Have you heard of (or seen) these stunning waves of light? We’re talking about the Aurora Borealis – pronounced as: uh·raw·ruh, baw·ree·aa·luhs
What is the Aurora Borealis?
These are basically a display of lights that occur naturally in the Earth’s Northern Hemisphere – hence also commonly called the northern lights.
When these are seen at the South Pole, it is called Aurora Australis or the Southern Lights.
What are Auroras and how are these lights formed?
An aurora is a natural light display in the sky that is caused by charged particles from the sun interacting with Earth’s magnetic field.
Let’s uncomplicate it further…
An aurora is a light display that occurs naturally, in the sky. These lights are usually blue, red, yellow, green, and orange lights. They are only visible at night, and usually only in lower polar regions.
Ok, and how exactly are auroras formed?
Here’s the interesting part. Auroras can best be seen at night, but, they are actually caused by the Sun!
The simple explanation
Auroras happen when electrically charged particles from the Sun meet (collide) with the gases in Earth’s upper atmosphere. These “collisions” cause billions of flashes of light in the night sky, which is what we see.
It looks like this:
The scientific explanation
The sun gives us heat and light. We all know that. But, it also sends to us other things like small electrically charged particles that are called ions.
This stream of ions is called the solar wind, and this wind constantly reaches the Earth from the Sun. It also sends us, solar storms – think of this as a massive bubble of electrically charged gas. This travels at a very high speed.
When this solar wind/storm (of hot and charged particles) reaches the Earth, it meets the Earth’s magnetic field (the protective layer around our Earth). This is when the ions from the Sun mix with the gases in our atmosphere – and this coming together results in stunning lights across the night sky in the polar regions.
Do you know that if there was no magnetic field, our planet would not be livable? The magnetic field protects the planet. If this was not there, the solar wind would blow away Earth’s fragile atmosphere thereby preventing all life from existing.
What do the different colours mean?
It’s the kind of gas that determines the colours.
Oxygen gives off green and red lights. Nitrogen glows blue and purple.
Every type of atom or molecule absorbs and radiates (sends outwards) its own unique set of colours.
Simply put – the colours of the aurora depend on altitude and the kind of atoms involved. If ions strike oxygen atoms high in the atmosphere, it results in a red-green glow, though this is not as common.
The most familiar display, a green-yellow hue, occurs as ions strike oxygen at lower heights. Blue and red light are produced by ions striking atoms of nitrogen at lower altitudes – these mix to give off purple-bluish light.
Other planets and auroras
Auroras don’t take place on the Earth only. They occur on other planets since all that is needed to make this is a planet’s atmosphere and a magnetic field.
What’s interesting is that while auroras have been seen in the atmospheres of the gas giant planets, they have also been spotted in Venus and Mars, which is surprising given the fact that both these planets have weak magnetic fields.
Origins of the name
The Italian astronomer Galileo Galilei coined the name ‘Aurora Borealis’ in the year 1619 — after the Roman goddess of dawn, Aurora, and the Greek god of the north wind, Boreas.
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