AURORA

Aurora is a natural display of light in the sky that can be seen with the unaided eye only at night. An auroral display in the Northern Hemisphere is called the aurora borealis, or the northern lights. A similar phenomenon in the Southern Hemisphere is called the aurora australis. Auroras are the most visible effect of the sun's activity on the earth's atmosphere.

Most auroras occur in far northern and southern regions. They appear chiefly as arcs, clouds, and streaks. Some move, brighten, or flicker suddenly. The most common color in an aurora is green. But displays that occur extremely high in the sky may be red or purple. Most auroras occur about 60 to 620 miles (97 to 1,000 kilometers) above the earth. Some extend lengthwise across the sky for thousands of miles or kilometers.

Auroral displays are associated with the solar wind. Solar wind is a stream of electrons and protons which are released from the sun due to the high kinetic energy. In other way, our planet is surrounded by a super-sized magnetic sheath which is usually called the Magnetic Field of the Earth. When these particles reach the earth's magnetic field, some get trapped. Many of these particles travel toward 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 colorful 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.

Now, Why Aurora is only found in the earth’s poles? This is the answer, because the north and South Pole magnetic field is very strong compared to other regions. So the phenomenon is more common in the Polar Regions.

However, sometimes the Aurora can also appear at the top of the mountain in a tropical climate, but this phenomenon is extremely rare.