Enter your location and email. We'll send an alert about 1 hour before astronomical dark on nights when conditions cross your threshold.
Want to check conditions manually first? Open Starcast →
A moonless, clear night with stable air and low Bortle class can produce images you'll look at for years. They don't announce themselves. You have to be watching.
A half moon can wash out the Milky Way core entirely. The window between new moon and a sky that's fully dark lasts days — sometimes less. Timing matters more than most realize.
Forecasts 48 hours out are unreliable. Checking every night wastes time. An alert sent 1 hour before dark — when forecast accuracy is highest — changes the math entirely.
Getting to a dark sky location, setting up, and letting your eyes adjust takes 45–60 minutes. Starcast alerts arrive 1 hour before astronomical dark — just enough lead time.
Choose any city worldwide. Set a score threshold: 55 for reliably good astrophotography nights, 70+ for exceptional ones where all variables align. Lower thresholds catch more nights; higher thresholds filter to only the best.
Cloud cover, moon illumination, Bortle class, atmospheric visibility, wind shear (seeing proxy), and dew point spread are all combined into a single Milky Way score for midnight conditions at your location.
The alert arrives about 1 hour before astronomical dark begins for your location — timed so you have just enough lead time to pack up and get into position. No alert means conditions don't meet your bar. Silence is information too.
The dominant variable. Even thin, scattered cloud at 20–30% meaningfully reduces contrast and star count. Below 10% is the target for Milky Way core work.
Moon percentage and rise/set timing are factored together. A 15% moon is manageable. A 60% moon rising at 10 PM eliminates the window. The score reflects both.
Estimated from your proximity to urban light pollution. Bortle 1–3 is pristine to semi-dark. Bortle 7+ makes the Milky Way core barely visible. Your location's Bortle class is baked into every score.
Smoke, haze, and particulates reduce star brightness and contrast. Visibility below 10 km significantly degrades deep-sky conditions. High visibility means clean, transparent air.
Thermal turbulence makes stars shimmer and blur — poor seeing hurts tracked deep-sky imaging most. Estimated from wind shear between surface and 80m altitude.
When air temperature drops within 2°C of the dew point, moisture condenses on cold lens elements. A dew heater helps, but knowing the risk in advance lets you prepare.
Planning a Milky Way arch over a mountain or canyon? The alert gives you the night before notice you need to coordinate the drive and setup.
Every imaging session is an investment in time and equipment. Know when the seeing and transparency are worth taking out the telescope.
You drive 45 minutes to escape light pollution. The alert ensures you only make that drive on nights where conditions meet your standard.
You shoot stars a few times a year and don't want to obsess over forecasts. Set a high threshold and only hear from us when it's truly exceptional.
Heading somewhere with low light pollution? Subscribe for your destination city to know which night of your trip is worth staying up for.
You can't check conditions every night. The alert does the monitoring for you. You only hear about it when the sky is actually worth rearranging your evening.
Free. No account. No app to install.
Just an email when the Milky Way is worth chasing.