For centuries, the ethereal dance of light across the polar skies has captivated humanity. Known as the aurora borealis in the Northern Hemisphere and the aurora australis in the Southern Hemisphere, these celestial displays, often called the ‘northern lights’ and ‘southern lights’, have inspired awe, wonder, and even fear. Modern photography now allows us to capture and share the breathtaking beauty of these atmospheric phenomena. But What Causes The Northern Lights?
The Solar Connection: How the Sun Fuels the Aurora
The secret behind the mesmerizing aurora borealis lies far beyond our planet, originating millions of miles away on the surface of our Sun. Our star is a dynamic and active entity, and occasionally, it experiences powerful solar storms. These storms unleash enormous clouds of electrically charged particles into space.
These energetic particles embark on a journey across vast distances, and some are directed towards Earth. While our planet possesses a natural defense mechanism, a magnetic field, to deflect most of this solar debris, some particles manage to penetrate this shield.
Earth’s Magnetic Field: Guiding Particles to the Poles
Instead of being completely repelled, a portion of these charged particles become ensnared by Earth’s magnetic field. This magnetic field acts like a funnel, channeling the particles towards the Earth’s magnetic poles, located near the geographic North and South Poles. This explains why aurora activity is predominantly observed in the polar regions.
As these particles are accelerated down towards the poles, they collide with our atmosphere. Tom Kerss, an astronomer at the Royal Observatory, explains the subsequent process: “These particles then slam into atoms and molecules in the Earth’s atmosphere and essentially heat them up. We call this physical process ‘excitation’, but it’s very much like heating a gas and making it glow.”
Therefore, the aurora borealis we witness is essentially the result of collisions between solar particles and the gases present in Earth’s atmosphere. The characteristic rippling curtains and wavy patterns of the aurora are shaped by the lines of force within the Earth’s magnetic field, adding to their otherworldly appearance. Auroras typically begin around 80 miles above the Earth’s surface, but the most spectacular displays can extend thousands of miles into the sky.
The Colorful Canvas: Oxygen and Nitrogen Paint the Aurora
The diverse and vibrant colors of the aurora are not arbitrary; they are a direct consequence of the types of atmospheric gases involved in the excitation process. Just as different chemical elements emit distinct colors when heated, the gases in our atmosphere contribute to the aurora’s palette.
Earth’s atmosphere is primarily composed of nitrogen and oxygen, and these two elements are the key players in aurora coloration. The familiar green hues often seen in auroras are characteristic of oxygen atoms at lower altitudes. In contrast, nitrogen is responsible for the hints of purple, blue, or pink that can also grace the aurora display.
Astronomer Tom Kerss further elaborates on the rarer scarlet red color: “We sometimes see a wonderful scarlet red colour, and this is caused by very high altitude oxygen interacting with solar particles. This only occurs when the aurora is particularly energetic.” This vibrant red is a sign of a particularly powerful and high-reaching aurora.
Spotting the Northern Lights: Visibility in the UK and Beyond
While the most frequent and intense aurora displays are observed closer to the polar regions, the aurora borealis can sometimes grace the skies of the UK and other mid-latitude locations. Generally, the further north you are, the greater your chances of witnessing the northern lights. However, periods of heightened solar activity can lead to auroral displays visible much further south, even as far as Cornwall and Brighton in the UK.
To maximize your chances of seeing the aurora, certain conditions are essential. Dark and clear nights are paramount, and minimizing light pollution from cities and towns will significantly improve visibility.
For those in the UK eager to track aurora possibilities, Lancaster University’s Department of Physics operates the website AuroraWatch UK. This valuable resource provides estimates of aurora visibility based on geomagnetic activity, helping sky watchers determine when conditions might be favorable for witnessing this incredible natural light show.
