المملكة: Jeddah Astronomer: The scattering of sunlight in the atmosphere is the reason for the blue sky in winter

Explain President of the Astronomical Society in Jeddah Engineer Majid Abu Zahra noted that the observation of an increase in the blueness and clarity of the sky during the winter season compared to the rest of the seasons of the year.

This is a natural phenomenon that has an accurate scientific explanation, linked to how sunlight interacts with the Earth’s atmosphere.

Abu Zahra explained that the light coming from the sun is exposed during its passage through the atmosphere to a physical process known as "Riley scatters"where light is scattered when it collides with tiny air molecules such as oxygen and nitrogen.

This scattering increases the shorter the wavelength of light, so blue light is scattered to a greater extent than red light, which makes the sky appear blue during daylight hours in Clear skies.

He pointed out that the scene differs at sunrise and sunset, as the light travels a longer path in the atmosphere, scattering the blue light away from the line of sight, while the red and orange light reaches our eyes, so the sky appears with distinct, warm hues.

The president of The Jeddah Astronomical Society notes that violet has a shorter wavelength than blue, but the human eye is more sensitive to blue light, so it appears to be the dominant color in the sky. He added that the winter season is characterized by a decrease in the path of the sun in the sky as a result of the tilt of the Earth’s axis, which increases the distance that sunlight travels within the atmosphere, and enhances the clarity of the scattering of blue light, in contrast to the decline in the effect of other colors on the background of the sky.

Abu Zahra explained that the decrease in humidity levels in the winter is an additional factor in increasing the clarity of the sky, as the amount of water vapor and droplets in the atmosphere decreases, and they are relatively large particles that cause what is known as “may scattering,” which gives the sky a white or white appearance. Misty.

As this type of scattering decreases, Rayleigh scattering remains dominant, so the sky appears bluer and purer.

He stressed that the combination of these factors in the winter, from the decrease in humidity and clarity of the air, the decrease in Mie scattering, and the increase in the effect of Rayleigh scattering due to the decrease in the sun in the sky, makes this season one of the best periods for viewing clear blue skies, especially in the temperate regions located between 30 and 60 degrees north latitude. And south, away from sources of pollution and dust.

Abu Zahira concluded his statement by emphasizing that understanding the causes of the blue sky is not limited to the aesthetic aspect only, but rather reflects a clear picture of the subtle interactions between solar rays and the atmosphere, and enhances appreciation of the beauty of the winter season and its specificity in observing the sky and astronomical phenomena.