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LETTERS
Decoding the ancient Greek astronomical calculator
known as the Antikythera Mechanism
T. Freeth
1,2
, Y. Bitsakis
3,5
, X. Moussas
3
, J. H. Seiradakis
4
, A. Tselikas
5
, H. Mangou
6
, M. Zafeiropoulou
6
, R. Hadland
7
,
D. Bate
7
, A. Ramsey
7
, M. Allen
7
, A. Crawley
7
, P. Hockley
7
, T. Malzbender
8
, D. Gelb
8
, W. Ambrisco
9
& M. G. Edmunds
1
The Antikythera Mechanism is a unique Greek geared device, con-
structed around the end of the second century
BC. It is known
1–9
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 societies
10
for timing agricul-
tural activity and fixing religious festivals. Eclipses and planetary
motions were often interpreted as omens, while the calm regular-
ity 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 controversial
11–14
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 mech-
anical display of planetary positions
9,14,15
, now lost. In the second
century
BC, Hipparchos developed a theory to explain the irregu-
larities of the Moon’s motion across the sky caused by its elliptic
orbit. We find a mechanical realization of this theory in the gear-
ing of the mechanism, revealing an unexpected degree of technical
sophistication for the period.
The bronze mechanism (Fig. 1), probably hand-driven, was ori-
ginally housed in a wooden-framed case
1
of (uncertain) overall size
315 3 190 3 100 mm (Fig. 2). It had front and back doors, with
astronomical inscriptions covering much of the exterior of the mech-
anism. Our new transcriptions and translations of the Greek texts are
given in Supplementary Note 2 (‘glyphs and inscriptions’). The
detailed form of the lettering can be dated to the second half of the
second century
BC, implying that the mechanism was constructed
during the period 150–100
BC, slightly earlier than previously sug-
gested
1
. This is consistent with a date of around 80–60 BC for the
wreck
1,16
from which the mechanism was recovered by some of the
first underwater archaeology. We are able to complete the recon-
struction
1
of the back door inscription with text from fragment E,
and characters from fragments A and F (see Fig. 1 legend for fragment
nomenclature). The front door is mainly from fragment G. The text is
astronomical, with many numbers that could be related to planetary
motions; the word ‘‘sterigmos’’ (STGRICMOS, translated as ‘sta-
tion’ or ‘stationary point’) is found, meaning where a planet’s appar-
ent motion changes direction, and the numbers may relate to
planetary cycles. We note that a major aim of this investigation is
to set up a data archive to allow non-invasive future research, and
access to this will start in 2007. Details will be available on www.an-
tikythera-mechanism.gr.
The back door inscription mixes mechanical terms about con-
struction (‘‘trunnions’’, ‘‘gnomon’’, ‘‘perforations’’) with astronom-
ical periods. Of the periods, 223 is the Saros eclipse cycle (see Box 1
for a brief explanation of astronomical cycles and periods). We
discover the inscription ‘‘spiral divided into 235 sections’’, which is
1
Cardiff University, School of Physics and Astronomy, Queens Buildings, The Parade, Cardiff CF24 3AA, UK.
2
Images First Ltd, 10 Hereford Road, South Ealing, London W5 4SE, UK.
3
National and Kapodistrian University of Athens, Department of Astrophysics, Astronomy and Mechanics, Panepistimiopolis, GR-15783, Zographos, G reece.
4
Aristotle University of
Thessaloniki, Department of Physics, Section of Astrophysics, Astronomy and Mechanics, GR-54124 Thessaloniki, Greece.
5
Centre for History and Palaeography, National Bank of
Greece Cultural Foundation, P. Skouze 3, GR-10560 Athens, Greece.
6
National Archaeological Museum of Athens, 1 Tositsa Str., GR-10682 Athens, Greece.
7
X-Tek Systems Ltd, Tring
Business Centre, Icknield Way, Tring, Hertfordshire HP23 4JX, UK.
8
Hewlett-Packard Laboratories, 1501 Page Mill Road, Palo Alto, California 94304, USA.
9
Foxhollow Technologies
Inc., 740 Bay Road, Redwood City, California 94063, USA.
Figure 1
|
The surviving fragments of the Antikythera Mechanism. The 82
fragments that survive in the National Archaeological Museum in Athens are
shown to scale. A key and dimensions are provided in Supplementary Note 1
(‘fragments’). The major fragments A, B, C, D are across the top, starting at
top left, with E, F, G immediately below them. 27 hand-cut bronze gears are
in fragment A and one gear in each of fragments B, C and D. Segments of
display scales are in fragments B, C, E and F. A schematic reconstruction is
given in Fig. 2. It is not certain that every one of the remaining fragments
(numbered 1–75) belong to the mechanism. The distinctive fragment A,
which contains most of the gears, is approximately 180 3 150 mm in size.
We have used three principal techniques to investigate the structure and
inscriptions of the Antikythera Mechanism. (1) Three-dimensional X-ray
microfocus computed tomography
24
(CT), developed by X-Tek Systems Ltd.
The use of CT has been crucial in making the text legible just beneath the
current surfaces. (2) Digital optical imaging to reveal faint surface detail
using polynomial texture mapping (PTM)
25,26
, developed by Hewlett-
Packard Inc. (3) Digitized high-quality conventional film photography.
Vol 444
|
30 November 2006
|
doi:10.1038/nature05357
587
Natu re
Pu blishin g
Gro u p
©2 0 0 6