|
Zero Shadow Day
A zero shadow day is a day on which the Sun does not cast a shadow of an object at noon, when the sun will be exactly at the zenith position. Zero shadow day happens twice a year for locations between +23.5 and -23.5 degrees of latitude (between the tropics of Cancer and Capricorn, respectively). The dates will vary for different locations on Earth. This phenomenon occurs when the Sun's declination becomes equal to the latitude of the location. On a zero shadow day, when the sun crosses the local meridian, the sun's rays will fall exactly vertical relative to an object on the ground and one cannot observe any shadow of that object. {{subsolar_point_date_graph.svg See also *Sundial *Lahaina Noon *Qibla observation by shadows Twice every year, the Sun culmination, culminates at the zenith of the ''Kaaba'' in Mecca, the Holiest sites in Islam, holiest site in Islam, at local solar noon, allowing the qibla (the direction towards the ''Kaaba'') to be ascertained in other ... Referenc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zero Shadow Day 2
0 (zero) is a number representing an empty quantity. In place-value notation such as the Hindu–Arabic numeral system, 0 also serves as a placeholder numerical digit, which works by multiplying digits to the left of 0 by the radix, usually by 10. As a number, 0 fulfills a central role in mathematics as the additive identity of the integers, real numbers, and other algebraic structures. Common names for the number 0 in English are ''zero'', ''nought'', ''naught'' (), ''nil''. In contexts where at least one adjacent digit distinguishes it from the letter O, the number is sometimes pronounced as ''oh'' or ''o'' (). Informal or slang terms for 0 include ''zilch'' and ''zip''. Historically, ''ought'', ''aught'' (), and ''cipher'', have also been used. Etymology The word ''zero'' came into the English language via French from the Italian , a contraction of the Venetian form of Italian via ''ṣafira'' or ''ṣifr''. In pre-Islamic time the word (Arabic ) had the meaning ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shadow
A shadow is a dark area where light from a light source is blocked by an opaque object. It occupies all of the three-dimensional volume behind an object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, or a reverse projection of the object blocking the light. Point and non-point light sources A point source of light casts only a simple shadow, called an "umbra". For a non-point or "extended" source of light, the shadow is divided into the umbra, penumbra, and antumbra. The wider the light source, the more blurred the shadow becomes. If two penumbras overlap, the shadows appear to attract and merge. This is known as the shadow blister effect. The outlines of the shadow zones can be found by tracing the rays of light emitted by the outermost regions of the extended light source. The umbra region does not receive any direct light from any part of the light source and is the darkest. A viewer located in the umbra region cannot directly se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zenith
The zenith (, ) is an imaginary point directly "above" a particular location, on the celestial sphere. "Above" means in the vertical direction (plumb line) opposite to the gravity direction at that location (nadir). The zenith is the "highest" point on the celestial sphere. Origin The word "zenith" derives from an inaccurate reading of the Arabic expression (), meaning "direction of the head" or "path above the head", by Medieval Latin scribes in the Middle Ages (during the 14th century), possibly through Old Spanish. It was reduced to "samt" ("direction") and miswritten as "senit"/"cenit", the "m" being misread as "ni". Through the Old French "cenith", "zenith" first appeared in the 17th century. Relevance and use The term ''zenith'' sometimes means the highest point, way, or level reached by a celestial body on its daily apparent path around a given point of observation. This sense of the word is often used to describe the position of the Sun ("The sun reached its zenit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surface is made up of the ocean, dwarfing Earth's polar ice, lakes, and rivers. The remaining 29% of Earth's surface is land, consisting of continents and islands. Earth's surface layer is formed of several slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Earth's liquid outer core generates the magnetic field that shapes the magnetosphere of the Earth, deflecting destructive solar winds. The atmosphere of the Earth consists mostly of nitrogen and oxygen. Greenhouse gases in the atmosphere like carbon dioxide (CO2) trap a part of the energy from the Sun close to the surface. Water vapor is widely present in the atmosphere and forms clouds that cover most of the planet. More solar e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Declination Of The Sun
The position of the Sun in the sky is a function of both the time and the geographic location of observation on Earth's surface. As Earth orbits the Sun over the course of a year, the Sun appears to move with respect to the fixed stars on the celestial sphere, along a circular path called the ecliptic. Earth's rotation about its axis causes diurnal motion, so that the Sun appears to move across the sky in a Sun path that depends on the observer's geographic latitude. The time when the Sun transits the observer's meridian depends on the geographic longitude. To find the Sun's position for a given location at a given time, one may therefore proceed in three steps as follows: # calculate the Sun's position in the ecliptic coordinate system, # convert to the equatorial coordinate system, and # convert to the horizontal coordinate system, for the observer's local time and location. This is the coordinate system normally used to calculate the position of the Sun in terms of solar zen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sundial
A sundial is a horological device that tells the time of day (referred to as civil time in modern usage) when direct sunlight shines by the apparent position of the Sun in the sky. In the narrowest sense of the word, it consists of a flat plate (the ''dial'') and a gnomon, which casts a shadow onto the dial. As the Sun appears to move through the sky, the shadow aligns with different hour-lines, which are marked on the dial to indicate the time of day. The ''style'' is the time-telling edge of the gnomon, though a single point or ''nodus'' may be used. The gnomon casts a broad shadow; the shadow of the style shows the time. The gnomon may be a rod, wire, or elaborately decorated metal casting. The style must be parallel to the axis of the Earth's rotation for the sundial to be accurate throughout the year. The style's angle from horizontal is equal to the sundial's geographical latitude. The term ''sundial'' can refer to any device that uses the Sun's altitude or azimut ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lahaina Noon
Lāhainā Noon is a semi-annual tropical solar phenomenon when the Sun culminates at the zenith at solar noon, passing directly overhead (above the subsolar point). The term ''Lāhainā Noon'' was coined by the Bishop Museum in Hawai'i. Details The subsolar point travels through the tropics. Hawaii is the only US state in the tropics and thus the only one to experience Lāhainā Noon. In 2022, the phenomenon occurred in Honolulu on May 26 and July 16. Hawaii and other locations between the Tropic of Cancer and Tropic of Capricorn receive the sun's direct rays as the apparent path of the sun passes overhead before and after the summer solstice. The Lāhainā Noon can occur anywhere from 12:16 to 12:43 p.m. Hawaii–Aleutian Standard Time. At that moment objects that stand straight up (flagpoles, bollards, telephone poles, etc.) cast no outward shadow. The most southerly points in Hawaii experience Lāhainā Noon on earlier and later dates than the northern parts. For e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Qibla Observation By Shadows
Twice every year, the Sun culmination, culminates at the zenith of the ''Kaaba'' in Mecca, the Holiest sites in Islam, holiest site in Islam, at local solar noon, allowing the qibla (the direction towards the ''Kaaba'') to be ascertained in other parts of the world by observing the shadows cast by vertical objects. This phenomenon occurs at 12:18 Saudi Arabia Standard Time (SAST; 09:18 UTC) on 27 or 28 May (depending on the year), and at 12:27 SAST (09:27 UTC) on 15 or 16 July (depending on the year). At these times, the sun appears in the direction of Mecca, and shadows cast by vertical objects determine the qibla. At two other moments in the year, the sun passes through the nadir (the Antipodal point, antipodal zenith) of the ''Kaaba'', casting shadows that point in the opposite direction, and thus also determine the qibla. These occur on 12, 13, or 14 January at 00:30 SAST (21:30 UTC on the preceding day), and 28 or 29 November at 00:09 SAST (21:09 UTC on the preceding day). The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
.svg "Click for more on -> Earth")
%2C_Phang_Nga_Bay%2C_Thailand.jpg "Click for more on -> Declination Of The Sun")
.jpg "Click for more on -> Lahaina Noon")
