What time are the northern lights tonight?

The short answer

Aurora can appear any time after astronomical darkness falls and before dawn returns. There is no scheduled start time, no predictable curtain-up. What determines the window is the combination of sky darkness and geomagnetic activity - both have to cooperate.

Astronomical darkness is when the Sun sits more than 18 degrees below the horizon. Before that point, residual twilight washes out faint aurora in the northern sky. In most aurora destinations at the right time of year, that threshold is crossed between 9pm and midnight local time, depending on latitude and season.

One important caveat: summer visits above the Arctic Circle are effectively wasted from an aurora perspective. Between May and July, Norway north of the Arctic Circle, Iceland, Svalbard, and northern Finland experience the midnight sun or near-continuous twilight. There is no astronomical darkness at all during this window, and no aurora is visible regardless of geomagnetic conditions.

Astronomical darkness and why it matters

Aurora is occurring above you whether or not you can see it. The auroral oval is always present; it simply expands or contracts depending on geomagnetic activity. The limiting factor for most observers is sky brightness, not aurora activity itself.

Sky darkness passes through three stages after sunset. Civil twilight ends when the Sun drops 6 degrees below the horizon - still too bright for aurora. Nautical twilight ends at 12 degrees below - the sky darkens significantly but faint aurora remains hard to pick out. Astronomical twilight ends at 18 degrees below, and the sky reaches its darkest possible state. This is when aurora becomes reliably visible, assuming dark-adapted eyes and minimal light pollution.

The timing shifts considerably by latitude and season. Some concrete examples:

• Northern Scotland in October: astronomical darkness from around 9:30pm to 6:00am
• Northern Norway in December: dark from around 1pm, lasting until 10am the following morning
• Iceland in September: astronomical darkness from around 10pm to 4:30am
• Central Finland in November: dark from around 5pm to 8am

The longer the dark window, the more opportunity there is to catch a display. This is one reason winter trips to high latitudes are statistically more productive than September or October - not because aurora is more active, but because there are more hours of darkness to observe it.

The midnight peak

Geomagnetic activity has a statistical peak around local magnetic midnight - roughly 11pm to 1am for most aurora destinations in the northern hemisphere. This is not a coincidence or a myth. It has a physical explanation.

At magnetic midnight, your location faces directly away from the Sun. The nightside of Earth's magnetosphere - where most of the aurora-producing energy is stored in the plasma sheet - is most directly overhead. The geometry of Earth's magnetic field relative to the solar wind is most favourable for particles to precipitate into the upper atmosphere at this time. The auroral oval also reaches furthest equatorward around magnetic midnight.

Aurora does occur outside this window. Substorms can fire at any point during a geomagnetic storm, and sustained activity during a major event can last from dusk to dawn. But if you have to choose a single two-hour window to go out, 11pm to 1am gives the best odds for most locations.

For context on what Kp levels to expect, see the full Kp guide.

The equinox effect

September and March are statistically the most active months for aurora, and the equinox timing is not coincidental. Around the equinoxes, Earth's magnetic field orientation relative to the solar wind is more favourable for energy transfer into the magnetosphere.

The mechanism is the Russell-McPherron effect. Twice per year, near the equinoxes, the geometry of Earth's orbit and the orientation of its magnetic axis align in a way that amplifies the southward component of the interplanetary magnetic field. A given solar wind condition at equinox produces a stronger geomagnetic response than the same condition in June or December.

In practice, this means more frequent storms in March and September, and stronger responses when storms do occur. Both equinox months tend to produce more events and more widespread displays than the mid-year periods. September has the additional advantage of offering long, dark nights without the extreme cold of midwinter.

How to use the 7-day forecast

The 7-day aurora outlook pulls Kp forecasts from NASA DONKI and shows predicted geomagnetic activity night by night. This is the starting point for deciding which evenings are worth planning around.

When reading the forecast, check four things in order:

Watching the Bz in real time

When an event is in progress, the most useful number is not the Kp - it is the Bz. Bz is the north-south component of the interplanetary magnetic field, measured in nanoteslas (nT). When Bz is negative, the solar wind is coupling efficiently with Earth's magnetosphere and aurora is active. When Bz returns to neutral or positive, the display typically fades within minutes.

Kp is a three-hour average. Bz updates every minute from satellites at the L1 Lagrange point, roughly 1.5 million km sunward of Earth. It gives you a 15-60 minute warning of conditions arriving at Earth. A Bz that drops from +3 nT to -15 nT in 20 minutes is a strong signal to head outside immediately.

The full explanation of Bz and how to interpret it is on the Bz guide. For real-time alerts when activity fires, see the northern lights alert page.

What to do tonight

If you want to see aurora tonight, run through these steps in order.

Location-specific darkness windows

Your latitude determines both when darkness arrives and how long it lasts - and therefore how much opportunity each night provides.

Shetland at 61°N is the UK's best-positioned aurora location. Astronomical darkness arrives earlier in autumn than anywhere else in Britain, and the Kp threshold is lower - Kp 2-3 can produce visible aurora from the islands' north-facing headlands. Tromsø in northern Norway enters polar night around 27 November, meaning continuous darkness from mid-afternoon to mid-morning - effectively a 16-hour observation window on cloudless nights. Iceland sits squarely in the auroral zone with a Kp threshold of around 2-3, but the midnight sun makes summer visits (June to mid-August) impossible for aurora observation. Mainland Scotland becomes viable from September, when nights lengthen rapidly and Kp 3-4 events start to produce results from dark hillsides and coast-facing viewpoints.