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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
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.
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 ...
A woman walking in the Czech Republic stumbled upon more than 2,150 early medieval silver coins. Originally stored in a ceramic pot during a time of political turmoil, the coins have sat in place ...
The customary design on coins is a portrait of a notable individual (living and/or deceased) on the obverse or reverse, unless the subject is depicted on both sides of the coin. Elizabeth II , former Queen of the Commonwealth realms and their territories and dependencies, features on more coins than any other person.
It is the first in a series of gold coins featuring Lady Liberty, which has been used on American coinage since the late 1790s, as an ethnic woman.
The plaques (which could be described as large plaquettes) about 120 mm (4.7 in) in diameter, were cast in bronze, and came to be known as the Dead Man's Penny or Widow's Penny because of the superficial similarity to the much smaller penny coin (which had a diameter of only 30.86 mm (1.215 in)). 1,355,000 plaques were issued, which used a ...