Some Singaporeans noticed a strange phenomenon in the sky on Wednesday evening, Feb. 13.

When they looked up, they saw that the sky was divided into two distinct shades of blue.

Split sky

This phenomenon was observed at various locations across Singapore at around 7pm.

Here are some photos posted on Instagram.

In Jurong

Here's the text in the post:

"SERIOUSLY there is no filter on the glass in the car. The sky is really divided in 2 different distinct shades of blue. Pollution? So straight and distinct the line?

Half the sky.

I thought it was my eye but the iphone camera also captures the same. Authenticated by another 2 persons in the car. Not a problem with my ?

What a sky!

Mum says u r really very free to look at the sky and the birds.

What is life if you don’t keep a look out and just blindly live by day? Hmmm. What do you think?"

In Bishan

Another Instagram user also caught this rare and peculiar sight.

"Split sky... ?"

"Here’s yet another pic of that “split sky”... Probably caused by a strange shadow effect from that huge cloud in my previous pic."

What happened?

The sky appeared to be divided because of an optical illusion attributed to anti-crepuscular rays.

Anti-what?

A spokesperson of Meteorological Service Singapore explained that anti-crepuscular rays are parallel shafts of sunlight that extend past clouds blocking the sun and are visible because of scattering of light by small water droplets or particles in the atmosphere.

Something like that:

The sun rays converge to a point in the sky that is directly opposite of the sun creating this rare sight.

This meteorological optical phenomenon typically occurs during sunrise or sunset.

Top photo collage from @eugenetan72 and @tplyn