Blue Hour Calculator

The blue hour is a brief period of twilight that occurs twice each day — shortly before sunrise and shortly after sunset — when the Sun sits between approximately 4 and 8 degrees below the horizon. During this window, sunlight scattered deep in the atmosphere illuminates the sky with a rich, even, diffuse blue light that is almost shadowless and highly flattering for photography. Unlike the warmer orange and pink tones of the golden hour that immediately precede or follow it, the blue hour produces a cool, saturated blue cast across the entire visible sky.

Despite its name, the "blue hour" is not a full 60 minutes. At mid-latitudes it typically lasts between 20 and 40 minutes in each occurrence. The duration depends heavily on the observer's latitude and the time of year: at high latitudes near the summer solstice, nautical twilight (which encompasses the blue hour) can persist for hours or even all night. Near the equator, twilight transitions happen quickly, and the blue hour may last only 15 minutes.

Photographers, cinematographers, and architects prizing mood and atmosphere plan shoots specifically around the blue hour. The combination of natural blue ambient light in the sky and the warm artificial light from city windows, street lamps, and car headlights creates a contrast that is impossible to replicate artificially. This is why the most iconic urban skyline photographs are nearly always shot during evening blue hour.

This calculator uses the input date, latitude, longitude, and UTC offset to compute the exact start, peak, and end times of both the morning and evening blue hour windows for any location on Earth.

The calculator derives blue hour from the computed sunrise and sunset times. The blue hour window is centered approximately 30 minutes before sunrise (morning) and 30 minutes after sunset (evening), spanning 25 minutes on each side of those peak times.

The golden hour and blue hour are adjacent twilight phenomena with very different photographic qualities. The golden hour occurs when the Sun is between 0 and about 6 degrees above the horizon — just after sunrise and just before sunset. During the golden hour, sunlight passes through a much longer atmospheric path, scattering short blue wavelengths and allowing warm red, orange, and yellow wavelengths to dominate. The directional light creates long shadows and a warm, three-dimensional quality ideal for portraiture and landscape photography.

The blue hour follows the golden hour in the morning (golden first, then blue) and precedes it in the evening (blue first, then golden as the Sun rises above the horizon). Blue hour light is non-directional, soft, and lacks shadows — quite different from the raking directional light of the golden hour. Both are "magic light" periods for photography, but they serve different creative purposes. Blue hour is particularly powerful for architecture, cityscapes, water reflections, and any scene where you want artificial lights to balance with a dramatic sky.

The transition from blue to golden hour happens rapidly — often in less than 10 minutes — so photographers targeting both windows need to be set up and ready to shoot both phases without delay. Use this calculator alongside the Golden Hour Calculator to plan a complete twilight shoot schedule.

Because blue hour light levels are significantly lower than daylight, long exposures become necessary. A sturdy tripod is non-negotiable — even with image stabilization, handheld exposures of 1/15 second or longer will show motion blur. Use a remote shutter release or the camera's self-timer to eliminate vibration from pressing the shutter button.

Camera settings for blue hour photography typically involve a wide aperture (f/2.8 to f/5.6 for shallow depth of field, or f/8 to f/11 for cityscape sharpness throughout), ISO 100 to 800 (higher if needed, accepting some grain), and shutter speeds from 1/30 second to several seconds depending on light levels. Shoot in RAW format to retain maximum dynamic range for post-processing, and set white balance to daylight (around 5500K) rather than auto to preserve the authentic blue tones that make blue hour unique.

For cityscapes, the evening blue hour is generally preferred over the morning blue hour because more windows are lit, traffic is denser (creating light trails), and the atmosphere typically has more aerosols from daily human activity that add interesting haze effects. The morning blue hour is ideal for calm water reflections and quieter urban environments.

At the equator (0° latitude), the Sun moves nearly perpendicular to the horizon, crossing the 4-8 degree below-horizon band very quickly. Blue hour at tropical locations may last only 15-20 minutes. At mid-latitudes (30° to 55°), the Sun sets at a shallower angle, extending the blue hour to 25-40 minutes — the most common experience for photographers in North America and Europe. At high latitudes (above 60°), the Sun sets at a very shallow angle, and blue hour can extend for 45 minutes to over an hour near the summer solstice.

In the Arctic and Antarctic circles during summer, there may be continuous twilight all night long where the Sun never drops far enough below the horizon to end blue hour before it begins again. This phenomenon, called the "midnight sun" or "white night," makes blue hour photography challenging because the sky never gets dark enough for artificial lights to contrast strongly against it.