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Liquid Mirror Telescopes
Liquid-mirror telescopes are telescopes with mirrors made with a reflective liquid. The most common liquid used is mercury, but other liquids will work as well (for example, low-melting alloys of gallium). The liquid and its container are rotated at a constant speed around a vertical axis, which causes the surface of the liquid to assume a paraboloidal shape. This parabolic reflector can serve as the primary mirror of a reflecting telescope. The rotating liquid assumes the same surface shape regardless of the container's shape; to reduce the amount of liquid metal needed, and thus weight, a rotating mercury mirror uses a container that is as close to the necessary parabolic shape as possible. Liquid mirrors can be a low-cost alternative to conventional large telescopes. Compared to a solid glass mirror that must be cast, ground, and polished, a rotating liquid-metal mirror is much less expensive to manufacture. Isaac Newton noted that the free surface of a rotating liquid forms ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Liquid Mirror Telescope
Liquid-mirror telescopes are telescopes with mirrors made with a reflective liquid. The most common liquid used is mercury, but other liquids will work as well (for example, low-melting alloys of gallium). The liquid and its container are rotated at a constant speed around a vertical axis, which causes the surface of the liquid to assume a paraboloidal shape. This parabolic reflector can serve as the primary mirror of a reflecting telescope. The rotating liquid assumes the same surface shape regardless of the container's shape; to reduce the amount of liquid metal needed, and thus weight, a rotating mercury mirror uses a container that is as close to the necessary parabolic shape as possible. Liquid mirrors can be a low-cost alternative to conventional large telescopes. Compared to a solid glass mirror that must be cast, ground, and polished, a rotating liquid-metal mirror is much less expensive to manufacture. Isaac Newton noted that the free surface of a rotating liquid forms ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inertial Space
In classical physics and special relativity, an inertial frame of reference (also called inertial reference frame, inertial frame, inertial space, or Galilean reference frame) is a frame of reference that is not undergoing any acceleration. It is a frame in which an isolated physical object — an object with zero net force acting on it — is perceived to move with a constant velocity (it might be a zero velocity) or, equivalently, it is a frame of reference in which Newton's first law of motion holds. All inertial frames are in a state of constant, rectilinear motion with respect to one another; in other words, an accelerometer moving with any of them would detect zero acceleration. It has been observed that celestial objects which are far away from other objects and which are in uniform motion with respect to the cosmic microwave background radiation maintain such uniform motion. Measurements in one inertial frame can be converted to measurements in another by a simple ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weight
In science and engineering, the weight of an object is the force acting on the object due to gravity. Some standard textbooks define weight as a vector quantity, the gravitational force acting on the object. Others define weight as a scalar quantity, the magnitude of the gravitational force. Yet others define it as the magnitude of the reaction force exerted on a body by mechanisms that counteract the effects of gravity: the weight is the quantity that is measured by, for example, a spring scale. Thus, in a state of free fall, the weight would be zero. In this sense of weight, terrestrial objects can be weightless: ignoring air resistance, the famous apple falling from the tree, on its way to meet the ground near Isaac Newton, would be weightless. The unit of measurement for weight is that of force, which in the International System of Units (SI) is the newton. For example, an object with a mass of one kilogram has a weight of about 9.8 newtons on the surface of the Earth, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Infinitesimal
In mathematics, an infinitesimal number is a quantity that is closer to zero than any standard real number, but that is not zero. The word ''infinitesimal'' comes from a 17th-century Modern Latin coinage ''infinitesimus'', which originally referred to the " infinity- th" item in a sequence. Infinitesimals do not exist in the standard real number system, but they do exist in other number systems, such as the surreal number system and the hyperreal number system, which can be thought of as the real numbers augmented with both infinitesimal and infinite quantities; the augmentations are the reciprocals of one another. Infinitesimal numbers were introduced in the development of calculus, in which the derivative was first conceived as a ratio of two infinitesimal quantities. This definition was not rigorously formalized. As calculus developed further, infinitesimals were replaced by limits, which can be calculated using the standard real numbers. Infinitesimals regained pop ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gravity Of Earth
The gravity of Earth, denoted by , is the net acceleration that is imparted to objects due to the combined effect of gravitation (from mass distribution within Earth) and the centrifugal force (from the Earth's rotation). It is a vector quantity, whose direction coincides with a plumb bob and strength or magnitude is given by the norm g=\, \mathit\, . In SI units this acceleration is expressed in metres per second squared (in symbols, m/ s2 or m·s−2) or equivalently in newtons per kilogram (N/kg or N·kg−1). Near Earth's surface, the gravity acceleration is approximately , which means that, ignoring the effects of air resistance, the speed of an object falling freely will increase by about per second every second. This quantity is sometimes referred to informally as ''little '' (in contrast, the gravitational constant is referred to as ''big ''). The precise strength of Earth's gravity varies depending on location. The nominal "average" value at Earth's surface ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parabola Shape In Rotating Layers Of Fluid
In mathematics, a parabola is a plane curve which is mirror-symmetrical and is approximately U-shaped. It fits several superficially different mathematical descriptions, which can all be proved to define exactly the same curves. One description of a parabola involves a point (the focus) and a line (the directrix). The focus does not lie on the directrix. The parabola is the locus of points in that plane that are equidistant from both the directrix and the focus. Another description of a parabola is as a conic section, created from the intersection of a right circular conical surface and a plane parallel to another plane that is tangential to the conical surface. The line perpendicular to the directrix and passing through the focus (that is, the line that splits the parabola through the middle) is called the "axis of symmetry". The point where the parabola intersects its axis of symmetry is called the "vertex" and is the point where the parabola is most sharply curved. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Revolutions Per Minute
Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionless unit equal to 1, which it refers to as a revolution, but does not define the revolution as a unit. It defines a unit of rotational frequency equal to s−1. The superseded standard ISO 80000-3:2006 did however state with reference to the unit name 'one', symbol '1', that "The special name revolution, symbol r, for this unit is widely used in specifications on rotating machines." The International System of Units (SI) does not recognize rpm as a unit, and defines the unit of frequency, Hz, as equal to s−1. :\begin 1~&\text &&=& 60~&\text \\ \frac~&\text &&=& 1~&\text \end A corresponding but distinct quantity for describing rotation is angular velocity, for which the SI unit is the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Large Zenith Telescope
The Large Zenith Telescope (LZT) was a 6.0-meter diameter liquid-mirror telescope located in the University of British Columbia's Malcolm Knapp Research Forest, about east from Vancouver, British Columbia, Canada (north from Maple Ridge). It was one of the largest optical telescopes in the world, but still quite inexpensive. The telescope was completed in the spring of 2003 and decommissioned in 2016. Design While a zenith telescope has the disadvantage of not being able to look anywhere but at a small spot straight up, its simplified setup permits the use of a mirror consisting of a smoothly spinning pan filled with liquid mercury. Such a mirror can be made much larger than a conventional mirror, greatly increasing light collecting ability. The LZT is used for ''transit imaging'', meaning that Earth's rotation moves stars along the sensor, and the latent image in the sensor is moved electronically in step with this movement, so that it is read out at the trailing edge. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
South Pole Telescope
The South Pole Telescope (SPT) is a diameter telescope located at the Amundsen–Scott South Pole Station, Antarctica. The telescope is designed for observations in the microwave, millimeter-wave, and submillimeter-wave regions of the electromagnetic spectrum, with the particular design goal of measuring the faint, diffuse emission from the cosmic microwave background (CMB). The first major survey with the SPT—designed to find distant, massive, clusters of galaxies through their interaction with the CMB, with the goal of constraining the dark energy equation of state—was completed in October 2011. In early 2012, a new camera (SPTpol) was installed on the SPT with even greater sensitivity and the capability to measure the polarization of incoming light. This camera operated from 2012–2016 and was used to make unprecedentedly deep high-resolution maps of hundreds of square degrees of the Southern sky. In 2017, the third-generation camera SPT-3G was installed on the tele ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extreme Points Of Earth
This article lists extreme locations on Earth that hold geographical records or are otherwise known for their geophysical or meteorological superlatives. All of these locations are Earth-wide extremes; extremes of individual continents or countries are not listed. Latitude and longitude Northernmost * The northernmost point on Earth is the Geographic North Pole, in the Arctic Ocean. ** The northernmost point of land is the northern tip of Kaffeklubben Island, north of Greenland (), which lies slightly north of Cape Morris Jesup, Greenland (). Various shifting gravel bars lie farther north, the most famous being Oodaaq. There have been other islands more northern such as 83-42 and ATOW1996 but they have not been confirmed as permanent. Southernmost * The southernmost point on Earth and the southernmost point on land is the Geographic South Pole, which is on the continent of Antarctica. ** The southernmost continental point of land outside Antarctica is in South Americ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
South Pole
The South Pole, also known as the Geographic South Pole, Terrestrial South Pole or 90th Parallel South, is one of the two points where Earth's axis of rotation intersects its surface. It is the southernmost point on Earth and lies antipodally on the opposite side of Earth from the North Pole, at a distance of 12,430 miles (20,004 km) in all directions. Situated on the continent of Antarctica, it is the site of the United States Amundsen–Scott South Pole Station, which was established in 1956 and has been permanently staffed since that year. The Geographic South Pole is distinct from the South Magnetic Pole, the position of which is defined based on Earth's magnetic field. The South Pole is at the centre of the Southern Hemisphere. Geography For most purposes, the Geographic South Pole is defined as the southern point of the two points where Earth's axis of rotation intersects its surface (the other being the Geographic North Pole). However, Earth's axis of rot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
