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Astronomical Imaging
Astrophotography, also known as astronomical imaging, is the photography or imaging of astronomical objects, celestial events, or areas of the night sky. The first photograph of an astronomical object (the Moon) was taken in 1840, but it was not until the late 19th century that advances in technology allowed for detailed stellar photography. Besides being able to record the details of extended objects such as the Moon, Sun, and planets, modern astrophotography has the ability to image objects invisible to the human eye such as dim stars, nebulae, and galaxies. This is done by long time exposure since both film and digital cameras can accumulate and sum photons over these long periods of time. Photography using extended exposure-times revolutionized the field of professional astronomical research, recording hundreds of thousands of new stars, and nebulae invisible to the human eye. Specialized and ever-larger optical telescopes were constructed as essentially big cameras to rec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orion Belt
Orion's Belt or the Belt of Orion, also known as the Three Kings or Three Sisters, is an asterism in the constellation Orion. It consists of the three bright stars Alnitak, Alnilam and Mintaka. Looking for Orion's Belt is the easiest way to locate Orion in the night sky. The stars are more or less evenly spaced in a nearly straight line, and so can be visualized as the belt of the eponymous hunter's clothing. They are best viewed in the early night sky during the Northern Winter/Southern Summer, in particular, the month of January at around 9:00 pm. Component stars The names of the three stars come from Arabic. () means " string of pearls" or is related to the word ("sapphire"); spelling variants include and , with all three evidently being mistakes in transliteration or copy errors. Alnitak Alnitak (ζ Orionis) is a triple star system at the eastern end of Orion's belt and is 1,260 light-years from the Earth. Alnitak B is a 4th-magnitude B-type star which orbits Al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
P48 1994 Jean Large standard
{{Letter-number combination disambiguation ...
P48 or P.48 may refer to: Aircraft * Douglas XP-48, a cancelled American fighter aircraft * Partenavia P.48 Astore, an Italian prototype light aircraft * Percival P.48 Merganser, a British civil utility aircraft Other uses * BMW P48 Turbo engine, an automobile engine * BRM P48, a Formula One racing car * , a P-class sloop of the Royal Navy * , a submarine of the Royal Navy * Papyrus 48 or P48, an early copy of a part of the New Testament in Greek * Pleasant Valley Airport, in Maricopa County, Arizona, United States * PTF1A, pancreas transcription factor 1 subunit alpha * P48, a Latvian state regional road * P48, a phantom power Phantom power, in the context of professional audio equipment, is DC electric power transmitted through microphone cables to operate microphones that contain active electronic circuitry. It is best known as a convenient power source for con ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astrometry
Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. History The history of astrometry is linked to the history of star catalogues, which gave astronomers reference points for objects in the sky so they could track their movements. This can be dated back to Hipparchus, who around 190 BC used the catalogue of his predecessors Timocharis and Aristillus to discover Earth's precession. In doing so, he also developed the brightness scale still in use today. Hipparchus compiled a catalogue with at least 850 stars and their positions. Hipparchus's successor, Ptolemy, included a catalogue of 1,022 stars in his work the '' Almagest'', giving their location, coordinates, and brightness. In the 10th century, Abd al-Rahman al-Sufi carried out observations on the stars and described their positions, ma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Star Cartography
Celestial cartography, uranography, astrography or star cartography is the aspect of astronomy and branch of cartography concerned with mapping stars, galaxies, and other astronomical objects on the celestial sphere. Measuring the position and light of charted objects requires a variety of instruments and techniques. These techniques have developed from angle measurements with quadrants and the unaided eye, through sextants combined with lenses for light magnification, up to current methods which include computer-automated space telescopes. Uranographers have historically produced planetary position tables, star tables, and star maps for use by both amateur and professional astronomers. More recently, computerized star maps have been compiled, and automated positioning of telescopes uses databases of stars and of other astronomical objects. Etymology The word "uranography" derived from the Greek "ουρανογραφια" (Koine Greek ''ουρανος'' "sky, heave ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cross Hair
A reticle, or reticule also known as a graticule, is a pattern of fine lines or markings built into the eyepiece of an optical device such as a telescopic sight, spotting scope, theodolite, optical microscope or the screen of an oscilloscope, to provide measurement references during visual inspections. Today, engraved lines or embedded fibers may be replaced by a digital image superimposed on a screen or eyepiece. Both terms may be used to describe any set of patterns used for aiding visual measurements and calibrations, but in modern use ''reticle'' is most commonly used for weapon sights, while ''graticule'' is more widely used for non-weapon measuring instruments such as oscilloscope display, astronomic telescopes, microscopes and slides, surveying instruments and other similar devices. There are many variations of reticle pattern; this article concerns itself mainly with the most rudimentary reticle: the crosshair. Crosshairs are typically represented as a pair of perpe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beam Splitter
A beam splitter or ''beamsplitter'' is an optical device that splits a beam of light into a transmitted and a reflected beam. It is a crucial part of many optical experimental and measurement systems, such as interferometers, also finding widespread application in fibre optic telecommunications. Beam-splitter designs In its most common form, a cube, a beam splitter is made from two triangular glass prisms which are glued together at their base using polyester, epoxy, or urethane-based adhesives. (Before these synthetic resins, natural ones were used, e.g. Canada balsam.) The thickness of the resin layer is adjusted such that (for a certain wavelength) half of the light incident through one "port" (i.e., face of the cube) is reflected and the other half is transmitted due to FTIR (Frustrated Total Internal Reflection). Polarizing beam splitters, such as the Wollaston prism, use birefringent materials to split light into two beams of orthogonal polarization states. Anoth ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit. If sufficiently bright, a comet may be seen from Earth without the aid of a telescope and may subtend an arc of 30° (60 Moons) across the sky. Comets have been observed and recorded since ancient times by many cultures and religions. Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several mill ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Guide Star
In astronomy, a guide star is a reference star used to accurately maintain the tracking by a telescope of a celestial body, whose apparent motion through the sky is primarily due to Earth's rotation. Accurate telescope pointing and tracking is critical for obtaining good astronomical images and astrophotographs. However, because Earth rotates, the sky appears to be in a constant state of motion relative to Earth. Although this movement appears to be relatively slow when viewed with the naked eye, with the high magnification and consequently smaller field of view provided by even a small telescope, this motion becomes apparent on timescales of the order of seconds. Though space telescopes are not mounted on a spinning planet, they still use guide stars including those listed in the HST Guide Star Catalog. Computer-controlled electric motors are commonly employed to allow the telescope to move in sync with the apparent motion of the sky, according to a pre-computed pointing mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telescope Mount
A telescope mount is a mechanical structure which supports a telescope. Telescope mounts are designed to support the mass of the telescope and allow for accurate pointing of the instrument. Many sorts of mounts have been developed over the years, with the majority of effort being put into systems that can track the motion of the fixed stars as the Earth rotates. Fixed mounts Fixed telescope mounts are entirely fixed in one position, such as Zenith telescopes that point only straight up and the National Radio Astronomy Observatory's Green Bank fixed radio 'horn' built to observe Cassiopeia A. Fixed altitude mounts Fixed-altitude mounts usually have the primary optics fixed at an altitude angle while rotating horizontally (in azimuth). They can cover the whole sky but only observe objects for the short time when that object passes a specific altitude and azimuth. Transit mounts Transit mounts are single axis mounts fixed in azimuth while rotating in altitude, usually orient ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Altazimuth Mount
An altazimuth mount or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two perpendicular axes – one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth (compass bearing) of the pointing direction of the instrument. Rotation about the horizontal axis varies the altitude angle (angle of elevation) of the pointing direction. These mounts are used, for example, with telescopes, cameras, radio antennas, heliostat mirrors, solar panels, and guns and similar weapons. Several names are given to this kind of mount, including altitude-azimuth, azimuth-elevation and various abbreviations thereof. A gun turret is essentially an alt-azimuth mount for a gun, and a standard camera tripod is an alt-azimuth mount as well. Astronomical telescope altazimuth mounts When used as an astronomical telescope mount, the biggest advantage of an alt-azimuth mount is the simplicity of its mechanical design. The primary disadv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equatorial Mount
An equatorial mount is a mount for instruments that compensates for Earth's rotation by having one rotational axis, the polar axis, parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras. The advantage of an equatorial mount lies in its ability to allow the instrument attached to it to stay fixed on any celestial object with diurnal motion by driving one axis at a constant speed. Such an arrangement is called a sidereal or clock drive. Equatorial mounts achieve this by aligning their rotational axis with the Earth, a process known as polar alignment. Astronomical telescope mounts In astronomical telescope mounts, the equatorial axis (the '' right ascension'') is paired with a second perpendicular axis of motion (known as the '' declination''). The equatorial axis of the mount is often equipped with a motorized "''clock drive''", that rotates that axis one revolution every 23 hours and 56 minutes in exact sync with the appar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diurnal Motion
Diurnal motion (, ) is an astronomical term referring to the apparent motion of celestial objects (e.g. the Sun and stars) around Earth, or more precisely around the two celestial poles, over the course of one day. It is caused by Earth's rotation around its axis, so almost every star appears to follow a circular arc path, called the diurnal circle, often depicted in star trail photography. The time for one complete rotation is 23 hours, 56 minutes, and 4.09 seconds – one sidereal day. The first experimental demonstration of this motion was conducted by Léon Foucault. Because Earth orbits the Sun once a year, the sidereal time at any given place and time will gain about four minutes against local civil time, every 24 hours, until, after a year has passed, one additional sidereal "day" has elapsed compared to the number of solar days that have gone by. Relative direction The relative direction of diurnal motion in the Northern Celestial Hemisphere are as follows: * Facing nort ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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