Any photographer knows that the middle of the day casts the harshest and most unflattering light. It's the light just before and after sunrise and sunset that we covet. But, if you go to a weather site and look up when sunrise and sunset are set to occur, you might be scratching your head since they list three different twilights. So, to make things easier on you, let's set the record straight and delve into the differences between civil twilight, nautical twilight and astronomical twilight.
Most of us would say that the sun comes up when it crosses the horizon - makes sense, right? Because just before then, it's still dark and when the sun rises, it's light! But, no, scientists show us a different story. Since the sun is quite large, it naturally takes time to rise above the horizon. When you go to the kitchen to pour a cup of coffee, the light starts coming in your window. By time you finish that cup of Joe, the light has become much brighter. So, sunrise begs the questions: Does daylight officially begin when the sun starts to rise? Or is it when it's official when the sun is fully above the horizon?
Want the crib sheet? Photographers who have been out there, ready to shoot with their cameras know that the color of the sky changes quite a bit during both dawn and dusk. The truth of the matter is, there are three official answers to when twilight occurs. Civil is when people are still out and about enjoying the remaining light. Nautical is when the sailors can no longer rely on the horizon to guide them, and astronomical is for astronomers and adventurous photographers who have the equipment and patience for capturing the moon and the stars.
Now, here's the (bit scientific and tricky) explanation to wrap your head around. It's worth understanding:
Civil twilight: Morning civil twilight starts when the geometric center of the sun is 6° below the horizon. Evening civil twilight begins at sunset and ends when the center of the sun reaches 6° below the horizon. The evening civil twilight is otherwise known as dusk. This is when the brightest stars will be visible under normal atmospheric conditions. You can capture a variety of images during civil twilight because the light changes so rapidly. Don't think that this is the end of good light though. Nautical twilight offers plenty of photo ops, too.
Only the brightest stars appear during the civil twilight. You'll also get to see some planets, such as Venus. During this period there is enough light from the sun that flashes or other lighting sources should not be needed. You can always adjust your ISO to 400 or even 800, if needed, during this time, but as you'll read below, there are some limitations to this.
Nautical Twilight: Ahoy, mates! Nautical twilight is the time when the center of the sun is between 6° and 12° below the horizon. During nautical twilight the illumination is such that the horizon is still visible even on a Moonless night, allowing mariners to take reliable star sights for navigational purposes, hence the name. At the beginning or end of nautical twilight, under good atmospheric conditions, vague outlines of ground objects may be distinguishable, but details are not likely.
The end of this period in the evening, or during its morning start, is also the time when traces of light near the sunset or sunrise point of the horizon are very difficult if not impossible to discern. It's often referred to as "first light" before civil dawn and "nightfall" after civil dusk. You'll definitely need to increase your ISO during nautical twilight.
Astronomical Twilight: Darker than civil or nautical, astronomical twilight occurs when the center of the sun is a full 18 degrees below the horizon. As its name suggests, this twilight period is of most interest to astronomers. There is no color in the sky during astronomical twilight. A popular type of photograph during this time is the star trail, since it will register some background glow near the horizon during this time. But, even die hard nature photographers will probably have called it a night by then. When the moon is full, they'll come back out with their tripod, however.
Gauging the Three Twilights
The kinds of photographs you want to capture during these three twilight periods will be distinctly different from the others. Naturally, astronomical twilight is for full moons, stars and if you're near a busy enough street, I'd add streaming headlight images. Silhouettes work best during civil and the beginning of nautical twilight, depending on the position of the subject in relation to your camera. You'll have to play with that a bit for optimal silhouette shots. During these twilights, your best subjects will be larger ones, such as mountains and landmarks. But, smaller subjects, like fine art shots of a bug on a leaf or a leaf on a tree, are limited to civil twilight. Even with increased ISOs, the low contrast light at that time of day makes it tough to capture enough detail in your subjects.
Though you probably knew these lighting situations by the changing light itself, it's good to be knowledgeable with the terms. They run in 6 degree differences, which makes it easy to remember, even if you can't visualize what 6 degrees below the horizon looks like, you'll be just dangerous enough to talk the talk while the rest of us are inside processing our images or cleaning our cameras for the next day's shoot.
Bonus video: The Golden Hour covers sunsets and creating silhouettes.
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