Greetings, comrades! Nautical twilight occurs when the sun's center is between 6 and 12 degrees below the horizon. Twilight in Astronomy: Astronomical twilight, which is darker than civil or nautical twilight, occurs when the sun's center is 18 degrees below the horizon.
Nautical twilight ends when the sky becomes completely dark. Civil twilight ends when the sun reaches its lowest point on the horizon, which is usually about an hour after sunrise and an hour before sunset.
During nautical twilight, the stars are visible to the naked eye if you know where to look. During astronomical twilight, only the brightest stars can be seen with the unaided eye.
The term "twilight" comes from the English word "to twinkle." When used to describe something that twinkles, such as a star or planet, this type of activity is called "astronomical illumination." The phrase "nautical twilight" comes from the need for sailors to be able to navigate by night using only the moon and stars. At sea, it is impossible to see anything beyond your own ship so all visibility needs to be enhanced as much as possible.
During nautical twilight, a sailor could use a sextant to make approximate measurements of the altitude of celestial objects such as the North Star or the Sun.
Civil twilight occurs when the sun is 6 degrees below the horizon and lasts from sunrise to sunrise for dawn - or from sunset to 6 degrees below the horizon for dusk. When the sun is 6-12 degrees below the horizon, it is said to be in nautical twilight. When the sun is 12–18 degrees below the horizon, it is said to be in astronomical twilight.
During civil twilight, objects that are normally visible to the naked eye become invisible unless they emit light themselves (such as streetlights). A person can still see objects with their eyes alone during this time, but not with both eyes and not enough light comes from outside sources to illuminate them.
In addition, during civil twilight animals such as cats, dogs, birds, and small mammals must rely on internal body clocks rather than external lights to tell night from day. Humans can work with only a little light during this time, so most people will want to keep electrical lights off during these hours if they are going to be driving or walking anywhere.
After dusk, you need artificial light to travel or hunt anymore. Natural light is too low at night to read by or shoot accurately.
During a lunar eclipse, the Earth's shadow falls on the moon. Because there is no sunlight around to reflect back into space, all the earth's illumination is refracted through the atmosphere to fall on one small area on the surface of the moon.
The most common definition of twilight used by the general public is civil twilight. The moment when the sun's center is 12 degrees below the horizon and only broad or hazy outlines of objects are visible. The sky had been absolutely black up until this point in the morning. Civil twilight ends when the sun reaches 12 degrees above the horizon.
During solar twilight, which occurs about an hour after sunrise and an hour before sunset, only the Sun is visible from earth. The cosmic microwave background radiation fills the universe, but we don't see it because it doesn't emit any light of its own. At night, when no sunlight is present, space is dark to us. But it's not completely dark - far-away stars and galaxies continue to glow with a faint light that reveals their distance.
Solar twilight comes in two forms: lunar and planetary. During lunar twilight, the Moon is responsible for illuminating the night sky, so it must be at least 3% illuminated to have any effect on visibility. The word "lunar" comes from the Latin word luna, meaning "moon". During planetary twilight, the planet Earth is the source of light, so it must be within 99% illumination for twilight to be considered absent. The word "planetary" comes from the Greek word planetes, meaning "wandering star".
Stars are bright lights in the night sky, while planets are bright lights on other worlds.
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