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sr is the unit, steradian, sr = rad 2. Because the surface area A of a sphere is 4πr 2, the definition implies that a sphere subtends 4π steradians (≈ 12.56637 sr) at its centre, or that a steradian subtends 1/4π ≈ 0.07958 of a sphere. By the same argument, the maximum solid angle that can be subtended at any point is 4π sr.
Diagram showing a section through the centre of a cone (1) subtending a solid angle of 1 steradian in a sphere of radius r, along with the spherical "cap" (2). The external surface area A of the cap equals r2 only if solid angle of the cone is exactly 1 steradian. Hence, in this figure θ = A/2 and r = 1.
IBM System/4 Pi, a family of avionics computers; 4Pi microscope, a microscope that uses interference and fluorescence computers; 4×π = 12.56637..., the solid angle of a complete sphere measured in steradians; Hermetic detector (also called a 4π detector)
In common usage, the symbol used for radiant exitance (often called radiant emittance) varies among different texts and in different fields. The Stefan–Boltzmann law may be expressed as a formula for radiance as a function of temperature. Radiance is measured in watts per square metre per steradian (W⋅m −2 ⋅sr −1).
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The full moon covers only about 0.2 deg 2 of the sky when viewed from the surface of the Earth. The Moon is only a half degree across (i.e. a circular diameter of roughly 0.5°), so the moon's disk covers a circular area of: π ( 0.5° / 2 ) 2, or 0.2 square degrees.
Some rare coins have reached a certain level of fame because of their backstories. Find Out: These 11 Rare Coins Sold for Over $1 Million Discover Next: 4 Things You Must Do When Your Savings ...
China based cryptocurrency, formerly ANT Shares and ANT Coins. The names were changed in 2017 to NEO and GAS. 2014 MazaCoin: MZC BTC Oyate Initiative SHA-256d: C++ [39] PoW: The underlying software is derived from that of another cryptocurrency, ZetaCoin. 2014 Monero: XMR Monero Core Team RandomX C++ [40] PoW