Northern Lights Tonight

Northern lights tonight: the science behind the forecast

Whether you can see the northern lights tonight depends on a chain of events that starts on the Sun, about 150 million kilometres away. The aurora is not weather. It is what happens when the Sun's outflow of charged particles collides with Earth's magnetic field, and knowing how that works tells you what the numbers in the live northern lights forecast actually mean.

• How the aurora forms
• What to check tonight
• Aurora colours
• Solar Cycle 25
• STEVE and other phenomena

How the northern lights form

Step 1: The solar wind leaves the Sun

The Sun continuously sheds charged particles called the solar wind, which normally flows past Earth at around 400 km/s. Violent eruptions called coronal mass ejections (CMEs) throw out up to a billion tonnes of plasma at speeds of up to roughly 3,000 km/s. A CME aimed at Earth arrives anywhere from under a day to about three days later, which is why a big flare today can mean northern lights tonight or later this week.

Step 2: Earth's magnetic field is disturbed

Earth's magnetosphere, the magnetic bubble around our planet, deflects most of the solar wind. A strong CME or fast stream compresses it on the day side and stretches it into a long tail on the night side. The Kp index measures how disturbed the field is on a scale from 0 (quiet) to 9 (extreme storm), and Kp 5 or higher counts as a geomagnetic storm.

The most important signal for northern lights tonight is Bz, the north-south direction of the solar wind's own magnetic field. When Bz turns southward (a negative value), it links up with Earth's field and lets energy pour in. A sustained Bz of about -5 nT or lower, together with a fast solar wind, is a strong sign that activity is about to rise.

Step 3: Magnetic reconnection sends particles toward the poles

As the magnetotail stretches, it eventually snaps back in a process called magnetic reconnection. That releases stored energy and sends electrons and protons down Earth's magnetic field lines toward the poles. This is why aurora forms in the auroral oval, a ring around each magnetic pole, and why the southern lights (aurora australis) appear at the same time as the northern lights. The stronger the storm, the farther the oval expands toward the equator, which is how a big night brings aurora to cities that rarely see it.

Step 4: Collisions in the upper atmosphere create the glow

The incoming particles strike oxygen and nitrogen atoms between roughly 80 and 650 km up and excite their electrons. When those electrons relax, they release light, the same basic physics as a neon sign. The colour depends on which gas is hit and at what altitude.

What to check before you go out to see the northern lights tonight

• Kp against your latitude. Places inside the auroral zone, like northern Scandinavia, Alaska and northern Canada, can see aurora at low Kp. Roughly Kp 5 to 7 is needed for the northern US and central Europe. The aurora forecast shows the Kp your city needs.
• Bz and solar wind speed. A southward Bz and a speed above about 500 km/s favour a stronger display within the hour.
• Cloud cover. Cloud blocks the aurora completely, so check the hour-by-hour outlook and pick the clearest window.
• Darkness and the Moon. You need the Sun well below the horizon, and a bright Moon in the sky washes out faint displays. Get away from city lights.
• Timing. Activity often peaks within a couple of hours of local midnight. Aurora happens all year, but the long dark nights of autumn, winter and spring are best, and activity tends to run higher around the equinoxes.
• Your eyes and camera. Give your eyes about 20 minutes to adapt. A phone in night mode will show more colour than your eyes can.

Northern lights colours explained

Most northern lights tonight will look green, but the colour mix depends on the gas and the height at which the particles stop.

Faint displays can look grey or white to the eye because our colour vision is weak in the dark. Cameras gather more light, so photos usually show stronger colour than you see in person.

Solar Cycle 25 and your chances of seeing the aurora

The Sun's activity rises and falls on a cycle of about 11 years. NASA and NOAA announced in October 2024 that the Sun had reached the solar maximum period of Solar Cycle 25, the busiest stretch for flares, CMEs and geomagnetic storms. The years just after the peak can still bring some of the strongest storms of a cycle, so a quiet-looking month does not rule out a big night. The solar activity monitor shows the live flare class and where the cycle stands now.

STEVE, dancing lights and aurora sounds

What is STEVE?

STEVE (Strong Thermal Emission Velocity Enhancement) is a narrow purple or mauve arc that stretches east to west, sometimes with green "picket fence" streaks beneath it. It is often mistaken for aurora. The arc is linked to a fast river of hot plasma flowing through the upper atmosphere at more than 20,000 km/h, so it is produced differently from the particle-driven glow of true aurora.

Why the northern lights dance and pulse

The flowing, curtain-like motion comes from shifting electric currents in the magnetosphere that steer the particle beams. Pulsating aurora, patches that blink on and off every few seconds, has a different cause. Plasma waves called chorus waves release bursts of electrons into the atmosphere in a repeating, heartbeat-like pattern.

Can you hear the northern lights?

Sámi and Inuit traditions describe the aurora crackling or clapping. Scientists were long sceptical, but in 2012 Finnish researchers recorded faint crackling sounds during geomagnetic activity. They linked them to static electricity discharging from a temperature inversion layer about 70 metres above the ground, which would explain sounds that seem to come from the lights overhead. The sounds are rare and quiet, so you need a very still night and a very active sky.