Aururas dance in the night sky:

You may think that the spectacular pictures here are those of a fireworks display held to usher in the New Year which dawned just yesterday, but they are not.The vibrant hues that light up the night sky have nothing to do with fireworks because they are the famous auroras or the northern or southern lights which occur as a natural phenomenon. Let's check out how these lights light up the sky just in case you are not familiar with them ....

First we need to know what an aurora is. An aurora is a natural display of light in the sky that can be seen without the aid of a telescope,that means, the naked eye or the unaided eye. However, an aurora can be seen only at night.

An auroral display in the Northern Hemisphere is called the Aurora borealis, or the Northern Lights while a similar display in the Southern Hemisphere is called the Aurora Australis or the Southern Lights .

These auroras which are known to be simply awesome to watch are the most visible effect of the sun's activity on the Earth's atmosphere.

Most of these auroras generally occur in far northern and southern regions. They appear mainly as arcs, clouds, and streaks. According to scientists some of these spectacular auroras either move, brighten up, or flicker suddenly.

When you look at the beautiful pictures of the auroras featured here you will be able to note that they come in many vibrant hues. The most common colour in an aurora is green. Scientists claim that displays that occur extremely high in the sky could be either red or purple.But auroras do not make their appearance just anywhere on the Earth, even in the regions they generally occur. Most auroras occur about 60 to 620 miles (97 to 1,000 kilometres) above the Earth. Some even extend lengthwise across the sky for thousands of miles or kilometres.

Auroral displays are associated with the solar wind, a continuous flow of electrically charged particles from the Sun. When these particles reach the Earth's magnetic field, some get trapped. Many of these particles travel towards the Earth's magnetic poles. When the charged particles strike atoms and molecules in the atmosphere, energy is released. Some of this energy appears in the form of Auroras. Auroras occur most frequently during the most intense phase of the 11-year sunspot cycle. During this phase, dark patches on the Sun's surface, called sunspots, increase in number. Violent eruptions on the Sun's surface, known as solar flares, are associated with sunspots.

Electrons and protons released by solar flares add to the number of solar particles that interact with the Earth's atmosphere. This increased interaction produces extremely bright auroras. It also results in sharp variations in the Earth's magnetic field called magnetic storms. During these storms, auroras may shift from the polar regions toward the equator.

How do auroras form?

Essentially, the light of auroras is emitted when charged particles in the solar wind excite the electrons of atmospheric atoms through collisions. As the electrons return to their original energy levels, these atoms, primarily oxygen and nitrogen, emit photons of visible light of distinct wavelengths to create the colours of the auroral display. The wavelength of the light depends upon the electronic structure of the atoms or molecules themselves, and on the energy of the charged particle colliding with the atom or molecule.

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FAST FACTS

*During the luminous phenomenon of an aurora, streams of colourful light appear as reds, greens, yellows, pinks, and purples.

* Auroras occur on other planets too. Auroras have been observed on Jupiter and Saturn which have magnetic fields much stronger than the Earth's.

* Auroras have been observed even on Venus and Mars. However, as Venus has no planetary magnetic field auroras appears as bright and widely spread patches of varying shapes and intensity

* The best aurora viewing time in the Arctic is during the Northern Hemisphere's winter, and in the Antarctic during the Southern Hemisphere's winter, when long, dark nights provide the best conditions. This is not because the auroras are seasonal" in fact, satellite pictures reveal that auroras occur simultaneously in the two polar regions of the magnetosphere.

* The Aurora Borealis and the Aurora Australis share many characteristics. The small differences between them depend on which pole is oriented towards the solar wind, and may also reveal irregularities in the Earth's magnetic field.

* The spring and summer equinoxes have been identified as another period of intense auroral activity. Scientists speculate that these two related points in Earth's orbit of the Sun favour the interaction of the magnetic activity between the two bodies.

* An aurora was detected on Mars on August 14, 2004 by the SPICAM instrument aboard the Mars Express.

* Images of auroras are common today due to the use of digital cameras that have high sensitivities.

* In ancient Roman mythology, Aurora is the goddess of the dawn, who renews herself every morning to fly across the sky, announcing the arrival of the Sun.

* An image of an aurora was used as part of the emblem for the 1994 Winter Olympics held in Lillehammer.

* Northern lights are named after the Roman goddess Aurora and the Greek name for the north wind Boreas.

*Australis is the Latin word for 'of the South'

* Aurora australis can be seen only from high southern latitudes in Antarctica, South America or Australasia.

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