We all have seen lightning when it rains. Sometimes its scary and sometimes its beautiful. But it is not possible to see it with a naked eye, so if you want to experience the same you must visit Aurora borealis, that creates natural light display.
An aurora is a natural light display that shimmers in the sky. Blue, red, yellow, green, and orange lights shift gently and change shape like softly blowing curtains. Auroras are only visible at night, and usually only appear in lower polar regions.
In the North, the display is called Aurora Borealis, or northern lights. In the south, it is called Aurora Australis, or southern lights.
The activity that creates Auroras begins on the sun. The sun is a ball of superhot gases made of electrically charged particles called ions.
The northern lights are an atmospheric phenomenon that’s regarded as the Holy Grail of skywatching.
The words “borealis” and “australis” are derived from the names of the ancient gods of the north wind (Boreas) and the south wind (Auster) in Greek mythology.
Most auroras occur in a band known as the “auroral zone”,most clearly seen at night against a dark sky. A region that currently displays an aurora is called the “auroral oval”, a band displaced by the solar wind towards the night side of Earth.
A geomagnetic storm causes the auroral ovals (north and south) to expand, bringing the aurora to lower latitudes. The instantaneous distribution of auroras is slightly different, being centered about 3–5° nightward of the magnetic pole, so that auroral arcs reach furthest toward the equator when the magnetic pole in question is in between the observer and the Sun. The aurora can be seen best at this time, which is called magnetic midnight.
Auroras seen within the auroral oval may be directly overhead, but from farther away, they illuminate the poleward horizon as a greenish glow, or sometimes a faint red, as if the Sun were rising from an unusual direction. Auroras also occur poleward of the auroral zone as either diffuse patches or arcs,which can be subvisual.
According to Clark (2007), there are four main forms that can be seen from the ground, from least to most visible.
Auroras change with time. Over the night, they begin with glows and progress towards coronas, although they may not reach them. They tend to fade in the opposite order. Until about 1963 it was thought that these changes are due to the rotation of the Earth under a pattern fixed with respect to the Sun.
Later it was found by comparing all-sky films of auroras from different places that they often undergo global changes in a process called auroral substorm. They change in a few minutes from quiet arcs all along the auroral oval to active displays along the darkside and after 1 to 3 hours they gradually change back. Changes in auroras over time are commonly visualised using keograms.
Aurora noise, similar to a crackling noise, begins about 70m above Earth’s surface and is caused by charged particles in an inversion layer of the atmosphere formed during a cold night. The charged particles discharge when particles from the Sun hit the inversion layer, creating the noise.