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speed of light in vacuum

speed of electromagnetic waves in vacuum
Thing physical_constant Q2111
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Summary

speed of light in vacuum is a physical constant[1]. It ranks in the top 2% of physical constant entities by monthly Wikipedia readership (31,548 views/month).[2]

Key Facts

  • Discoverer or inventor: Ole Rømer[3]
  • Instance of: unit of speed[4], fundamental limit[5], constant[6], UCUM constant[7], scalar quantity[8]
  • Measured physical quantity: speed[9]
  • Commons category: Speed of light[10]
  • Said to be the same as: speed of gravity[11]
  • Topic's main category: Category:Speed of light[12]
  • Numeric value: 299,792,458 metre per second[13], 220,000 kilometre per second[14]
  • Facet of: massless quantum particle[15], vacuum[16], special relativity[17], electromagnetism[18]
  • Described by source: ISO 80000-7:2008 Quantities and units—Part 7: Light[19], IEC 80000-6:2008 Quantities and units—Part 6: Electromagnetism[20], IEC 80000-6:2022 Quantities and units — Part 6: Electromagnetism[21]
  • Different from: speed of light in a medium[22]
  • Conversion to SI unit: 299792458.0147178 metre per second[23]
  • Conversion to standard unit: 1079252848.8 kilometre per hour[24], 670616629.384 mile per hour[25]
  • On focus list of Wikimedia project: Wikipedia:List of articles all languages should have[26], Wikipedia:Vital articles/Level/4[27]
  • Unit symbol: c[28]
  • Maintained by WikiProject: WikiProject Mathematics[29], WikiProject Physics[30]
  • Recommended unit of measurement: metre per second[31]

Body

Influence

Things named for speed of light in vacuum include Hikari[32], a named passenger train service[33], in Japan[34], founded in 1964[35] and speed of light[36], a rate[37].

Why It Matters

speed of light in vacuum has Wikipedia articles in 30 language editions, a strong signal of global cultural recognition.[38] It is known by 65 alternative names across languages and contexts.[39]

Entities named for it include Hikari[32], a named passenger train service[33], in Japan[34], founded in 1964[35] and speed of light[36], a rate[37].

Related Entities

Geelong Ole Rømer

References

Programmatic citations — every numbered marker resolves to a verifiable graph row below.

Direct Wikidata claims

  1. [4] ↑ . wikidata.org.
  2. [5] ↑ . wikidata.org.
  3. [6] ↑ . wikidata.org.
  4. [7] ↑ . wikidata.org.
  5. [8] ↑ . wikidata.org.
  6. [3] ↑ . A Short History of Astronomy. wikidata.org.
  7. [9] ↑ . wikidata.org.
  8. [10] ↑ . wikidata.org.
  9. [11] ↑ . wikidata.org.
  10. [12] ↑ . wikidata.org.
  11. [13] ↑ . 2018 CODATA recommended values. wikidata.org.
  12. [14] ↑ . wikidata.org.
  13. [15] ↑ . wikidata.org.
  14. [16] ↑ . wikidata.org.
  15. [17] ↑ . wikidata.org.
  16. [18] ↑ . wikidata.org.
  17. [19] ↑ . wikidata.org.
  18. [20] ↑ . wikidata.org.
  19. [21] ↑ . wikidata.org.
  20. [22] ↑ . wikidata.org.
  21. [23] ↑ . wikidata.org.
  22. [24] ↑ . wikidata.org.
  23. [25] ↑ . wikidata.org.
  24. [26] ↑ . wikidata.org.
  25. [27] ↑ . wikidata.org.
  26. [28] ↑ . wikidata.org.
  27. [29] ↑ . wikidata.org.
  28. [30] ↑ . wikidata.org.
  29. [31] ↑ . IEC 80000-6:2008 Quantities and units—Part 6: Electromagnetism. wikidata.org.

Inverse relationships (entities pointing at this one)

  1. [32] ↑ . wikidata.org. → on this site
  2. [36] ↑ . wikidata.org. → on this site

Inline context (facts about related entities)

  1. [33] ↑ . Wikidata. wikidata.org. → on this site
  2. [34] ↑ . Wikidata. wikidata.org. → on this site
  3. [35] ↑ . Wikidata. wikidata.org. → on this site
  4. [37] ↑ . Wikidata. wikidata.org. → on this site

Class ancestry

  1. [1] ↑ . Wikidata. wikidata.org.

Aggregate / graph-position facts

  1. [2] ↑ . Wikimedia Foundation. dumps.wikimedia.org.
  2. [38] ↑ . Wikidata sitelinks. wikidata.org.
  3. [39] ↑ . Wikidata aliases. wikidata.org.

📑 Cite this page

Use these citations when quoting this entity in research, articles, AI prompts, or wherever provenance matters. We aggregate Wikidata + Wikipedia + authoritative open-data sources; the stitched, scored, cross-referenced view is what 4ort.xyz contributes.

APA 4ort.xyz Knowledge Graph. (2026). speed of light in vacuum. Retrieved October 20, 2026, from https://4ort.xyz/entity/speed-of-light
MLA “speed of light in vacuum.” 4ort.xyz Knowledge Graph, 4ort.xyz, 20 Oct. 2026, https://4ort.xyz/entity/speed-of-light.
BibTeX @misc{4ortxyz_speed-of-light_2026, author = {{4ort.xyz Knowledge Graph}}, title = {{speed of light in vacuum}}, year = {2026}, url = {https://4ort.xyz/entity/speed-of-light}, note = {Accessed: 2026-10-20}}
LLM prompt According to 4ort.xyz Knowledge Graph (aggregator of Wikidata, Wikipedia, and authoritative open-data sources): speed of light in vacuum — https://4ort.xyz/entity/speed-of-light (retrieved 2026-10-20)

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Edit History

Rolling log of changes to this entity's Wikidata record. Values shown reflect the current state of each edited property — follow the history link to see the precise diff for any edit.

  1. 16d ago · Iketsi · 2026-10-05 view diff on Wikidata ↗
    Wikipedia languages → ['af', 'als', 'am', 'an', 'ar', 'arz', 'as', 'ast', 'az', 'ba', 'bat_smg', 'bcl'
    Sitelink count → 141
    Claims rich → —
    "/* wbeditentity-update-languages-short:0||it, ca, nn, gl, eo, cs, pt-br, pt, pl, mul */ Remove all redundant labels/aliases same as [[WD:MUL|mul]] label/aliases via [[User:Midleading/RemoveRedundantLa"
  2. 9w ago · Mariobanana · 2026-08-14 view diff on Wikidata ↗
    Niconicopedia id → 光速
    "/* wbsetclaim-create:2||1 */ Niconicopedia id: 光速"
  3. 11w ago · WikiLucas00 · 2026-08-02 view diff on Wikidata ↗
    Pronunciation audio → LL-Q9610 (ben)-Tahmid-আলোর গতিবেগ.wav, De-Vakuumlichtgeschwindigkeit.ogg, LL-Q8097 (tel)-ప్రశాంతి-కాంతి వేగం.wav
    "/* wbcreateclaim-create:1| */ Pronunciation audio: LL-Q8097 (tel)-ప్రశాంతి-కాంతి వేగం.wav"
  4. 14w ago · Nyuhn · 2026-07-10 view diff on Wikidata ↗
    P14541 → LwoZY
    "/* wbeditentity-update:0| */ QuickStatements 3.0 [[:toollabs:qs-dev/batch/40849|batch #40849]]: ZGBK ID"
  5. 24w ago · Stuchalk · 2026-05-02 view diff on Wikidata ↗
    Instance of → physical constant, unit of speed, fundamental limit +4
    "/* wbremoveclaims-remove:1| */ Instance of: unit of measurement"
Live feed via Wikidata EventStreams. New edits appear within minutes of being made on Wikidata.