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Circumference
In geometry, the circumference (from Latin circumferens, meaning "carrying around") is the perimeter of a circle or ellipse.^{[1]} That is, the circumference would be the arc length of the circle, as if it were opened up and straightened out to a line segment.^{[2]} More generally, the perimeter is the curve length around any closed figure. Circumference may also refer to the circle itself, that is, the locus corresponding to the edge of a disk. The circumference of a circle is the distance around it, but if, as in many elementary treatments, distance is defined in terms of straight lines, this cannot be used as a definition [...More Info...] [...Related Items...] 

Radiance
In radiometry, radiance is the radiant flux emitted, reflected, transmitted or received by a given surface, per unit solid angle per unit projected area. Spectral radiance is the radiance of a surface per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength. These are directional quantities. The SI unit of radiance is the watt per steradian per square metre (W·sr^{−1}·m^{−2}), while that of spectral radiance in frequency is the watt per steradian per square metre per hertz (W·sr^{−1}·m^{−2}·Hz^{−1}) and that of spectral radiance in wavelength is the watt per steradian per square metre per metre (W·sr^{−1}·m^{−3})—commonly the watt per steradian per square metre per nanometre (W·sr^{−1}·m^{−2}·nm^{−1}) [...More Info...] [...Related Items...] 

Volume
Volume is the quantity of threedimensional space enclosed by a closed surface, for example, the space that a substance (solid, liquid, gas, or plasma) or shape occupies or contains.^{[1]} Volume is often quantified numerically using the SI derived unit, the cubic metre. The volume of a container is generally understood to be the capacity of the container; i. e., the amount of fluid (gas or liquid) that the container could hold, rather than the amount of space the container itself displaces. Three dimensional mathematical shapes are also assigned volumes. Volumes of some simple shapes, such as regular, straightedged, and circular shapes can be easily calculated using arithmetic formulas. Volumes of complicated shapes can be calculated with integral calculus if a formula exists for the shape's boundary [...More Info...] [...Related Items...] 

Surface Area
The surface area of a solid object is a measure of the total area that the surface of the object occupies.^{[1]} The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of arc length of onedimensional curves, or of the surface area for polyhedra (i.e., objects with flat polygonal faces), for which the surface area is the sum of the areas of its faces. Smooth surfaces, such as a sphere, are assigned surface area using their representation as parametric surfaces. This definition of surface area is based on methods of infinitesimal calculus and involves partial derivatives and double integration.
A general definition of surface area was sought by Henri Lebesgue and Hermann Minkowski at the turn of the twentieth century. Their work led to the development of geometric measure theory, which studies various notions of surface area for irregular objects of any dimension


Galactic Plane
The galactic plane is the plane on which the majority of a diskshaped galaxy's mass lies. The directions perpendicular to the galactic plane point to the galactic poles. In actual usage, the terms galactic plane and galactic poles usually refer specifically to the plane and poles of the Milky Way, in which Planet Earth is located. Some galaxies are irregular and do not have any welldefined disk. Even in the case of a barred spiral galaxy like the Milky Way, defining the galactic plane is slightly imprecise and arbitrary since the stars are not perfectly coplanar. In 1959, the IAU defined the position of the Milky Way's north galactic pole as exactly RA = 12^{h} 49^{m} , Dec = 27° 24′ in the thenused B1950 epoch; in the currentlyused J2000 epoch, after precession is taken into account, its position is RA 12^{h} 51^{m} 26.282^{s}, Dec 27° 07′ 42.01″ [...More Info...] [...Related Items...] 

Radius
In classical geometry, a radius of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the Latin radius, meaning ray but also the spoke of a chariot wheel.^{[1]} The plural of radius can be either radii (from the Latin plural) or the conventional English plural radiuses.^{[2]} The typical abbreviation and mathematical variable name for radius is r. By extension, the diameter d is defined as twice the radius:^{[3]} If an object does not have a center, the term may refer to its circumradius, the radius of its circumscribed circle or circumscribed sphere. In either case, the radius may be more than half the diameter, which is usually defined as the maximum distance between any two points of the figure. The inradius of a geometric figure is usually the radius of the largest circle or sphere contained in it [...More Info...] [...Related Items...] 

Velocity
The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of an object's speed and direction of motion (e.g. 60 km/h to the north). Velocity is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of bodies.
Velocity is a physical vector quantity; both magnitude and direction are needed to define it. The scalar absolute value (magnitude) of velocity is called speed, being a coherent derived unit whose quantity is measured in the SI (metric system) as metres per second (m/s) or as the SI base unit of (m⋅s^{−1}). For example, "5 metres per second" is a scalar, whereas "5 metres per second east" is a vector


False Color
False color (or pseudo color) refers to a group of color rendering methods used to display images in color which were recorded in the visible or nonvisible parts of the electromagnetic spectrum. A falsecolor image is an image that depicts an object in colors that differ from those a photograph (a truecolor image) would show. In this image, colors have been assigned to three different wavelengths that our eyes cannot normally see. In addition, variants of false color such as pseudocolor, density slicing, and choropleths are used for information visualization of either data gathered by a single grayscale channel or data not depicting parts of the electromagnetic spectrum (e.g [...More Info...] [...Related Items...] 

Julian Year (astronomy)
In astronomy, a Julian year (symbol: a) is a unit of measurement of time defined as exactly 365.25 days of 86400 SI seconds each.^{[1]}^{[2]}^{[3]}^{[4]} The length of the Julian year is the average length of the year in the Julian calendar that was used in Western societies until the adoption of the Gregorian Calendar, and from which the unit is named. Nevertheless, because astronomical Julian years are measuring duration rather than designating dates, this Julian year does not correspond to years in the Julian calendar or any other calendar. Nor does it correspond to the many other ways of defining a year. A Julian year shouldA Julian year should not be confused with the Julian day, which is also used in astronomy (more properly called the Julian day number or JDN) [...More Info...] [...Related Items...] 

Luminous Efficacy
Luminous efficacy is a measure of how well a light source produces visible light. It is the ratio of luminous flux to power, measured in lumens per watt in the International System of Units (SI). Depending on context, the power can be either the radiant flux of the source's output, or it can be the total power (electric power, chemical energy, or others) consumed by the source.^{[1]}^{[2]}^{[3]} Which sense of the term is intended must usually be inferred from the context, and is sometimes unclear. The former sense is sometimes called luminous efficacy of radiation, and the latter luminous efficacy of a source or overall luminous efficacy.^{[4]}^{[5]} Not all wavelengths of light are equally visible, or equally effective at stimulating human vision, due to the spectral sensitivity of the human eye; radiation in the infrared and ultraviolet parts of the spectrum is useless for illumination [...More Info...] [...Related Items...] 

Minutes Of Arc
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , 