Common questions

Check the "Tonight" card at the top of the Live page. Set your location and it puts together activity right now, any substorm that is running, your cloud, the Moon and darkness, and tells you in plain words. For the best chance you need activity that is reaching far enough south (the chain card shows how far), a dark sky away from lights, and clear skies.

At Hp30 4 aurora is possible from Scotland. At Hp30 5 it is likely from Scotland. At Hp30 6 it is likely from Scotland and northern England. At Hp30 8 or more it may be seen from most of the UK and all of Ireland. The line moves south as Hp30 rises, rather like a tide coming in. That is only a rough guide: Hp30 says how strong things are around the world, not where. The chain card on the Live page shows how far south it is actually reaching tonight.

Hp30 is a geomagnetic index from GFZ Potsdam that measures how disturbed Earth's magnetic field is. It is recalculated every 30 minutes instead of every 3 hours. It starts at 0 and uses the same steps as the older Kp index, but unlike Kp it has no ceiling at 9: it reached 11.3 in May 2024. That extra resolution catches the sharp onset of a substorm far sooner than Kp does.

Bz is the north-south component of the solar wind's magnetic field. When it turns negative (southward), it connects with Earth's magnetosphere and energy flows in to power the aurora. Bz going below −10 nT is a very good sign, and worth watching closely if it is dark and clear where you are. It's the single most important real-time number.

The equinoxes, late March and late September, tend to produce more frequent geomagnetic storms due to the alignment of Earth's magnetic field with the solar wind. Winter (October to February) also works well because nights are long, giving more dark sky time. Summer is mostly useless because nights never get fully dark. Around midsummer there is no astronomical darkness anywhere in the UK: roughly late May to late July in London, and early May to early August in Edinburgh.

Astronomical twilight ends when the Sun is more than 18° below the horizon. At that point the sky is truly dark and even faint astronomical objects become visible. In mid September it starts around 9 pm in England and a little later in Scotland, by early November it is about 6:30 pm once the clocks have gone back, and in December about 6 pm. In mid April and mid August it is not until somewhere between 10 pm and midnight, depending how far north you are, and around midsummer there is none at all. Sky Tonight shows you the exact dusk-to-dawn dark window each night, or warns you if there is no astronomical darkness.

Noctilucent clouds are wispy, electric-blue clouds that form at around 80 km altitude, far higher than ordinary clouds, and are lit by the Sun even after it has set. They appear in the northern sky during late June and July, roughly between latitudes 50 and 65°N. Sky Tonight shows an NLC alert panel during the season (June and July) so you know when to look north around midnight.

Not always. On stronger nights it reaches further south: as a rough guide, around Hp30 6 it is likely from northern England, and at 8 or more it may be seen from most of the UK and all of Ireland. The chain card on the Live page shows how far south it is actually reaching. Wherever you are, you need a dark sky away from town lights and a clear view north.

Often yes, but not as the photographs show it. To the naked eye an aurora from here usually looks like a pale grey or whitish glow low on the northern horizon, and only the biggest storms show colour clearly. Your phone camera will pick up the green long before your eyes do.

Yes, and modern smartphones are excellent. iPhone: use Night mode or a Pro/manual camera app. Pixel: Astrophotography mode in Google Camera. Other Android: Pro mode with ISO 1600 and a 5 to 10 second exposure. Key rule: keep the phone completely still (lean it against something or use a small tripod).

A good starting point for a DSLR or mirrorless: ISO 1600, shutter 10 to 15 s, aperture f/2.8 or wider. During an active display, drop the shutter to 3 to 6 s to freeze the motion. Use our Settings Calculator on the Guide page. It adjusts recommendations for your sensor type and activity level.

No. A smartphone on Night mode can take stunning aurora photos. An entry-level DSLR or mirrorless with a kit lens will give you a clear step up. You only need the more expensive gear (fast wide primes, full-frame sensors) if you want to push into video, timelapse, or very faint displays.

Use the 500 rule: divide 500 by your focal length × crop factor to get the maximum shutter time before stars streak. For a 24mm lens on APS-C (crop 1.5): 500 / (24 × 1.5) ≈ 14 seconds. Our Settings Calculator does this for you automatically.

Almost always camera shake. At 10+ second exposures even breathing can blur a shot. Use a tripod, set a 2-second self-timer or a remote shutter release, and turn off image stabilisation (it can fight against a stationary tripod).

Sky Tonight (/sky-tonight) is a complete night-sky planning dashboard for your location. It shows: moon phase and illumination, planets visible tonight (with rise/set times and brightness), the dark sky window (astronomical dusk to dawn), Milky Way visibility, active meteor showers, ISS passes for the next 10 days, noctilucent cloud alerts (June and July), upcoming sky events, golden hour times, and photography tips. Everything is calculated for your saved home location.

Check the "Planets tonight" section on the Sky Tonight page. It lists all major planets currently above the horizon with their magnitude (brightness), altitude, and rise/set times. Venus and Jupiter are usually the brightest and easiest to spot even from light-polluted areas.

Solar wind readings (Bz, speed, density) come from Solar1 (SWFO-L1), NOAA's newest satellite parked at the L1 Lagrange point about 1.5 million km sunward of Earth, giving 15 to 60 minutes of advance warning. There are other satellites out there, ACE and IMAP among them, and NOAA switch between them, but Solar1 is the one we stay on because it is the most accurate. If it stops reporting the site falls back to whichever is live and names it on screen, so you always know which satellite you are looking at.

The solar wind data comes from NOAA satellites in space, and now and then NOAA's feed has a short gap, usually a few minutes and occasionally a few hours, while a spacecraft or ground station catches up. When that happens the site is upfront about it: it labels the reading "delayed" and shows how old it is, instead of presenting old numbers as if they were live. This is a gap on NOAA's side, not a fault with the site. It clears on its own the moment fresh data arrives, so you do not need to refresh or do anything. And your headline Hp30 reading comes from a completely separate source (GFZ Potsdam), so it keeps working normally the whole time.

The 3-day Hp30 forecast from GFZ Potsdam gives a rough indication of activity. It is useful for planning but not reliable for specific hours. The real-time Bz and solar wind data is far more actionable. If Bz goes suddenly and strongly negative, that matters more than whatever the forecast said.

Click "Enable alerts" on the Live page and allow notifications, or sign up for email alerts, or both. On an iPhone, push alerts only work once you have added the site to your Home Screen (Share, then Add to Home Screen) and opened it from there. Choose how strong activity has to be before you are told, and tick substorm and shock alerts if you want those too. CME alerts come to every phone with alerts on, and by email if you tick them. Alerts are only sent from about an hour before sunset to just after sunrise. You can also turn on the sound alert, and a tone will play through your browser when conditions improve.

The weather card needs your location to work. Tap or click "Use my location" to grant access, or search for your nearest town. If you are signed in, your location is saved to your account so it follows you to other devices. If not, it stays in your browser.

Hp30 index: every 30 minutes. Solar wind (Bz, speed, density): every 1 to 2 minutes via Solar1 satellite, pushed live to your screen via a socket connection. Ground magnetometers (substorm detector): checked every 5 minutes, though the observatories themselves publish in batches, so a reading can be up to an hour old and the site tells you when it is. Weather: every 10 minutes.

The sun constantly emits a stream of charged particles, called the solar wind. When this wind carries a southward magnetic field (negative Bz), it reconnects with Earth's magnetosphere, channelling energy into the polar regions. Charged particles spiral down magnetic field lines into the upper atmosphere, exciting oxygen and nitrogen molecules which release light as they relax, and that is the aurora.

Green comes from oxygen atoms at around 100 km altitude releasing energy at a wavelength of 557.7 nm, right in the middle of the visible spectrum where your eyes are most sensitive. Higher up (above 200 km), oxygen produces rare red aurora. Pink/mauve at the bottom edge comes from nitrogen molecules.

A geomagnetic storm is a disturbance in Earth's magnetic field caused by solar wind. NOAA classify storms G1 (minor) to G5 (extreme), and that scale is defined on Kp, an index calculated once every three hours. This site uses Hp30, which is recalculated every 30 minutes, so it catches the sharp start of a substorm far sooner. We deliberately do not convert one into the other: a single half hour of Hp30 is not the same measurement as a three hour average, and treating it as one would announce a storm off a brief spike. The G5 storm in May 2024 was the strongest in 20 years and was seen across the whole of the UK, including southern England.

A substorm is a sudden surge of energy in Earth's magnetosphere, rather like a sudden spark in the magnetic battery. Even when overall storm levels are modest, a substorm expansion can cause the aurora to erupt and brighten dramatically. Auroracast watches eight ground magnetometers in Sweden, Finland, Svalbard and the Faroe Islands, from Uppsala up to Hornsund, for a rapid drop in the horizontal magnetic field. Each station is judged against its own normal level, because a drop that matters at one latitude is ordinary at another. When one is detected the Live page says so, and if it is dark where you are, look north. The magnetometer data comes from INTERMAGNET and the institutes that run those observatories.

The sun follows an approximately 11-year cycle of activity. Solar maximum is the peak of that cycle, when sunspot activity and solar flares are most frequent. Solar Cycle 25 peaked in 2024, so we are now on the way down from it. That is not the bad news it sounds like. The years just after a maximum are often excellent for aurora, because coronal holes on the sun send out fast streams of solar wind that sweep past Earth every few weeks, and some of the biggest storms on record have happened on this side of the peak.