Disfrutar del espectáculo de una aurora boreal puede
ser una de esas experiencias que serán imposibles de borrar de tu mente.
Estos fotográfos de Flickr nos traen un pedazo de esta maravilla bautizada por Galileo Galilei.
Foto de Terje Lein-Mathisen/Flickrmar, 4 feb 2014
Las
auroras se forman a causa de las partículas solares que desencandenan
la actividad geomagnética de la Tierra. Aparecen como por arte de magia
en nuestro cielo y permiten que te deleites con uno de los fenómenos
naturales más impresionantes del mundo.
Podemos
encontrarlas entre los meses de septiembre a marzo, siempre y cuando el
frío acompañe al cielo despejado. El norte de Noruega, de Suecia o de
Finlandia son algunos de los mejores destinos para poder verlas. Se
caracterizan por sus colores fluorescentes y sus formas onduladas que se
entremezclan con el cielo estrellado del norte.
Si
estás pensando disfrutar de esta maravilla natural, no olvides que se
pueden predecir con hasta tres dias de antelación, y que enero y febrero
son los meses con mayor actividad.
Fuente: noticias.yahoo.com/fotos/2014
Información:
AURORA BOREALIS FULL [HD] VIDEO - Vangelis - Rachel's Song - NORTHERN LIGHTS- Blade Runner theme
"Aurora Borealis" and "Aurora Australis" Aurora boreal /polar
An
aurora (plural: aurorae or auroras; from the Latin word aurora, "dawn")
is a natural light display in the sky particularly in the high latitude
(Arctic and Antarctic) regions, caused by the collision of energetic
charged particles with atoms in the high altitude atmosphere
(thermosphere). The charged particles originate in the magnetosphere and
solar wind and, on Earth, are directed by the Earth's magnetic field
into the atmosphere. Aurora is classified as diffuse or discrete aurora.
Most aurorae occur in a band known as the auroral zone, which is
typically 3° to 6° in latitudinal extent and at all local times or
longitudes. The auroral zone is typically 10° to 20° from the magnetic
pole defined by the axis of the Earth's magnetic dipole. During a
geomagnetic storm, the auroral zone will expand to lower latitudes. The
diffuse aurora is a featureless glow in the sky which may not be visible
to the naked eye even on a dark night and defines the extent of the
auroral zone. The discrete aurorae are sharply defined features within
the diffuse aurora which vary in brightness from just barely visible to
the naked eye to bright enough to read a newspaper at night. Discrete
aurorae are usually observed only in the night sky because they are not
as bright as the sunlit sky. Aurorae occasionally occur poleward of the
auroral zone as diffuse patches[3] or arcs (polar cap arcs, which are
generally invisible to the naked eye.
In northern latitudes, the
effect is known as the aurora borealis (or the northern lights), named
after the Roman goddess of dawn, Aurora, and the Greek name for the
north wind, Boreas, by Pierre Gassendi in 1621. Auroras seen near the
magnetic pole may be high overhead, but from farther away, they
illuminate the northern horizon as a greenish glow or sometimes a faint
red, as if the Sun were rising from an unusual direction. Discrete
aurorae often display magnetic field lines or curtain-like structures,
and can change within seconds or glow unchanging for hours, most often
in fluorescent green. The aurora borealis most often occurs near the
equinoctes. The northern lights have had a number of names throughout
history. The Cree call this phenomenon the "Dance of the Spirits". In
Europe, in the Middle Ages, the auroras were commonly believed a sign
from God.
Its southern counterpart, the aurora australis (or the
southern lights), has almost identical features to the aurora borealis
and changes simultaneously with changes in the northern auroral zone and
is visible from high southern latitudes in Antarctica, South America,
New Zealand, and Australia.
Aurorae occur on other planets. Similar to the Earth's aurora, they are visible close to the planet's magnetic poles.
Modern style guides recommend that the names of meteorological phenomena, such as aurora borealis, be uncapitalized.
Auroras
result from emissions of photons in the Earth's upper atmosphere, above
80 km (50 mi), from ionized nitrogen atoms regaining an electron, and
oxygen and nitrogen atoms returning from an excited state to ground
state.[9] They are ionized or excited by the collision of solar wind and
magnetospheric particles being funneled down and accelerated along the
Earth's magnetic field lines; excitation energy is lost by the emission
of a photon, or by collision with another atom or molecule: oxygen
emissions green or brownish-red, depending on the amount of energy
absorbed. nitrogen emissions blue or red; blue if the atom regains an
electron after it has been ionized, red if returning to ground state
from an excited state.
Oxygen is unusual in terms of its return to
ground state: it can take three quarters of a second to emit green light
and up to two minutes to emit red. Collisions with other atoms or
molecules will absorb the excitation energy and prevent emission.
Because the very top of the atmosphere has a higher percentage of oxygen
and is sparsely distributed such collisions are rare enough to allow
time for oxygen to emit red. Collisions become more frequent progressing
down into the atmosphere, so that red emissions do not have time to
happen, and eventually even green light emissions are prevented.
Auroras are associated with the solar wind, a flow of ions continuously flowing outward from the Sun.
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