Interactive Blue Hour Calculator
Calculate exact twilight phases and photography shoot viability for any location.
Data Source
Based on NOAA Earth System Research Laboratory guidelines.
Note
Calculations use geometric elevation; local topography and weather may alter perceived twilight times.
Quick Overview
At a Glance
The blue hour is a brief period of twilight loved by photographers for its cool, deep blue light. Unlike standard sunset trackers that stop when the sun hits the horizon, this tool helps you find the exact start and end times for this magical window.
It relies on geometric solar elevation to pinpoint exact times for any location you provide.
Quick Answer: The blue hour is a short twilight period occurring twice daily—just before sunrise and immediately after sunset—when the sun is between -4° and -6° below the horizon. It is characterized by deep blue sky tones and soft, shadowless ambient light.
Astronomical Threshold
Typical Duration
Phase Sequencing
Weather Dependency
The main feature of the blue hour is the fast shift in light and color. While your golden hour is full of warm reds, the blue hour fills the landscape with deep blue and violet tones.
This effect comes from atmospheric physics, specifically something called Chappuis absorption. As the sun dips below -4°, its light travels a much longer path through the air.
The Earth's ozone layer absorbs the long red and orange light waves. This leaves the sky looking deep blue.
Pro Tip
Scientific studies show that Chappuis absorption creates a much deeper blue than the Rayleigh scattering that makes the sky blue during the day. This makes your camera sensors very sensitive to these colors.
It is vital for you to know the difference between the blue hour and other times. A common mistake is trying to shoot "blue hour" too late, which makes your photos look too dark.
| Light Phase | Solar Elevation | Light Quality | Shadow Profile |
|---|---|---|---|
| Golden Hour | +6° to -4° | Warm, highly directional | Hard, elongated shadows |
| Blue Hour | -4° to -6° | Cool, balanced, ambient | Soft, virtually shadowless |
| Nautical Twilight | -6° to -12° | Dark, star-visibility begins | Pitch black landscape |
Finding your exact times requires solving for the Solar Hour Angle. Astronomers use spherical math to find how long it takes for the sun to reach -4° and -6°.
The core math relies on your precise latitude (Φ) and the current solar declination (δ), which maps the tilt of the Earth.
H = arccos( (sin(a) − sin(Φ) × sin(δ)) ÷ (cos(Φ) × cos(δ)) )In this formula:
- H (Hour Angle): Your result in degrees from solar noon.
- a (Solar Elevation): Your target angle (-4° for start, -6° for end).
- Φ (Latitude): Your geographical latitude.
- δ (Solar Declination): The seasonal angle of the sun.
The Earth spins at a rate of 15° per hour. You divide your result (H) by 15 to find the exact time offset in hours.
Standard sun tools adjust for light bending at sunset (0°). However, blue hour math (-4° to -6°) relies strictly on geometric elevation, so no light-bending adjustment is needed.
δ = 23.45 × sin(360 ÷ 365 × (d − 81))To prove the math, we will walk through a manual calculation for an evening shoot. We will use Los Angeles on the Vernal Equinox as our benchmark.
Our parameters are: your Latitude (Φ) of 34°, your Declination (δ) of 0°, and your Local Solar Noon at exactly 13:00.
Calculating the Blue Hour Window
Calculate the Start Angle (-4°)
We put a = -4° into the formula. This gives you an hour angle of 94.827°.
Convert to Local Time
Divide by 15. 94.827 ÷ 15 = 6.322 hours. This is 6 hours and 19 minutes. Your start time is 19:19.
Calculate the End Angle (-6°)
We use a = -6°. This gives you an hour angle of 97.243°.
Convert to Local Time
Divide by 15. 97.243 ÷ 15 = 6.483 hours. This is 6 hours and 29 minutes. Your end time is 19:29.
Result
The evening blue hour in Los Angeles on the Vernal Equinox lasts exactly 10 minutes.
Knowing the exact time is only your first step. Most pros divide the window into two phases. Each one needs different settings from you.
Also, these math models assume perfect skies. In the real world, the weather will dictate if your shoot can happen.
Early vs. Late Phase Guidance
The light levels drop very fast between -4° and -6°. A shutter speed that works at the start will give you a black photo just ten minutes later.
| Phase | Solar Elevation | Light Level | Gear Requirement |
|---|---|---|---|
| Early Blue Hour | -4° to -5° | High ambient light | Handheld feasible |
| Late Blue Hour | -5° to -6° | Low ambient light | Tripod strictly required |
Shoot Viability Score
Our tool gives you a Shoot Viability Score based on cloud cover. Deep blue skies need a clear line of sight.
Clouds block the scattered light. This leaves you with a flat, gray dusk instead of beautiful colors.
V = 100 − Cloud Cover PercentageExcellent (80-100)
Fair (50-79)
Poor (0-49)
A good blue hour shoot needs you to plan for light loss. As light drops, your camera's auto mode will struggle. This often leads to blurry or noisy photos.
Stability is the most important thing. Because the sun is below your horizon, you must use long exposure times to capture the light.
Use a Tripod
Essential for late phases to stop blur.
Base ISO
Set ISO to 100 to keep your photos clean.
Aperture
Use f/8 to f/11 to keep everything sharp.
Directional Shooting Advice
The sky is not the same color in every direction. Where you point your camera changes the look of your photo.
Facing away from the sun (East in the evening) lets you see the "Earth's shadow." This gives you the classic, saturated blue look.
Facing toward the sun (West in the evening) gives you the brightest glow. Architects love this to balance the warm lights of city buildings.
Our math models assume a flat horizon at sea level. In the real world, things change.
You must know when your local landscape or buildings will change the times.
Topography Blocking
Mountains or trees can block your horizon. This makes the light drop much faster than our math predicts.
Light Pollution
City lights can drown out the natural blue color. In big cities, the blue light is often washed out by orange streetlights.
Total Cloud Cover
Our tool assumes a clear sky. Total clouds block the blue light from reaching you. The sky will just look gray.
The length of your blue hour is not the same everywhere. Because the Earth tilts, the angle of the sun changes based on how far you are from the equator.
Near the equator, the sun sets very fast. The blue hour there might last only 10 minutes.
Extended Twilight Phenomena
At high latitudes, the sun crosses the horizon at a shallow angle. This makes the blue hour last much longer.
In some northern places in summer, the evening blue hour merges right into the morning one. True night never happens.
| Location | Latitude | Season | Avg. Duration |
|---|---|---|---|
| Quito, Ecuador | 0° | Equinox | ~10 minutes |
| Los Angeles, USA | 34° | Equinox | ~12 minutes |
| London, UK | 51° | Winter Solstice | ~25 minutes |
| Oslo, Norway | 60° | Summer Solstice | 55+ minutes |