September 18, 2021, 02:26 PM
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Another bright sunny day in Singapore, another sun halo.
For at least an hour before and after noon on Sep. 18, a distinct halo could be observed around the sun from various parts of Singapore.
Photo by Eng Kuan Mooi/FB.
Photo by June Lim/FB.
Photo by June Lim/FB.
Photo by Fa Xin Lim/FB.
What are sun halos?
When the sun is behind high, thin cirrus clouds, a faint ring encircling the sun appears.
Higher than six kilometers above ground level, these wispy clouds contain millions of tiny ice crystals which refract and reflect sunlight.
According to the National Environment Agency, sun halos are created when light is refracted through these ice crystals.
They then appear as a halo positioned with respect to your eye.
According to the University of Illinois, this happens when sunlight enters one side of an ice crystal in the cloud and exits through the side at a 22-degree angle.
Sun halos are therefore also known as 22 degree halos because the light is bent through refraction by 22 degrees.
With the right conditions, our moon can also create halos.
Though uncommon, there have been several sightings in the past month - so keep a lookout for them around noon and remember to bring your sunglasses.
Image by Cynthia Swee Swee Ng/FB.
Image by Cynthia Swee Swee Ng/FB.
Image by Ladini Ransirini Sondarangalla/FB.
Image by Jane Zhang.
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