Tuesday, 7 May 2013
The word ‘Aurora’ comes from the Latin word which means ‘sunrise’. An aurora is a natural light display in the sky found particularly in the Artic and Antartic regions. This phenomenon occurs due to the collisions between electrically charged particles from the sun that enter the earth’s atmosphere. The lights are seen above the magnetic poles of the northern and southern hemispheres; also known as the ‘Aurora borealis’ and ‘Aurora australis’ respectively.
Aurorae are classified as diffuse and discrete. The diffuse aurora is a featureless glow in the sky that may not be visible to the naked eye, even on a dark night. It defines the extent of the auroral zone. The discrete aurora are sharply defined features within the diffuse aurora that vary in brightness from just barely visible to the naked eye, to bright enough to read a newspaper at night.
The Northern lights are a result of collisions between gaseous particles in the earth’s atmosphere with charged particles released from the sun’s atmosphere. The connections between the Northern Lights and sunspot activity have been known since 1880. Since the temperature above the surface of the sun is millions of degrees Celsius, collisions between gas molecules are frequent and explosive. Free electrons and protons are thrown from the sun’s atmosphere by the rotation of the sun and escape through holes in the magnetic field.
Variations in color are seen due to the type of gas particles colliding and on how much energy is being exchanged. Oxygen emits either a greenish-yellow light or a red light. Auroral displays appear in many colors like shades of red, yellow, blue and violet. Pale green and pink are the most common ones. These lights appear in many forms from patches or scattered clouds of light to streamers, arcs, rippling curtains or shooting rays that light up the sky with an eerie glow.
Aurora’s usually occur in ring-shaped areas centered around the magnetic poles of the Earth. The complete rings, called the auroral ovals, can only be seen from space. The best places to see the Aurora are in Alaska, Canada and Scandinavia, during the late evening hours.
The shape of the aurora depends on where in the magnetosphere the electrons came from and what caused them to precipitate into the atmosphere. Dramatically, different auroral shapes can be seen in a single night.