When an interplanetary shock wave – a supersonic disturbance in the gaseous material of the solar wind usually delivered by coronal mass ejections (CMEs) – hit Earth’s magnetic field on April 19th, northern skies lit up with electric blue auroras. Southern skies lit up, too, but the palette was different. Peter Sayers sends this photo of red, yellow and green lights over Wilmot, Tasmania:
Similar colors were observed in New Zealand:
And Antarctic skywatchers witnessed almost pure green:
What’s the difference?
Northern Lights stimulated by the shock wave were dominated by ionized nitrogen molecules, which produce a blue glow at the upper limits of Earth’s atmosphere like below:
Southern Lights, on the other hand, were dominated by oxygen. Oxygen atoms glow red and green when excited by incoming particles from space.
Oxygen and nitrogen are abundant in both hemispheres – so why they dominated in different places is anyone’s guess. Consider it a beautiful mystery.