Aurora
A giant neon light show in the night sky, switched on when Earth's magnetic shield intercepts particles hurled by the Sun.
Definition An aurora is a natural light display in the sky, produced when energetic charged particles from the Sun are guided by Earth's magnetic field into polar upper atmospheres and collide with oxygen and nitrogen gases.
Cosmic Particles and Earth's Magnetic Shield
When you flip on a fluorescent lamp in a dark room, gas inside the tube gets energized by electricity and instantly glows. An aurora works on the very same principle, lighting up the entire night sky like a giant, natural fluorescent bulb.
The Sun does not just emit heat and light; it constantly spews countless electrically charged subatomic particles in all directions. Scientists call this rushing stream of particles the solar wind. If this powerful blast rained directly down onto Earth's surface, life on our planet could hardly survive.
Fortunately, Earth has an invisible protective shield. Because Earth behaves like a giant magnet, a spherical magnetic field surrounds the planet. This magnetic shield deflects most of the hazardous particles and safely channels some toward the polar skies of the North and South Poles.
A Celestial Light Party of Atmospheric Gases
Funneled by Earth's magnetic field into the high polar atmosphere, solar particles plunge into the upper air at blistering speeds of millions of miles per hour. There, they violently slam into oxygen and nitrogen atoms floating in the upper atmosphere.
The moment they collide, atmospheric atoms absorb intense energy from the solar particles and become excited. Packed with excess energy, these atoms enter an unstable state. To calm down and regain stability, they release that surplus energy back out as brilliant flashes of light.
The color of the glow depends on which gas is struck and at what altitude. When particles collide with oxygen at altitudes between 60 and 120 miles (100โ200 km), they produce the iconic soft green glow. When they strike nitrogen, they paint the sky with vivid crimson and violet curtains.
A Closer Look at the Physics
Auroras are not exclusive to the Arctic. An equally stunning light display occurs in the Antarctic skies, known as the aurora australis or Southern Lights. This happens because solar particles stream simultaneously down both magnetic funnels of Earth.
In physics, this emission of light is explained by atomic energy level transitions. When incoming particles kick electrons into higher outer orbits, the electrons quickly drop back down to their ground state, releasing precise packets of light called photonsโa textbook quantum mechanical process.
Another key fact is that auroras are not caused by freezing winter weather. They are not reflections off polar ice crystals; rather, they occur in the near-vacuum of space more than 60 miles above the ground. How large and bright an aurora appears depends entirely on solar flares and sunspot activity, not ground weather.
๐ค Common misconceptions
Auroras are caused by freezing polar weather and light reflecting off snow and ice.
Auroras have nothing to do with surface weather or cold temperatures. They are physical reactions occurring over 60 miles (100 km) up in space, where solar particles collide with atmospheric gases.
๐งบ Where you meet it
A celestial light show created when charged particles from the Sun are funneled by Earth's magnetic field to collide with upper atmospheric gases.