Blue Hour Calculator
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—This blue hour calculator shows the exact morning and evening blue hour times (sun 4°–8° below horizon) for any location.
What Is Blue Hour?
Blue hour is the short twilight window when the sun sits between roughly 4 and 8 degrees below the horizon, casting a deep cobalt and indigo glow across the sky. This color originates from Rayleigh scattering combined with ozone absorption in the upper atmosphere — the same physics that makes the daytime sky blue, but amplified by the sun's position below the horizon. Unlike golden hour, blue hour produces a cool, even light with minimal shadows.
There's no universal standard for blue hour's exact boundaries — different sources use different definitions. Timeanddate.com defines it as 4° to 8° below the horizon, while PhotoPills uses 4° to 6°. Our calculator uses the 4°-8° definition (matching timeanddate.com), which captures the full period when the sky displays its characteristic deep blue tone. This is the broader window that gives you more time to shoot and plan.
How Our Blue Hour Calculator Works
Our blue hour calculator pinpoints the exact solar depression angle — when the sun is 4 to 8 degrees below the horizon — to define the start and end of the morning and evening blue hour for any location and date. It uses the SunCalc library with standard atmospheric refraction of 0.833° applied.
The tool first computes nautical dawn and nautical dusk times, then refines the window using the precise altitude of the sun below the horizon. It outputs both morning blue hour (before sunrise) and evening blue hour (after sunset) durations accurate to the nearest minute. Everything runs locally in your browser — no server calls.
FAQ — Blue Hour Calculator
When does blue hour start and end?
Blue hour begins when the sun reaches 4° below the horizon and ends when it drops to 8° below. In practical terms, this is roughly 20-40 minutes before sunrise and 20-40 minutes after sunset, depending on your latitude and season. Use the calculator above for exact times — the duration varies significantly between equatorial and high-latitude locations.
Can I shoot blue hour on a cloudy day?
Light clouds can actually enhance blue hour by catching the blue tones and spreading them across the sky. Heavy overcast, however, blocks the light entirely. In my experience, partly cloudy skies produce the most dramatic blue hour conditions — the clouds add texture while the gaps let the blue sky show through. Check the forecast for clearing conditions around the blue hour window.
How does blue hour compare to nautical twilight?
Blue hour (4°-8° below horizon) falls entirely within nautical twilight (6°-12° below horizon). They overlap significantly — the first half of blue hour coincides with the end of civil twilight, and the second half overlaps with early nautical twilight. Blue hour is essentially the visually most dramatic portion of the nautical twilight period for photographers.
What's the best camera settings for blue hour?
I typically start with ISO 400-800, f/2.8-f/5.6, and 5-15 second exposures on a tripod. The low light requires longer shutter speeds, which is why a tripod is essential. White balance set to tungsten or around 3500K enhances the blue tones. For cityscapes, I bracket exposures to capture both the sky and artificial lights without blowing out highlights.
Why does blue hour look different in different cities?
Local atmospheric conditions — humidity, pollution, dust — affect how blue hour appears. Clean, dry air produces deeper blues, while humid or hazy conditions create lighter, more washed-out tones. Light pollution in cities also affects the perceived intensity of blue hour. I've noticed equatorial cities tend to have shorter but more intense blue hours due to the sun's steeper angle.