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OPINION
NATURE|Vol 462|24/31 December 2009
Johannes Kepler on Christmas
When was Jesus born? On 25 December
Kepler’s treatise can be acclaimed
as a work of science in the modern
in the year that starts the Christian
sense. For instance, he uses the lack
calendar, is what wide belief would
have it. Greek and Russian Orthodox
of diurnal parallax from the new star
churches retain the date of 7 Janu— that is, the inability to measure its
ary in accordance with the old Julian
distance using the angle at two difcalendar, rather than the Gregorian
ferent points on Earth’s surface — to
revision that was introduced in 1582.
infer that it resided in the sphere of
the fixed stars. This provided furInternal evidence from the Bible
ther evidence that the sphere was
rules out the designated year because
not as immutable as the ancients
Herod the Great, who was responsible for the massacre of the innocents,
had assumed. But De Stella Nova, as
from which the infant Jesus escaped, is
its extended title declares, explicitly
known to have died in 4 bc. This is one
involved metaphysics and astrology,
reason why the now-obscure Polish
and it climaxed in an appendix on
scholar, Laurence Suslyga, argued in
biblical chronology.
his 1605 thesis on the birth and death
Within this, we cannot separate
what we regard as the real science
of Christ that Jesus was actually born
in 5 bc.
from the astrology and theology. For
Suslyga’s tract unexpectedly gained
Kepler, mathematics and meaning
a significance beyond the specialist
comprised a unified whole. The great
realm of biblical chronology. The cirastronomer, best known for identifycumstances are best explained by the
ing the elliptical paths of the planets,
great German astronomer, Johannes
became increasingly concerned in
Kepler: “I found for sale at Graz a
the years following publication of De
small book by Laurence Suslyga of
Stella Nova with the construction of
Poland,” with which Kepler agreed
a ‘purified’ version of ancient astrothat at least “four years must be added
logical wisdom, purged of the myths
to the Epoch of Christianity now in Artwork from De Stella Nova shows the constellation Ophiuchus with
that had accumulated around the
use”. Suslyga provided Kepler with the 1604 supernova (N; in the foot, lower left) observed by Kepler.
zodiacal signs. He later referred to
the necessary licence to correlate the
the mystic symbolism of traditional
dramatic appearance of a ‘new star’ in 1604 which it faded from view as the flash from its astrology as “filthy mud” from which “one
with the act of stellar navigation performed by explosion declined in intensity.
can glean even an occasional escargot, oysters
the biblical Magi when they journeyed to see
In 1606, Kepler published a pamphlet on the or an eel for one’s nutrition”.
the Christ child in Bethlehem.
new star in German, while planning a more
Kepler gained his “nutrition” from the
In 1604, astronomers keenly awaited the substantial account in Latin: On the New Star mathematical ratios of the ‘aspects’ between
shift of the conjunction of Jupiter and Saturn in the Foot of the Ophiuchus and on the Fiery the planets. He defined an aspect as “a geointo the ‘Fiery Trigon’ of the zodiac (Sagit- Trigon that Began Anew at its Rising. A Booklet metrical construction [of an angle] between
tarius, Aries and Leo), which initiated a new Full of Astronomical, Physical, Metaphysical, light beams of two planets here on Earth”. The
cycle of conjunctions in the Trigon — an event Meteorological and Astrological Disputations ratios were integral to the celestial geometry
that was calculated to recur about every 800 (beginning in Latin, De Stella Nova in Pede that manifests the mathematical “music” of the
years. Mars also moved close to Saturn and Serpentarii …). The second of two substan- heavens. He explained that earthly nature canthen Jupiter, thus outlining a triangular array tial appendices in the book dealt with the year not help but respond to the dictates of heavenly
that was of great interest to astrologers.
of Christ’s birth “in the light of the new pro- harmonies, and said that nature is affected by
During his time in Prague as mathemati- nouncements of Laurentius Suslyga”.
an aspect “just as a farmer is moved by music
In a series of arguments that even he admit- to dance”.
cian to the Holy Roman Emperor Rudolf II,
Kepler observed this remarkable cluster of ted were hard to follow, Kepler claimed that the
De Stella Nova serves to remind us that it was
planets and the new star on 17 October 1604, star followed by the Magi was the equivalent of not possible in the era of Kepler and Galileo
when the clouds over the city finally lifted. the stella nova of 1604–5, and that it had arisen to pursue astronomy in such a way that the
The star burned brightly in the evening and during a series of related planetary conjunc- mathematical study of the heavenly bodies
was even visible as a morning star, located in tions in the years 7–5 bc — which he took to was divorced from the theology of a heaven
the foot of the constellation of the Serpent cover the period of Christ’s conception and the inhabited by God.
■
Bearer, or Ophiuchus (pictured). He made his Magi’s journey to Bethlehem, as recounted in Martin Kemp is emeritus professor in history of
last observation of the star a year later, after Matthew 2:9–10.
art at the University of Oxford, Oxford, UK.
© 2009 Macmillan Publishers Limited. All rights reserved
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CALTECH ARCHIVES/SPL
Kepler’s interpretation of the supernova of 1604, De Stella Nova, interwove the science of astronomy with
astrology and theology in an attempt to determine the correct birthdate of Jesus, explains Martin Kemp.