Auroras

– By Amna Batool

During my childhood, whenever I had the opportunity of sleeping out in the open, I’d gaze constantly at the stars, somehow secretly wishing for them to show the slightest of dynamism. Then one day I heard of the “curtains of light”: bright green rays flashing with red, and streamers of white. Conjuring the most stunning sights. What overwhelmed me the most was these shimmering curtains do not remain static. They dance through the sky like a celestial ballerina, weaving and twirling.

Source: nasa-spacestation-info.blogspot.com

How I’ve always aspired to see the curtains of light ever since! To experience a cold, dark polar night where nature suddenly rewards you with the spectacular view. The northern lights have had a number of names throughout history. The Cree call this phenomenon the “Dance of the Spirits“. In Europe, in the Middle Ages, the auroras were commonly believed to be a sign from God. If all this wasn’t miraculous enough, I recently found out about the songs of the dancing spirits, The Sounds of the Aurora.

Beautiful images of the aurora are a staple on all science and photography pages. They’re just gorgeous, aren’t they?

But what actually *is* the aurora borealis? Where do these lights come from?

They’ve been spotted throughout human history, but were officially named in 1621 by French scientist Pierre Gassendi. He named them after the Roman goddess of dawn, Aurora, and the Roman god of the north wind, Boreas. In the southern hemisphere, they’re known as aurora australis (meaning “southern”). Although the look very calm and serene, they’re actually the result of millions of explosions of magnetic energy.

Scientifically speaking, energetic particles that enter the atmosphere from the magnetosphere make aurora. Millions and millions of electrically charged particles are emitted from the sun and hit the Earth’s magnetosphere, a volume of space around the Earth caused by Earth’s internal magnetic field. This field extends to space until it is balanced by the solar winds, which would make the planet uninhabitable without the magnetosphere (even if we could breathe without an atmosphere, that is).

Particles from the sun hitting the Earth’s magnetosphere.
Source: earthlyissues.com

The energetic particles are mostly electrons, but can be protons as well. The electrons travel along Earth’s magnetic field lines that (like a dipole magnet) are coming out and going into the Earth near the poles. The auroral electrons are thus guided to high latitude atmosphere where they collide with an atom or molecule and move to an excited state. An excited atom or molecule can return to the ground state by sending off a photon, i.e., by making light.

So, these particles, emitted by the sun, smash into our atmospheric gases. The auroras are colored because at very high altitudes there is atomic oxygen in addition to normal air. The energetic electrons split molecules in air into nitrogen and oxygen atoms. Photons that come out of aurora have, therefore, signature colors of nitrogen and oxygen molecules and atoms.

Auroras on Other Planets:

Aurora on Jupiter.
Credits: John T. Clarke (U. Michigan), ESA, NASA

Auroras do occur on most of the other planets. Auroras have been observed on Jupiter, Saturn, Uranus, Neptune, Venus, and Mars. That leaves only Mercury as the lone planet where an aurora has never been observed. In addition, Jupiter’s moons, Io, Europa, and Ganymede, have been observed with auroras.

Sounds Of the Aurora:

This is a question that’s difficult to answer on scientific grounds as the upper atmosphere is too thin to carry sound waves, and the aurora is so far away that it would take a sound wave 5 minutes to travel from an overhead aurora to the ground. But many people claim that they hear something at the same time when there is an aurora in the sky. I read of only one case where a microphone has been able to detect audible sound associated with aurora.

But what hinders scientists to dismiss the possibility of the phenomenon is the frequency with which these are heard. The sounds are describes as whistling, hissing, bristling, or swooshing. What it is that gives people the sensation of hearing sound during auroral displays is an unanswered question. By searching for an answer to that question, we will probably learn more about the brain and how sensory perception works than about the aurora.

“The whistling crackling noise which sometimes accompanies the aurora is the voices of these spirits trying to communicate with the people of the Earth. They should always be answered in a whispering voice.” 
~ Ernest W. Hawkes, The Labrador Eskimo, 1916

Your Auroral Telegram :

The auroral current can also be used for transmitting and receiving telegraphic dispatches. This was done between 8:30 and 11:00 in the morning, on September 2, 1859, on the wires of the American Telegraph Company between Boston and Portland, and upon the wires of the Old Colony and Fall River Railroad Company between South Braintree and Fall River, among others. The length of time during each positive wave was only, however, 15 to 60 seconds. The following account came from between Boston and Portland.

Portland: “Please cut off your battery, and let us see if we cannot work with the auroral current alone.”
Boston: “I have already done so. We are working with the aid of the aurora alone. How do you receive my writing?”
Portland: “Very well indeed – much better than when the batteries were on; the current is steadier and more reliable. Suppose we continue to work so until the aurora subsides?”
Boston: “Agreed. Are you ready for business?”
Portland: “Yes, go ahead.”

This went on for a period of two hours. After the current from the aurora subsided, the battery was reconnected. The parties at Fort Braintree and Fall River did the same for over an hour, over a distance of 40 miles.

– The author is a senior at Atta-ur-Rahman School of Applied Biosciences.

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