Introduction:
Dawn and twilight are the periods of partial light between night and day (dawn) and day and night (twilight). They're not completely dark because of how sunlight interacts with the Earth's atmosphere.
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What they are:
- Dawn: The time between sunrise and full daylight.
- Twilight: The time between sunset and complete darkness.
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Why they happen: Even when the sun is below the horizon (meaning we can't see it directly), its light is still scattered (diffused) and bent (refracted) by the Earth's atmosphere. This scattered and bent light reaches us, creating the dim light of dawn and twilight.
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Effect of Latitude (Location on Earth): The length of dawn and twilight depends on where you are on Earth:
- Equator: Because the sun rises and sets straight up and down (vertically) at the equator, the periods of dawn and twilight are short.
- Temperate Latitudes (Mid-latitudes): In places like Europe and much of the US, the sun rises and sets at an angle (obliquely). This means the period of refracted light, and therefore dawn and twilight, is longer than at the equator.
- Poles (North and South): At the poles, the sun's path is almost horizontal. This results in very long periods of twilight. During the winter, when the sun doesn't rise for months, it's not completely dark; it's mostly a long twilight period.
Think of it like this:
Imagine shining a flashlight at a ball.
- If you shine it straight at the ball's "equator," the area that goes from light to dark is a very sharp line. This is like the short dawn/twilight at the equator.
- If you shine the flashlight at an angle, the transition from light to dark is more gradual. This is like the longer dawn/twilight in temperate areas.
- If you shine the flashlight almost parallel to the ball's surface (like at the poles), a large area is dimly lit. This is like the long twilight at the poles.
In Short:
Dawn and twilight are caused by the scattering and bending of sunlight by the Earth's atmosphere. The length of these periods varies depending on your location on Earth, with shorter periods near the equator and much longer periods at the poles.