Plan around the conditions you shoot — sunrise and sunset color, stars, fog, storm light, and the aurora — anywhere in the world. · Data sources & credits
Halcyon scores each day on the conditions photographers actually care about and gives you a simple number from 0 to 100 for each one. The scores are not percentages — think of them as a confidence rating: 80 and up means the conditions are strongly aligned, 30 and below means it's probably not worth the drive.
Most tabs forecast seven days out; the aurora tab looks three days ahead. Halcyon also includes a Milky Way planning calendar for trip planning and a history view for scoring past dates, and it installs as an app on your phone or desktop with offline support.
It doesn't replace checking conditions the evening before. Use it to find the days worth watching, then confirm closer to the time.
How much color you're likely to see during the morning golden hour. A flat, clear sky and a fully socked-in sky both tend to score low; the best mornings usually have some cloud to catch the light. Open the day to see the exact light-window times and the cloud picture around them.
The same idea, for the evening golden hour. Coastal evenings often do well when there's broken cloud with a clear band at the horizon. Check the verdict and the hourly cloud table to decide whether it's worth setting up.
Rates the night ahead for stars and Milky Way work — how clear, dark, and dry the sky looks, and how much the moon is in play. A bright moon pulls the score down even under a clear sky. The detail view shows the dark window, the moon-free hours, and the Milky Way core window for the night.
Your odds of catching the northern or southern lights, based on the forecast geomagnetic activity and how favorable your latitude is. Because that forecast is only reliable a few days out, this tab shows three days where the others show seven. For a fast-moving event, watch the trend across the three days rather than a single number.
How likely fog is in the early-morning hours. At a coast this points to marine fog; at a ridge or summit a high fog score can mean a sea of clouds below you rather than fog at your feet — the verdict will tell you which.
Flags days with dramatic, stormy light and the clearing that can follow a front — the moody, high-contrast conditions that don't register as "nice weather" but often make the strongest images.
All your spots live in one My locations section near the top of the page. A few locations come preloaded to get you started — remove or replace any of them with your own.
To add a location: search any city, postcode, or place name, pick it from the results, and save it. Saved locations persist in your browser across sessions. To remove one, tap the ✕ on its card.
Each location carries a terrain badge — coast, mountain, highland, valley, woodland, desert, or plains — set automatically. If the auto-detected type looks wrong, tap the badge to change it.
The seven-day forecast answers "should I go this week?" The Milky Way calendar answers "which nights this year?" — for any location, in any year, past or future.
For each night it shows whether the galactic core is visible at all, how long the shootable window lasts, and how much the moon interferes — so you can find the dark, moon-free nights. A meteor-shower overlay marks the major annual showers.
The history view scores any date going back decades. Pull up a shoot you've already done and see how the conditions scored — a good way to build a feel for what the numbers mean at the places you know.
Halcyon can be added to your home screen or desktop so it opens like any other app and works offline once a forecast has loaded. Watch for the install prompt, or use "Add to Home Screen" from your browser menu.
Scores are estimates, not guarantees. They're based on weather-model output, which has real limits — especially for fog, which can form or clear within an hour from local effects no model captures well. Always verify before committing to a long drive.
Accuracy degrades further out. The later days of the forecast are useful for spotting trends and blocking your calendar; treat them as rough guidance, not firm predictions.
Tide predictions are for planning only. They aren't suitable for navigation or safety decisions — always check official local sources before entering the water or accessing coastal areas.
Milky Way visibility is geometry and weather combined. The calendar can't account for horizon obstructions like mountains or trees at your exact spot.
Some data may not always load. Light-pollution and air-quality figures come from separate services; if one is briefly unavailable, the forecast still works without it.