AURORA OPS

How to read the chance

Each night gets one number that combines four things. All four must line up:

• Activity – is the aurora strong enough to reach where the ship is? Up in the Arctic (Tromsø, Alta) it is overhead on most nights, even when "quiet". Further south it needs a geomagnetic storm.
• Clear sky – the chance of at least a 2-hour gap with ≤40% cloud in the dark. In October this is usually the deciding factor on the Norwegian coast.
• Darkness – the sky is fully dark (in October about 1.5–2 hours after sunset).
• Moon & lights – moonlight and town lights wash out faint aurora. The moon is new on 10 Oct, so this trip is well timed.

Ratings are conservative: ▲ GOOD ≥40% · ◆ FAIR 25–40% · ▼ LOW 10–25% · ✕ POOR <10%.

Confidence (the little green signal bars on every night: 1 bar = trend only, 2 = low, 3 = medium, 4 = high) tells you how far ahead we are looking. Weeks ahead only the trend is known; aurora itself can only be predicted reliably 30–90 minutes in advance.

The numbers the experts watch

• Kp (0–9) – global geomagnetic activity. about Kp 0.5–1 is enough in Tromsø/Alta, about Kp 3 around Trondheim/Ålesund, Kp 6+ over the southern North Sea.
• Kp forecast vs. Kp needed – "forecast" is the activity expected for that hour; "needed" is the level at which aurora is clearly visible where the ship is at that hour (it depends on the ship's geomagnetic latitude, so it rises as we sail south). When the forecast is at or above the needed level, activity is on our side. The activity chance is the probability that the real Kp reaches the needed level; it stays above zero even when the forecast is lower, because forecasts days ahead are often off by 1–2 points.
• Bz – direction of the solar wind's magnetic field. Negative (south) for 20+ minutes = the door is open; the stronger and longer, the better. When a strong field (Bt 10+ nT) turns south (Bz −5 or less for 15 minutes), the robot sends a 🚪 door open alert in the dark: aurora usually brightens within the hour.
• Solar wind speed – above ~500 km/s helps.
• Density and Bt – how many particles the solar wind carries (per cm³, calm 2–10) and how strong its magnetic field is (in nanotesla, nT; calm ~5, storms 10–30+). Measured 1.5 million km towards the Sun (L1), 40–85 minutes before it reaches us. A sudden jump of speed, density and Bt together = a CME's front arriving (☄️ alert).
• OVATION – NOAA's 30–90 minute aurora model: the probability of aurora overhead at a given spot. Its hemispheric power (GW) is the total aurora energy over the northern hemisphere: calm under 20, active 20–50, storm 50+, big storm 100+.
• 27-day recurrence – the Sun turns every ~27 days, so what happened 27 days before a night often repeats.
• CME – a solar eruption; if one is heading to Earth, NASA's model gives an arrival time and expected Kp. Followed in two steps: the model gives a rough arrival days ahead (often hours off, sometimes a miss); when its front reaches the solar wind satellite, the robot sees the jump and sends a ☄️ alert 40–85 minutes before it reaches us.
• G1–G5 – NOAA's storm scale: G1 minor (Kp 5, from 4.7), G2 moderate (6), G3 strong (7), G4 severe (8), G5 extreme (9). A storm matters most further south: up north even quiet activity is enough.

How to use this page

Until ~10 days before: Nights (overall chance per night) and Trend (is it moving up or down?). Weather shows typical October weather. The morning notification sums it up; a change alert comes when a night moves a lot.

3–10 days before: Weather switches to real forecasts for each port day; At sea shows the waves for each crossing. Model check shows how well the forecasts have been hitting.

1–2 days before: Hour by hour for each night gets GO / TRY / NO verdicts from MET Norway, plus the ★ Best window.

Tromsø and Alta port nights: the 🚗 Inland line under Tonight compares the clouds with the usual chase-tour areas behind the mountains (Nordkjosbotn, Skibotn, Kilpisjärvi; Gargia, Masi, Kautokeino), so you can see whether a tour inland has a clearer sky. Before the cruise it runs for Tromsø every night, for practice.

On board, every evening:

1. Around 17:00: the evening outlook notification → tap it for tonight's hour-by-hour.
2. After dark, check Live now: Bz negative (south)? Hp30 above the level needed here? Magnetometer swinging 50+ nT? Aurora on the map over or north of the ship?
3. Sky: clear? (see Hour by hour, or just look up)
4. If a "go outside" alert comes: darkest open deck, face north, give your eyes 10–15 minutes, use your phone's night mode.

Reading the sea (Weather → At sea tab)

• Feel – the one column to look at: calm (hardly noticeable) · gentle (light motion) · rough (noticeable rolling, seasick-prone take precautions) · very rough (strong motion, some outer decks may close).
• Waves – the typical height of the bigger waves (what your eye would call "the waves"); now and then a single wave can be higher. Feel comes from this: under 1.25 m calm, 1.25–2.5 m gentle, 2.5–4 m rough, over 4 m very rough.
• Period – seconds between two waves. Short (4–7 s): quick, choppy motion that a big ship damps well. Long (10 s or more): slow, long rise and fall that you notice even on a big ship, so Feel is made one step worse.
• Wind – km/h, gust in brackets. Above ~50 km/h it is very windy on open deck; above ~70 km/h some outer decks may be closed.

In practice: motion is smallest in the middle of the ship and on lower decks. Sky Princess is a 145,000-tonne ship with stabilisers, so up to about 3 m most people barely notice it.

Alerts on your iPhone

1. Install ntfy from the App Store (free, no account needed).
2. Tap +, then subscribe to the topic name you were given (it is private, so don't share it).
3. Allow notifications. For night-time alerts: Settings → Focus → Sleep → Apps → add ntfy, and turn on Time Sensitive Notifications.

Already now: a morning outlook every day around 08:15 (Hungarian/ship time) with the change since the day before, and a change alert whenever an Arctic night (13–18 Oct) moves 5+ points, or a solar eruption is heading our way (max 2 a day).

During the cruise you also get an evening outlook around 17:00 ship time, and a "go outside" alert when live activity is good, or a nearby magnetometer shows a substorm (Tromsø and Alta area: the fastest sign), the sky over the ship is clear (MET Norway) and it is dark. At most one alert per 90 minutes (30 minutes for a new substorm), sooner when it gets stronger; under clouds a "look for gaps" message instead (again after an hour while it is strong). South of the Arctic, when activity is too faint for the eye but a phone's night mode can catch it low in the north, a "📷 try a camera" alert (clear sky only; again every hour while it lasts, at most 6 a night). Tapping a notification opens that night on this page.

A ☄️ CME alert when a solar eruption's front reaches the solar wind satellite (once per arrival, day or night; before the cruise as a test), and a 🚪 door open alert in the dark when the solar wind's strong field turns south (at most every 3 hours). A 📷 camera alert when the all-sky camera at Tromsø (before the cruise, and on the Tromsø port night) sees aurora: then the sky is really open (at once when it appears after a break, then every 30 minutes while it lasts). Days ahead: a ☄️ CME on the way message when NASA's model has a solar eruption reaching Earth, and a ⚠️ NOAA storm watch when NOAA's 3-day forecast expects a G1 storm or more.