Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Decoding the ancient Greek astronomical calculator known as the Antikythera Mechanism

Abstract

The Antikythera Mechanism is a unique Greek geared device, constructed around the end of the second century bc. It is known1,2,3,4,5,6,7,8,9 that it calculated and displayed celestial information, particularly cycles such as the phases of the moon and a luni-solar calendar. Calendars were important to ancient societies10 for timing agricultural activity and fixing religious festivals. Eclipses and planetary motions were often interpreted as omens, while the calm regularity of the astronomical cycles must have been philosophically attractive in an uncertain and violent world. Named after its place of discovery in 1901 in a Roman shipwreck, the Antikythera Mechanism is technically more complex than any known device for at least a millennium afterwards. Its specific functions have remained controversial11,12,13,14 because its gears and the inscriptions upon its faces are only fragmentary. Here we report surface imaging and high-resolution X-ray tomography of the surviving fragments, enabling us to reconstruct the gear function and double the number of deciphered inscriptions. The mechanism predicted lunar and solar eclipses on the basis of Babylonian arithmetic-progression cycles. The inscriptions support suggestions of mechanical display of planetary positions9,14,15, now lost. In the second century bc, Hipparchos developed a theory to explain the irregularities of the Moon’s motion across the sky caused by its elliptic orbit. We find a mechanical realization of this theory in the gearing of the mechanism, revealing an unexpected degree of technical sophistication for the period.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Prices may be subject to local taxes which are calculated during checkout

Figure 1: The surviving fragments of the Antikythera Mechanism.
Figure 2: A schematic view of the mechanism to illustrate the position of major inscriptions and dials.
Figure 3: The ‘pointer-follower’ lunar month indicator of the upper back dial.
Figure 4: Reconstruction of the back dials.
Figure 5: New reconstruction of the gear trains.
Figure 6: The ‘Hipparchos’ lunar mechanism mounted on gear e3.

Similar content being viewed by others

References

  1. Price, D. de S. Gears from the Greeks: The Antikythera Mechanism — A calendar computer from ca. 80 BC. Trans Am. Phil. Soc. New Ser. 64, 1–70 (1974); reprinted by Science History Publications, New York. (1975)

    Article  Google Scholar 

  2. Wright, M. T. Epicyclic gearing and the Antikythera Mechanism, Part I. Antiquar. Horol. 27, 270–279 (2003)

    Google Scholar 

  3. Wright, M. T., Bromley, A. G. & Magou, H. Simple X-ray tomography and the Antikythera Mechanism. PACT J. Eur. Study Group Phys. Chem. Biol. Math. Tech. Appl. Archaeol. 45, 531–543 (1995)

    Google Scholar 

  4. Wright, M. T. The Antikythera Mechanism: a New Gearing Scheme. Bull. Sci. Instrum. Soc. 85, 2–7 (2005)

    Google Scholar 

  5. Wright, M. T. Epicyclic gearing and the Antikythera Mechanism, Part II. Antiquar. Horol. 29, 51–63 (2005)

    Google Scholar 

  6. Wright, M. T. Counting months and years: The upper back dial of the Antikythera Mechanism. Bull. Sci. Instrum. Soc. 87, 8–13 (2005)

    Google Scholar 

  7. Wright, M. T. The Antikythera Mechanism and the early history of the moon-phase display. Antiquar. Horol. 29, 319–329 (2006)

    Google Scholar 

  8. Wright, M. T. in Proc. 2nd Int. Conf. on Ancient Greek Technology (ed. Tassios, Th.) 49–60 (Technical Chamber of Greece, Athens, 2006)

  9. Wright, M. T. A planetarium display for the Antikythera Mechanism. Horol. J. 144(5), 169–173 (2002); erratum. 144, 193 (2002)

    Google Scholar 

  10. North, J. D. The Fontana History of Astronomy and Cosmology (Fontana, London, 1994)

    Google Scholar 

  11. Bromley, A. G. The Antikythera Mechanism. Horol. J. 132, 412–415 (1990)

    Google Scholar 

  12. Bromley, A. G. in Bassernet Vol. 2, No. 3 (Basser Department of Computer Science, Univ. Sydney, June, 1993)

    Google Scholar 

  13. Freeth, T. The Antikythera Mechanism: 1. Challenging the classic research. Mediterr. Archaeol. Archaeom. 2, 21–35 (2002)

    ADS  Google Scholar 

  14. Edmunds, M. & Morgan, P. The Antikythera Mechanism: still a mystery of Greek astronomy? Astron. Geophys. 41, 6.10–6.17 (2000)

    Article  Google Scholar 

  15. Freeth, T. The Antikythera Mechanism: 2. Is it Posidonius’ orrery? Mediterr. Archaeol. Archaeom. 2, 45–58 (2002)

    ADS  Google Scholar 

  16. Illsley, J. S. History and Archaeology of the Ship—Lecture Notes. 〈http://cma.soton.ac.uk/HistShip/shlect36.htm〉 (1998)

  17. Stephenson, F. R. Historical Eclipses and Earth’s Rotation (Cambridge Univ. Press, Cambridge, UK, 1997)

    Book  Google Scholar 

  18. Steele, J. M. Observations and Predictions of Eclipse Times by Early Astronomers (Kluwer Academic, Dordrecht, 2000)

    Book  Google Scholar 

  19. Steele, J. M. Eclipse prediction in Mesopotamia. Arch. Hist. Exact Sci. 54, 421–454 (2000)

    Article  ADS  MathSciNet  Google Scholar 

  20. Wright, M. T. The Scholar, the Mechanic and the Antikythera Mechanism. Bull. Sci. Instrum. Soc. 80, 4–11 (2003)

    Google Scholar 

  21. Espenak, F. NASA Eclipse Home Page. 〈http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html〉 (2005)

  22. Jones, A. The adaptation of Babylonian methods in Greek numerical astronomy. Isis 82, 440–453 (1991)

    Article  ADS  MathSciNet  Google Scholar 

  23. Britton, J. P. in Die Rolle der Astronomie in den Kulturen Mesopotamiens (ed. Galter, H. D.) 61–76 (rm-Druck & Vergansgesellschaft, Graz, 1993)

    Google Scholar 

  24. X-Tek Systems Ltd. 3-D computed tomography. 〈http://www.xtek.co.uk/ct/〉 (2006)

  25. Malzbender, T. & Gelb, D. Polynomial texture mapping. 〈http://www.hpl.hp.com/research/ptm/〉 (2006)

  26. Brooks, M. Tricks of the light. New Sci. 170, 38–49 (2001)

    Google Scholar 

  27. Chapman, A. Dividing the Circle (Wiley, Chichester, 1995)

    Google Scholar 

  28. Toomer, G. J. Ptolemy’s Almagest (transl. Toomer, G. J.) (Princeton Univ. Press, Princeton, New Jersey, 1998)

    Google Scholar 

Download references

Acknowledgements

This work was financed by the Leverhulme Trust, the Walter Hudson Bequest, the University of Athens Research Committee and the Cultural Foundation of the National Bank of Greece. For essential support we thank the Ministry of Culture, Greece (P. Tatoulis), and the National Archaeological Museum of Athens (N. Kaltsas). We acknowledge help and advice from J. Ambers, J. Austin, G. Dermody, H. Forsyth, I. Freestone, P. Haycock, V. Horie, A. Jones, M. Jones, P. Kipouros, H. Kritzas, J. Lossl, G. Makris, A. Ray, C. Reinhart, A. Valassopoulos, R. Westgate, T. Whiteside, S. Wright and C. Xenikakis. Author Contributions T.F. carried out most of the CT analysis of structure and its interpretation. Y.B., A.T. and X.M. read, transcribed and translated the inscriptions. H.M and M.Z. catalogued the fragments, provided guidance on X-ray examination, and measured the fragments with J.H.S. R.H. led the team (D.B., A.R., M.A., A.C. and P.H.) that built and operated the Bladerunner CT machine, and provided CT reconstructions and advice. T.M., D.G. and W.A. built, operated and provided software for the PTM. M.G.E. was academic lead, and undertook the statistical analysis. T.F. and Y.B. organised the logistics of the experimental work, with inter-agency liaison by X.M. and J.H.S. The manuscript was written by T.F. and M.G.E. including material from Y.B., A.T., X.M., J.H.S., H.M. and M.Z. T.F. designed the illustrations.

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to M. G. Edmunds.

Ethics declarations

Competing interests

Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.

Supplementary information

Supplementary notes

This file contains supplementary notes giving a key to fragment identification for Figure 1 of the main text and the dimensions of the fragments; further notes giving details of the script of the characters, their dating and the Greek text and its provisional translation from the Front Door inscriptions, the Back Door inscriptions and the Back Plate inscriptions near the Lower Back Dial. Also further notes giving a table to compare gear nomenclature and the gear tooth count estimates with previous estimates and to tabulate measured radii. Some notes are given on the individual gears and on the tooth count estimation procedure, including the effects of uncertainty in determining the centres of the gears. The gear train ratios are explained on the basis of simple Babylonian period relations. The equivalence of the epicyclic gearing and pin-and-slot mechanism to Hipparchos’ theory of the moon is proved. (PDF 1525 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Freeth, T., Bitsakis, Y., Moussas, X. et al. Decoding the ancient Greek astronomical calculator known as the Antikythera Mechanism. Nature 444, 587–591 (2006). https://doi.org/10.1038/nature05357

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature05357

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing