Sunrise or sunup is the moment when the upper rim of the Sun appears on the horizon in the morning.The term can also refer to the entire process of the solar disk crossing the horizon and its accompanying atmospheric effects.Although the Sun appears to “rise” from the horizon, it is actually the Earth’s motion that causes the Sun to appear.
The illusion of a moving Sun results from Earth observers being in a rotating reference frame; this apparent motion is so convincing that many cultures had mythologies and religions built around the geocentric model, which prevailed until astronomer Nicolaus Copernicus formulated Twilight on Earth is the illumination of the lower atmosphere when the Sun is not directly visible because it is below the horizon.
Twilight is produced by sunlight scattering in the upper atmosphere, illuminating the lower atmosphere so that Earth’s surface is neither completely lit nor completely dark. The word twilight is also used to denote the periods of time when this illumination occurs.
heliocentric model in the 16th century.
The lower the Sun is beneath the horizon, the dimmer the twilight (other factors such as atmospheric conditions being equal). When the Sun reaches 18° below the horizon, the twilight’s brightness is nearly zero, and evening twilight becomes nighttime. When the Sun again reaches 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, who sometimes refer to it as “sweet light”, and painters, who often refer to it as the blue hour, after the French expression l’heure bleue.