Aurora: The holy grail of skywatching
Have you seen light shows in the night sky? The green, blue, pink dancing waves of light? They are very delightful to watch. These lights are named Aurora Borealis (Northern lights) and Aurora Australis (Southern lights). On Arctic nights the aurora often flames across the winter sky.
Aurora is the Roman goddess of dawns. In Greco- Roman mythology, Aurora was the sister of the Sun and the Moon. They believed that Aurora flew in her chariot everyday to alert her brothers about the arrival of a new day.
Sun ! This is where the tale of the Aurora starts. A collection of charged particles from the Sun’s outermost atmosphere is expanded outwards . This collection of charged particles is called a plasma. Sun becomes unable to hold the plasma once it is heated to a certain temperature. Then it travels along the Sun’s Magnetic field causing a solar wind. During the solar wind, ie, the sudden release of energy stored in the magnetic fields of the sun, a large number of electrons and protons are ejected from the sun. This solar wind can reach speeds over eight million kilometers in an hour. After six hours it blows past the planet Mercury. After twelve hours , the planet Venus and after 18 hours the solar wind reaches Earth. When it reaches the earth something strange happens. Earth’s magnetic field deflects the wind, and they couple together. At that instant, some of the charged particles get trapped in the earth’s magnetic field and traverse across the field in a helical path.
The Earth’s magnetic field lines come closer to each other near the magnetic poles. Hence the density of charges increases near the poles. These particles collide with the atoms and molecules of the earth’s atmosphere. The energy emitted from this crash produces spectacles of light the mankind has marveled at for centuries. The excited oxygen atoms emit green or orange red light and excited nitrogen atoms emit purple, blue or red light.
Now it must be clear why this captivating phenomenon occurs at the poles. It is also named Polar lights. They are best seen on clear nights in regions close to magnetic north and south poles. Night time is ideal because Aurora is much dimmer than the sunlight.
Are they observed only on Earth?
Nope! They are hosted on many planets in the solar system along with some natural satellites. With the help of the Hubble Space Telescope, Aurora has been observed on Jupiter, Saturn and even on some planet’s moons. Both these gas planets have Magnetic fields stronger than that of Earth. The first extra- solar aurora was observed above the brown dwarf in July 2015.To get more information about these lights, specially designed satellites were launched by the scientists.
Where to spot Aurora ?
Iceland is the only location in which Borealis can be spotted almost anywhere in the country. Finland, Sweden, Alaska, Canada, Norway, Russia, Greenland, Scotland, Denmark etc are the other countries which host the northern lights. Whereas, the southern lights can be best seen from Tasmania, New Zealand, Australia and Antarctica. Antarctica is the classic place for viewing them but, due to the inhospitable climate, only researchers could go that far when the conditions for auroras are at their best.
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