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Sunrise
Sunrise (or sunup) is the moment when the upper rim of the Sun appears on the horizon in the morning, at the start of the Sun path. The term can also refer to the entire process of the solar disk crossing the horizon. Terminology 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 caused many cultures to have mythologies and religions built around the geocentric model, which prevailed until astronomer Nicolaus Copernicus formulated his heliocentric model in the 16th century. Architect Buckminster Fuller proposed the terms "sunsight" and "sunclipse" to better represent the heliocentric model, though the terms have not entered into common language. Astronomically, sunrise occurs for only an instant, namely the moment at which the upper limb of the Sun appears tangent to the horizon. However, th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sunrise - Libreville, Gabon - 2008
Sunrise (or sunup) is the moment when the upper rim of the Sun appears on the horizon in the morning, at the start of the Sun path. The term can also refer to the entire process of the solar disk crossing the horizon. Terminology 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 caused many cultures to have mythologies and religions built around the geocentric model, which prevailed until astronomer Nicolaus Copernicus formulated his heliocentric model in the 16th century. Architect Buckminster Fuller proposed the terms "sunsight" and "sunclipse" to better represent the heliocentric model, though the terms have not entered into common language. Astronomically, sunrise occurs for only an instant, namely the moment at which the upper limb of the Sun appears tangent to the horizon. However, the te ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sunrise Equation
The sunrise equation or sunset equation can be used to derive the time of sunrise or sunset for any solar declination and latitude in terms of local solar time when sunrise and sunset actually occur. Formulation It is formulated as: :\cos \omega_\circ = -\tan \phi \times \tan \delta where: :\omega_\circ is the solar hour angle at either sunrise (when negative value is taken) or sunset (when positive value is taken); :\phi is the latitude of the observer on the Earth; :\delta is the sun declination. Principles The Earth rotates at an angular velocity of 15°/hour. Therefore, the expression \omega_\circ / \mathrm^\circ, where \omega_\circ is in degree, gives the interval of time in hours from sunrise to local solar noon or from local solar noon to sunset. The sign convention is typically that the observer latitude \phi is 0 at the equator, positive for the Northern Hemisphere and negative for the Southern Hemisphere, and the solar declination \delta is 0 at the vernal a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Analemma
In astronomy, an analemma (; ) is a diagram showing the position of the Sun in the sky as seen from a fixed location on Earth at the same Solar time#Mean solar time, mean solar time over the course of a year. The change of position is a result of the shifting of the angle in the sky of the path that the Sun takes Celestial sphere, in respect to the stars (the ecliptic). The diagram resembles a lemniscate, figure eight. Globes of the Earth often display an analemma as a two-dimensional figure of equation of time ("sun fast") vs. declination of the Sun. The north–south component of the analemma results from the change in the Sun's declination due to the axial tilt, tilt of Earth's Rotation around a fixed axis, axis of rotation as it orbits around the Sun. The east–west component results from the equation of time, nonuniform rate of change of the Sun's right ascension, governed by the combined effects of Earth's axial tilt and its orbital eccentricity. An analemma can be Phot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Time Zone
A time zone is an area which observes a uniform standard time for legal, Commerce, commercial and social purposes. Time zones tend to follow the boundaries between Country, countries and their Administrative division, subdivisions instead of strictly following longitude, because it is convenient for areas in frequent communication to keep the same time. Each time zone is defined by a standard offset from Coordinated Universal Time (UTC). The offsets range from UTC−12:00 to UTC+14:00, and are usually a whole number of hours, but a few zones are offset by an additional 30 or 45 minutes, such as in Indian Standard Time, India and Nepal Time, Nepal. Some areas in a time zone may use a different offset for part of the year, typically one hour ahead during spring (season), spring and summer, a practice known as daylight saving time (DST). List of UTC offsets In the table below, the locations that use daylight saving time (DST) are listed in their UTC offset when DST is ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Summer Solstice
The summer solstice or estival solstice occurs when one of Earth's poles has its maximum tilt toward the Sun. It happens twice yearly, once in each hemisphere ( Northern and Southern). The summer solstice is the day with the longest period of daylight and shortest night of the year in that hemisphere, when the sun is at its highest position in the sky. At either pole there is continuous daylight at the time of its summer solstice. The opposite event is the winter solstice. The summer solstice occurs during the hemisphere's summer. In the Northern Hemisphere, this is the June solstice (20, 21 or 22 June) and in the Southern Hemisphere, this is the December solstice (20, 21, 22 or 23 of December). Since prehistory, the summer solstice has been a significant time of year in many cultures, and has been marked by festivals and rituals. Traditionally, in temperate regions (especially Europe), the summer solstice is seen as the middle of summer and referred to as midsum ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 (other factors such as atmospheric conditions being equal). 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 . By analogy with eve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Night
Night, or nighttime, is the period of darkness when the Sun is below the horizon. Sunlight illuminates one side of the Earth, leaving the other in darkness. The opposite of nighttime is daytime. Earth's rotation causes the appearance of sunrise and sunset. Moonlight, airglow, starlight, and light pollution dimly illuminate night. The duration of day, night, and twilight varies depending on the time of year and the latitude. Night on other celestial bodies is affected by their rotation and orbital periods. The planets Mercury and Venus have much longer nights than Earth. On Venus, night lasts about 58 Earth days. The Moon's rotation is tidally locked, rotating so that one of the sides of the Moon always faces Earth. Nightfall across portions of the near side of the Moon results in lunar phases visible from Earth. Organisms respond to the changes brought by nightfall: darkness, increased humidity, and lower temperatures. Their responses include direct reactions a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sun Path
Sun path, sometimes also called day arc, refers to the diurnal motion, daily (sunrise to sunset) and seasonal arc (geometry), arc-like path that the Sun appears to follow across the sky as the Earth Earth's rotation, rotates and Earth's orbit, orbits the Sun. The Sun's path affects the length of daytime experienced and amount of daylight received along a certain latitude during a given season. The relative position of the Sun is a major factor in the solar gain, heat gain of buildings and in the performance of solar energy systems. Accurate location-specific knowledge of sun path and climatic conditions is essential for economic decisions about solar thermal collector, solar collector area, orientation, landscaping, summer shading, and the cost-effective use of solar trackers. Angles Effect of the Earth's axial tilt Sun paths at any latitude and any time of the year can be determined from basic geometry. The Earth's axis of Earth's rotation, rotation tilts about Axial ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dawn
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 , "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. The morning twilight is divided in three phases, which are determined by the angular distance of the centre of the Sun (degree (angle), degrees below the horizon) in the morning. These are astronomical, nautical and civil twilight. Astronomical dawn Astronomical dawn begins when the center of the Sun is 18 d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Daylight
Daylight is the combination of all direct and indirect sunlight during the daytime. This includes direct sunlight, diffuse sky radiation, and (often) both of these reflected by Earth and terrestrial objects, like landforms and buildings. Sunlight scattering, scattered or reflected by astronomical objects is generally not considered daylight. Therefore, daylight excludes moonlight, despite it being reflected indirect sunlight. Definition Daylight is present at a particular location, to some degree, whenever the Sun is above the local horizon. This is true for slightly more than 50% of the Earth at any given time, since the Earth's atmosphere refracts some sunlight even when the Sun is below the horizon. Outdoor illuminance varies from 120,000 lux for direct sunlight at noon, which may cause eye pain, to less than 5 lux for thick storm clouds with the Sun at the horizon (even <1 lux for the most extreme case), which may make shadows from distant street lights visible. It may be d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
False Sunrise
A false sunrise is any of several atmospheric optical phenomena in which the Sun appears to have risen, but is actually still some distance below the horizon. A number of different atmospheric conditions can be responsible for this effect, all of which divert the sunlight in such a way as to allow it to reach the observer's eye, thereby giving the impression that the light comes directly from the Sun itself. The spread of light can sometimes resemble that of the true sun. Several atmospheric phenomena that may alternatively be called a "false sunrise" are: * Simple reflection of the sunlight off the bottom of the clouds. * A type of ice crystal halo, such as an upper tangent arc or, more commonly, an upper sun pillar (similar to a subsun, but extending above the sun instead of below it). Like all halos, these phenomena are caused by the reflection and/or refraction of sunlight by ice crystals suspended in the atmosphere, often in the form of cirrus or cirrostratus clouds. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Altitude
Altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum (geodesy), datum and a point or object. The exact definition and reference datum varies according to the context (e.g., aviation, geometry, geographical survey, sport, or atmospheric pressure). Although the term ''altitude'' is commonly used to mean the height above sea level of a location, in geography the term elevation is often preferred for this usage. In aviation, altitude is typically measured relative to mean sea level or above ground level to ensure safe navigation and flight operations. In geometry and geographical surveys, altitude helps create accurate topographic maps and understand the terrain's elevation. For high-altitude trekking and sports, knowing and adapting to altitude is vital for performance and safety. Higher altitudes mean reduced oxygen levels, which can lead to altitude sickness if proper acclimatization measures are not taken. Vertical distance ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
