But it’s lethally thin air is incapable of producing anything that resembles our own planet’s rich hues. You could argue that our neighbor Mars has something of a twilight. There, the choice is either daytime or twilight. From the latitude of New York, 1 1/2 hours is about average, while from Alaska there simply is no night at all between May and August. Depending on the time of year and the latitude of the observer, twilight can expire in less than an hour or linger throughout the night! Twilight is always shortest in the tropics, where less than one hour is the most you ever get. Twilight’s duration is not usually expressed in units of time, but rather degrees, and for good reason: its length varies. Stages of dawn occur before sunrise, in the reverse order as described for dusk. (Sunset can be defined as the moment when the top of the sun’s disk has passed the horizon.) As with twilight, there is civil dusk, nautical dusk, and astronomical dusk, occurring at the exact moment when the center of the sun’s disk is at 6°, 12°, and 18° below the horizon, respectively. See the Almanac’s sunrise/set calculator to get all three twilight times!īy the way, twilight is different than dusk, which occurs after sunset. The conclusion of this stage of twilight heralds the arrival of full darkness. After this point, the faintest stars emerge. Astronomical twilight occurs when the sun’s center is between 12 and 18 degrees below the horizon.After this, the horizon vanishes, when a mariner cannot distinguish between sea and sky. Nautical twilight occurs when the sun’s center is between 6 and 12 degrees below the horizon.That’s when streetlights must be on, according to most municipal ordinances. Civil twilight starts at sunset and ends roughly 45 minutes later, when the sun’s center has plunged six degrees below the horizon-equal to 12 times its own width.These stages also occur before sunrise, in the reverse order. Below describe the stages of twilight as they occur in the evening. And there’s really not one twilight but three! And they’re each so distinct, they have their own names. But in actuality, it’s a very specific event. What is the correct definition of twilight? The concept suggest vagueness. Image: Earth at twilight. Blue sunlight fades into darkness. The Captivating Crescent Moon: All About the Crescent Moon Phase
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