What is the aurora oval?

Two ovals, one mechanism

There are two of these rings. The northern one (aurora borealis) hovers above Norway, Iceland, Greenland, northern Canada, and Alaska on quiet nights. The southern one (aurora australis) sits over the Antarctic and only reaches Tasmania and New Zealand when the sun gets cranky.

Both ovals are tied to the magnetic poles, not the geographic ones. That is why Iceland sees more aurora than equally northern parts of Siberia: the magnetic pole is currently drifting through the Canadian Arctic, which pulls the oval closer to North America and northern Europe.

How the oval moves

The ring is not static. It pulses with the solar wind. When a coronal mass ejection (CME) hits Earth, the oval expands toward the equator within minutes, and parts of it can lobe out into long streamers reaching far further south than the average shape would suggest.

You can think of it as a constantly breathing, slightly wobbling halo. Even on a quiet night it shifts a few degrees north or south every few hours. On a stormy night it can grow to twice its quiet size in under an hour.

How to read an oval forecast map

NOAA publishes the live oval forecast under the name OVATION Prime. Apps that show "where is the aurora right now" all pull from this or one of its derivatives. The map uses three things you should know how to read:

• Position: the band shows where the oval sits at this moment. If your city is inside the band, you are in the right zone.
• Intensity: brighter colours (yellow, red) mean the oval is producing more light there. Black or dark green means the oval has reached you but is quiet.
• Direction: most maps show the oval as a continuous loop, but you should pay attention to which side is brighter. The aurora often lobes out toward midnight (local time), so the bright side of the oval moves around the planet as the Earth rotates.

If you are standing outside, look toward the pole. The oval is always poleward of you, even if its lower edge is right overhead. The lights themselves can appear anywhere between the horizon and zenith.

The southern oval is harder to see

Most people who see the aurora live in the northern hemisphere because most populated land sits closer to the northern magnetic pole. Tasmania, southern New Zealand, and the southern tip of Chile and Argentina are the populated places that can occasionally catch the southern oval. Antarctica is, of course, directly under it, but few people are watching from there.