The Green Comet will be closest to earth on Feb 1. Here's the science behind its ghoulish glow.

• A green comet is whizzing past the earth for the first time since the ice age. 
• The comet's head shines green, while its tail shines white. 
• Scientists found out why it glows this way in 2021, and it comes down to physics. Here's how it works. 

A green comet called C/2022 E3 (ZTF), or Comet ZTF for short, is nearing its closest approach to earth for the first time since the ice age. 

Comet ZTF will come within 26 million miles (42 million kilometers) of our planet on Wednesday, about a third of the distance between the earth and the sun.