Tadokoro, M.«A Study of the Local Group by Use of the Virial Theorem».Publications of the Astronomical Society of Japan,20,1968,p.230. Bibcode: 1968PASJ...20..230T. Aquesta font estima una densitat de 7 × 10−29 g/cm per al Grup Local. Una unitat de massa atòmica és 1.66 × 10−24 g, al voltant de 40 àtoms per metre cúbic.
El-Bizri, Nader«In Defence of the Sovereignty of Philosophy: Al-Baghdadi's Critique of Ibn al-Haytham's Geometrisation of Place».Arabic Sciences and Philosophy.Cambridge University Press,17,2007,p.57–80. DOI: 10.1017/S0957423907000367.
Squire, Tom.«U.S. Standard Atmosphere, 1976».Thermal Protection Systems Expert and Material Properties Database. NASA,27-09-2000.[Consulta: 18 abril 2022].
Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, p. 64-69 (cf. Donald Routledge Hill, Mechanical EngineeringArxivat 2007-12-25 a Wayback Machine.)
Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, p. 64-69 (cf. Donald Routledge Hill, Mechanical EngineeringArxivat 2007-12-25 a Wayback Machine.)