AURORA [POLARIS]

The Northern Lights (aurora borealis) and the Southern Lights (aurora australis)

As seen from the Space Shuttle:

Internet Resources
The Aurora Page of the Poker Flats Rocket Range is a good launch pad into auroral cyberspace
Aurora's Northern Lights site by Jan Curtis with links to photos and other stuff
University of Oulu's Aurora Page
Space Environment Center's pdf file on Aurora
Windows to the Universe Aurora page
Michigan Tech University's Aurora Links Page
UCAR's (University Corporation for Atmospheric Research) Physics of the Aurora webcast

MOST RECENT MAPS of the position and extent of the northern and southern auroral ovals

The Luminous Aurora

Among the oldest known geophysical phenomena
The most obvious characteristic of the high latitude ionosphere
The most readily observable consequence of the dynamic magnetosphere

PHOTOGRAPHY

Internet Resource:
Tips on Photographing the Aurora.
Pekka Parviainen's Polar Image site

Historical outline of Auroral Imaging

20,000 B.C. earliest depictions(?): Serpertine meanders (macaronis) in cave drawings by Cro-Magnon

1575 First published scientific illustration by Cornelius Gemma

1885 Sophus Tromholt attempts photography; gets a blurry blob after 8 minute exposure

1892 Martin Brendel obtains first useful (B&W) photographs

1910-43 Carl Störmer takes thousands of photos

1913 Störmer records movie (4 seconds per frame)

1940 Störmer begins unsuccessful attempts at color photography

1951 Gartlein and Petrie present color photos at Auroral Conference in London, Canada

June 1953 Life Magazine publishes color photos

1968 Imaging with orbiting satellites begins

1970's Color movies become practical with availability of high-speed color film

1980's Significant improvements due to low light television technology

International Brightness Coefficient

Coefficient Appearance Equivalent to: Brightness

IBC0 subvisual < 1 kRa

IBC1 appears white Milky Way 1 kRa

IBC2 onset of color perception Thin moonlit cirrus 10 kRa

IBC3 bright stars don't shine through Moonlit cumulus 100 kRa

IBC4 casts shadows Full moonlight 1000 kRa

HISTORICAL RECORD

Ancient chroniclers described what are now known as aurorae in various terms including flaming heavens, cracks in the heavens, burning clouds, fire dragons, and heavenly armies or battles. Sometimes it is difficult to discerned whether other phenomena (meteors, comets, St. Elmo's fire) are actually being described.

ca. 2600 BC	Possibly first written description in Bamboo Album of Chronology (Chu-Shu-Chi-Nien)
8th c. BC	Hesiod in Theogony describes flaming heavens, fiery sky dragons
687 BC	First aurora listed in Chinese historical catalogs (through to the 10th c. AD)
ca. 460 BC	Mention in histories of Livy and Dionysius (Roman)
ca. 340 BC	Infiltration during night of the army of Philip of Macedonia into the city of Byzantium reputably foiled by light from aurora
37 AD	Tiberius mistakenly sends Roman army to put out fire seen on the horizon
555	Earliest mention in England by Mathew of Westminster
919	Earliest event known in written Russian record
1100's	regular observers (Mathieu of Edesse - Middle East; Vysehrad - Prague; Gervasius - England)
1111	Victory of outnumbered Russian army over Polovtsy attributed to appearance of aurora behind Russian forces
1192	Great Aurora of 1192
1200-1500	few recorded auroral sightings due to warfare (e.g. Mongol threat, Crusades), plague (Black Death), religious dogma (generally a bad time had by all)
1400-1500	Spörer Minimum (little solar activity)
1500's	Renewed auroral activity reported in Europe
1643	First sighting with known written report in North America (by John Winthrop, Governor of Massachusetts)
1645-1715	Maunder Minimum (little solar activity)
3/17/1716	Great Aurora over Europe
1719	Bright aurora over New England and China
9/2/1859	Brightest aurora ever reliably reported occurs day after Carrington discovers solar flare

Historical Auroras
List of some great aurora and recent bright displays

CULTURAL IMPACT

In locations of common occurrence aurora was incorporated into myth and legend. In places where aurorae occur rarely, they were often associated with significant events or considered omens (usually of the ill-tempered variety)

Aurora as Omen

Some events that have been associated with the appearance of an aurora:

44 BC The assassination of Julius Caesar

1st c. AD Pliny the Elder describes earlier aurorae as "presage of woe"

451 The defeat of Attila at Catalaunic Fields

566 The invasion of Italy by Lombards in 568; aurora receives moniker "acies igneae" (battle lines of fire)

566 The birth of Mohammed in 570

793 Anglo-Saxon Chronicles notes "this year dire forewarnings came over the land"

1170 The blood of Thomas à Becket rising to heaven

Jan 15,1192 Famine of 1197 in Europe

Nov 14,1574 Earthquake on Feb 26,1575

March 6,1716 The execution of Lord Derwentwater (Jacobite uprising)

Oct 8,1728 Earthquakes in Sicily and England

Jan. 25, 1938 World War II

Aurora in Legend and Folklore

See these brief on-line descriptions:
Auroral Folklore
Native American Legend and Folklore
Aurora in Eskimo Legend
Legends and Medieval Depictions

Possible source of Greek myth of Mount Olympus as home of the Gods
Probably only instance where the aurora is actually a deity (god of birth) is among the Chuvash, an ethnic group with a republic in the Russian Federation

An "old-fashioned" source (a book): Majestic Lights by Robert Eather

Possible Biblical References

Genesis 15:17 (from ca. 2000 BC)
Jeremiah 1:13 (from 626 BC)
Ezekiel 1:1-28 (from 593 BC)
Zechariah 1:8 (from 518 BC)
Maccabees II 5:2-3 (from 168 BC)

The Arts

A clear description of an aurora is found in Book I of the epic poem The Civil War about the struggle between Julius Caesar and the Roman Senate written in 60 AD by Marcus Lucanus
"Strange constellations sparkled through the gloom: The pole was all afire, and torches flew Across the depths of heaven; with horrid hair A blazing comet stretched from east to west And threatened change to kingdoms. From the blue Pale lightning flashed, and in the murky air The fire took divers shapes; a lance afar Would seem to quiver or a misty torch; A noiseless thunderbolt from cloudless sky Rushed down, and drawing fire in northern parts"
William Shakespeare in the play Julius Caesar (first known performance in 1599). In Act 2, Scene II, Calpurnia, Caesar's wife, warns: "Besides the things that we have heard and seen, Recounts most horrid sights seen by the watch. A lioness hath whelped in the streets; And graves have yawn'd, and yielded up their dead; Fierce fiery warriors fought upon the clouds, In ranks and squadrons and right form of war, Which drizzled blood upon the Capitol; The noise of battle hurtled in the air, Horses did neigh, and dying men did groan, And ghosts did shriek and squeal about the streets. O Caesar! these things are beyond all use, And I do fear them. "
Richard Wagner in the opera The Ring of the Nibelung in instructions for stage direction suggested that the destruction of Valhalla should be indicated by a red glow similar to an aurora (Wagner probably observed aurora during activity of 1846).
The 2006 animated movie Happy Feet includes a scene with an aurora prominent in the background
Many well-known poets have used the verbal imagery of aurorae including Longfellow, Coleridge in The Rime of the Ancient Mariner, Goethe, Byron in Don Juan, Keats, Tennyson, Sir Walter Scott in The Lay of the Last Minstrel, Burns, Browning, Whittier, and Emily Dickinson
"The Poet of the Yukon" Robert Service penned one of the better known poems about the aurora The Ballad of the Northern Lights published in 1908. The popularity of this poem is suggested by the fact that it is posted on many web sites including this one and another and another and yet one more and even an on-line recital. Maybe you get the idea by now.

Feel inspired? Contribute your aurora inspired poetry here

AURORAL FORMS and TYPES

Auroral Forms:

The visible aurora extends vertically along magnetic field lines often for tens of miles and horizontally east-west for hundreds of miles, but the auroral feature is usually only 100 yards or so thick (north-south). The shape or form of an aurora therefore is dependent on the perspective of the observer.

Basic forms
- arc: a slightly curving arc of light with smooth lower borders
- band: continuous but irregular lower borders with kinks and folds
- patch: isolated small region of luminosity like a patch of cloud
- veil: uniform luminosity covering a large fraction of the sky
- ray: a streak or shaft of luminosity
An example of each of these basic Auroral Forms
More description of arcs, bands and rays
Other shapes and forms
- curl: a counter-clockwise (in northern hemisphere) rotation having a diameter of 0.5 to 3 miles (1 to 5 km); a ray viewed from the bottom rather than the side
- fold: an S-shaped curve on a similar scale as a curl
- spiral: a larger scale (50 to 1000 miles) curled pattern
- drape(ry): long-rayed band with folds
- curtain: similar to drape with large vertical extent having sharp lower edge and gradually fading upwards
- corona aurora: rays converging onto a point (which indicates the overhead position of the magnetic field along which the observer is located). A movie clip of one.
- black aurora: a well-defined dark region within an extensive, otherwise uniform, auroral display
Descriptors of spatial structure
- homogeneous: lacking internal structure
- striated: having fine filaments
- rayed: having rays within a basic form
Descriptors of temporal behavior
- quiet: steady luminosity
- pulsating: rhythmic fading and brightening (every 10 to 100 seconds)
- flickering: rapid intensity changes (about 5 to 10 times per second)
- flaming: luminosity bursts from bottom to top
- streaming: varying brightness progressing horizontally

Auroral Types:

Discrete aurora (the bright visible form is classified by Color Types)
Note that the three primary colors (red, blue, and green) can be produced so that the aurora may appear to have a wide range of colors depending on the observer's perspective.
- Type A aurora (green with red tops):
  - energetic electrons flow directly down magnetic field lines
  - usually red at high altitude (>150 miles)
  - yellowish green at lower altitude (60-150 miles)
  - colors due to emission by atomic oxygen
  - more commonly occurs on day side of geomagnetic pole (visible during polar winter)
- Type B aurora (green with red lower edges):
  - energetic electrons from edge of plasma sheet in geotail
  - crimson and blues at low altitude (<60 miles)
  - colors due to molecular emissions (nitrogen, oxygen)
  - yellowish green above 60 miles (vide supra)
  - more commonly occurs on night side of geomagnetic pole
- Type C aurora (green):
  - most commonly observed color Type
  - essentially Type A or B without visible upper or lower red regions
- Type D aurora (red):
  - bombarding particles lack sufficient energy to penetrate below 150 miles altitude
  - red color due to emission by atomic oxygen (as in Type A)
- Type E aurora (a rapidly moving Type B aurora)
- Type F aurora (blue-purple):
  - auroral altitude is still in sunlight but lower altitudes in darkness
  - color due to resonance scattering (see airglow) by molecular nitrogen ion N₂⁺
- Proton aurora:
  - protons (hydrogen ions) contribute as bombarding particles
  - additional red and blue from atomic hydrogen emission
Diffuse aurora (observed by satellite; not typically seen from the ground)
Polar cap (or Theta) aurora: has a sun-aligned arc stretching over the pole. More info on polar cap aurora.

AURORA PHYSICS

Main topics of auroral research involve determining and understanding:

morphology
- occurrence in time and space
- details of fine structure in individual forms
spectroscopy
- spectrum of emitted light
- photochemical processses causing that light

A crude analogy
like a television:

The electrical socket = The Sun
The current in the power cord = The solar wind
The electrodes of the picture tube = The magnetosphere
The television screen = Earth's atmosphere (specifically, the ionosphere)
The television picture = The aurora

Another crude analogy
like a toaster:

The electrical socket = The Sun
The current in the power cord = The solar wind
The toaster wire (resistor) = Earth's ionosphere
The current through the toaster = The Birkeland currents and the auroral electrojets
The glow of the toaster wire = The aurora

Note that:

Auroral substorms (bursts of auroral activity) are related to magnetospheric substorms

More energetic particles (electrons, protons, etc.) penetrate deeper into the atmosphere so the characteristics of a particular auroral display depends of the energy distribution of these particles as they enter the atmosphere.

The Auroral Oval: the instantaneous position of luminosity below which the Earth rotates. Typically around 67 degrees geomagnetic latitude around midnight and moving to 78 degrees geomagnetic latitude at midday. The picture below shows the auroral oval in winter approaching midnight in Albany, NY

The Auroral Zone: the position of maximum probability of observing auroral luminosity. Viewing conditions are best around midnight and the aurora also tends to be brighter in this section of the oval. Consequently the highest probability of viewing aurora occurs around the geomagnetic latitude of 67 degrees

Note that the Auroral Zone passes through central Alaska, but in the picture below taken just after sunset in Alaska, the Auroral Oval lies to the north. The aurora may be visible at this latitude only during winter; at other times of the year the aurora is not usually visible here because of daylight. The Auroral Oval will pass over central Alaska later in the evening.

Conjugacy

OTHER AURORAL PHENOMENA (non-luminous)

Radar aurora: reflection of radio signals in E-region
Auroral radio absorption: absorption of radio waves in D-region due to enhanced ionization by energetic electrons
Auroral X-rays: Bremsstrahlung (braking) radiation due to decelertating electrons
Magnetic disturbances
- Magnetic Bays: deviations in the magnetic field at the surface due to the auroral electrojet which significantly enhances magnetic field if before midnight and significantly reduces magnetic field if after midnight
- Micropulsations: small regularly occurring fluctuations (seconds to minutes) due to Alfven-type (hydomagnetic) waves
Radio aurora: Low frequency radio emissions (vlf and ulf) generated in magnetosphere by wave-particle interactions including chorus (structured), hiss (unstructured), and lion roar. See radio aurora and "Sounds" of the Magnetosphere

Audible Aurora: some witnesses report hearing swishing or crackling while observing an aurora
This phenomena has not been documented, but some proposed causes are:

psychosomatic (observer expects to hear something)
tinnitus
physiological leakage of current from optic nerve to auditory senses
brush discharge due to electric fields
natural transduction of radio waves into acoustic waves

See The Audible Aurora?; More on some theories.

HISTORY of AURORAL SCIENCE

5th c. BC Hippocrates suggests aurora is caused by reflected sunlight

332 BC Aristotle in Meteorologica suggests flammable vapors produce "chasmata"

585 AD Gregory of Tours describes aurorae as natural phenomena (not supernatural)

1527 Peter Creutzer produces first printed description

1563 William Fulke treatise claims aurorae are burning vapors

1575 Cornelius Gemma publishes first scientific illustration

1607 Johannes Kepler describes aurora

ca. 1620 Galileo Galilei or Pierre Gassendi coin name "aurora borealis"

ca. 1620 René Descartes proposes sunlight scattered from ice crystals in clouds

1719 Edmund Halley proposes "magnetic effluvia"

1728 W. Derham suggests venting of vapors and association with earthquakes

1733 Jean Jacques d'Ortous de Mairan publishes first textbook devoted to aurora; proposes mingling of Earth and solar atmospheres/zodiacal light; suggests sunspot correlation, existence of southern aurora

1741 Anders Celsius and Olof Hiorter note coincidence of magnetic storms and aurorae

1746 Leonhard Euler proposes escaping particles at the poles

1750 Mairan obtains report of 1745 southern aurora (from Capt. Don Ulloa)

1752 William Watson invents discharge tube; leads to electrical discharge theories of aurora by Mikhail Lomonosov and Ben Franklin among others

1777 J.C. Wilcke notes corona aurora converges on local magnetic field line

1790 Henry Cavendish measures height successfully, 50 - 70 miles high

1792 John Dalton proposes luminous magnetic (iron) particles

1806 Alexander von Humboldt notes coincidence of auroral display with magnetic storm

1815 Alessandro Volta proposes condensing electrical fluids

1817 Jean Batiste Biot proves aurora is self luminous (not reflected sunlight)

1819-47 John Franklin arctic exploration and disappearance

1822 Franklin notes decrease in auroral frequency toward pole

1835 Denison Olmstead proposes cosmic origin (ferric cosmic dust clouds)

Sep 1, 1859 Carrington discovers solar flare; brilliant aurora occurs evening of the 2nd

1860 Elias Loomis maps northern auroral zone

1868 Anders Angstrom finds auroral green line and later other lines

1873 Loomis shows frequency of mid-latitude auroral displays correlates with sunspot cycle

1878 William Crookes invents cathode ray tube and discovers rays are deflected by magnetic fields

1878 Henri Bequerel proposes aurora caused by hydrogen from Sun (discovered natural radioactivity 1896; Nobel Prize 1903)

1880 Eugen Goldstein proposes aurora caused by cathode rays from Sun

1881-82 First Polar Year

1881 Hermann Fritz improves auroral map, solar cycle connection

1885 Sophus Tromholt notes change of position of aurora with time of day

1897 J. J. Thomson discovers electrons as particles in cathode rays (Nobel Prize 1906)

1903 Kristian Birkeland infers existence of large currents associated with aurora (auroral electrojets)

1900-13 Birkeland conducts demonstrations with physical model terrella (info on design for museum exhibits)

1911 Alfred Wegener proposes green line is due to "geocoronium"

1911-43 Carl Störmer makes extensive auroral observations

1912-13 Lars Vegard identifies auroral nitrogen bands (blue, red)

1915 William Ramsay proposes green line is due to krypton (Nobel Prize in 1904 for discovery in air of argon, helium, krypton, neon and xenon in the 1890's)

1928 John McLennan identifies green line to be due to atomic oxygen

1930 Störmer classifies auroral forms

1930-31 Second Polar Year

1939 Southern auroral zone is mapped

1939 Vegard identifies red & blue hydrogen lines

1948 Vegard detects fast protons from Doppler shift of hydrogen lines

1954 Rockets detect fast electrons as source of aurora

1957-58 Int'l Geophysical Year - numerous amateur reports; all-sky cameras

1957 John Winckler discovers auroral X-rays

1963 Yasha Feldstein maps auroral oval

1964 Syun Akasofu connects auroral bursts to magnetospheric substorms

1968 Conjugacy (mirroring) of northern and southern aurorae is shown

1972 ISIS-2 satellite discovers diffuse aurora

1974 Triad satellite provides evidence for "Birkeland Curents"

1981 Dynamics Explorer 1 satellite provides first full image of auroral oval

20,000 B.C.	earliest depictions(?): Serpertine meanders (macaronis) in cave drawings by Cro-Magnon
1575	First published scientific illustration by Cornelius Gemma
1885	Sophus Tromholt attempts photography; gets a blurry blob after 8 minute exposure
1892	Martin Brendel obtains first useful (B&W) photographs
1910-43	Carl Störmer takes thousands of photos
1913	Störmer records movie (4 seconds per frame)
1940	Störmer begins unsuccessful attempts at color photography
1951	Gartlein and Petrie present color photos at Auroral Conference in London, Canada
June 1953	Life Magazine publishes color photos
1968	Imaging with orbiting satellites begins
1970's	Color movies become practical with availability of high-speed color film
1980's	Significant improvements due to low light television technology

Coefficient	Appearance	Equivalent to:	Brightness
IBC0	subvisual		< 1 kRa
IBC1	appears white	Milky Way	1 kRa
IBC2	onset of color perception	Thin moonlit cirrus	10 kRa
IBC3	bright stars don't shine through	Moonlit cumulus	100 kRa
IBC4	casts shadows	Full moonlight	1000 kRa

44 BC	The assassination of Julius Caesar
1st c. AD	Pliny the Elder describes earlier aurorae as "presage of woe"
451	The defeat of Attila at Catalaunic Fields
566	The invasion of Italy by Lombards in 568; aurora receives moniker "acies igneae" (battle lines of fire)
566	The birth of Mohammed in 570
793	Anglo-Saxon Chronicles notes "this year dire forewarnings came over the land"
1170	The blood of Thomas à Becket rising to heaven
Jan 15,1192	Famine of 1197 in Europe
Nov 14,1574	Earthquake on Feb 26,1575
March 6,1716	The execution of Lord Derwentwater (Jacobite uprising)
Oct 8,1728	Earthquakes in Sicily and England
Jan. 25, 1938	World War II

5th c. BC	Hippocrates suggests aurora is caused by reflected sunlight
332 BC	Aristotle in Meteorologica suggests flammable vapors produce "chasmata"
585 AD	Gregory of Tours describes aurorae as natural phenomena (not supernatural)
1527	Peter Creutzer produces first printed description
1563	William Fulke treatise claims aurorae are burning vapors
1575	Cornelius Gemma publishes first scientific illustration
1607	Johannes Kepler describes aurora
ca. 1620	Galileo Galilei or Pierre Gassendi coin name "aurora borealis"
ca. 1620	René Descartes proposes sunlight scattered from ice crystals in clouds
1719	Edmund Halley proposes "magnetic effluvia"
1728	W. Derham suggests venting of vapors and association with earthquakes
1733	Jean Jacques d'Ortous de Mairan publishes first textbook devoted to aurora; proposes mingling of Earth and solar atmospheres/zodiacal light; suggests sunspot correlation, existence of southern aurora
1741	Anders Celsius and Olof Hiorter note coincidence of magnetic storms and aurorae
1746	Leonhard Euler proposes escaping particles at the poles
1750	Mairan obtains report of 1745 southern aurora (from Capt. Don Ulloa)
1752	William Watson invents discharge tube; leads to electrical discharge theories of aurora by Mikhail Lomonosov and Ben Franklin among others
1777	J.C. Wilcke notes corona aurora converges on local magnetic field line
1790	Henry Cavendish measures height successfully, 50 - 70 miles high
1792	John Dalton proposes luminous magnetic (iron) particles
1806	Alexander von Humboldt notes coincidence of auroral display with magnetic storm
1815	Alessandro Volta proposes condensing electrical fluids
1817	Jean Batiste Biot proves aurora is self luminous (not reflected sunlight)
1819-47	John Franklin arctic exploration and disappearance
1822	Franklin notes decrease in auroral frequency toward pole
1835	Denison Olmstead proposes cosmic origin (ferric cosmic dust clouds)
Sep 1, 1859	Carrington discovers solar flare; brilliant aurora occurs evening of the 2nd
1860	Elias Loomis maps northern auroral zone
1868	Anders Angstrom finds auroral green line and later other lines
1873	Loomis shows frequency of mid-latitude auroral displays correlates with sunspot cycle
1878	William Crookes invents cathode ray tube and discovers rays are deflected by magnetic fields
1878	Henri Bequerel proposes aurora caused by hydrogen from Sun (discovered natural radioactivity 1896; Nobel Prize 1903)
1880	Eugen Goldstein proposes aurora caused by cathode rays from Sun
1881-82	First Polar Year
1881	Hermann Fritz improves auroral map, solar cycle connection
1885	Sophus Tromholt notes change of position of aurora with time of day
1897	J. J. Thomson discovers electrons as particles in cathode rays (Nobel Prize 1906)
1903	Kristian Birkeland infers existence of large currents associated with aurora (auroral electrojets)
1900-13	Birkeland conducts demonstrations with physical model terrella (info on design for museum exhibits)
1911	Alfred Wegener proposes green line is due to "geocoronium"
1911-43	Carl Störmer makes extensive auroral observations
1912-13	Lars Vegard identifies auroral nitrogen bands (blue, red)
1915	William Ramsay proposes green line is due to krypton (Nobel Prize in 1904 for discovery in air of argon, helium, krypton, neon and xenon in the 1890's)
1928	John McLennan identifies green line to be due to atomic oxygen
1930	Störmer classifies auroral forms
1930-31	Second Polar Year
1939	Southern auroral zone is mapped
1939	Vegard identifies red & blue hydrogen lines
1948	Vegard detects fast protons from Doppler shift of hydrogen lines
1954	Rockets detect fast electrons as source of aurora
1957-58	Int'l Geophysical Year - numerous amateur reports; all-sky cameras
1957	John Winckler discovers auroral X-rays
1963	Yasha Feldstein maps auroral oval
1964	Syun Akasofu connects auroral bursts to magnetospheric substorms
1968	Conjugacy (mirroring) of northern and southern aurorae is shown
1972	ISIS-2 satellite discovers diffuse aurora
1974	Triad satellite provides evidence for "Birkeland Curents"
1981	Dynamics Explorer 1 satellite provides first full image of auroral oval