Aurora Northern Lights Info

7/28/2019 Aurora Northern Lights Info

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Aurora (astronomy)

Auroras, sometimes called the northern and southern (polar) lights or aurorae (singular: aurora),are natural light displays in the sky, usually observed at night, particularly in the polar regions.They typically occur in the ionosphere. They are also referred to as polar auroras.

In northern latitudes, the effect is known as the aurora borealis, named after the Roman goddessof dawn, Aurora, and the Greek name for north wind, Boreas, by Pierre Gassendi in 1621.[1] The

aurora borealis is also called the northern polar lights, as it is only visible in the sky from theNorthern Hemisphere, the chance of visibility increasing with proximity to the North MagneticPole, which is currently in the arctic islands of northern Canada. Auroras seen near the magneticpole may be high overhead, but from further away, they illuminate the northern horizon as agreenish glow or sometimes a faint red, as if the sun were rising from an unusual direction. Theaurora borealis most often occurs near the equinoxes; from September to October and fromMarch to April. The northern lights have had a number of names throughout history. The Creepeople call this phenomenon the "Dance of the Spirits." In the middle age the auroras has beencalled by sign of God (see Wilfried Schrder, Das Phnomen des Polarlichts, Darmstadt 1984).

Auroras can be spotted throughout the world. It is most visible closer to the poles due to thelonger periods of darkness and the magnetic field.

Its southern counterpart, the aurora australis or the southern polar lights, has similar properties,

but is only visible from high southern latitudes in Antarctica, South America, or Australasia.Australis is the Latin word for "of the South."

Auroral mechanism

Auroras are the result of the emissions of photons in the Earth's upper atmosphere, above 80 km(50 miles), from ionized nitrogen atoms regaining an electron, and oxygen and nitrogen atomsreturning from an excited state to ground state. They are ionized or excited by the collision ofsolar wind particles being funneled down and accelerated along the Earth's magnetic field lines;excitation energy is lost by the emission of a photon of light, or by collision with another atom ormolecule:

oxygen emissionsGreen or brownish-red, depending on the amount of energy absorbed.

nitrogen emissionsBlue 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 a little unusual in terms of its return to ground state, it can take three quarters of asecond to emit green light, and up to two minutes to emit red. Collisions with other atoms ormolecules will absorb the excitation energy and prevent emission. The very top of theatmosphere is both a higher percentage of oxygen, and so thin that such collisions are rare


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enough to allow time for oxygen to emit red. Collisions become more frequent progressing downinto the atmosphere, so that red emissions do not have time to happen, and eventually evengreen light emissions are prevented.

This is why there is a colour differential with altitude; at high altitude oxygen red dominates, thenoxygen green and nitrogen blue/red, then finally nitrogen blue/red when collisions prevent oxygen

from emitting anything.

A predominantly red aurora australis

Auroras are associated with the solar wind, a flow of ions continuously flowing outward from thesun. The Earth's magnetic field traps these particles, many of which travel toward the poles wherethey are accelerated toward earth. Collisions between these ions and atmospheric atoms andmolecules causes energy releases in the form of auroras appearing in large circles around thepoles. Auroras are more frequent and brighter during the intense phase of the solar cycle whencoronal mass ejections increase the intensity of the solar wind.[2] Seen from space, these fierycurtains form a thin ring in the shape of a monks tonsure.

Forms and magnetismNorthern lights over Calgary

Typically the aurora appears either as a diffuse glow or as "curtains" that approximately extend inthe east-west direction. At some times, they form "quiet arcs"; at others ("active aurora"), theyevolve and change constantly. Each curtain consists of many parallel rays, each lined up with thelocal direction of the magnetic field lines, suggesting that aurora is shaped by Earth's magneticfield. Indeed, satellites show electrons to be guided by magnetic field lines, spiraling around themwhile moving towards Earth.

The similarity to curtains is often enhanced by folds called "striations". When the field line guidinga bright auroral patch leads to a point directly above the observer, the aurora may appear as a"corona" of diverging rays, an effect of perspective.

Although it was first mentioned by Ancient Greek explorer/geographer Pytheas, Hiorter andCelsius first described in 1741 evidence for magnetic control, namely, large magnetic fluctuations

occurred whenever the aurora was observed overhead. This indicates (it was later realized) thatlarge electric currents were associated with the aurora, flowing in the region where auroral lightoriginated. Kristian Birkeland (1908)[3] deduced that the currents flowed in the east-westdirections along the auroral arc, and such currents, flowing from the dayside towards(approximately) midnight were later named "auroral electrojets" (see also Birkeland currents).

On 26 February 2008, THEMIS probes were able to determine, for the first time, the triggeringevent for the onset of magnetospheric substorms [4]. Two of the five probes, positionedapproximately one third the distance to the moon, measured events suggesting a magneticreconnection event 96 seconds prior to auroral intensification [5]. Dr. Vassilis Angelopoulos of the


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The Earth's magnetic fieldOur planet is like a gigantic magnet, because the Earth's magnetic field surrounds the entireplanet and comes together in a funnel shape near the north and south poles. The Earth'smagnetic field, called the magnetosphere, protects our planet from the Sun's radiation, thisradiation is called the solar wind.

What is the source of the aurora?The energy source of these dazzling lights in the night sky is the solar wind. The solar wind is aplasma sream of electrically charged particles that continuously flow out from the Sun.Theparticles from the solar wind get trapped and create the spectacle called the "aurora borealis".

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How the Lights got their colors

Have you ever wondered how the Northern Lights get their different colors... or how neon lightsget their color?

The glass tubes of neon signs are filled with gas. When they are turned on, the electrical voltageenergizes electrons in the gas, causing them to emit light. The color of the light you see dependson the type of gas in the tube.

Every gas creates a different color of light: helium - orange/white, neon - red/orange, argon -lavender, krypton - gray/green, and so on.

Click for more information. The colors of auroras are determined by the gases in the Earth'satmosphere, and incoming solar particles tend to collide with different gases at different heights.

Very high up (above 300 km / 185 miles), oxygen is the most common gas, and collisions there

can create a rare red aurora.

The common yellow-to-green light is produced by collisions with oxygen at lower altitudes(between 100-300 km / 60-185 miles).

Around 100 km / 60 miles, nitrogen molecules produce a red light that often seems to form thelower fringes on auroral curtains.

Lighter gases high in the atmosphere, like hydrogen and helium, make blue and purple colors,but we cannot always see them in the night sky.-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Q: Why does it have different colors for the northern lights?

A: Answer

Because diffrent types of solar flare radiation traveling at diffrent speeds hit the Earth'satmosphere thus projecting red, green, blue,and white

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Why its easier to see the Northern Lights at the poles:-------------------------------------------------------------------------------

Northern Lights in AlaskaViewing the Northern Lights

The Northern Lights are curtains of colored light in the upper atmosphere, caused by magneticdisturbances from the sun collide with atoms there. Technically known as an "aurora" (the NorthPole aurora is called the aurora borealis), the Northern Lights give off colors that include red,green, blue, and violet, and a single display can last 10 to 15 minutes.Where to See the Northern Lights in AlaskaThe Northern Lights can be seen to some extent anywhere above 60 degrees north latitude. At 65degrees, Fairbanks is within the so-called "aurora oval," the area where Northern Lights occurmost often and are brightest. In fact, the Fairbanks Visitors Bureau says you have an 80 percentchance of seeing them if you stay there for three nights.

Denali, at 63 degrees north, is also a good spot to view the Northern Lights. Other Alaska placesare far enough north for good for viewing, but are hard to get to and offer fewer accommodations.The next-best options are Nome (64 degrees) and Anchorage (61 degrees). However, the

Northern Lights can sometimes be seen as far south as Juneau or Sitka.When to See the Northern Lights in AlaskaBy the time you get far enough north to see the Northern Lights more reliably, you've entered thearea of perpetual twilight from late April through September. Seasonal cloudiness is also worst in

August.

What's the best time to see the Northern Lights? September 22 or March 22, on a new moonnight, very late at night or early in the morning, a "perfect storm" that may not occur very often normatch your travel plans. These characteristics may help you decide when to make your trip to seethe Northern Lights. They are:

* Most frequent around the spring and fall equinoxes (September 22 and March 22)* Most active late at night or early in the morning

* Most intense from December to March when nights are longer, the sky clearer and darker.This is also the coldest part of the year, reaching as low as -40 F.

* Brighter during the new moon.

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Aurora Northern Lights Info