Polar Aurora (or aurora polaris) is a phenomenon in the form of glitter or glow on the night sky , common in polar regions, but can occur in other parts of the world for short periods. In the northern hemisphere the phenomenon is known as aurora borealis, named after Aurora , the Roman goddess of dawn, and the Greek Boreas , meaning north, because in Europe it commonly appears in the horizon with a reddish hue, as if the sun emerged from an unusual direction, and in the southern hemisphere as aurora australis,.
The Northern Lights are visible from September to March, though at times makes its appearance over the course of months, as long as the atmospheric temperature is low enough. The best months to see it are January and February, as it is in these months where temperatures are lower.
Science behind the Phenomena
An aurora occurs when a solar mass ejection collides with the north and south poles of the magnetosphere Earth, producing a diffuse but predominantly light projected on the ionosphere land.
Sun, located 150 million km from Earth, is continually emitting particles. That is the flow of particles called solar wind . The sun's surface or photosphere is about 6000 ° C, but when you go into the sun's atmosphere to upper layers the temperature increases rather than decreases, as the intuition would suggest. The temperature of the solar corona , the outermost zone that can be seen with the naked eye only during total solar eclipses, reaches temperatures of up to 3 million degrees. As the pressure on the surface of G major in the empty space, the charged particles found in the atmosphere of the Sun tend to escape and are accelerated and channelled by the magnetic field of the sun reaching the orbit of the Earth and there. There are very energetic phenomena, such as flares or coronal mass ejections that increase the intensity of the solar wind.
The solar wind particles travelling at speeds from 300 to 1000 km / s, so walking the Earth-Sun distance in about two days. In the vicinity of the Earth, the solar wind is deflected by the Earth's magnetic field or magnetosphere. The particles flow in the magnetosphere of the same way as a river around a stone or a pillar of a bridge. The solar wind also pushes the magnetosphere and deformed so that instead of a uniform magnetic lines as they show an imaginary magnet placed in a north-south direction in the interior of the Earth beam field, what you have is an elongated structure shaped kite with a long tail in the opposite direction to the sun's charged particles have the property of being trapped and travel along the magnetic field lines, so that will track you mark them. Trapped particles in the magnetosphere collide with atoms and molecules of Earth's atmosphere, typically oxygen (O), nitrogen (N) atomic and molecular nitrogen (N 2) that are in their lowest energy, called fundamental level. The energy input provided by the particles disturbs those atoms and molecules, leading to excited energy states. After a very small, on the order of millionths of a second or even less time, atoms and molecules return to the ground level, and return the energy as light. That light is what we see from the ground and called auroras. Auroras are kept above 95 km because at that altitude the atmosphere, although very thin, it's dense enough for collisions with charged particles occur so frequently that the atoms and molecules are practically at rest. On the other hand, the aurora can not be higher than the 500-1000 km because at that point the atmosphere is too thin-sparse-for the few collisions that occur have a significant effect.
It's called aurora borealis when this phenomenon is observed in the northern hemisphere and aurora australis when observed in the southern hemisphere . There is no actual difference between them.
More about Auroras
Shape and Colour
Auroras can be of different colours even though it commonly appears with a reddish hue, More interestingly, it occurs in different shapes and changes shape constantly with respect to time. The shape can be like an elongated string at midnight while it can slowly change and expand to have different other shapes as well.
As far as the colour of an aurora is concerned Oxygen is responsible for two primary colours of the aurora, green / yellow for a transition of energy 557.7 nm , while the red produces a less frequent 630.0 nm transition. To get an idea, our eye can see colours from violet in the spectrum would have a wavelength of about 390.0 nm to the red, about 750.0 nm. Nitrogen is the major colliding particle to produce blue light while the Helium is responsible for red light.
Auroras on other planets
This phenomenon also exists in other planets of the Solar System, as in the case of Jupiter and Saturn which have stronger magnetic fields than Earth ( Uranus , Neptune and Mercury also possess magnetic fields ), and both have large radiation belts . Auroras have been observed on both planets with the Hubble telescope.
Auroras have also been detected on Mars by the NASA spacecraft, by some observations made in 2004 and published a year later. Mars lacks a magnetic field similar to Earth, but has local fields associated with its bark. These are apparently responsible for the auroras on this planet.