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Civil dawn begins when there is enough light for most objects to be distinguishable, so that some outdoor activities can commence. It occurs when the center of the Sun is 6 degrees below the horizon in the morning. [5] When the sky is clear, it is blue colored, and if there are clouds or haze, bronze, orange and yellow colors are seen.
The sky has many colors at this time, such as orange and red. Beyond this point artificial light may be needed to carry out outdoor activities, depending on atmospheric conditions and location. At nautical dusk, the Sun moves to 12° below the horizon in the evening. It marks the end of nautical twilight, which begins at civil dusk.
More blue light is scattered, so if the sun is present, its light appears more reddish. In addition, the sun's low angle above the horizon produces longer shadows. The term hour is used figuratively; the effect has no clearly defined duration and varies according to season and latitude.
Here's a breakdown of how and why it all happens. But the science behind a blue sky isn't that easy. For starters, it involves something called the Rayleigh effect, or Rayleigh scattering.
Blue hour at the Old Cathedral of the Holy Name of Jesus, Bragança in Portugal. The blue hour (from French l'heure bleue; [1] [a] pronounced [lœʁ blø]) is the period of twilight (in the morning or evening, around the nautical stage) when the Sun is at a significant depth below the horizon.
Twilight occurs according to the solar elevation angle θ s, which is the position of the geometric center of the Sun relative to the horizon. There are three established and widely accepted subcategories of twilight: civil twilight (nearest the horizon), nautical twilight, and astronomical twilight (farthest from the horizon).
Noon (also known as noontime or midday) is 12 o'clock in the daytime. It is written as 12 noon, 12:00 m. (for meridiem, literally 12:00 midday), 12 p.m. (for post meridiem, literally "after midday"), 12 pm, or 12:00 (using a 24-hour clock) or 1200 (military time). Solar noon is the time when the Sun appears to contact the local celestial meridian.
Mie scattering is responsible for the light scattered by clouds, and also for the daytime halo of white light around the Sun (forward scattering of white light). [16] [17] [18] Sunset colors are typically more brilliant than sunrise colors, because the evening air contains more particles than morning air.