**DSCOVR, ACE and the 13 Observatories Behind Kp | Lumavik** > Every aurora app reads the same public instruments: DSCOVR and ACE at L1, GOES magnetometers, the 13 ground observatories behind Kp — and what none of them measure. Source: https://lumavik.org/skywatch/where-aurora-data-comes-from/ · updated: 2026-08-07 - [Home](https://lumavik.org/)/ - [Skywatch](https://lumavik.org/skywatch/) # Where aurora forecast data comes from: the instruments Published August 7, 2026 Lumavik editorial Every aurora app reads the same public instruments: DSCOVR and ACE at L1, GOES magnetometers, the 13 ground observatories behind Kp — and what none of them measure. Every aurora app, website and alert service in existence reads from the same short list of public instruments. There is no proprietary aurora data. Knowing which instrument produces which number tells you what each figure can and cannot support, and it explains most of the disagreements between apps. The chain runs from the Sun to your screen through four layers: spacecraft watching the Sun itself, spacecraft sampling the solar wind upstream of Earth, satellites and ground stations measuring Earth’s response, and the agencies that turn those measurements into published products. ## The four layers, and what each one can tell you | Layer | Instruments | Where | What it provides | Warning time | | --- | --- | --- | --- | --- | | Solar imaging | SOHO coronagraphs, GOES X-ray sensors | L1 and geostationary | Detection of flares and CMEs, rough CME speed and direction | 15–90 hours for a CME | | Upstream solar wind | DSCOVR, ACE | L1, ~1.5 million km sunward | Speed, density, and the IMF including Bz | 20–60 minutes | | Earth’s response, space | GOES magnetometers, particle sensors | Geostationary, ~35,800 km | Local field, particle environment, storm onset | None — concurrent | | Earth’s response, ground | 13 Kp observatories, Dst and AE station chains, SuperMAG | Surface | Kp, ap, Dst, AE, station K | None — after the fact | *The instrument layers behind an aurora forecast, with the warning time each provides. Only one layer gives useful advance notice of the decisive quantity, and it gives less than an hour. Free to reuse with a link to this page.* Read the warning-time column first. It contains the whole argument about forecast accuracy: the layer that sees days ahead cannot measure the variable that matters, and the layer that measures it sees less than an hour ahead. - [How accurate the aurora forecast is by lead time](https://lumavik.org/skywatch/aurora-forecast-accuracy/) works through the consequences. ## Watching the Sun: SOHO and GOES SOHO, the Solar and Heliospheric Observatory, is a joint NASA and ESA mission operating from the L1 region. Its LASCO coronagraphs block the solar disc to image the faint corona around it, which is how coronal mass ejections are detected and their speed estimated. A coronagraph sees a CME as it leaves the Sun. From a sequence of images, forecasters estimate its speed and whether it is directed toward Earth, and models project an arrival time. Transit typically takes 15 to 90 hours. What a coronagraph cannot see is the magnetic field inside the CME. That orientation determines whether the arrival produces a major storm or very little, and it is not measurable remotely by any current instrument. This single limitation is why a three-day aurora forecast is a statement about probability rather than about outcome. The GOES satellites carry X-ray sensors that detect flares directly. Flares matter for radio propagation, and a large flare is often the first sign that an active region is capable of launching a CME — but a flare on its own produces no aurora. ## Measuring the wind: DSCOVR and ACE at L1 DSCOVR, the Deep Space Climate Observatory, is the primary real-time solar wind monitor. It operates near L1, the Sun-Earth Lagrange point about 1.5 million kilometres sunward of Earth, where a spacecraft can hold station upstream in the flow. It measures solar wind speed, density and the vector interplanetary magnetic field, including the Bz component. NASA’s ACE, the Advanced Composition Explorer, launched in 1997 and occupies a similar region. It has served as the real-time solar wind source and now provides backup and complementary measurements. Between them they have kept a continuous upstream watch for decades. The travel time from L1 to Earth is simple arithmetic and it sets the forecast horizon. At a solar wind speed of 800 kilometres per second, 1.5 million kilometres takes about 31 minutes. At 400 kilometres per second it takes about 62 minutes. Everything anyone knows about the incoming magnetic field orientation comes from that window. This is the measurement that matters most for a decision tonight. A sustained southward Bz means energy is being transferred efficiently into the magnetosphere; the same wind speed with a northward field means much less. - [How to read solar wind speed, density and Bz](https://lumavik.org/skywatch/solar-wind-and-aurora/) covers the interpretation, and the - [live aurora forecast](https://lumavik.org/tools/aurora-forecast/) shows the current values. There is a practical caveat worth stating. L1 is a single point in a very large flow. Structures in the solar wind are not uniform across the distance between L1 and Earth, so the wind that passes the spacecraft is a good but imperfect sample of the wind that arrives. ## Measuring Earth’s response Once the wind arrives, the measurement problem changes from prediction to observation, and two networks handle it. **In space**, the GOES satellites sit in geostationary orbit about 35,800 kilometres up — inside the magnetosphere rather than outside it. Their magnetometers record the local field, which compresses when solar wind pressure rises and stretches during substorm growth. This is a direct look at the magnetosphere responding, and it is concurrent rather than predictive. **On the ground**, magnetometer observatories record the surface field. The 13 observatories behind Kp are sited between 44 and 60 degrees geomagnetic latitude, deliberately below the auroral zone so the index reflects planetary conditions rather than local extremes. Dst comes from four near-equatorial observatories, and AE from a chain inside the auroral zone. SuperMAG, run from the Johns Hopkins Applied Physics Laboratory, collates data from a far larger worldwide collection of magnetometers into a common format. It is the resource to reach for when the standard indices are too coarse, either in space or in time. ## Who publishes what Instrument ownership and data publication are separate things, which is why several agencies appear in any honest source list. - **NOAA’s Space Weather Prediction Center** is the operational forecaster for the United States and the origin of most feeds an app reads: real-time solar wind, the estimated planetary K-index, the 3-day geomagnetic forecast, the 27-day outlook, and the OVATION 30-minute aurora model. All of it is public domain. - **GFZ in Potsdam** is the official service for the definitive Kp and ap indices under IAGA, and it also publishes the high-cadence Hp30 and Hp60 series. - **The World Data Center for Geomagnetism in Kyoto** publishes Dst and AE. - **The International Service of Geomagnetic Indices** coordinates the index services under IAGA. - **NOAA’s NCEI** archives the long-term space-weather record and publishes the International Geomagnetic Reference Field, which is what geomagnetic coordinate calculations are computed against. - **Natural Resources Canada** and **ESA** operate their own forecast services, and **AuroraWatch UK** at Lancaster University runs a UK-specific magnetometer alert. The practical consequence is that when two aurora apps disagree about tonight, they are almost never reading different instruments. They are applying different thresholds, different location models and different presentation choices to identical public numbers. That is worth knowing before treating one app’s confidence as independent confirmation of another’s. ## What none of these instruments measure Four things decide whether a person sees aurora, and the instrument chain above measures exactly one of them. **Cloud.** No space-weather instrument sees it. A perfect forecast above complete overcast produces nothing, and this remains the most common single reason an aurora night fails. **Darkness at your location.** Astronomical twilight is a matter of solar geometry, not space weather. Above the Arctic Circle the sky does not get dark enough for months around midsummer regardless of activity — see - [why the aurora has a season](https://lumavik.org/skywatch/northern-lights-season/) and the - [dark-hours calculator](https://lumavik.org/tools/dark-hours-calendar/). **Your position relative to the oval.** The instruments measure planetary and upstream conditions. Turning that into an answer for one address requires corrected geomagnetic latitude, which is computed rather than measured — the - [geomagnetic latitude calculator](https://lumavik.org/tools/geomagnetic-latitude-calculator/) does it. **Whether the display is bright enough for human vision.** Emission energy is not visual brightness. A camera routinely records displays that a dark-adapted eye cannot distinguish from grey sky, which is the source of a great deal of disappointment covered in - [the diagnostic table](https://lumavik.org/skywatch/why-you-did-not-see-the-aurora/). Any product presenting a single confident number has combined a measured quantity with several modelled and unmeasured ones. That is legitimate — it is what our own tools do — but the confidence of the presentation should not exceed the confidence of the weakest input. ## Bottom line Aurora forecasting runs on public instruments and there is no private data. Solar imaging by SOHO coronagraphs and GOES X-ray sensors detects coronal mass ejections 15 to 90 hours before arrival but cannot measure the magnetic orientation that decides their effect. DSCOVR and ACE at the L1 point, about 1.5 million kilometres sunward, measure solar wind speed, density and the interplanetary magnetic field including Bz, giving 20 to 60 minutes of warning depending on wind speed — that interval is the hard physical ceiling on short-range forecasting. GOES magnetometers in geostationary orbit and ground observatories record Earth’s response as it happens: 13 stations between 44 and 60 degrees geomagnetic latitude produce Kp, four near-equatorial stations produce Dst, an auroral-zone chain produces AE, and SuperMAG collates a far wider network. NOAA SWPC, GFZ Potsdam and the Kyoto World Data Center publish the results, all free. None of these instruments measures cloud, darkness, your geomagnetic position or whether a display is bright enough to see — and those four decide the night. ## Sources Every figure on this page traces to one of these. All are public and free to read; where a number depends on the data version or the interval examined, we say so rather than printing a single tidy value. - [DSCOVR: Deep Space Climate Observatory](https://www.nesdis.noaa.gov/dscovr-deep-space-climate-observatory)NOAA NESDIS - [DSCOVR mission](https://science.nasa.gov/mission/dscovr/)NASA - [Advanced Composition Explorer (ACE)](https://science.nasa.gov/mission/ace/)NASA - [SOHO: Solar and Heliospheric Observatory](https://soho.nascom.nasa.gov/)NASA / ESA - [Real-Time Solar Wind](https://www.swpc.noaa.gov/products/real-time-solar-wind)NOAA SWPC - [GOES Magnetometer](https://www.swpc.noaa.gov/products/goes-magnetometer)NOAA SWPC - [Station K and Indices](https://www.swpc.noaa.gov/products/station-k-and-indices)NOAA SWPC - [Kp index data and description](https://kp.gfz.de/en/data)GFZ Helmholtz Centre for Geosciences - [International Service of Geomagnetic Indices](https://isgi.unistra.fr/)IAGA / ISGI - [SuperMAG magnetometer collaboration](https://supermag.jhuapl.edu/)Johns Hopkins Applied Physics Laboratory - [Space weather data](https://www.ncei.noaa.gov/products/space-weather)NOAA NCEI - [Canadian Space Weather Forecast Centre](https://www.spaceweather.gc.ca/)Natural Resources Canada - [AuroraWatch UK](https://aurorawatch.lancs.ac.uk/)Lancaster University - [Space Weather Service Network](https://swe.ssa.esa.int/)ESA **Where the numbers come from.** Kp values, the 3-day geomagnetic forecast, the OVATION auroral-oval model and real-time solar wind are published by the NOAA Space Weather Prediction Center in the public domain. Lumavik is not affiliated with NOAA. Forecasts are probabilities: activity, latitude, darkness and cloud all have to cooperate, and cloud cover alone can end the night regardless of everything else. ### Get this as an alert instead of a browser tab Lumavik watches the same NOAA feeds and pushes a notification when the aurora is actually plausible where you are — scored against your geomagnetic latitude and whether it is dark yet, not against a planetary average. - [Get the app](https://lumavik.org/get/) Free · NOAA data · no account ## Frequently asked questions Which satellite measures the solar wind for aurora forecasts? DSCOVR, the Deep Space Climate Observatory, is the primary real-time solar wind monitor. It sits near the L1 Lagrange point about 1.5 million kilometres sunward of Earth and measures solar wind speed, density and the interplanetary magnetic field, including the Bz component. NASA's ACE spacecraft, launched in 1997, occupies a similar position and serves as a backup. Both are operated in partnership between NASA and NOAA, and the data is public. How much warning does the L1 point give? Roughly 20 to 60 minutes, depending on solar wind speed. L1 is about 1.5 million kilometres upstream, so wind travelling at 800 kilometres per second covers that distance in about 31 minutes, while wind at 400 kilometres per second takes about 62 minutes. That interval is the hard physical limit on how far ahead the decisive measurement — the magnetic field orientation — can be known. Do aurora apps use different data from each other? Mostly no. Nearly all of them read the same public feeds published by NOAA's Space Weather Prediction Center, which draws on DSCOVR, ACE, GOES and the ground observatory network. Apps differ in how they process and present that data, not in what they measure. When two apps disagree about tonight, the disagreement is in the interpretation layer, not in the underlying instruments. Is aurora forecast data free? Yes. NOAA publishes its space-weather products in the public domain, including real-time solar wind, the planetary K-index, the 3-day geomagnetic forecast and the OVATION auroral model. GFZ in Potsdam publishes the definitive Kp and ap series, and the World Data Center in Kyoto publishes Dst and AE. Anyone can read the same feeds an app reads. What is the difference between DSCOVR and GOES? They measure different things in different places. DSCOVR sits at L1, about 1.5 million kilometres sunward, and samples the solar wind before it reaches Earth, which is what provides advance warning. The GOES satellites are in geostationary orbit about 35,800 kilometres up, inside the magnetosphere, and measure the local magnetic field, X-ray flux and particle environment — that is a measurement of what is already happening to Earth, not a forecast input. Who publishes the definitive Kp index? GFZ in Potsdam, Germany, is the official service for Kp and ap under IAGA. NOAA's Space Weather Prediction Center publishes an estimated planetary K-index in near-real time for operational users, which is later superseded by the GFZ definitive values. Both are correct for their purpose, and small differences between a live app reading and a later archive value are expected rather than an error. ## Keep reading - [Skywatch **Solar Wind Aurora Forecast: Read Bz, Speed and Density**](https://lumavik.org/skywatch/solar-wind-and-aurora/) - [Skywatch **How to read the OVATION aurora model honestly**](https://lumavik.org/skywatch/ovation-aurora-model/) - [Skywatch **How accurate is the aurora forecast, really?**](https://lumavik.org/skywatch/aurora-forecast-accuracy/) - [Comparison **Lumavik vs Aurora Forecast.: Which Aurora App Fits You?**](https://lumavik.org/compare/lumavik-vs-aurora-forecast/) - [Skywatch **Kp index explained, and what it cannot tell you**](https://lumavik.org/skywatch/kp-index-explained/) - [Skywatch **Best Aurora Forecast App: An Honest Comparison**](https://lumavik.org/skywatch/aurora-forecast-apps/) - [Skywatch **Aurora glossary: the space-weather terms defined**](https://lumavik.org/skywatch/aurora-glossary/) - [Comparison **Lumavik vs My Aurora Forecast & Alerts**](https://lumavik.org/compare/lumavik-vs-my-aurora-forecast-and-alerts/) --- HTML version: https://lumavik.org/skywatch/where-aurora-data-comes-from/ Structured data for this site: https://lumavik.org/api/v1/openapi.json · https://lumavik.org/llms.txt Free to quote and reuse with a link back to the source URL above (CC BY 4.0).