Night Sky Photography Calculators
Two free tools for planning a night shoot: find the longest shutter speed before stars start to streak, and see when the Milky Way's core is up in a dark, moonless sky. Made by Nicholas O'Toole of Camera Clarity.
Shutter speed calculator: 500 rule and NPF rule
How long can you keep the shutter open before stars turn into short trails? Enter your camera and lens.
Milky Way planner
Pick a place and a date to see when the sky is fully dark, where the Moon is, and when the Milky Way's bright core is above the horizon.
The next 30 nights
Hours when the core is up in a dark sky with the Moon down or nearly new. Tap a night to see it above.
| Night of | Moon | Best hours | Clouds |
|---|
Times are calculated from the positions of the Sun, Moon and galactic center and are accurate to within a few minutes. "Core up" means at least 10° above a flat horizon; hills and trees will hide it for longer. The cloud forecast covers about the next 9 days. Weather data from MET Norway, licensed under CC BY 4.0; summarized here by Camera Clarity.
500 rule vs NPF rule
The 500 rule divides 500 by your focal length (after multiplying by your sensor's crop factor). It was made for film, and on modern high-megapixel sensors stars can look slightly stretched when you zoom in.
The NPF rule also uses your aperture and the size of your sensor's pixels, so it gives a shorter, sharper result. Use NPF when you want pinpoint stars, and the 500 rule as an upper limit.
How to read the planner
Fully dark sky is astronomical night, when the Sun is more than 18° below the horizon. Best time is when it's dark, the Moon is down (or under 10% lit) and the galactic core is at least 10° up.
In the Northern Hemisphere the core is best placed from spring to early autumn. Near the new moon you'll get the longest windows.
New to night photography? Start with the guide to shooting in manual mode, try the Night Sky Quiz, or browse Milky Way prints.