What is blue hour?

What does blue hour mean?

Blue hour, from the French l'heure bleue, is the period of twilight at dawn or dusk when the sun is at a significant depth below the horizon and the remaining light takes on a mostly blue shade. Wikipedia places it around the nautical stage of twilight and notes that it has no official definition, since the term is colloquial (Wikipedia: Blue hour).

It is not the same as golden hour. Golden hour is warm light while the sun is still up. Blue hour begins after the sun is gone.

Why is the light blue?

The common story says the sky is blue because blue light scatters, as it does at noon. Wikipedia calls that explanation incorrect for blue hour. The blue shade appears because, with the sun far below the horizon, the light that reaches you passes through the ozone layer, where the Chappuis absorption removes yellow and red light and leaves the blue to dominate.

The effect is easiest to see on a clear evening. Clouds and haze mix in other colors, so a blue hour with some cloud can show yellow, orange and pink next to the blue.

How long does blue hour last?

Wikipedia puts it at roughly 20 to 96 minutes right after sunset and right before sunrise, with time of year, location and air quality all changing the figure. As a worked example, it lists Egypt on June 21, when sunset is at 7:59 PM and blue hour runs until about 9:35 PM.

Near the equator the sun drops steeply and blue hour is short. Close to the poles the sun sinks at a shallow angle, so twilight and blue hour stretch out. The pattern is the same one that makes golden hour longer in northern cities.

How does Afterhue define blue hour?

The app picks fixed numbers so it can compute times on the phone. Blue hour is the sun between 4 and 6 degrees below the horizon, right after golden hour ends. It is a narrower window than the 4 to 8 degrees photographers often quote, so Afterhue's blue hour is shorter than what you will see in a photo guide. The calculation uses the date and your position and works offline.

The Tonight screen lists golden hour, sunset and blue hour in a Light tonight block, and a timeline lets you drag through the evening to read the sun's height in degrees at any minute.

What should I photograph at blue hour?

Anything that has its own light. Streetlamps, lit windows, bridges, cars and storefronts glow against the blue sky and give an image depth. Water is also a good subject, since it reflects the sky and goes smooth when the exposure is long.

• Cityscapes with lit buildings.
• Harbors and piers with boats.
• Mountain ridges against a deep blue sky.
• Snow, which picks up the blue cast strongly.
• Silhouettes, such as those in our guide to sunset silhouette photos.

How do I shoot blue hour on an iPhone?

The light is dim, so the phone needs help staying still.

1. Arrive while the sky still has some glow, around the end of sunset.
2. Rest the phone on a wall, a rail or a small tripod.
3. Let Night mode switch on. When the phone detects it is steady, it can use a longer exposure.
4. Tap the brightest part of the sky, then slide the exposure down to keep the blue rich.
5. Check the picture after each shot and adjust.
6. Keep shooting as the sky darkens, because every five minutes changes the balance between sky and city lights.

Why do the colors look different on screen?

Phones brighten dim scenes and add contrast, so a photo can look bluer or more purple than real life. If you want it to look as it felt, lower the exposure a touch and avoid heavy saturation. Our guide to editing a sunset photo on iPhone covers the sliders.

Does blue hour happen every day?

Yes, twice a day, once before sunrise and once after sunset, but you only see it when the sky is clear enough and you are not hemmed in by buildings. Near the poles in summer the sun may never get far enough below the horizon, so there is no true blue hour at all. In some winter weeks the opposite is true and twilight blends into a long, soft dusk.

That variety is why a fixed one-hour rule fails. Check the time for your place and date, or let an app calculate it, and treat the result as a window to be early for.

What mistakes spoil blue hour photos?

Most come from impatience. People arrive at sunset, take two pictures and leave before the deepest blue. Others hold the phone by hand in dim light and get blur. A third mistake is shooting too late, when the sky has turned black and the city lights are the only thing left, which makes a flat, noisy photo.

Plan to be set up ten minutes before the end of sunset and work for about half an hour.

Is blue hour a good time to see the afterglow?

Yes. The pink and purple light after sunset overlaps with the early part of blue hour. Wikipedia describes the purple light of the afterglow as appearing a few degrees below the horizon (Wikipedia: Afterglow). If you leave at sunset you will miss the best part of the evening. A golden-hour reminder can nudge you to get outside early enough to stay through both.