Northern Lights Explained: What Causes Aurora Borealis?

The northern lights, or aurora borealis, are a spectacular display of natural light which have captivated humans for millennia. This celestial phenomenon regarded as the Holy Grail of skywatching results from a rather violent event.

What Causes Aurora Borealis?

The upper atmosphere of the Sun, known as the corona, contains charged particles that could be ejected at any given moment to create solar wind. These particles can travel up to 45 million mph (72 million kph), and some can eventually reach our planet.

As these particles collide with the Earth, most are deflected away, but some get captured in the magnetic field, accelerating down towards the north and south poles into the atmosphere. This is why aurora activity is concentrated only at the magnetic poles.

When these particles slam into atoms and molecules in the Earth's atmosphere, they get heated in the process called 'excitation,' like heating gas and making it glow. Therefore, the colorful display of light is the atoms and molecules in our atmosphere colliding with charged particles from the Sun.

The characteristic wavy patterns and 'curtains' of light are caused by the lines of force in the Earth's magnetic field. Meanwhile, the different colors observed in this phenomenon are due to varying gases like nitrogen and oxygen. The green color is emitted by oxygen gas, while the hints of pink, blue, or purple are caused by nitrogen.

Since an atmosphere and a magnetic field are all required to make an aurora, this celestial display can also occur on other planets. This phenomenon has been observed in the atmosphere of all the gas giant planets, and it is not surprising considering these planets all have strong magnetic fields.

Where and When to See the Northern Lights

The northern lights are happening all the time - 24 hours a day, seven days a week, 365 days a year. However, it does not mean that they are easy to spot, so you need to be at the right place at the right time.

According to the Tromsø Geophysical Observatory in Norway, the best place to see the northern lights is any point in the "auroral zone." This region is located within an approximately 1,550-mile (2,500 km) radius of the North Pole. This is where the aurora most frequently occurs, although this phenomenon can also creep farther south, especially during intense solar storms. Within the auroral zone, it is best to be as far away from city lights as possible for maximum visibility.

Meanwhile, the best time of the year to see aurora borealis is between September and April, as these are the months when the sky gets dark enough to see the light displays. The Geophysical Institute of the University of Alaska Fairbanks suggests that the most action usually occurs between 9 p.m. and 3 a.m.

In watching aurora borealis, the moon phases must also be considered since the bright full moon could fill the night sky with light. The local weather forecast must also be checked because the aurora cannot be spotted through the clouds.