainbow appearing in the Vinh Yen area (Vinh Phuc). She said while returning from the market, she accidentally saw a rainbow in the sky.

The second rainbow appeared more and more clearly. According to her, a long time ago, she saw a double rainbow, and only yesterday had the opportunity to see it again. As for the normal single rainbow phenomenon, I have seen it many times.

Mr. Le Trung Hieu in My Dinh (Nam Tu Liem, Hanoi) said that initially a sphere appeared in the sky, but then there was a phenomenon of two concentric spheres, creating quite brilliant colors. Many people think that this is a double rainbow or double rainbow.

Explaining this phenomenon, Mr. Nguyen Anh Tuan, former Chairman of the Ho Chi Minh City Amateur Astronomy Club (HAAC), said that double rainbows appear less frequently than single rainbows but are not a rare phenomenon. Rainbows often appear after rain, when the air has a lot of moisture. The nature of the rainbow is the dispersion of sunlight when refracted and reflected through raindrops.

Water droplets in the air act like a prism. When sunlight passes through the prism, the light rays are bent, reflected and exit the water droplet at a 42 degree angle. The double rainbow phenomenon occurs when we can simultaneously see two angles of 42 degrees and 52 degrees compared to sunlight.

"With the double rainbow phenomenon, the secondary rainbow appears due to the diffraction of light at an angle of 52 degrees compared to sunlight. We can completely see the refraction of light on the inside of the water drops, before the light is reflected and goes outside. This explains why the secondary rainbow has inverted colors and is often fainter than the main rainbow" - Mr. Tuan explained.

The rainbow phenomenon often appears after rain because the air has a lot of water vapor, high humidity... leading to light refraction. Double rainbows appear more rarely, in which the lower arc is the main rainbow, and the higher arc, with lighter color, is the secondary rainbow, or called the secondary rainbow. What's interesting is that the color order of the secondary rainbow is opposite to the main rainbow: Red is on the inside and purple is on the outside.

Double rainbows often appear when the Sun is low in the sky, like early morning or late afternoon. A double rainbow forms when sunlight is reflected twice in the same raindrop. Purple light reaches the observer's eye from higher raindrops and red light from lower raindrops. Therefore, the color sequence of the two new rainbows is reversed.

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