History of Aurora in Timeline
Auroras, commonly known as the northern or southern lights, are natural light displays predominantly seen in Earth's high-latitude regions. They exhibit dynamic patterns of brilliant lights, appearing as curtains, rays, spirals, or dynamic flickers across the sky. These mesmerizing displays result from interactions between charged particles from the sun and Earth's magnetic field. The colors vary based on the type of gas particles being excited by solar energy.
1908: The Ballad of the Northern Lights
Robert W. Service's 1908 poem, "The Ballad of the Northern Lights," humorously depicts a prospector believing the aurora is the glow of a radium mine.
1920: Tycho Brahe's theory on sulfur and aurora
In 1920, Walter William Bryant wrote that Tycho Brahe believed that infectious diseases were caused by "sulfurous vapours of the Aurora Borealis" and could be cured with sulfur.
1949: Early Auroral Imaging
In 1949, the University of Saskatchewan used SCR-270 radar to conduct early work on auroral imaging. Carl Størmer and colleagues used cameras to triangulate over 12,000 auroras, discovering that most auroral light is produced between 90 and 150 km above ground, sometimes extending to over 1,000 km.
1955: Jupiter's aurorae and radio emissions
Starting in 1955, studies began on radio emissions linked to Jupiter's aurorae. These emissions are connected to electric currents along magnetic field lines caused by the interplay between Jupiter's rotation and the movement of its moon, Io, known for its active volcanoes and ionosphere.
1960: Discovery of Cause of Auroral Emissions
In 1960, a rocket flight from Fort Churchill, Canada, revealed that a flux of electrons entering the atmosphere causes the ionization and excitation of atmospheric constituents leading to auroral emissions.
1963: Auroral Substorms
Before 1963, auroral changes were thought to be due to Earth's rotation. However, studies during the International Geophysical Year revealed global changes called auroral substorms. These substorms shift quiet arcs to active displays in minutes, then gradually back over 1-3 hours.
1967: Conjugate Auroras Imaging Attempts
Attempts to image conjugate auroras (mirror-image auroras in northern and southern hemispheres) via aircraft from Alaska and New Zealand began in 1967, with some success. Further attempts followed in 1968, 1970, and 1971.
1968: Conjugate Auroras Imaging Attempts
In 1968, further attempts were made to image conjugate auroras by aircraft from Alaska and New Zealand, following similar efforts in 1967.
1969: Birkeland Currents and Auroras
In 1969, research by Schield et al. indicated that bright auroras are linked with Birkeland currents, which flow into and out of the ionosphere around the poles. Some current connects through the E layer, while the rest detours and closes through the "partial ring current".
1970: Conjugate Auroras Imaging Attempts
Following previous attempts in 1967 and 1968, efforts continued in 1970 to image conjugate auroras using aircraft from Alaska and New Zealand.
1971: Conjugate Auroras Imaging Attempts
In 1971, further attempts to image conjugate auroras were carried out by aircraft from Alaska and New Zealand, continuing the series of experiments that started in 1967.
1972: Auroral Kilometric Radiation
In 1972, a strong radio emission around 150 kHz called Auroral Kilometric Radiation (AKR) was discovered. AKR is associated with auroras and their related currents, and is only observable from space due to ionospheric absorption. X-ray emissions from aurora-associated particles were also detected.
1973: Auroral Currents and Driving Voltage
In 1973, studies by Zmuda and Armstrong reinforced the association between bright auroras and Birkeland currents. These currents, flowing in and out of the ionosphere, suggest a driving voltage from a dynamo mechanism, as the ionosphere acts as an ohmic conductor. Another interpretation sees these currents as a result of electron acceleration via wave/particle interactions.
1994: Curtain-like Auroras
Brekke, in 1994, described some auroras as resembling "curtains", with folds enhancing this appearance. These arcs can fragment into rapidly changing, rayed features, sometimes bright enough to read by.
2000: Legend of Fubao and the Emperor Xuanyuan
Around 2000 BC, a legend tells of Fubao witnessing a brilliant aurora borealis, which led to the birth of Emperor Xuanyuan, a key figure in Chinese culture. The event is described as a "magical band of light" resembling "moving clouds and flowing water" forming a halo around the Big Dipper.
August 2004: Aurora on Mars
On August 14, 2004, the SPICAM instrument on Mars Express detected an aurora on Mars, localized to a region about 30 km across and 8 km high. This aurora was linked to electron movement along crustal magnetic lines.
2007: Five Main Auroral Forms
In 2007, Clark identified five main auroral forms visible from the ground, ranging from least to most visible.
February 2008: Triggering Event for Magnetospheric Substorms
On February 26, 2008, THEMIS probes identified a magnetic reconnection event 96 seconds before auroral intensification, pinpointing the triggering event for magnetospheric substorms.
2014: Cometary auroras on 67P/Churyumov–Gerasimenko (2014)
Between 2014 and 2016, the Rosetta spacecraft discovered auroras on comet 67P. In 2014, these were initially observed in the far-ultraviolet wavelengths, revealing atomic emissions of hydrogen and oxygen caused by photodissociation of water molecules.
July 2015: First extra-solar auroras
In July 2015, the first extra-solar auroras were discovered on the brown dwarf LSR J1835+3259. This aurora, predominantly red and a million times brighter than the Northern Lights, is likely due to charged particle interactions with hydrogen.
2016: Cometary auroras on 67P/Churyumov–Gerasimenko (2016)
By 2016, more data was collected by the Rosetta spacecraft on the cometary auroras of comet 67P/Churyumov-Gerasimenko, solidifying the understanding of their diffuse and unique characteristics in comparison to auroras found on planets with magnetic fields.
2016: STEVE Phenomenon
In 2016, citizen scientists reported an unknown auroral type called STEVE (Strong Thermal Emission Velocity Enhancement). STEVE is a 25 km-wide ribbon of hot plasma at 450 km altitude, not a true aurora.
2017: Discovery of 1770 Japanese Diary
A 1770 Japanese diary discovered in 2017 described auroras over Kyoto, suggesting a storm potentially 7% larger than the Carrington Event.
March 2020: Red Pheasant Tails and the Aurora
In March 2020, researchers proposed that a sighting of red pheasant tails in the night sky over Japan in 620 A.D. might have been a red aurora caused by a magnetic storm.
2020: Dune Aurora Discovery
The dune aurora phenomenon, featuring regularly-spaced stripes in the green diffuse aurora, was first reported in 2020 by Finnish citizen scientists.
2021: Networked Substorms
In 2021, evidence suggested that individual substorms might be interconnected, networked communities. It was also noted that geomagnetic storms causing auroras could be more frequent around equinoxes, possibly due to the tilt of the Earth's and Sun's axes affecting the interaction between the interplanetary magnetic field and Earth's magnetosphere.
2021: Dune Aurora Confirmation
In 2021, the dune aurora phenomenon, initially reported in 2020, was confirmed. It's believed to be caused by modulated atomic oxygen density due to atmospheric waves.