Walter William Bryant wrote in his book Kepler (1920) that Tycho Brahe "seems to have been something of a homœopathist, for he recommends sulfur to cure infectious diseases 'brought on by the sulphurous vapours of the Aurora Borealis '". [87] Earth is constantly immersed in the solar wind, a flow of magnetized hot plasma (a gas of free electrons and positive ions) emitted by the Sun in all directions, a result of the two-million-degree temperature of the Sun's outermost layer, the corona. The solar wind reaches Earth with a velocity typically around 400km/s, a density of around 5 ions/cm 3 and a magnetic field intensity of around 2–5 nT (for comparison, Earth's surface field is typically 30,000–50,000 nT). During magnetic storms, in particular, flows can be several times faster; the interplanetary magnetic field (IMF) may also be much stronger. Joan Feynman deduced in the 1970s that the long-term averages of solar wind speed correlated with geomagnetic activity. [57] Her work resulted from data collected by the Explorer 33 spacecraft. The earliest datable record of an aurora was recorded in the Bamboo Annals, a historical chronicle of the history of ancient China, in 977 or 957 BC. [76] Like the neolithic humans of Robinson’s last novel, Shaman, the characters in Aurora learn what it means to go chronically hungry. As in his kaleidoscopic 2312, terraforming new worlds proves much harder than fixing the environmental problems of our own beautiful planet – although we seem to be finding it difficult to do even that simple thing. Robinson is wise on the whys of this. As he puts it in Galileo’s Dream: “Fights over ideas are the most vicious of all. If it were merely food, or water, or shelter, we would work something out. But in the realm of ideas one can become idealistic.” Ideas simplify and metaphors distort. Reality is otherwise. Aurora’s ship’s computer notes: “Life is complex and entropy is real.” The novel dramatises these two great truths stunningly well.

Thomson, E. (1917). "Inferences concerning auroras". Proceedings of the National Academy of Sciences of the United States of America. 3 (1): 1–7. Bibcode: 1917PNAS....3....1T. doi: 10.1073/pnas.3.1.1. PMC 1091158. PMID 16586674. A mid 19th-century British source says auroras were a rare occurrence before the 18th century. [94] It quotes Halley as saying that before the aurora of 1716, no such phenomenon had been recorded for more than 80 years, and none of any consequence since 1574. It says no appearance is recorded in the Transactions of the French Academy of Sciences between 1666 and 1716; and that one aurora recorded in Berlin Miscellany for 1797 was called a very rare event. One observed in 1723 at Bologna was stated to be the first ever seen there. Celsius (1733) states the oldest residents of Uppsala thought the phenomenon a great rarity before 1716. The period between approximately 1645 and 1715 corresponds to the Maunder minimum in sunspot activity. A mild glow, near the horizon. These can be close to the limit of visibility, [20] but can be distinguished from moonlit clouds because stars can be seen undiminished through the glow. Hearne, Samuel (1958). A Journey to the Northern Ocean: A journey from Prince of Wales' Fort in Hudson's Bay to the Northern Ocean in the years 1769, 1770, 1771, 1772. Richard Glover (ed.). Toronto: The MacMillan Company of Canada. pp. 221–222. Gurnett, D.A. (1974). "The Earth as a radio source". Journal of Geophysical Research. 79 (28): 4227. Bibcode: 1974JGR....79.4227G. doi: 10.1029/JA079i028p04227.In Scandinavia, the first mention of norðrljós (the northern lights) is found in the Norwegian chronicle Konungs Skuggsjá from AD 1230. The chronicler has heard about this phenomenon from compatriots returning from Greenland, and he gives three possible explanations: that the ocean was surrounded by vast fires; that the sun flares could reach around the world to its night side; or that glaciers could store energy so that they eventually became fluorescent. [86] Reiff, P. H.; Collin, H. L.; Craven, J. D.; Burch, J. L.; Winningham, J. D.; Shelley, E. G.; Frank, L. A.; Friedman, M. A. (1988). "Determination of auroral electrostatic potentials using high- and low-altitude particle distributions". Journal of Geophysical Research. 93 (A7): 7441. Bibcode: 1988JGR....93.7441R. doi: 10.1029/JA093iA07p07441.

The theme of waiting for light is one Lent shares with Advent, as each week, candles are lit to anticipate the coming of Christ into the world”, writes Arun. As Archbishop of York, Stephen Cottrell, writes in his foreword to the book, Advent is not only a time for anticipating the moment Jesus Christ came into the world but also reflecting on the ‘last things’ foretold in the Book of Revelation where people of every tribe, tongue and nation rejoice before the throne of God.Arun emphasises his own experiences of alienation in the church as a UK-born bishop from an Indian family (his mother was Hindu and his father Sikh). His reflection on responding to the oft asked question “Where are you really from?” raises issues of belonging and identity for all of those who together form the body of Christ. The first ever extra-solar auroras were discovered in July 2015 over the brown dwarf star LSR J1835+3259. [101] 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. [102] See also [ edit ] Andrews, Robin George (3 May 2019). "Steve the odd 'aurora' revealed to be two sky shows in one". National Geographic. Archived from the original on 4 May 2019 . Retrieved 4 May 2019. Davis, Neil (1992). The Aurora Watcher's Handbook. University of Alaska Press. pp.117–124. ISBN 0-912006-60-9.

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. [100] However, there is no current detection of an exoplanet aurora. The accelerated electrons carry an electric current along the magnetic field lines (a Birkeland current). Since the electric field points in the same direction as the current, there is a net conversion of electromagnetic energy into particle energy in the auroral acceleration region (an electric load). The energy to power this load is eventually supplied by the magnetized solar wind flowing around the obstacle of Earth's magnetic field, although exactly how that power flows through the magnetosphere is still an active area of research. [66] While the energy to power the aurora is ultimately derived from the solar wind, the electrons themselves do not travel directly from the solar wind into Earth's auroral zone; magnetic field lines from these regions do not connect to the solar wind, so there is no direct access for solar wind electrons. Stewart, Balfour (1861). "On the Great Magnetic Disturbance of 28 August to 7 September 1859, as Recorded by Photography at the Kew Observatory". Philosophical Transactions of the Royal Society of London. 151: 423–430. doi: 10.1098/rstl.1861.0023. See p. 428. Yellow and pink are a mix of red and green or blue. Other shades of red, as well as orange, may be seen on rare occasions; yellow-green is moderately common. [ clarification needed] As red, green, and blue are linearly independent colors, additive synthesis could, in theory, produce most human-perceived colors, but the ones mentioned in this article comprise a virtually exhaustive list.

The solar wind and the magnetosphere, being two electrically conducting fluids in relative motion, should be able in principle to generate electric currents by dynamo action and impart energy from the flow of the solar wind. However, this process is hampered by the fact that plasmas conduct readily along magnetic field lines, but less readily perpendicular to them. Energy is more effectively transferred by the temporary magnetic connection between the field lines of the solar wind and those of the magnetosphere. Unsurprisingly this process is known as magnetic reconnection. As already mentioned, it happens most readily when the interplanetary field is directed southward, in a similar direction to the geomagnetic field in the inner regions of both the north magnetic pole and south magnetic pole.