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Full Moon
The full moon is the lunar phase when the Moon appears fully illuminated from Earth's perspective. This occurs when Earth is located between the Sun and the Moon (when the ecliptic longitudes of the Sun and Moon differ by 180°). This means that the lunar hemisphere facing Earth—the near side—is completely sunlit and appears as an approximately circular disk. The full moon occurs roughly once a month. The time interval between a full moon and the next repetition of the same phase, a synodic month, averages about 29.53 days. Therefore, in those lunar calendars in which each month begins on the day of the new moon, the full moon falls on either the 14th or 15th day of the lunar month. Because a calendar month consists of a whole number of days, a month in a lunar calendar may be either 29 or 30 days long. Characteristics A full moon is often thought of as an event of a full night's duration, although its phase seen from Earth continuously waxes or wanes, and is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Supermoon Nov-14-2016-minneapolis
A supermoon is a full moon or a new moon that nearly coincides with perigee—the closest that the Moon comes to the Earth in its elliptic orbit—resulting in a slightly larger-than-usual apparent size of the lunar disk as viewed from Earth. The technical name is a perigee syzygy (of the Earth–Moon–Sun system) or a full (or new) Moon around perigee. Because the term ''supermoon'' is astrological in origin, it has no precise astronomical definition. The real association of the Moon with both oceanic and crustal tides has led to claims that the supermoon phenomenon may be associated with increased risk of events like earthquakes and volcanic eruptions, but no such link has been found. The opposite phenomenon, an apogee syzygy or a full (or new) Moon around apogee, has been called a micromoon. Definitions The term ''supermoon'' is attributed to astrologer Richard Nolle ''while reading "Strategic Role Of Perigean spring tides in Nautical History and Coastal flooding"'' pu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Calendar
A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A date is the designation of a single and specific day within such a system. A calendar is also a physical record (often paper) of such a system. A calendar can also mean a list of planned events, such as a court calendar or a partly or fully chronological list of documents, such as a calendar of wills. Periods in a calendar (such as years and months) are usually, though not necessarily, synchronized with the cycle of the sun or the moon. The most common type of pre-modern calendar was the lunisolar calendar, a lunar calendar that occasionally adds one intercalary month to remain synchronized with the solar year over the long term. Etymology The term ''calendar'' is taken from , the term for the first day of the month in the Roman calendar, related to the verb 'to call out', referring to the "calling" of the new moon when it was fir ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rayleigh Scattering
Rayleigh scattering ( ), named after the 19th-century British physicist Lord Rayleigh (John William Strutt), is the predominantly elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation. For light frequencies well below the resonance frequency of the scattering particle (normal dispersion regime), the amount of scattering is inversely proportional to the fourth power of the wavelength. Rayleigh scattering results from the electric polarizability of the particles. The oscillating electric field of a light wave acts on the charges within a particle, causing them to move at the same frequency. The particle, therefore, becomes a small radiating dipole whose radiation we see as scattered light. The particles may be individual atoms or molecules; it can occur when light travels through transparent solids and liquids, but is most prominently seen in gases. Rayleigh scattering of sunlight in Earth's atmospher ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earth's Shadow
Earth's shadow (or Earth shadow) is the shadow that Earth itself casts through its atmosphere and into outer space, toward the antisolar point. During the twilight period (both early dusk and late dawn), the shadow's visible fringe – sometimes called the dark segment or twilight wedge – appears as a dark and diffuse band just above the horizon, most distinct when the sky is clear. Since Earth's diameter is 3.7 times the Moon's, the length of the planet's umbra is correspondingly 3.7 times that of the lunar umbra: roughly . Appearance Earth's shadow cast onto the atmosphere can be viewed during the "civil" stage of twilight, assuming the sky is clear and the horizon is relatively unobstructed. The shadow's fringe appears as a dark bluish to purplish band that stretches over 180° of the horizon opposite the Sun, i.e. in the eastern sky at dusk and in the western sky at dawn. Before sunrise, Earth's shadow appears to recede as the Sun rises; after sunset, the shad ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Full Moon Cycle
A supermoon is a full moon or a new moon that nearly coincides with perigee—the closest that the Moon comes to the Earth in its elliptic orbit—resulting in a slightly larger-than-usual apparent size of the lunar disk as viewed from Earth. The technical name is a perigee syzygy (of the Earth–Moon–Sun system) or a full (or new) Moon around perigee. Because the term ''supermoon'' is astrological in origin, it has no precise astronomical definition. The real association of the Moon with both oceanic and crustal tides has led to claims that the supermoon phenomenon may be associated with increased risk of events like earthquakes and volcanic eruptions, but no such link has been found. The opposite phenomenon, an apogee syzygy or a full (or new) Moon around apogee, has been called a micromoon. Definitions The term ''supermoon'' is attributed to astrologer Richard Nolle ''while reading "Strategic Role Of Perigean spring tides in Nautical History and Coastal flooding"'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Synodic Month
In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. Variations In Shona, Middle Eastern, and European traditions, the month starts when the young crescent moon first becomes visible, at evening, after conjunction with the Sun one or two days before that evening (e.g., in the Islamic calendar). In ancient Egypt, the lunar month began on the day when the waning moon could no longer be seen just before sunrise. Others run from full moon to full moon. Yet others use calculation, of varying degrees of sophistication, for example, the Hebrew calendar or the ecclesiastical lunar calendar. Calendars count integer days, so months may be 29 or 30 days in length, in some regular or irregular sequence. Lunar cycles are prominent, and calculated with great precision, in the ancient Hindu Panchangam calendar, widely used in the Indian subco ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
New Moon
In astronomy, the new moon is the first lunar phase, when the Moon and Sun have the same ecliptic longitude. At this phase, the lunar disk is not visible to the naked eye, except when it is silhouetted against the Sun during a solar eclipse. The original meaning of the term 'new moon', which is still sometimes used in calendrical, non-astronomical contexts, is the first visible crescent of the Moon after conjunction with the Sun. This thin waxing crescent is briefly and faintly visible as the Moon gets lower in the western sky after sunset. The precise time and even the date of the appearance of the new moon by this definition will be influenced by the geographical location of the observer. The first crescent marks the beginning of the month in the Islamic calendar and in some lunisolar calendars such as the Hebrew calendar. In the Chinese calendar, the beginning of the month is marked by the last visible crescent of a waning Moon. The astronomical new moon occur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Universal Time
Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with respect to the International Celestial Reference Frame (ICRF), called the Earth Rotation Angle (ERA, which serves as a modern replacement for Greenwich Mean Sidereal Time). UT1 is the same everywhere on Earth. UT1 is required to follow the relationship :ERA = 2π(0.7790572732640 + 1.00273781191135448'' · Tu'') radians where ''Tu'' = ( Julian UT1 date - 2451545.0). History Prior to the introduction of standard time, each municipality throughout the clock-using world set its official clock, if it had one, according to the local position of the Sun (see solar time). This served adequately until the introduction of rail travel in Britain, which made it possible to travel fast enough over long distances to require contin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ephemeris
In astronomy and celestial navigation, an ephemeris (pl. ephemerides; ) is a book with tables that gives the trajectory of naturally occurring astronomical objects as well as artificial satellites in the sky, i.e., the position (and possibly velocity) over time. Historically, positions were given as printed tables of values, given at regular intervals of date and time. The calculation of these tables was one of the first applications of mechanical computers. Modern ephemerides are often provided in electronic form. However, printed ephemerides are still produced, as they are useful when computational devices are not available. The astronomical position calculated from an ephemeris is often given in the spherical polar coordinate system of right ascension and declination, together with the distance from the origin if applicable. Some of the astronomical phenomena of interest to astronomers are eclipses, apparent retrograde motion/planetary stations, planetary es, sidereal t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Terrestrial Time
Terrestrial Time (TT) is a modern astronomical time standard defined by the International Astronomical Union, primarily for time-measurements of astronomical observations made from the surface of Earth. For example, the Astronomical Almanac uses TT for its tables of positions ( ephemerides) of the Sun, Moon and planets as seen from Earth. In this role, TT continues Terrestrial Dynamical Time (TDT or TD),TT is equivalent to TDT, see IAU conference 1991, Resolution A4, recommendation IV, note 4. which succeeded ephemeris time (ET). TT shares the original purpose for which ET was designed, to be free of the irregularities in the rotation of Earth. The unit of TT is the SI second, the definition of which is based currently on the caesium atomic clock,IAU conference 1991, Resolution A4, recommendation IV, part 2 states that the unit for TT is to agree with the SI second 'on the geoid'. but TT is not itself defined by atomic clocks. It is a theoretical ideal, and real clocks can onl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Skyglow
Skyglow (or sky glow) is the diffuse luminance of the night sky, apart from discrete light sources such as the Moon and visible individual stars. It is a commonly noticed aspect of light pollution. While usually referring to luminance arising from artificial lighting, skyglow may also involve any scattered light seen at night, including natural ones like starlight, zodiacal light, and airglow. In the context of light pollution, skyglow arises from the use of artificial light sources, including electrical (or rarely gas) lighting used for illumination and advertisement and from gas flares. Light propagating into the atmosphere directly from upward-directed or incompletely shielded sources, or after reflection from the ground or other surfaces, is partially scattered back toward the ground, producing a diffuse glow that is visible from great distances. Skyglow from artificial lights is most often noticed as a glowing dome of light over cities and towns, yet is pervasive through ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Opposition Surge
The opposition surge (sometimes known as the opposition effect, opposition spike or Seeliger effect) is the brightening of a rough surface, or an object with many particles, when illuminated from directly behind the observer. The term is most widely used in astronomy, where generally it refers to the sudden noticeable increase in the brightness of a celestial body such as a planet, moon, or comet as its phase angle of observation approaches zero. It is so named because the reflected light from the Moon and Mars appear significantly brighter than predicted by simple Lambertian reflectance when at astronomical opposition. Two physical mechanisms have been proposed for this observational phenomenon: shadow hiding and coherent backscatter. Overview The phase angle is defined as the angle between the observer, the observed object and the source of light. In the case of the Solar System, the light source is the Sun, and the observer is generally on Earth. At zero phase angle, t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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