In polar regions of the world, a dazzling light show often plays out in the night sky. It’s called an “aurora“. Up North, it’s also known as the “northern lights“. It looks as if someone had stirred bright lights into the darkness, like cream into coffee. The lights are often green, but they also might glow red, yellow or other colors. Every so often, these lights explode in brightness. Such dramatic flare-ups are called “auroral substorms“.
They produce a surge of intense light that travels westward. Now, two Japanese researchers have unraveled the physics behind these substorms. In short, they say: Blame the sun.
A stream of charged particles, called the “solar wind“, constantly flows out from the sun. When those particles collide with the Earth’s magnetic field, they set off a cascade of collisions. That eventually leads to the light show.
The aurora first appears as a faint shine, usually only visible after the sun goes down. Substorms occur after the initial glow. To an observer on the ground, a substorm looks like the aurora gets brighter. Then sparks seem to travel westward.
MORE ABOUT AURORAS…
Northern Lights can be seen in the northern or southern hemisphere, in an irregularly shaped oval centred over each magnetic pole. The lights are known as “Aurora borealis” in the north and “Aurora australis” in the south.
Scientists have learned that in most instances northern and southern auroras are mirror-like images that occur at the same time, with similar shapes and colours.
Researchers have also discovered that auroral activity is cyclic, peaking roughly every 11 years. The next peak period is 2024, 2013 being the last.
Winter in the north is generally a good season to view lights. The long periods of darkness and the frequency of clear nights provide many good opportunities to watch the auroral displays. Areas that are not subject to ‘light pollution’ are the best places to watch for the lights. Areas in the north, in smaller communities, tend to be best.