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Aurora facts for kids

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Aurora Borealis and Australis Poster
Auroras worldwide
Polarlicht 2
An aurora

An aurora, also called polar light, northern light or southern light, is a natural light display in the sky. They are usually seen in the high latitudes (Arctic and Antarctic) regions. Auroras are produced when the Earth's magnetosphere is disturbed by the solar wind.

An aurora around the North Pole is called the Aurora borealis or 'northern lights'. Around the South Pole it is the Aurora australis or 'dawn of the south' or 'southern lights'. It can be seen from long distances, stretching in the sky many hundreds of miles far.

Auroras can happen at any time, however they can only be seen at night because their light is not as strong as the light of day. Faint stars can even be seen through the aurora.

Many legends are associated with the aurora in all countries where this phenomenon regularly occurs.

How it happens

An aurora occurs when the Sun sends off small particles into space. These particles are mainly electrons, with charge and energy, which means they contribute to electricity. Earth has a protective shield of energy around it. This is called the "magnetic field" and forms an elongated sphere around the Earth called the "magnetosphere". The Earth’s magnetic field keeps off most of the solar wind.

At high-latitude areas (polar areas), the magnetic field is vertical. It does not keep off particles of the solar wind which can come from the magnetosphere and hit the particles of the air (Earth's atmosphere). When they hit, the atmosphere is heated and excited and the excess energy gets away, a phenomenon which we see as moving lights in the sky above 100 km altitude typically. An aurora can be especially bright following a solar flare and coronal mass ejection (CME), when the charged particles rip through the electromagnetic field because of their power.

On other planets

Jupiter aurora; the far left bright spot connects magnetically to Io; the spots at the bottom of the image lead to Ganymede and Europa.
Saturns Northern Aurora still
An aurora high above the northern part of Saturn; image taken by the Cassini spacecraft. A movie shows images from 81 hours of observations of Saturn's aurora.

Both Jupiter and Saturn have magnetic fields that are stronger than Earth's, and both have extensive radiation belts. Auroras have been observed on both gas planets, most clearly using the Hubble Space Telescope, and the Cassini and Galileo spacecraft, as well as on Uranus and Neptune.

Auroras have also been observed on Venus and Mars. Venus has no magnetic field and so Venusian auroras appear as bright and diffuse patches of varying shape and intensity, sometimes distributed over the full disc of the planet. A Venusian aurora originates when electrons from the solar wind collide with the night-side atmosphere.

An aurora was detected on Mars, on 14 August 2004, by the SPICAM instrument aboard Mars Express. The aurora was located at Terra Cimmeria, in the region of 177° east, 52° south. The total size of the emission region was about 30 km across, and possibly about 8 km high.

Between 2014 and 2016, cometary auroras were observed on comet 67P/Churyumov–Gerasimenko by multiple instruments on the Rosetta spacecraft. The auroras were observed at far-ultraviolet wavelengths.

Exoplanets, such as hot Jupiters, have been suggested to experience ionization in their upper atmospheres and generate an aurora modified by weather in their turbulent tropospheres. However, there is no current detection of an exoplanet aurora.

The first ever extra-solar auroras were discovered in July 2015 over the brown dwarf star LSR J1835+3259. The mainly red aurora was found to be a million times brighter than the northern lights, a result of the charged particles interacting with hydrogen in the atmosphere. It has been speculated that stellar winds may be stripping off material from the surface of the brown dwarf to produce their own electrons. Another possible explanation for the auroras is that an as-yet-undetected body around the dwarf star is throwing off material, as is the case with Jupiter and its moon Io.

Images for kids

See also

Kids robot.svg In Spanish: Aurora polar para niños

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