Aurora Borealis: What Causes Northern and Southern Lights?
Ever thought you could see a multicolored night sky with vivid hues of glorious greens, roaring reds and vivacious violets dancing enchantingly? Surprisingly, this isn’t a description of a background drop for a Disney movie and even though it sounds like pure magic, it is actually a natural phenomenon that occurs high up in the upper atmosphere!
These phenomena are known as Northern lights and Southern lights or according to their Latin names, as Aurora Borealis and Aurora Australis respectively. Aurora Borealis being the more famous sibling, was given its Latin name by Galileo Galilei in 1619 after the Greek goddess of dawn, Aurora and the god of the north winds, Boreas. They were found to be first described in cave paintings in France around 30,000 years ago!
As the names suggest both Northern and Southern lights occur at separate locations with Northern lights occurring nearer to the North Pole or the Northern Hemisphere which covers central and northern Alaska and Canada, Greenland, northern Scandinavia and Russia. These regions within the northern hemisphere are known as the Auroral Zone, having an approximate radius of 1550 miles from the North Pole. Similarly, Southern lights occur in the Southern Hemisphere nearer to the South Pole with Antarctica, Southern Australia, New Zealand and Chile being the prime spots to view them from.
The lights typically occur at altitudes of 100 to 250 kilometers above the Earth’s surface and are mostly distinctly viewed during nighttime away from populous, well lit towns and cities. It incites wonder about how these ethereal phenomena occur, does it not? Well, let’s take a look! These magnificent events occur due to a rather dramatic interaction between the solar activity coming from the Sun and the magnetic field of the Earth.
The Sun’s outermost atmospheric region is called the Corona and this region is filled with hot ionised gases (plasma) which eject these charged particles away from the Sun in the form of solar winds. Some of these high energy particles slam into the Earth’s ionosphere or the upper atmosphere, after being deflected to the poles due to the interference of the Earth’s magnetic field.
These high energy particles coalesce with the atoms present in the upper atmosphere, mainly nitrogen and oxygen, stripping them of their electrons leaving them as charged and excited ions. These excited ions, in order to come down from their excited state to the ground level of energy, start emitting radiation at wavelengths unique to them creating the characteristic colors we see in the sky! Collisions of the high energy solar particles with oxygen creates red and green lights, while collision with nitrogen gives green or purple lights.
The solar winds that come from the sun are constant, however, they differ in energy according to the sun’s solar cycle. This means that sometimes there is a lull in the solar winds creating hazy aurorae while during others the earth is bombarded by so much high energy plasma causing the northern lights to be at their brightest and most frequent in appearance! It is also to be noted that this phenomena isn’t restricted to our planet alone, rather it occurs on other gas planets as well. A great example for this is in the case of planet jupiter.
As mentioned earlier, both Aurora Borealis and Aurora Australis only differ with respect to their locations. However, despite the scientists expectation of mirrored aurorae formations at both Northern and Southern hemispheres due to the high energy particles travelling through symmetrical magnetic field lines in both direction, it was actually observed that sometimes there was a lag in the occurrence of the aurorae at one end when compared to the other causing them to occur at different times in both the poles. This asymmetry in aurorae formation was reasoned to be because of the interference caused by the sun’s magnetic field on that of Earth’s and is a topic where much research is still going on!
Seeing the Northern lights is a definite Bucket List activity for most and therefore it is always good to keep in mind when, where and how you can get the best out of this experience! It is always better to keep within the auroral zone while being away from city lights as they can interfere with the visibility of the lights.
The best time to view these beauties are during the winter months between September and April from 9 PM to 3 AM during a moonless night since it illuminates the sky. Keeping these tiny titbits in mind, start planning your trip to see this ethereal phenomena now!
