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  2. Small-angle approximation - Wikipedia

    en.wikipedia.org/wiki/Small-angle_approximation

    In astronomy, the angular size or angle subtended by the image of a distant object is often only a few arcseconds (denoted by the symbol ″), so it is well suited to the small angle approximation. [6] The linear size (D) is related to the angular size (X) and the distance from the observer (d) by the simple formula:

  3. Microsecond - Wikipedia

    en.wikipedia.org/wiki/Microsecond

    A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10 −6 or 1 ⁄ 1,000,000) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is to one second, as one second is to approximately 11.57 days.

  4. Perimeter of an ellipse - Wikipedia

    en.wikipedia.org/wiki/Perimeter_of_an_ellipse

    An ellipse is defined by two axes: the major axis (the longest diameter) of length and the minor axis (the shortest diameter) of length , where the quantities and are the lengths of the semi-major and semi-minor axes respectively.

  5. Half cent (United States coin) - Wikipedia

    en.wikipedia.org/wiki/Half_cent_(United_States_coin)

    First authorized by the Coinage Act of 1792 on April 2, 1792, [1] the coin was produced in the United States from 1793 to 1857. The half-cent piece was made of 100% copper and half of a cent, or one two-hundredth of a dollar (five milles).

  6. HD 168871 - Wikipedia

    en.wikipedia.org/wiki/HD_168871

    The object is located relatively close at a distance of 89.2 light-years based on Gaia DR3 parallax measurements, [1] but it is drifting away with a heliocentric radial velocity of 35.1 km/s. [6] At its current distance, HD 168871’s brightness is diminished by an interstellar extinction of 0.14 magnitudes [ 16 ] and it has a visual absolute ...

  7. Particular values of the Riemann zeta function - Wikipedia

    en.wikipedia.org/wiki/Particular_values_of_the...

    For the even positive integers , one has the relationship to the Bernoulli numbers: = + (!). The computation of () is known as the Basel problem.The value of () is related to the Stefan–Boltzmann law and Wien approximation in physics.

  8. Twaddell scale - Wikipedia

    en.wikipedia.org/wiki/Twaddell_scale

    The Twaddell scale is a hydrometer scale used for measuring the specific gravity of liquids relative to water. On this scale, a specific gravity of 1.000 is reported as 0, and a specific gravity of 2.000 is reported as 200. [1]

  9. Influential observation - Wikipedia

    en.wikipedia.org/wiki/Influential_observation

    Various methods have been proposed for measuring influence. [3] [4] Assume an estimated regression = +, where is an n×1 column vector for the response variable, is the n×k design matrix of explanatory variables (including a constant), is the n×1 residual vector, and is a k×1 vector of estimates of some population parameter .