Twilight

Twilight

Twilight is daylight illumination produced by diffuse sky radiation when the Sun is below the horizon as sunlight from the upper atmosphere is scattered in a way that illuminates both the Earth's lower atmosphere and also the Earth's surface. Twilight also may be any period when this illumination occurs, including dawn and dusk. The lower the Sun is beneath the horizon, the dimmer the sky. When the Sun reaches 18° below the horizon, the illumination emanating from the sky is nearly zero, and evening twilight becomes nighttime. When the Sun approaches re-emergence, reaching 18° below the horizon, nighttime becomes morning twilight. Owing to its distinctive quality, primarily the absence of shadows and the appearance of objects silhouetted against the lit sky, twilight has long been popular with photographers and painters, who often refer to it as the blue hour, after the French expression l'heure bleue.

Data Source : Wikipedia

• Related Topics:  Afterglow - In Meteorology, An Afterglow Is An Optical Phenomenon, Generally Referring To A Broad Arch Of Whitish Or Pinkish Sunlight In The Twilight Sky After Sunset, Consisting Of Purple Light And Bright Segment. It Consists Of Several Atmospheric Optical Phenomena., Belt Of Venus - The Belt Of Venus, Also Called Venus's Girdle, The Antitwilight Arch, Or Antitwilight, Is An Atmospheric Phenomenon Visible Shortly Before Dawn Or After Dusk, During Twilight. It Is A Pinkish Glow That Surrounds The Observer, Extending Roughly 10–20° Above The Horizon., Blue Hour - The Blue Hour Is The Period Of Twilight When The Sun Is Several Degrees Below The Horizon. During This Time, The Remaining Sunlight Takes On A Mostly Blue Shade. This Shade Differs From The Colour Of The Sky On A Clear Day, Which Is Caused By Rayleigh Scattering., Diffuse Sky Radiation - Diffuse Sky Radiation, Is Solar Radiation Reaching The Earth's Surface After Having Been Scattered From The Direct Solar Beam By Molecules Or Particulates In The Atmosphere. It Is Also Called Sky Radiation, The Determinative Process For Changing The Colors Of The Sky., Earth's Shadow , Visible At Twilight., Gloom - Gloom Is A Low Level Of Light Which Is So Dim That There Are Physiological And Psychological Effects. Human Vision At This Level Becomes Monochrome And Has Lessened Clarity., Dawn, Parts Of A Day, Visibility, Earth Phenomena, Night