Polar aurora

Polar aurora is an optical phenomenon composed of a glow observed in the night skies in the polar regions, due to the impact of solar wind particles and space dust found in the Milky Way with the Earth's upper atmosphere, channeled by the earth's magnetic field. In the northern hemisphere it is known as northern lights or northern lights (most common name among Scandinavians), and usually occurs from September to October and from March to April. In the southern hemisphere is known as aurora austral.

The phenomenon is not unique to Earth alone, but is also observable on other planets such as Jupiter, Saturn, Mars, and Venus. Similarly, the phenomenon is not unique to nature, but is also reproducible artificially through nuclear or laboratory explosions.

The aurora typically appears as either a diffused glow or as a horizontally extended curtain. Sometimes arcs are formed that can constantly change shape.

Each curtain consists of several parallel rays aligned in the direction of the magnetic field lines, suggesting that the phenomenon on our planet is aligned with the earth's magnetic field. Similarly, the combination of several factors can lead to the formation of auroral lines of specific color tones.

In general, the light effect is dominated by the emission of oxygen atoms in high atmospheric layers (around 200 km altitude), which produces the green tint. When solar storms are strong, the lower layers of the atmosphere are hit by the solar wind (around 100 km altitude), producing a deep red hue by the emission of nitrogen and oxygen atoms. Oxygen atoms emit widely varying shades of color, but the predominant ones are red and green.

The Earth is constantly hit by solar winds, which are a thin stream of hot plasma (free electron gas and cations) emitted by the Sun in all directions, a result of millions of degrees of temperature from the outermost layer of the star, the crown. solar.

During magnetic storms, the fluxes can be much stronger, as can the interplanetary magnetic field between the two celestial bodies, causing disturbances by the ionosphere in response to the storms.

Such disturbances affect the quality of radio communication or navigation systems, as well as damage to astronauts in that region, artificial satellite solar cells, compass movement, and radar action. The ionosphere response is complex and difficult to model, making prediction for such events difficult.

The terrestrial magnetosphere is a region of space dominated by its magnetic field. It forms an obstacle in the solar wind path, causing it to scatter around you. Its width is approximately 190,000 km, and at night a long magnetic tail is extended to even greater distances.

The auroras are usually confined in oval-shaped regions near the magnetic poles. When solar activity is calm, the region has an average size of 3,000 km and may increase to 4,000 or 5,000 km when the solar winds are more intense.

Since the magnetic and geographic poles of our planet are not aligned, so the auroral regions are not aligned with the geographic pole. The best points (called peak points) for aurora viewing are in Canada for northern lights, and on the island of Tasmania or southern New Zealand for southern auroras.

The auroras can also be formed by nuclear explosions in high layers of the atmosphere (around 400 km). This phenomenon was demonstrated by the artificial dawn created by the American Starfish Prime nuclear test on July 9, 1962. At that time the Pacific Ocean sky was lit by the dawn for more than seven minutes. Such an effect was predicted by scientist Nicholas Christofilos, who had worked on other projects on nuclear explosions.

Laboratory aurora simulations began in the late nineteenth century by Norwegian scientist Kristian Birkeland, who proved, using a vacuum chamber and a sphere, that electrons were guided in such an effect to the polar regions of the sphere.

Recently, researchers have been able to create a modest auroral effect visible from Earth by emitting radio rays into the night sky, turning a green tint. Like the natural phenomenon, the particles hit the ionosphere, exciting the electrons in the plasma. With the collision of electrons with the earth's atmosphere, lights were emitted. Such an experiment also increased knowledge of the effects of the ionosphere on radio communications.

Both Jupiter and Saturn have much stronger magnetic fields than ours, and both have auroras. The polar aurora effect has been observed in both, and most clearly with the Hubble telescope.

Such auroras seem to originate from the solar wind. On the other hand, Jupiter's moons, especially Io, are also powerful sources of auroras.

Like terrestrial ones, the auroras of Saturn create full or partial oval regions around the magnetic pole. On the other hand, the auroras of that planet usually last for days, unlike the terrestrial ones that last for a few minutes only. Evidence shows that the emission of light in the auroras of Saturn relies on the emission of hydrogen atoms.

An aurora was recently detected on Mars by the Mars Express space probe during its observations of the planet in 2004, with results published the following year. Mars has a weaker magnetic field than Earth, and until then it was thought that the lack of a strong magnetic field would make such an effect impossible.

It has been realized that the aurora system of Mars is very similar to that of Earth, and is comparable to our low and medium intensity storms. As the planet is always directed towards our planet with its daytime side, aurora observation is only possible through spacecraft investigating the night side of the red planet and never from Earth.

Venus, which does not have a magnetic field, also presents the phenomenon, in which the particles of the atmosphere are directly ionized by solar winds, a phenomenon also present on Earth.