The northern lights, also known as the aurora borealis, are a breathtaking natural phenomenon that has fascinated humanity for centuries. These mesmerizing displays of colorful lights in the night sky occur primarily in polar regions, such as north of the Arctic Circle. The science behind the northern lights is a captivating tale of interactions between the Earth’s atmosphere, charged particles from the sun, and our planet’s magnetic field.
At the heart of the northern lights is the sun, a massive star that emits a continuous stream of charged particles, mainly superheated electrons and protons, known as the solar wind or plasma. These particles carry a significant amount of energy and are constantly streaming out into space. Occasionally, the sun releases solar eruptions, like solar flares or coronal mass ejections (CME), which release even larger quantities of charged particles into space. If you want to know when they happen I reccomend subscribing to the Space Weather Live webpage.
When these charged particles from the sun reach Earth, they interact with our planet’s magnetic field, also known as the magnetosphere. Earth’s magnetosphere is generated by the motion of molten iron in its outer core, creating a protective magnetic shield around the planet. This shield deflects most of the solar wind particles away from Earth.
Once inside the magnetosphere, some of the particles are channeled along the Earth´s magnetic field lines towards the polar regions. These charged particles follow the field lines to regions near the north- and south poles. As these energetic particles enter the Earth’s atmosphere, they collide with gas molecules, predominantly oxygen and nitrogen. In short - we have both northern- and southern lights.
These collisions cause the gas molecules to become excited. In their excited state, the electrons in these molecules move to higher energy levels. To return to their normal energy levels (equilibrium), they release the excess energy in the form of light - also known as photons. The color of the light emitted depends on the type of gas molecules involved and the altitude at which the collisions occur.
Oxygen molecules, for instance, emit predominantly green and red light when they return to their normal energy levels, creating the classic green and red hues of the northern lights. Nitrogen molecules can emit a variety of colors, including pink, purple, and blue. The altitude at which these interactions take place also influences the appearance of the auroras. The typical altitude for the northern lights is between 80 and 300 kilometers (50 to 186 miles) above the Earth’s surface.
The intensity, color, and shape of the northern lights vary depending on several factors, including the energy of the incoming solar particles, the altitude of the interactions, and the composition of the Earth’s atmosphere at that location.
The northern lights are not a constant phenomenon, but follow an approximately 11-year cycle known as the solar cycle, which corresponds to the Sun’s varying activity. During solar maximum, when solar activity is at its peak, the northern lights become more frequent and spectacular.
In conclusion, the northern lights are a beautiful result of the complex interplay between the sun, the Earth’s magnetic field, and our planet’s atmosphere. They serve as a stunning reminder of the dynamic and interconnected nature of our universe, captivating both scientists and spectators alike with their ethereal dance across the polar skies.
Tromsø is a particularly good spot to get a glimpse of the lights. The city is situated directly under the Northern Lights oval at 69 degrees north, and there are plenty of options to find clear skies. Tromsø is also the 2nd largest city north of the Arctic Circle with 80.000 people. There are plenty of options if you want to spend a week with a few days aurora hunting, and maybe a day or two dogsledding and snowshoeing.
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