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Belogradchik Observatory
The Astronomical Observatory of Belogradchik or Belogradchik Observatory is an astronomical observatory owned and operated by the Institute of Astronomy of the Bulgarian Academy of Sciences. It is located near the town of Belogradchik in northwestern Bulgaria, at the foot of the Western Balkan Mountains. The other observatory operated by the same institute is the Rozhen Observatory. History Built in 1961 by a group of astronomy enthusiasts led by high school physics teacher and later chief assistant professor in Sofia University Hristo Kostov (1932-1982), Belogradchik Observatory became the first school observatory in Bulgaria. Official opening ceremony was held on 21.06.1965, by its first director Dr. Alexander Tomov (1930-2009), and was attended by much of Bulgarian leading astronomers - Acad. Nikola Bonev (1898-1979), Prof. Malina Popova (1922-2011), Prof. Tsvetan Bonchev, Assoc. Prof. Bogomil Kovachev, and already Chief Assist. Prof. Hristo Kostov. From 1964 till 1974 it was ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Institute Of Astronomy Of The Bulgarian Academy Of Sciences
The Institute of Astronomy of the Bulgarian Academy of Sciences is a leading Bulgarian research facility in the field of astronomy and astrophysics, located in Sofia, Bulgaria. The institute co-operates closely with the other two institutions involved in the same field of research in the country - the Department of Astronomy at the Faculty of Physics of Sofia University and the Astronomical centre at the Faculty of Natural Sciences of Shumen University. It owns and operates the Bulgarian National Rozhen Observatory located at an altitude of 1750 m in the Rhodopi mountains in south Bulgaria, as well as the Belogradchik Observatory situated at 650 m at the foot of the Western Balkan Mountains in north-west Bulgaria. The institute was inaugurated in 1958 as an independent section of the larger Institute of Physics of the Bulgarian Academy of Sciences The Bulgarian Academy of Sciences (abbreviated BAS; bg, Българска академия на науките, ''Balgars ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cassegrain Reflector
The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas, the main characteristic being that the optical path folds back onto itself, relative to the optical system's primary mirror entrance aperture. This design puts the focal point at a convenient location behind the primary mirror and the convex secondary adds a telephoto effect creating a much longer focal length in a mechanically short system. In a symmetrical Cassegrain both mirrors are aligned about the optical axis, and the primary mirror usually contains a hole in the center, thus permitting the light to reach an eyepiece, a camera, or an image sensor. Alternatively, as in many radio telescopes, the final focus may be in front of the primary. In an asymmetrical Cassegrain, the mirror(s) may be tilted to avoid obscuration of the primary or to avoid the need for a hole in the primary mirror (or both). The classic Cassegr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Constant Fraction Discriminator
A constant fraction discriminator (CFD) is an electronic signal processing device, designed to mimic the mathematical operation of finding a maximum of a pulse by finding the zero of its slope. Some signals do not have a sharp maximum, but short rise times t_r. Typical input signals for CFDs are pulses from plastic scintillation counters, such as those used for lifetime measurement in positron annihilation experiments. The scintillator pulses have identical rise times that are much longer than the desired temporal resolution. This forbids simple threshold triggering, which causes a dependence of the trigger time on the signal's peak height, an effect called ''time walk'' (see diagram). Identical rise times and peak shapes permit triggering not on a fixed threshold but on a ''constant fraction'' of the total peak height, yielding trigger times independent from peak heights. From another point of view A time-to-digital converter assigns timestamps. The time-to-digital converte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Preamplifier
A preamplifier, also known as a preamp, is an electronic amplifier that converts a weak electrical signal into an output signal strong enough to be noise-tolerant and strong enough for further processing, or for sending to a power amplifier and a loudspeaker. Without this, the final signal would be noisy or distorted. They are typically used to amplify signals from analog sensors such as microphones and pickups. Because of this, the preamplifier is often placed close to the sensor to reduce the effects of noise and interference. Description An ideal preamp will be linear (have a constant gain through its operating range), have high input impedance (requiring only a minimal amount of current to sense the input signal) and a low output impedance (when current is drawn from the output there is minimal change in the output voltage). It is used to boost the signal strength to drive the cable to the main instrument without significantly degrading the signal-to-noise ratio (SNR) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photomultiplier
A photomultiplier is a device that converts incident photons into an electrical signal. Kinds of photomultiplier include: * Photomultiplier tube, a vacuum tube converting incident photons into an electric signal. Photomultiplier tubes (PMTs for short) are members of the class of vacuum tubes, and more specifically vacuum phototubes, which are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum. ** Magnetic photomultiplier, developed by the Soviets in the 1930s. ** Electrostatic photomultiplier, a kind of photomultiplier tube demonstrated by Jan Rajchman of RCA Laboratories in Princeton, NJ in the late 1930s which became the standard for all future commercial photomultipliers. The first mass-produced photomultiplier, the Type 931, was of this design and is still commercially produced today. * Silicon photomultiplier, a solid-state device converting incident photons into an electric signal. Silicon photomu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diaphragm (optics)
In optics, a diaphragm is a thin opaque structure with an opening (aperture) at its center. The role of the diaphragm is to ''stop'' the passage of light, except for the light passing through the ''aperture''. Thus it is also called a stop (an aperture stop, if it limits the brightness of light reaching the focal plane, or a field stop or flare stop for other uses of diaphragms in lenses). The diaphragm is placed in the light path of a lens or objective, and the size of the aperture regulates the amount of light that passes through the lens. The centre of the diaphragm's aperture coincides with the optical axis of the lens system. Most modern cameras use a type of adjustable diaphragm known as an iris diaphragm, and often referred to simply as an iris. See the articles on aperture and f-number for the photographic effect and system of quantification of varying the opening in the diaphragm. Iris diaphragms versus other types A natural optical system that has a diaphragm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
UBV Photometric System
The UBV photometric system (from ''Ultraviolet, Blue, Visual''), also called the Johnson system (or Johnson-Morgan system), is a photometric system usually employed for classifying stars according to their colors. It was the first standardized photometric system. The apparent magnitudes of stars in the system are often used to determine the color indices B-V and U-B, the difference between the B and V magnitudes and the U and B magnitudes respectively. The choice of colors on the blue end of the spectrum was assisted by the bias that photographic film has for those colors. It was introduced in the 1950s by American astronomers Harold Lester Johnson and William Wilson Morgan. A telescope and the telescope at McDonald Observatory were used to define the system. The filters are selected so that the mean wavelengths of response functions (at which magnitudes are measured to mean precision) are 364 nm for U, 442 nm for B, 540 nm for V. Zero points were calibrate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photometer
A photometer is an instrument that measures the strength of electromagnetic radiation in the range from ultraviolet to infrared and including the visible spectrum. Most photometers convert light into an electric current using a photoresistor, photodiode, or photomultiplier. Photometers measure: *Illuminance * Irradiance *Light absorption * Scattering of light * Reflection of light * Fluorescence * Phosphorescence * Luminescence History Before electronic light sensitive elements were developed, photometry was done by estimation by the eye. The relative luminous flux of a source was compared with a standard source. The photometer is placed such that the illuminance from the source being investigated is equal to the standard source, as the human eye can judge equal illuminance. The relative luminous fluxes can then be calculated as the illuminance decreases proportionally to the inverse square of distance. A standard example of such a photometer consists of a piece of paper ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Catadioptric System
A catadioptric optical system is one where refraction and reflection are combined in an optical system, usually via lenses ( dioptrics) and curved mirrors ( catoptrics). Catadioptric combinations are used in focusing systems such as searchlights, headlamps, early lighthouse focusing systems, optical telescopes, microscopes, and telephoto lenses. Other optical systems that use lenses and mirrors are also referred to as "catadioptric", such as surveillance catadioptric sensors. Early catadioptric systems Catadioptric combinations have been used for many early optical systems. In the 1820s, Augustin-Jean Fresnel developed several catadioptric lighthouse reflectors. Léon Foucault developed a catadioptric microscope in 1859 to counteract aberrations of using a lens to image objects at high power. In 1876 a French engineer, A. Mangin, invented what has come to be called the Mangin mirror, a concave glass reflector with the silver surface on the rear side of the glass. The two ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bulgarian Lev
The lev ( bg, лев, plural: / , ; ISO 4217 code: BGN; numeric code: 975) is the currency of Bulgaria. In old Bulgarian the word "lev" meant "lion", the word 'lion' in the modern language is ''lаv'' (; in Bulgarian: ). The lev is divided in 100 ''stotinki'' (, singular: , ). Stotinka in Bulgarian means "a hundredth" and in fact is a translation of the French term "centime". Grammatically the word "stotinka" comes from the word "sto" (сто) - a hundred. Since 1997, the lev has been in a currency board arrangement with initially the Deutsche Mark at a fixed rate of BGL 1000 to DEM 1. After the introduction of the euro and the redenomination of the lev in 1999, this has resulted in a fixed rate to the euro of BGN 1.95583 : EUR 1. Since 2020, the lev has been a part of the European Exchange Rate Mechanism (ERM II). The lev is scheduled to be supplanted by the euro on 1 January 2024. Etymology The currency's name comes from the archaic Bulgarian word "lev," which meant "lion ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Balkans
The Balkans ( ), also known as the Balkan Peninsula, is a geographical area in southeastern Europe with various geographical and historical definitions. The region takes its name from the Balkan Mountains that stretch throughout the whole of Bulgaria. The Balkan Peninsula is bordered by the Adriatic Sea in the northwest, the Ionian Sea in the southwest, the Aegean Sea in the south, the Turkish Straits in the east, and the Black Sea in the northeast. The northern border of the peninsula is variously defined. The highest point of the Balkans is Mount Musala, , in the Rila mountain range, Bulgaria. The concept of the Balkan Peninsula was created by the German geographer August Zeune in 1808, who mistakenly considered the Balkan Mountains the dominant mountain system of Southeast Europe spanning from the Adriatic Sea to the Black Sea. The term ''Balkan Peninsula'' was a synonym for Rumelia in the 19th century, the European provinces of the Ottoman Empire. It had a ge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
