{ "$schema": "https://lumavik.org/api/v1/openapi.json", "endpoint": "https://lumavik.org/api/v1/visibility.json", "description": "Auroral visibility thresholds: the modelled equatorward edge of the auroral oval at each Kp step, the NOAA G-scale mapped onto the same scale with its published frequency, and the editorial viewing bands by geomagnetic latitude. It says what a location needs. It is not a forecast.", "model": { "geomagnetic_pole": { "latitude": 80.8, "longitude": -72.7, "model": "IGRF tilted dipole, approx. epoch 2025" }, "twilight_threshold_degrees": -18, "horizon": { "emission_altitude_km": 100, "earth_radius_km": 6371, "geometric_horizon_km": 1100, "formula": "sqrt(2 * R * h)", "source": "https://lumavik.org/skywatch/aurora-oval-explained/" } }, "provenance": "The oval-edge table and the tilted-dipole coordinate transform are the model this site's own calculators run, ported from public/js/aurora-engine.js at build time rather than copied. The viewing bands are the editorial table published on the page named in `source`. The NOAA G-scale mapping and its published average frequency per solar cycle come from NOAA SWPC, \"NOAA Space Weather Scales\".", "caveats": [ "There are two different \"Kp you need\" numbers and confusing them is the most common error made with this data. `kp_oval_overhead` is the Kp at which the modelled auroral oval expands far enough for emission to be produced roughly above that location. `kp_visible_from_area` is the editorial estimate of when a display becomes worth going outside for from there, which is lower, because emission around 100 km up has a geometric horizon of about 1100 km and is routinely seen on the poleward horizon by people far outside the oval. Quote whichever you mean, and say which.", "The oval-edge table is a modelled approximation of where auroral emission typically reaches at each Kp, not a boundary. The oval is a ring around the geomagnetic pole that moves within a single three-hour Kp interval, and emission around 100 km up is visible from roughly 1100 km equatorward of where it is produced.", "Geomagnetic latitude here is the tilted-dipole approximation, not corrected geomagnetic (CGM) coordinates from the full IGRF model. The two differ by up to about two degrees in places, which near a threshold is one Kp step. Use it to decide roughly what a location needs, not to settle an argument about one degree.", "Kp is reported once per three-hour UT interval on a quasi-logarithmic scale and is published after the interval it describes. A substorm can brighten the sky for twenty minutes without moving it. Treat a Kp figure as a summary of three hours that have already happened, never as a live reading.", "None of this predicts a specific night. It says what a location needs; whether the Sun supplies it is a separate question answered by NOAA SWPC in real time." ], "counts": { "kp_steps": 10, "viewing_bands": 5 }, "related": { "cities": "https://lumavik.org/api/v1/cities.json", "darkness": "https://lumavik.org/api/v1/darkness.json", "human_page": "https://lumavik.org/skywatch/what-kp-index-to-see-northern-lights/", "calculator": "https://lumavik.org/tools/geomagnetic-latitude-calculator/" }, "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." }, "oval_edge_by_kp": [ { "kp": 0, "oval_edge_geomagnetic_latitude": 66.5, "noaa_storm_level": null, "noaa_storm_name": null, "average_events_per_solar_cycle": null }, { "kp": 1, "oval_edge_geomagnetic_latitude": 64.5, "noaa_storm_level": null, "noaa_storm_name": null, "average_events_per_solar_cycle": null }, { "kp": 2, "oval_edge_geomagnetic_latitude": 62.4, "noaa_storm_level": null, "noaa_storm_name": null, "average_events_per_solar_cycle": null }, { "kp": 3, "oval_edge_geomagnetic_latitude": 60.4, "noaa_storm_level": null, "noaa_storm_name": null, "average_events_per_solar_cycle": null }, { "kp": 4, "oval_edge_geomagnetic_latitude": 58.3, "noaa_storm_level": null, "noaa_storm_name": null, "average_events_per_solar_cycle": null }, { "kp": 5, "oval_edge_geomagnetic_latitude": 56.3, "noaa_storm_level": "G1", "noaa_storm_name": "Minor", "average_events_per_solar_cycle": 1700 }, { "kp": 6, "oval_edge_geomagnetic_latitude": 54.2, "noaa_storm_level": "G2", "noaa_storm_name": "Moderate", "average_events_per_solar_cycle": 600 }, { "kp": 7, "oval_edge_geomagnetic_latitude": 52.2, "noaa_storm_level": "G3", "noaa_storm_name": "Strong", "average_events_per_solar_cycle": 200 }, { "kp": 8, "oval_edge_geomagnetic_latitude": 50.1, "noaa_storm_level": "G4", "noaa_storm_name": "Severe", "average_events_per_solar_cycle": 100 }, { "kp": 9, "oval_edge_geomagnetic_latitude": 48.1, "noaa_storm_level": "G5", "noaa_storm_name": "Extreme", "average_events_per_solar_cycle": 4 } ], "viewing_bands": [ { "geomagnetic_latitude": "65–70°", "kp_from": 2, "kp_to": 4, "means": "Aurora can be nearby or overhead; faint activity may still need dark skies", "source": "https://lumavik.org/skywatch/what-kp-index-to-see-northern-lights/" }, { "geomagnetic_latitude": "60–65°", "kp_from": 3, "kp_to": 5, "means": "A realistic chance, often low on the poleward horizon at the lower end", "source": "https://lumavik.org/skywatch/what-kp-index-to-see-northern-lights/" }, { "geomagnetic_latitude": "55–60°", "kp_from": 5, "kp_to": 7, "means": "Strong activity may bring a visible northern arc or rays", "source": "https://lumavik.org/skywatch/what-kp-index-to-see-northern-lights/" }, { "geomagnetic_latitude": "50–55°", "kp_from": 6, "kp_to": 8, "means": "Aurora becomes possible during major disturbances, usually low and toward the north", "source": "https://lumavik.org/skywatch/what-kp-index-to-see-northern-lights/" }, { "geomagnetic_latitude": "below 50°", "kp_from": 8, "kp_to": 9, "means": "Rare, demanding conditions; a high Kp alone still does not guarantee visibility", "source": "https://lumavik.org/skywatch/what-kp-index-to-see-northern-lights/" } ], "forecast_products": [ { "product": "Solar-wind data (L1)", "from_minutes": 5, "to_minutes": 60, "covers": "Upstream conditions as measured at the L1 point, minutes of context", "source": "https://lumavik.org/skywatch/ovation-aurora-model/" }, { "product": "L1 nowcast", "from_minutes": 30, "to_minutes": 60, "covers": "The only product resting on a direct measurement of the magnetic field that is arriving", "source": "https://lumavik.org/skywatch/aurora-forecast-accuracy/" }, { "product": "OVATION 30-minute forecast", "from_minutes": 30, "to_minutes": 90, "covers": "Modelled auroral emission, roughly 30 to 90 minutes ahead", "source": "https://lumavik.org/skywatch/ovation-aurora-model/" }, { "product": "Kp index", "from_minutes": 180, "to_minutes": 540, "covers": "Three-hour blocks, looking backwards", "source": "https://lumavik.org/skywatch/kp-index-explained/" }, { "product": "Three-day forecast", "from_minutes": 1440, "to_minutes": 4320, "covers": "Identifies nights worth keeping free; never an hour", "source": "https://lumavik.org/skywatch/aurora-forecast-accuracy/" }, { "product": "27-day outlook", "from_minutes": 30240, "to_minutes": 38880, "covers": "Recurrence from solar rotation, not a prediction", "source": "https://lumavik.org/skywatch/aurora-forecast-accuracy/" } ], "emission_by_altitude": [ { "colour": "Blue / violet", "wavelength_nm": null, "from_km": 80, "to_km": 100, "emitter": "Nitrogen", "note": "The lower edge of a curtain; needs energetic particles to penetrate this deep", "source": "https://lumavik.org/skywatch/why-is-the-aurora-green/" }, { "colour": "Green", "wavelength_nm": 557.7, "from_km": 100, "to_km": 150, "emitter": "Atomic oxygen", "note": "The emission the dark-adapted eye is most sensitive to", "source": "https://lumavik.org/skywatch/why-is-the-aurora-green/" }, { "colour": "Red", "wavelength_nm": 630, "from_km": 200, "to_km": 400, "emitter": "Atomic oxygen", "note": "A long-lived state that only survives where collisions are rare", "source": "https://lumavik.org/skywatch/why-is-the-aurora-green/" } ] }