{
  "$schema": "https://lumavik.org/api/v1/openapi.json",
  "endpoint": "https://lumavik.org/api/v1/glossary.json",
  "description": "Aurora and space-weather terms, each defined in one sentence that stands alone. The set a reader needs before any of the other endpoints mean anything: Kp, ap, Dst, Bz, substorm, auroral oval, geomagnetic latitude, OVATION, IBC, STEVE.",
  "count": 41,
  "provenance": "The definitions rendered as schema.org DefinedTerm on the glossary page, read at build time from the page itself. Editing a definition here is not possible: it is the page.",
  "field_notes": {
    "definition": "Written to be extractable: one sentence, no anaphora, the term itself as the subject. A definition that begins \"it is\" is useless once it has been retrieved on its own."
  },
  "related": {
    "thresholds": "https://lumavik.org/api/v1/visibility.json",
    "sources": "https://lumavik.org/api/v1/sources.json",
    "human_page": "https://lumavik.org/skywatch/aurora-glossary/"
  },
  "licence": {
    "name": "CC BY 4.0",
    "url": "https://creativecommons.org/licenses/by/4.0/",
    "attribution": "Lumavik — https://lumavik.org",
    "note": "Free to reuse, including commercially, with a link back to the endpoint or the page a figure came from."
  },
  "terms": [
    {
      "term": "AE index",
      "definition": "AE, the auroral electrojet index, measures magnetic disturbance produced by currents flowing in the auroral ionosphere, computed at one-minute cadence from a chain of auroral-zone observatories.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Airglow",
      "definition": "Airglow is faint continuous emission from the upper atmosphere present on every clear night regardless of geomagnetic activity, and it is a common cause of false aurora reports in long-exposure photographs.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "ap index",
      "definition": "ap is the linear equivalent of Kp for the same three-hour interval, expressed in nanotesla, so that values can be averaged arithmetically in a way Kp values cannot.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Ap index",
      "definition": "Ap is the daily average of the eight three-hourly ap values for one UT day.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Aurora",
      "definition": "Aurora is light emitted by atoms and molecules in Earth's upper atmosphere after they are excited by charged particles guided along magnetic field lines, seen as the aurora borealis in the north and the aurora australis in the south.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Auroral arc",
      "definition": "An auroral arc is a smooth band of auroral light stretching roughly east to west across the sky with a lower edge that appears sharp and an upper edge that fades gradually.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Auroral corona",
      "definition": "An auroral corona is the appearance of rays converging on a point overhead, a perspective effect that occurs when the observer is directly beneath the emitting region rather than a distinct type of aurora.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Auroral electrojet",
      "definition": "The auroral electrojet is a strong horizontal current flowing in the auroral ionosphere at about 100 kilometres altitude, and the ground magnetic disturbance it produces is what drives geomagnetically induced currents in power grids and pipelines.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Auroral oval",
      "definition": "The auroral oval is the ring-shaped region around each geomagnetic pole where auroral emission is most likely at a given moment; it expands toward lower geomagnetic latitudes as geomagnetic activity increases.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Bt",
      "definition": "Bt is the total strength of the interplanetary magnetic field vector in nanotesla, and it sets the ceiling on how large a southward Bz can be.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Bz",
      "definition": "Bz is the north-south component of the interplanetary magnetic field in geocentric solar magnetospheric coordinates; a sustained negative, or southward, Bz couples strongly with Earth's field and is the single most useful short-range predictor of auroral activity.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Coronal hole",
      "definition": "A coronal hole is a region of open magnetic field in the Sun's corona from which fast solar wind escapes, producing recurring moderate disturbances that can repeat at roughly 27-day intervals.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Coronal mass ejection",
      "definition": "A coronal mass ejection, abbreviated CME, is a large expulsion of plasma and magnetic field from the Sun's corona that can reach Earth in roughly 15 to 90 hours and drive the strongest geomagnetic storms.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Corotating interaction region",
      "definition": "A corotating interaction region, abbreviated CIR, is the compressed boundary formed where fast solar wind from a coronal hole overtakes slower wind ahead of it, and it can trigger geomagnetic activity without any eruption on the Sun.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Corrected geomagnetic latitude",
      "definition": "Corrected geomagnetic latitude, abbreviated CGM, is a coordinate obtained by tracing the magnetic field line through a location in a field model and relating it to an equivalent latitude, which represents the field's real distortion better than a simple dipole offset.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Dark adaptation",
      "definition": "Dark adaptation is the physiological process by which the eye becomes sensitive to low light over roughly 20 to 30 minutes, during which colour vision is largely lost, which is why a faint display looks grey to the eye and green to a camera.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Diffuse aurora",
      "definition": "Diffuse aurora is the broad, structureless glow produced by scattered electrons precipitating over a wide area, often too faint for the unaided eye but readily captured by a camera.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Discrete aurora",
      "definition": "Discrete aurora is the bright, structured aurora of arcs, bands and rays produced by electrons accelerated in field-aligned potential drops, and it is what most people mean by the northern lights.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Dst index",
      "definition": "Dst, the disturbance storm time index, is an hourly measure in nanotesla of the depression in Earth's horizontal magnetic field caused by the ring current, derived from four near-equatorial observatories and maintained by the World Data Center for Geomagnetism in Kyoto.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Geomagnetic latitude",
      "definition": "Geomagnetic latitude is a coordinate measuring position relative to Earth's magnetic pole rather than the geographic pole, and it is the coordinate the auroral oval follows.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Geomagnetic storm",
      "definition": "A geomagnetic storm is a sustained disturbance of Earth's magnetosphere driven by an extended period of energy transfer from the solar wind, lasting hours to days and reaching much lower latitudes than quiet-time auroral activity.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Geomagnetically induced current",
      "definition": "A geomagnetically induced current, abbreviated GIC, is a quasi-direct current driven through long grounded conductors such as transmission lines and pipelines by the changing magnetic field during a storm.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Hp30 and Hp60",
      "definition": "Hp30 and Hp60 are high-cadence geomagnetic indices published by GFZ on the same scale as Kp but computed over 30-minute and 60-minute intervals, and unlike Kp they are not capped at 9.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "IGRF",
      "definition": "The International Geomagnetic Reference Field is the standard mathematical model of Earth's main magnetic field, revised every five years by IAGA, and it is what geomagnetic coordinate calculations are computed against.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "International Brightness Coefficient",
      "definition": "The International Brightness Coefficient, abbreviated IBC, rates visual auroral brightness on a four-step scale from IBC I, comparable to the Milky Way, to IBC IV, comparable to full moonlight.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Interplanetary magnetic field",
      "definition": "The interplanetary magnetic field, abbreviated IMF, is the Sun's magnetic field carried outward by the solar wind, and its orientation on arrival determines how efficiently energy enters Earth's magnetosphere.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Kp index",
      "definition": "Kp is a planetary index of geomagnetic disturbance reported for each three-hour UT interval on a quasi-logarithmic scale from 0 to 9, derived from magnetic observations at 13 subauroral observatories and published by GFZ in Potsdam.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "L1 point",
      "definition": "L1 is the Sun-Earth Lagrange point about 1.5 million kilometres sunward of Earth, where spacecraft sample the solar wind roughly 20 to 60 minutes before it reaches the magnetosphere.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Magnetic local time",
      "definition": "Magnetic local time, abbreviated MLT, is local time measured in the magnetic coordinate system rather than by the Sun, and auroral activity is organised by MLT rather than by clock time.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Magnetic midnight",
      "definition": "Magnetic midnight is the moment when a location passes through 00 magnetic local time, and it is statistically the most active period for auroral displays at a given site.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Magnetic reconnection",
      "definition": "Magnetic reconnection is the process in which oppositely directed magnetic field lines break and reconnect, converting stored magnetic energy into particle energy and heat; it is the mechanism that both loads the magnetotail and later releases that energy.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Magnetosphere",
      "definition": "The magnetosphere is the region around Earth where the planet's magnetic field dominates over the interplanetary field, compressed on the dayside and drawn into a long tail on the nightside.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Magnetotail",
      "definition": "The magnetotail is the extended nightside portion of the magnetosphere where energy from the solar wind is stored before being released in substorms.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "NOAA G-scale",
      "definition": "The NOAA G-scale rates geomagnetic storms from G1 (minor, Kp 5) to G5 (extreme, Kp 9) and pairs each level with documented effects on power systems, spacecraft and radio.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Nowcast",
      "definition": "A nowcast is a short-range forecast based on conditions already measured, in aurora forecasting typically the 30-to-60-minute outlook derived from solar wind sampled at L1.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "OVATION",
      "definition": "OVATION is the empirical auroral precipitation model used by NOAA to produce the 30-minute aurora forecast, showing modelled energy deposited into the atmosphere at each point rather than the probability that an observer will see something.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Ring current",
      "definition": "The ring current is a westward electric current carried by energetic ions drifting around Earth at a few Earth radii, whose strengthening during storms is what the Dst index measures.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Solar flare",
      "definition": "A solar flare is a sudden release of energy in the solar atmosphere seen as a brightening across the electromagnetic spectrum; its radiation reaches Earth in about eight minutes and affects radio propagation, but a flare by itself does not produce aurora.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Solar wind",
      "definition": "The solar wind is the continuous outflow of charged particles and embedded magnetic field from the Sun's corona, arriving at Earth at speeds typically between about 300 and 800 kilometres per second.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "STEVE",
      "definition": "STEVE, short for Strong Thermal Emission Velocity Enhancement, is a narrow mauve arc seen at lower latitudes than typical aurora, produced by heated fast-flowing plasma rather than by the particle precipitation that causes aurora.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    },
    {
      "term": "Substorm",
      "definition": "An auroral substorm is a cycle of roughly one to three hours in which energy stored in the magnetotail is released abruptly, brightening the aurora and driving it poleward before it fades.",
      "source": "https://lumavik.org/skywatch/aurora-glossary/"
    }
  ]
}