Gross, CG (1999). "The Fire That Comes from the Eye". Neuroscientist. 5: 58–64. doi: 10.1177/107385849900500108. S2CID 84148912. a b c d e Gibbs, P (1997). "How is the speed of light measured?". Usenet Physics FAQ. University of California, Riverside. Archived from the original on 21 August 2015 . Retrieved 13 January 2010. Ben-Menahem, Shahar (November 1990). "Causality between conducting plates". Physics Letters B. 250 (1–2): 133–138. Bibcode: 1990PhLB..250..133B. doi: 10.1016/0370-2693(90)91167-A. OSTI 1449261. Taylor, EF; Wheeler, JA (1992). Spacetime Physics. W.H. Freeman. pp. 74–75. ISBN 978-0-7167-2327-1. a b c "Demonstration tovchant le mouvement de la lumiere trouvé par M. Rŏmer de l'Académie Royale des Sciences"[Demonstration to the movement of light found by Mr. Römer of the Royal Academy of Sciences] (PDF). Journal des sçavans (in French): 233–236. 1676.

The astronomical unit was defined as the radius of an unperturbed circular Newtonian orbit about the Sun of a particle having infinitesimal mass, moving with an angular frequency of 0.017 202 098 95 radians (approximately 1⁄ 365.256 898 of a revolution) per day. [99] Barger, R.; Hall, J. (1973). "Wavelength of the 3.39-μm laser-saturated absorption line of methane". Applied Physics Letters. 22 (4): 196. Bibcode: 1973ApPhL..22..196B. doi: 10.1063/1.1654608. S2CID 1841238. Aoki, K; Mitsui, T (2008). "A small tabletop experiment for a direct measurement of the speed of light". American Journal of Physics. 76 (9): 812–815. arXiv: 0705.3996. Bibcode: 2008AmJPh..76..812A. doi: 10.1119/1.2919743. S2CID 117454437. Liu, C; Dutton, Z; Behroozi, CH; Hau, LV (2001). "Observation of coherent optical information storage in an atomic medium using halted light pulses" (PDF). Nature. 409 (6819): 490–493. Bibcode: 2001Natur.409..490L. doi: 10.1038/35054017. PMID 11206540. S2CID 1894748.An option for deriving c that does not directly depend on a measurement of the propagation of electromagnetic waves is to use the relation between c and the vacuum permittivity ε 0 and vacuum permeability μ 0 established by Maxwell's theory: c 2=1/( ε 0 μ 0). The vacuum permittivity may be determined by measuring the capacitance and dimensions of a capacitor, whereas the value of the vacuum permeability was historically fixed at exactly 4π ×10 −7H⋅m −1 through the definition of the ampere. Rosa and Dorsey used this method in 1907 to find a value of 299 710 ±22km/s. Their method depended upon having a standard unit of electrical resistance, the "international ohm", and so its accuracy was limited by how this standard was defined. [108] [109] Cavity resonance Electromagnetic standing waves in a cavity Pais, A (1982). Subtle is the Lord: The Science and the Life of Albert Einstein. Oxford University Press. ISBN 978-0-19-520438-4. a b Froome, KD (1958). "A New Determination of the Free-Space Velocity of Electromagnetic Waves". Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences. 247 (1248): 109–122. Bibcode: 1958RSPSA.247..109F. doi: 10.1098/rspa.1958.0172. JSTOR 100591. S2CID 121444888.

Radar systems measure the distance to a target by the time it takes a radio-wave pulse to return to the radar antenna after being reflected by the target: the distance to the target is half the round-trip transit time multiplied by the speed of light. A Global Positioning System (GPS) receiver measures its distance to GPS satellites based on how long it takes for a radio signal to arrive from each satellite, and from these distances calculates the receiver's position. Because light travels about 300 000kilometres ( 186 000mi) in one second, these measurements of small fractions of a second must be very precise. The Lunar Laser Ranging experiment, radar astronomy and the Deep Space Network determine distances to the Moon, [89] planets [90] and spacecraft, [91] respectively, by measuring round-trip transit times.

James, MB; Ormond, RB; Stasch, AJ (1999). "Speed of light measurement for the myriad". American Journal of Physics. 67 (8): 681–714. Bibcode: 1999AmJPh..67..681J. doi: 10.1119/1.19352. Sarton, G (1993). Ancient science through the golden age of Greece. Courier Dover. p.248. ISBN 978-0-486-27495-9. Imbs, D; Raynal, Michel (2009). Malyshkin, V (ed.). Software Transactional Memories: An Approach for Multicore Programming. 10th International Conference, PaCT 2009, Novosibirsk, Russia, 31 August – 4 September 2009. Springer. p.26. ISBN 978-3-642-03274-5.

a b "Resolution B2 on the re-definition of the astronomical unit of length" (PDF). International Astronomical Union. 2012.Foschi, Renato; Leone, Matteo (August 2009). "Galileo, Measurement of the Velocity of Light, and the Reaction Times". Perception. 38 (8): 1251–1259. doi: 10.1068/p6263. hdl: 2318/132957. ISSN 0301-0066. PMID 19817156. S2CID 11747908. Sydenham, PH (2003). "Measurement of length". In Boyes, W (ed.). Instrumentation Reference Book (3rded.). Butterworth–Heinemann. p.56. ISBN 978-0-7506-7123-1. ... if the speed of light is defined as a fixed number then, in principle, the time standard will serve as the length standard ... Pitjeva, EV; Standish, EM (2009). "Proposals for the masses of the three largest asteroids, the Moon–Earth mass ratio and the Astronomical Unit". Celestial Mechanics and Dynamical Astronomy. 103 (4): 365–372. Bibcode: 2009CeMDA.103..365P. doi: 10.1007/s10569-009-9203-8. S2CID 121374703. In exotic materials like Bose–Einstein condensates near absolute zero, the effective speed of light may be only a few metres per second. However, this represents absorption and re-radiation delay between atoms, as do all slower-than- c speeds in material substances. As an extreme example of light "slowing" in matter, two independent teams of physicists claimed to bring light to a "complete standstill" by passing it through a Bose–Einstein condensate of the element rubidium. The popular description of light being "stopped" in these experiments refers only to light being stored in the excited states of atoms, then re-emitted at an arbitrarily later time, as stimulated by a second laser pulse. During the time it had "stopped", it had ceased to be light. This type of behaviour is generally microscopically true of all transparent media which "slow" the speed of light. [68] It is generally assumed that fundamental constants such as c have the same value throughout spacetime, meaning that they do not depend on location and do not vary with time. However, it has been suggested in various theories that the speed of light may have changed over time. [33] [34] No conclusive evidence for such changes has been found, but they remain the subject of ongoing research. [35] [36]