What Is Blue Hour? The Cool Light After Sunset (and How It Differs From Golden Hour)

What is blue hour? It’s the stretch of twilight, just before sunrise and just after sunset, when the sun sits well below the horizon and the sky turns a deep, saturated blue. The sun is gone from view, but its light still scatters through the upper atmosphere — and because the longer red wavelengths have dropped below the horizon with it, what reaches you is overwhelmingly blue. It’s softer and cooler than golden hour, and for many photographers it’s the more atmospheric of the two twilight windows.

This guide explains what causes blue hour, when it happens, how long it lasts, and how it differs from the golden hour that precedes it.

Key takeaways

• Blue hour is the twilight period when the sun is roughly 4° to 8° below the horizon — after golden hour in the evening, before it in the morning.
• The light is cool, even, and low-contrast, with a deep-blue sky that balances beautifully against artificial light.
• Like golden hour, it isn’t a fixed sixty minutes — its length depends on your latitude and the season, and near the equator it can be very short.
• To see blue hour times for any location and date, check the blue hour section of the sun times calculator.

What blue hour actually is

Blue hour is a stage of twilight. Once the sun drops below the horizon, it doesn’t get dark all at once — sunlight keeps illuminating the sky from below for a while, growing dimmer in stages. Blue hour is the part of that fade when the sun is low enough that the warm tones are gone but there’s still enough light to colour the sky a rich blue rather than black.

The colour comes from the same physics that makes the daytime sky blue, taken to an extreme. Sunlight passing through that much atmosphere has its longer red and orange wavelengths scattered away and absorbed, while the shorter blue wavelengths survive the journey. There’s a contribution from ozone in the upper atmosphere too, which absorbs remaining red light and deepens the blue. The result is a sky that glows an even, twilight blue from horizon to horizon.

Astronomically, blue hour lines up roughly with the civil-to-nautical twilight range — when the sun’s centre is about 4° to 8° below the horizon. Above that (down to about 4° below) you’re still in golden hour; below it, the blue drains toward true night. Like golden hour, the “hour” is a loose label — it’s defined by the sun’s angle, not by the clock.

Blue hour vs. golden hour

The two are neighbours in time and constantly confused, so it helps to set them side by side. They happen back to back: in the evening, golden hour comes first while the sun is just above to just below the horizon, then blue hour follows as the sun sinks deeper. In the morning the order reverses — blue hour first, then golden hour as the sun climbs toward sunrise.

The difference in the light is what matters:

• Golden hour is warm and directional. The sun is still visible (or nearly so), casting long shadows and side-light that models texture and shape. Think glowing skin tones, rim-lit subjects, and long warm shadows.
• Blue hour is cool and diffuse. The sun is gone, so there are no direct shadows at all — just soft, even light from the whole sky. Contrast is low, colours are muted, and the deep-blue sky sets off any warm artificial light beautifully.

That last point is why cityscape and architecture photographers prize blue hour: street lamps, windows, and signage read as warm gold against a sky that’s still blue rather than black, and the two balance in a way they never do in full daylight or full night. Golden hour flatters faces and landscapes; blue hour flatters skylines and lit interiors. Neither is “better” — they’re different tools, and the same outing can give you both if you stay put through the transition.

When blue hour happens and how long it lasts

Blue hour occurs twice a day, bracketing the golden hours: shortly after sunset in the evening and shortly before sunrise in the morning. Its exact timing and length depend on the same factors that move golden hour.

Your latitude is the biggest one. Near the equator the sun drops steeply and vertically below the horizon, racing through the twilight angles — blue hour there can last just 20 minutes. At higher latitudes the sun sets at a shallow angle and lingers in those angles far longer, stretching blue hour out; close to the poles in summer, twilight can persist so long that proper blue hour barely resolves at all.

The season shifts it too, along with the sunrise and sunset times it’s anchored to. And as always, the standard figures assume a flat horizon at sea level — hills, buildings, and weather change what you actually see, even when the astronomical timing is unchanged.

Because of all that, there’s no universal clock answer. The reliable approach is to calculate it for your exact spot: NOAA’s solar calculator gives the underlying sunrise, sunset, and twilight angles for any latitude and longitude, and the SunCast sun times calculator reports the morning and evening blue-hour windows directly, alongside golden hour and every twilight phase, for a place and date you choose.

How to shoot blue hour

Blue hour is short and the light changes minute to minute, so a little preparation goes a long way:

• Arrive during golden hour and stay. The easiest way to catch blue hour is to shoot the sunset golden hour first and simply keep going as the warm light fades to blue. You get two distinct looks from one location. (For the golden-hour half of that plan, see what time golden hour is today and the golden hour calculator.)
• Bring a tripod. Light levels fall fast, so exposures lengthen into the seconds. A tripod keeps long exposures sharp and lets you drop to a clean, low ISO.
• Look for artificial light. Blue hour is at its best where city lights, lit windows, or signage can play warm against the blue sky. Scout a composition that includes them.
• Work quickly and bracket. The blue deepens and darkens throughout the window, so the “right” exposure is a moving target. Shoot more than you think you need.

For a fuller walkthrough of planning a shoot around the light — scouting, timing, and reading the sun’s direction — see how photographers use SunCast for photography.

The short version

Blue hour is the cool, deep-blue twilight just before sunrise and just after sunset, when the sun sits a few degrees below the horizon and only the short blue wavelengths still light the sky. It sits right next to golden hour — warm and directional — and the two trade off in minutes, which is why it pays to shoot through the whole transition. Its timing and length are set by the sun’s angle, so they shift with your latitude and the season; calculate them for your location rather than trusting a generic table. For more on the science, Wikipedia’s blue hour and twilight entries are clear primers.