This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A125560 #30 Feb 16 2025 08:33:04 %S A125560 4,1,2,5,2,9,6,1,2,4,9,4,1,9,2,7,1,0,3,1,2,9,4,6,7,1,4,6,6,1,5,5,7,2, %T A125560 2,6,3,9,3,3,1,9,4,0,1,7,5,9,2,6,3,1,1,5,1,5,3,9,5,3,7,5,5,8,0,0,6,6, %U A125560 0,4,9,9,4,6,7,9,1,5,1,7,8,9,5,3,5,7,4,9,7,6,7,7,0,1,2,7,9,9,8,7,9,8,1,4,0 %N A125560 Full solid angle of 4*Pi steradians (sr) in square degrees (degree^2). %C A125560 "A 35 mm camera with a standard 50 mm lens covers an area some 38 degrees x 27 degrees. Theoretically, one can cover the sky with about 40 photographs." [A Field Guide] %C A125560 One sphere = 4*Pi steradians, a spherical right angle = 1/4 hemisphere = 1/8 sphere = Pi/2 steradian. %D A125560 John A. Adam, Mathematics in Nature, Modeling Pattern in the Natural World, Princeton University Press, Princeton & Oxford, 2003, page 78. %D A125560 Patrick Kelly, Editor, Observer's Handbook 2007, The Royal Astronomical Society of Canada, page 32. %D A125560 Donald H. Menzel, A Field Guide to the Stars and Planets, Houghton Mifflin Co., Boston, MA, 1964, page 317. %H A125560 Rod Pierce, <a href="http://www.mathsisfun.com/geometry/steradian.html">MathIsFun: Steradian</a>, 2012. %H A125560 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/SolidAngle.html">Solid Angle</a>. %H A125560 Wikipedia, <a href="http://en.wikipedia.org/wiki/Solid_angle">Solid Angle</a>. %F A125560 4Pi*(180/Pi)^2 = 10*A019694*A072097^2 = 129600/Pi = 129600*A049541. %e A125560 41252.96124941927103129467146615572263933194017592631151539537558... deg^2. %e A125560 = 148510660.979093757126608172781606015015949846333347214554233520... min^2. %e A125560 = 534638377792.473752565578942201378165405741944680004997239524067... sec^2. %t A125560 RealDigits[2^6*3^4*5^2/Pi, 10, 111][[1]] %o A125560 (PARI) 129600/Pi \\ _Charles R Greathouse IV_, Nov 06 2017 %Y A125560 Cf. A000796, A072097, A049541. %K A125560 cons,nonn,easy %O A125560 5,1 %A A125560 _Robert G. Wilson v_, Dec 31 2006 %E A125560 Definition changed to make it more rigorous by _Stanislav Sykora_, Nov 14 2013