You may have noticed that the night sky appears a little reddish sometimes after it rains, especially on some days. However, during the day you would not see the same thing. So, why does the sky turn reddish in the evening after rain?
It is believed that the colour of the sky can predict the weather. It’s said that “Red sky at night is a sailor’s delight”. When the sky is red at night, high pressure is moving in from the west, and the next day is usually dry and pleasant.
- Firstly, the sun rises in the East during the day, and storms like to move from West to East during the night. As the sun rises in the morning, it will shine from the east, and it will reflect from the approaching storm clouds to the west, before returning to you in the form of a red hue. This is why storm clouds and the sky appear red during the night when storms leave.
- Secondly, while the sun sets in the west, its light travels through hundreds of miles of atmosphere before hitting the clouds above us, becoming extremely red as it does so. Red skies at night indicate that there are clouds overhead but clear skies to the west, which means the weather will likely improve.
- Thirdly, when dust and small particles are trapped in the atmosphere by high pressure, a red sky appears. In turn, this scatters blue light, leaving only red to create the sky’s characteristic appearance. The red wavelengths penetrate the air more readily than the blue ones. Among the visible colours, red has the longest wavelength, so when the sun is on the horizon, it appears red.
- Lastly, it appears that the sky is red because of the reflected city lights, even though the city lights don’t appear strongly red. Based on a theory, this is due to the minimization of blue and indigo components of light in the reflection process and its passage through the atmosphere. Thus, we perceive a red sky due to orange and red components left behind.
Also published on Medium.