Sources ledger
Answer
Glow quotes 65 figures from NOAA SWPC and NCEI, the US Naval Observatory and the National Weather Service, each checked against the source on 2026-09-30. Everything else on the site is computed from the 8 inputs listed below.
65
cited figures
Cited figures
| Figure | Value | Excerpt | Source URL | Date checked |
|---|---|---|---|---|
| G1 Minor storm | Kp = 5; 1700 per cycle (900 days per cycle) | "aurora is commonly visible at high latitudes (northern Michigan and Maine)" | https://www.spaceweather.gov/noaa-scales-explanation | 2026-09-30next 2026-12-31 |
| G2 Moderate storm | Kp = 6; 600 per cycle (360 days per cycle) | "aurora has been seen as low as New York and Idaho (typically 55° geomagnetic lat.)" | https://www.spaceweather.gov/noaa-scales-explanation | 2026-09-30next 2026-12-31 |
| G3 Strong storm | Kp = 7; 200 per cycle (130 days per cycle) | "aurora has been seen as low as Illinois and Oregon (typically 50° geomagnetic lat.)" | https://www.spaceweather.gov/noaa-scales-explanation | 2026-09-30next 2026-12-31 |
| G4 Severe storm | Kp = 8, including a 9-; 100 per cycle (60 days per cycle) | "aurora has been seen as low as Alabama and northern California (typically 45° geomagnetic lat.)" | https://www.spaceweather.gov/noaa-scales-explanation | 2026-09-30next 2026-12-31 |
| G5 Extreme storm | Kp = 9; 4 per cycle (4 days per cycle) | "aurora has been seen as low as Florida and southern Texas (typically 40° geomagnetic lat.)" | https://www.spaceweather.gov/noaa-scales-explanation | 2026-09-30next 2026-12-31 |
| Kp 0 to 2 wording | Kp 0 to 2 | "For Kp in the range 0 to 2, the aurora will be far north, quite dim in intensity, and not very active." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Kp 3 to 5 wording | Kp 3 to 5 | "For Kp in the range of 3 to 5, the aurora will move further from the poles, it will become brighter and there will be more auroral activity" | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Kp 6 to 7 wording | Kp 6 to 7 | "For Kp in the range 6 to 7, the aurora will move even further from the poles and will become quite bright and active." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Kp 8 to 9 wording | Kp 8 to 9 | "For Kp in the range 8 to 9, the aurora will move even further towards the equator and it will become very bright and very active." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| OVATION forecast lead | 30 to 90 minutes | "This product is based on the OVATION model and provides a 30 to 90 minute forecast of the location and intensity of the aurora." | https://www.spaceweather.gov/products/aurora-30-minute-forecast | 2026-09-30next 2026-12-31 |
| Lead time source | Solar wind travel time from L1 | "The forecast lead time is the time it takes for the solar wind to travel from the L1 observation point to Earth." | https://www.spaceweather.gov/products/aurora-30-minute-forecast | 2026-09-30next 2026-12-31 |
| Viewing distance | 1000 km | "The aurora does not need to be directly overhead but can be observed from as much as a 1000 km away when the aurora is bright and if conditions are right." | https://www.spaceweather.gov/products/aurora-30-minute-forecast | 2026-09-30next 2026-12-31 |
| Viewing distance, tips page | 1000 km (600 miles) | "Given the right vantage point, say for example on top of a hill in the northern hemisphere with an unobstructed view toward the north, a person can see aurora even when it is 1000 km (600 miles) further north." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Best time of night | 10 PM to 2 AM local time | "Best aurora is usually within an hour or two of midnight (between 10 PM and 2 AM local time)." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Best seasons | Around the equinoxes | "The best Seasons for aurora watching are around the spring and fall equinoxes." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Full moon | Diminishes apparent brightness | "The full moon will also diminish the apparent brightness of the aurora (not the actual brightness)." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| IGRF-14 degree 1 coefficients, 2025.0 | g10 -29350.0 nT, g11 -1410.3 nT, h11 4545.5 nT | "Glow computes the centered dipole pole at 80.79N, 72.76W from these three terms. IGRF-14 is valid through 2030." | https://www.ngdc.noaa.gov/IAGA/vmod/coeffs/igrf14coeffs.txt | 2026-09-30next 2026-12-31 |
| Aurora cause | Electrons colliding with the upper atmosphere | "The Aurora Borealis (Northern Lights) and Aurora Australis (Southern Lights) are the result of electrons colliding with the upper reaches of Earth's atmosphere." | https://www.swpc.noaa.gov/phenomena/aurora | 2026-09-30next 2026-12-31 |
| Aurora height | 80 to 500 km | "The aurora typically forms 80 to 500 km above Earth's surface." | https://www.swpc.noaa.gov/phenomena/aurora | 2026-09-30next 2026-12-31 |
| Auroral ovals | Centered on the magnetic poles | "Earth's magnetic field guides the electrons such that the aurora forms two ovals approximately centered at the magnetic poles." | https://www.swpc.noaa.gov/phenomena/aurora | 2026-09-30next 2026-12-31 |
| Best viewing zone | About 60 to 75 degrees; more than half of nights | "The best place to observe the aurora is under an oval shaped region between the north and south latitudes of about 60 and 75 degrees. At these polar latitudes, the aurora can be observed more than half of the nights of a given year." | https://www.swpc.noaa.gov/phenomena/aurora | 2026-09-30next 2026-12-31 |
| Substorm timing | Near midnight | "Late in the evening, near midnight, the arcs often begin to twist and sway, just as if a wind were blowing on the curtains of light." | https://www.swpc.noaa.gov/phenomena/aurora | 2026-09-30next 2026-12-31 |
| Clear and dark sky needed | Midnight sun prevents viewing | "Of course, to observe the aurora, the skies must be clear and free of clouds. It must also be dark so during the summer months at auroral latitudes, the midnight sun prevents auroral observations." | https://www.swpc.noaa.gov/phenomena/aurora | 2026-09-30next 2026-12-31 |
| K-index range | 0 to 9; 5 or more is a storm | "The K-index quantifies disturbances in the horizontal component of earth's magnetic field with an integer in the range 0-9 with 1 being calm and 5 or more indicating a geomagnetic storm." | https://www.swpc.noaa.gov/products/planetary-k-index | 2026-09-30next 2026-12-31 |
| K-index interval | 3 hours | "It is derived from the maximum fluctuations of horizontal components observed on a magnetometer during a three-hour interval." | https://www.swpc.noaa.gov/products/planetary-k-index | 2026-09-30next 2026-12-31 |
| Kp observatories | 13 observatories, 44 to 60 degrees geomagnetic | "The planetary 3-hour-range index Kp is the mean standardized K-index from 13 geomagnetic observatories between 44 degrees and 60 degrees northern or southern geomagnetic latitude." | https://www.swpc.noaa.gov/products/planetary-k-index | 2026-09-30next 2026-12-31 |
| Estimated Kp magnetometers | 8 stations | "The Estimated 3-hour Planetary Kp-index is derived at the NOAA Space Weather Prediction Center using data from the following ground-based magnetometers: Sitka, Alaska; Meanook, Canada; Ottawa, Canada; Fredericksburg, Virginia; Hartland, UK; Wingst, Germany; Niemegk, Germany; and Canberra, Australia." | https://www.swpc.noaa.gov/products/planetary-k-index | 2026-09-30next 2026-12-31 |
| Estimated Kp chart updates | Every minute | "This chart updates every minute." | https://www.swpc.noaa.gov/products/planetary-k-index | 2026-09-30next 2026-12-31 |
| K-index origin | Julius Bartels, 1938 | "The K-index was introduced by Julius Bartels in 1938." | https://www.swpc.noaa.gov/products/planetary-k-index | 2026-09-30next 2026-12-31 |
| K label | Kennziffer, characteristic digit | "The label 'K' comes from the German word 'Kennziffer' meaning 'characteristic digit.'" | https://www.swpc.noaa.gov/products/planetary-k-index | 2026-09-30next 2026-12-31 |
| K-index watches | Kp 5, 6, 7, 8 and above | "K-index Watches are issued when the highest predicted NOAA estimated Kp-indices for a day are K = 5, 6, 7, or >= 8 and is reported in terms of the NOAA G scale." | https://www.swpc.noaa.gov/products/planetary-k-index | 2026-09-30next 2026-12-31 |
| K-index warnings | Kp 4, 5, 6, 7 and above | "K-index Warnings are issued when NOAA estimated Kp-indices of 4, 5, 6, and 7 or greater are expected." | https://www.swpc.noaa.gov/products/planetary-k-index | 2026-09-30next 2026-12-31 |
| K-index alerts | Kp 4 to 9 | "K-index Alerts are issued when the NOAA estimated Kp-indices reach 4, 5, 6, 7, 8, or 9." | https://www.swpc.noaa.gov/products/planetary-k-index | 2026-09-30next 2026-12-31 |
| Oval edge at Kp 0 | About 66 degrees geomagnetic, 2 degrees per Kp | "At Kp = 0, the equator ward edge of the auroral oval is approximately 66 degrees. And it moves equatorward about 2 degrees for each level of Kp." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Oval edge frame | Geomagnetic latitude | "This relationship holds true in geomagnetic latitude, not geographic." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Kp and latitude caveat | Approximate averages | "It should be noted that the relationship between Kp and auroral latitude are approximate and represent averages." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| North magnetic pole | About 400 km from the geographic pole | "The north magnetic pole is currently about 400 km (250 miles) from the geographic pole and is located in the islands of north east Canada." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Low Kp under the oval | Kp 3 or 4 | "It should be noted that if you are in the right place under the aurora, you can see very nice auroral displays even with low geomagnetic activity (Kp = 3 or 4)." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Summer at high latitude | Usually no aurora viewing | "So combining a summer vacation to the arctic with aurora watching usually doesn't work." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Active hours widen | Toward evening and morning with activity | "These hours of active aurora expand towards evening and morning as the level of geomagnetic activity increases." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Equinox storms | Tendency toward larger storms | "Due to subtleties in the way the solar wind interacts with Earth's magnetosphere, there is a tendency towards larger geomagnetic storms, and thus better auroras, to occur near the equinoxes." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Darkness near equinoxes | Changes rapidly | "However, the number of hours of darkness decreases (increases) rapidly near the spring (fall) equinox so this caveat must be considered for those traveling to see the aurora." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Kp 6 to 7 reach | Northern edge of the United States | "At this geomagnetic activity level, it might be possible to see the aurora from the northern edge of the United States." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Kp 8 to 9 reach | Overhead in the northern states | "At these levels, aurora may be seen directly overhead from the northern states of the USA." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| Viewing equatorward | Hundreds of km | "It should be noted that the aurora can often be observed hundreds of kilometers (miles) equatorward of the actual aurora so these figures do not indicate where the aurora may be but rather the point from which it may be observed." | https://www.spaceweather.gov/content/tips-viewing-aurora | 2026-09-30next 2026-12-31 |
| L1 distance | 1.6 million km | "The model uses the solar wind velocity and interplanetary magnetic field measured at the L1 orbit position at 1.6 million km (1 million miles) upstream from earth as input" | https://www.spaceweather.gov/products/aurora-30-minute-forecast | 2026-09-30next 2026-12-31 |
| OVATION probability | Linear in aurora intensity | "An estimate of aurora viewing probability can be derived by assuming a linear relationship to the intensity of the aurora." | https://www.spaceweather.gov/products/aurora-30-minute-forecast | 2026-09-30next 2026-12-31 |
| OVATION 2020 | In operations since 2020 | "In 2020, NOAA SWPC implemented the new version of the OVATION Prime model into operations." | https://www.spaceweather.gov/products/aurora-30-minute-forecast | 2026-09-30next 2026-12-31 |
| Original OVATION limit | Reliable to Kp 7 | "The original model, based solely on DMSP data, was only reliable to Kp of 7." | https://www.spaceweather.gov/products/aurora-30-minute-forecast | 2026-09-30next 2026-12-31 |
| Daylight | Aurora not visible | "The aurora is not visible during daylight hours." | https://www.spaceweather.gov/products/aurora-30-minute-forecast | 2026-09-30next 2026-12-31 |
| CME travel time | Several days; as short as 18 hours | "CMEs typically take several days to arrive at Earth, but have been observed, for some of the most intense storms, to arrive in as short as 18 hours." | https://www.swpc.noaa.gov/phenomena/geomagnetic-storms | 2026-09-30next 2026-12-31 |
| Storm driver | Southward solar wind magnetic field | "The solar wind conditions that are effective for creating geomagnetic storms are sustained (for several to many hours) periods of high-speed solar wind, and most importantly, a southward directed solar wind magnetic field (opposite the direction of Earth's field) at the dayside of the magnetosphere." | https://www.swpc.noaa.gov/phenomena/geomagnetic-storms | 2026-09-30next 2026-12-31 |
| High-speed streams | Create CIRs | "HSSs plow into the slower solar wind in front and create co-rotating interaction regions, or CIRs." | https://www.swpc.noaa.gov/phenomena/geomagnetic-storms | 2026-09-30next 2026-12-31 |
| Civil twilight | Sun 6 degrees below the horizon | "Civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 6 degrees below the horizon." | https://aa.usno.navy.mil/faq/RST_defs | 2026-09-30next 2026-12-31 |
| Nautical twilight | Sun 12 degrees below the horizon | "Nautical twilight is defined to begin in the morning, and to end in the evening, when the center of the sun is geometrically 12 degrees below the horizon." | https://aa.usno.navy.mil/faq/RST_defs | 2026-09-30next 2026-12-31 |
| Astronomical twilight | Sun 18 degrees below the horizon | "Astronomical twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 18 degrees below the horizon." | https://aa.usno.navy.mil/faq/RST_defs | 2026-09-30next 2026-12-31 |
| Astronomical night | Sunlight below starlight | "Before the beginning of astronomical twilight in the morning and after the end of astronomical twilight in the evening, scattered light from the Sun is less than that from starlight and other natural sources." | https://aa.usno.navy.mil/faq/RST_defs | 2026-09-30next 2026-12-31 |
| Sunrise definition | Zenith distance 90.8333 degrees | "For computational purposes, sunrise or sunset is defined to occur when the geometric zenith distance of center of the Sun is 90.8333 degrees." | https://aa.usno.navy.mil/faq/RST_defs | 2026-09-30next 2026-12-31 |
| NWS sky condition basis | Octants of opaque cloud | "Used in a forecast to describes the predominant/average sky condition based upon octants (eighths) of the sky covered by opaque (not transparent) clouds." | https://forecast.weather.gov/glossary.php?letter=s | 2026-09-30next 2026-12-31 |
| Solar cycle length | 11 years | "Average Frequency (1 cycle = 11 years)" | https://www.spaceweather.gov/noaa-scales-explanation | 2026-09-30next 2026-12-31 |
| NWS sky condition: Clear / Sunny | 0/8 of the sky | "Clear / Sunny 0/8" | https://forecast.weather.gov/glossary.php?letter=s | 2026-09-30next 2026-12-31 |
| NWS sky condition: Mostly Clear / Mostly Sunny | 1/8 to 2/8 of the sky | "Mostly Clear / Mostly Sunny 1/8 to 2/8" | https://forecast.weather.gov/glossary.php?letter=s | 2026-09-30next 2026-12-31 |
| NWS sky condition: Partly Cloudy / Partly Sunny | 3/8 to 4/8 of the sky | "Partly Cloudy / Partly Sunny 3/8 to 4/8" | https://forecast.weather.gov/glossary.php?letter=s | 2026-09-30next 2026-12-31 |
| NWS sky condition: Mostly Cloudy / Considerable Cloudiness | 5/8 to 7/8 of the sky | "Mostly Cloudy / Considerable Cloudiness 5/8 to 7/8" | https://forecast.weather.gov/glossary.php?letter=s | 2026-09-30next 2026-12-31 |
| NWS sky condition: Cloudy | 8/8 of the sky | "Cloudy 8/8" | https://forecast.weather.gov/glossary.php?letter=s | 2026-09-30next 2026-12-31 |
Live and computed inputs
- NOAA SWPC OVATION JSONAurora value per 1 degree cell, observation and forecast timeU.S. Government work, generally public domain
- NWS gridpoint skyCoverPercent of sky covered per forecast interval, US onlyU.S. Government work; see the NWS disclaimer
- GeoNames cities15000, cities5000, admin1 codes, country infoTowns, regions, coordinates, population and IANA time zones for the atlas, the town search and time zone guessesCC BY 4.0
- NASA POWER climatology API, CLOUD_AMTMean cloud amount per month, 2001 to 2020, for each town's 1 degree cellNASA open data; cite NASA POWER
- GFZ Potsdam Kp index since 1932Kp history by year, storm events and month rates for each townCC BY 4.0 (Kp, ap, Ap); the sunspot column is not used
- SunCalcSun and moon altitude, twilight angles, moon illuminationBSD-2-Clause library, computed locally
- US Naval Observatory twilight definitionsThe -6, -12 and -18 degree thresholds Glow appliesU.S. Government work
- Natural Earth 1:50m landCoastline on the polar mapPublic domain
Review schedule
Cited figures are re-read against the source pages every quarter. The last check was 2026-09-30; the next is due 2026-12-31. The IGRF-14 coefficients are valid through 2030. When a source changes its wording, the ledger changes with it and the change is logged.
Found a figure that does not match its source? Use the contact page. Corrections are made at the ledger, so every page that quotes the figure updates at once.