|
Dawn Wildsmith
Dawn is the time that marks the beginning of twilight before sunrise. It is recognized by the diffuse sky radiation, appearance of indirect sunlight being Rayleigh scattering, scattered in Earth's atmosphere, when the centre of the Sun's disc has reached 18° below the observer's horizon. This morning twilight period will last until sunrise (when the Sun's upper limb breaks the horizon), when daylight, direct sunlight outshines the light scattering by particles, diffused light. Etymology "Dawn" derives from the Old English verb ''dagian'', "to become day". Types of dawn Dawn begins with the first sight of lightness in the morning, and continues until the Sun breaks the horizon. This morning twilight before sunrise is divided into three categories depending on the amount of sunlight that is present in the sky, which is determined by the angular distance of the centre of the Sun (degree (angle), degrees below the horizon) in the morning. These categories are ''astronomical'', ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Desert Dawn
A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the land surface of the Earth is arid or semi-arid. This includes much of the polar regions, where little precipitation occurs, and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location. Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks, which consequently break in pieces. Although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter, and the resulting fragments and rubble strewn over the de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
