**Free Aurora Forecast Tools — Kp, Latitude, Darkness | Lumavik**

> Five free aurora tools that run in your browser: live Kp index, a tonight verdict for your location, geomagnetic latitude, camera settings and a dark-hours calendar.

Source: https://lumavik.org/tools/

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Free tools

# Space weather tools that answer one question each.

These are the calculations that sit inside the Lumavik app, pulled out and made free
on the web. They need no account, no download and no payment, they work on any
device with a browser, and nothing you type into them is sent anywhere — the
arithmetic runs on your machine, and the only network request any of them makes is to
NOAA for public space-weather data.

We publish them for a straightforward reason. Aurora forecasting has a small number of
genuinely useful calculations buried under a large amount of vague writing, and most
of the pages that rank for these questions either hand you a single global number that
does not apply to you or bury the answer inside a tour booking. A calculator cannot be
vague. It either gives you a number you can check or it does not.

## Which one you need

If you are outside right now and want to know whether to keep waiting, the live
forecast is the fastest answer, and the tonight verdict is the more useful one because
it accounts for where you are standing. If you are planning rather than watching, the
geomagnetic latitude calculator and the dark-hours calendar are the two that change
decisions: one tells you how often the aurora will reach your latitude at all, the
other tells you which months your sky is dark enough to show it.

The pairing of those last two is where most trip planning goes wrong. Going further
north improves your geomagnetic latitude, which sounds like an unambiguous win, and it
is not — because the further north you go, the longer the summer keeps your sky too
bright, and the more of the year is closed to you entirely. Above the Arctic Circle
there are months when the geomagnetic forecast is completely irrelevant, because there
is no darkness for anything to be visible against. Tromsø has a better latitude than
Reykjavik and a shorter season. Neither is simply better; they are a trade-off, and the
two calculators together show you the shape of it.

## What these tools will not do

None of them can see your sky. Cloud cover is the single most common reason an aurora
night fails, it has an absolute veto over everything else on this page, and no
geomagnetic model contains it. A forecast of Kp 7 under solid overcast is a night
indoors. Check an ordinary weather forecast alongside anything here, and treat a clear
sky as the first condition rather than the last.

None of them can promise a sighting, and we would rather say that plainly than imply
otherwise with confident-looking output. Aurora forecasting past about an hour ahead is
probabilistic in a way that resists precision, because the variable that decides
whether energy actually enters the magnetosphere — the orientation of the magnetic
field carried in the solar wind — is only measured when that wind passes the spacecraft
sitting upstream of Earth, roughly half an hour to an hour before it arrives. Everything
beyond that horizon is an informed probability.

The coordinate conversions use the tilted-dipole approximation rather than the full
field model, which is accurate enough for planning and can differ from corrected
geomagnetic coordinates by a degree or two in some parts of the world. The solar
geometry uses a standard low-precision series, accurate to a few minutes of twilight
time. Both are stated on the pages themselves, because a tool that hides its
approximations is harder to trust than one that names them.

If you find an error in any of them, tell us and we will fix it and say that we did.
Several of these calculations exist in the app precisely because we could not find a
version on the web we trusted enough to link to instead.

## Using them offline

Four of the five work without a network connection once the page has loaded, because
the arithmetic is local. Only the live forecast and the tonight verdict need to reach
NOAA. If you are heading somewhere with no signal, open the geomagnetic latitude
calculator and the dark-hours calendar before you leave and note the two numbers that
matter for your destination: the minimum Kp it needs, and how much true darkness the
month gives you. Those do not change on the timescale of a trip, and knowing them means
a single glance at any Kp figure you can get hold of is enough to make a decision.

## The vocabulary, in one place

Every tool here uses at least one term that gets thrown around without definition in
aurora forecasting. These are the ones worth knowing before you read any forecast,
ours or anyone else's.

**Kp index.** A planetary measure of geomagnetic disturbance on a quasi-logarithmic
scale from 0 to 9, derived from magnetometer stations spread around the world and
reported in three-hour blocks. It describes how disturbed the field was globally over
three hours. It is not a measure of aurora brightness and it is not local to you.

**Estimated Kp.** The near-real-time figure NOAA publishes every minute so that
people have a current number to work with. The definitive Kp is calculated later from
the full station network and can differ slightly. The live tools here show the
estimated value, which is the right one for deciding whether to go outside now.

**G-scale.** NOAA's storm classification, running from G1 for a minor geomagnetic
storm to G5 for an extreme one, mapped onto Kp 5 through 9. It exists mainly to
communicate infrastructure risk to power and satellite operators, but it is a
convenient shorthand for how unusual a night is.

**Auroral oval.** The ring-shaped region around each geomagnetic pole where aurora
occurs. It is offset toward the night side and it stays roughly fixed relative to the
sun while the Earth rotates underneath it. During a storm it expands equatorward,
which is what a rising Kp physically means for you.

**Geomagnetic latitude.** Latitude measured from the geomagnetic pole rather than
the geographic one. Because the two poles do not coincide, this can differ from your
map latitude by several degrees, and it is the coordinate that determines your aurora
odds. Corrected geomagnetic latitude is the more rigorous version, derived from the
full field model rather than a dipole approximation.

**Magnetic midnight.** The moment your location passes closest to the midnight side
of the auroral oval, which is usually the most active part of the night. It does not
coincide with clock midnight, and the offset depends on where you sit within your time
zone and on your longitude relative to the geomagnetic pole.

**Substorm.** A sudden release of energy stored in the magnetotail, lasting tens of
minutes, that produces the fast, bright, structured displays people remember. Because
Kp averages over three hours, a substorm can deliver an excellent night inside a block
that reports an unremarkable number.

**Bz.** The north-south component of the interplanetary magnetic field carried by
the solar wind. When it points south it can reconnect with Earth's field and let energy
in, which makes it the single most informative variable in short-term forecasting and
the one most consumer apps never show.

**L1.** The point roughly 1.5 million kilometres sunward of Earth where spacecraft
measure the solar wind before it arrives. It buys forecasters something between about
thirty and sixty minutes of warning, and that lead time is the hard limit on how far
ahead anyone can forecast with confidence.

**OVATION.** The statistical model NOAA uses to produce the familiar coloured oval
map, estimating auroral emission from solar-wind input. It is a model rather than an
observation, and it shows emission overhead at each point — not the probability that
you personally will see something from your garden.

**Substorm onset.** The moment a substorm begins, when a quiet arc suddenly
brightens and breaks into moving structure. It is the difference between seeing the
aurora and watching it, and it is the reason experienced observers stay out after a
display appears to have settled down.

**Astronomical twilight.** The period when the sun is between 12 and 18 degrees
below the horizon. Below 18 degrees the sky is as dark as it will get, which is the
threshold a faint aurora needs. It is the constraint that closes the season in summer
at high latitudes, and the one the dark-hours calendar is built on.

- [You want the number right now. **Live aurora forecast** The current planetary Kp index and NOAA’s three-hour forecast blocks, read straight from the Space Weather Prediction Center.](https://lumavik.org/tools/aurora-forecast/)
- [You want a yes or a no, not a dashboard. **Can I see the aurora tonight?** A plain verdict for one location, combining live activity, your geomagnetic latitude and tonight’s darkness window.](https://lumavik.org/tools/can-i-see-the-aurora-tonight/)
- [You are deciding where to go, or why your neighbour sees more than you. **Geomagnetic latitude calculator** Converts coordinates to geomagnetic latitude and returns the minimum Kp the aurora needs before it reaches you.](https://lumavik.org/tools/geomagnetic-latitude-calculator/)
- [You are standing outside with a camera and cold hands. **Aurora camera settings** A starting exposure derived from the display in front of you, your lens speed, focal length and the moon.](https://lumavik.org/tools/aurora-camera-settings/)
- [You are booking a trip and need to know which months work. **Dark-hours calendar** Hours of true astronomical darkness per month at any latitude, and which months close the season entirely.](https://lumavik.org/tools/dark-hours-calendar/)

## Frequently asked questions

Do these tools need an account?

No. There is no sign-up, no email and no payment. Every calculation runs in your browser, and the coordinates or settings you type are never transmitted to us. Closing the tab discards everything.

Where does the space weather data come from?

From the NOAA Space Weather Prediction Center, which publishes the planetary K-index, the three-day geomagnetic forecast, the OVATION auroral-oval model and real-time solar wind in the public domain. Lumavik is not affiliated with NOAA.

What is geomagnetic latitude and why does it matter?

It is latitude measured from the geomagnetic pole rather than the geographic one. Because the two poles do not coincide, it can differ from your map latitude by several degrees, and it is the coordinate that decides how much geomagnetic activity you need before the aurora reaches you.

Do the tools work offline?

Four of the five do once the page has loaded, because the arithmetic is local. Only the live forecast and the tonight verdict need to reach NOAA. Before travelling somewhere without signal, note your required Kp and your dark-hours figure; neither changes on the timescale of a trip.

How accurate are the calculations?

Geomagnetic coordinates use the tilted-dipole approximation, which can differ from full corrected geomagnetic coordinates by a degree or two. Twilight uses a standard low-precision solar position series accurate to a few minutes. Both are good planning figures and neither is survey-grade.

Can any tool tell me whether it will be cloudy?

No, and that is the single largest cause of a disappointing aurora night. Cloud cover has an absolute veto over everything else and no geomagnetic model contains it. Check an ordinary weather forecast alongside anything here.

### Or let it watch for you

Lumavik runs these calculations continuously for your saved locations and sends a push
notification when the answer turns into a yes. Free on iPhone, no account needed.

[Get the app](https://lumavik.org/get/) Free · NOAA data · no account

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