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Starry skies on the wrist
Timm Delfs
IWC emerged from the summer break with a very
complicated watch called the Portuguese Sidérale
Scafusia. It was launched successively in the
southern hemisphere at the Paranal Observatory
in Chile and at Schaffhausen in Switzerland, the
birthplace of this unusual watch. This model represents a milestone in the journey of this brand, for it
joins the small number of astronomical wristwatches that display a map of the heavens.
Although the watch features such exotic complications as sidereal time, the hours of sunrise and
sunset as well as a constant-force tourbillion, the
real eye-catcher is the starry sky.
The new IWC product gives Watch Around the
excuse to take a wider view of this horological rarity, past and present, beginning with a look at the
astronomical principles on which it is based.
The universe might be expanding at a tremendous
rate ever since the Big Bang, but from our point of
view on Earth, the familiar constellations haven’t
changed in generations. The stars might be a few
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light years away or a few thousand, but to us they
appear dotted on a giant dome rotating above the
Earth. Although we now know that it is the Earth
that rotates, the illusion serves as a convenient
model.
Since the axis of the Earth’s rotation goes through
the poles, a patient observer at the North Pole will
see the stars orbiting anti-clockwise around a point
directly above his head, where the Pole Star
appears immobile. The orbits of the stars increase
with their distance from the Pole Star.
This phenomenon can be observed at all latitudes,
except that the Pole Star is no longer directly overhead. Its angle above the horizon decreases the
further south you go, but it can be seen from any
point in the northern hemisphere and always in the
same place every night.
Flattening the sky. It is possible to lay out a somewhat distorted version of the heavenly dome on a
flat disc thereby contriving a rotating map of the
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firmament, which is a great help in identifying the
stars when you don’t have an iPhone at hand. The
projection of a hemisphere on a flat surface, called
a planisphere, is an old skill. In the 16th century,
Arab scientists were famous for their brass astrolabes, which were nothing more than rotatable star
charts that determined the time at night from the
position of the stars.
When you go out to observe the night sky, you
stand in the middle of a circle formed by the horizon where the stars rise and set. On a planisphere,
the horizon is represented as an ellipse inscribed
on a transparent disc above the rotating disc of
stars. As the star chart rotates, the stars rise across
the horizon in the east and disappear in the west.
over his home in Ohio. The best-known example of
this rivalry is the 1933 Graves watch with 24 complications, delivered to the New York financier,
Henry Graves Jr. It was superseded in 1989 when
Patek Philippe built the Calibre 89 to mark its 150th
anniversary. Among its 33 complications is a realistic depiction of the night sky in the northern hemisphere. The Geneva company went on in 2000 to
produce the 21-complication Star Calibre pocketwatch, which has a revolving planisphere that also
shows the position and phases of the moon. These
indications appeared in Patek Philippe’s most
complicated wristwatch, the Sky Moon Tourbillon,
and lately in the Celestial model, which is devoted
entirely to representing the night sky.
Time from an infinite point in space. Sidereal
time is the time scale that navigators use when
they take the altitude of a star. It’s a much more
constant scale of time than solar time because it is
based on the actual time of the Earth’s 360° rotation against an infinite point in space – the vernal
equinox. The sidereal day is about four minutes
shorter than the mean solar day. Sidereal time, like
solar time is local; the sidereal noon is when the
vernal equinox is directly above the meridian of the
locality.
The introduction of the astrolabe to Europe
inspired efforts to drive the mechanism by clockwork to get the positions of the heavenly bodies in
real time. The best-known machine of this kind was
the 14th-century astrarium by Giovanni Dondi. The
clock was lost but replicas – one of them in the
International Horology Museum in La Chaux-deFonds – have been made from the original notes
and drawings. In addition to the astrolabe, the
clock has five other dials showing the planetary
orbits from the geocentric point of view of the time.
Astrolabes also featured in tower and church
clocks: the one on Prague’s town hall, the
Zytglogge in Bern and the Strasbourg cathedral
clock are notable examples.
Stars for rival collectors. Watches with celestial
charts appeared in the 20th century to gratify
wealthy Americans vying to own the most complicated Swiss watches. The industrialist, James
Ward Packard, had Patek Philippe provide a
pocket-watch with a chart of the sky as it appeared
James Ward Packard paid 12,815 Swiss francs for this 1927
Patek Philippe pocket-watch with star chart.
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This brings us to today’s watches that bring sky to
wrist, starting with the earliest astrolabe-inspired
models:
1 Ulysse Nardin Astrolabe Galileo Galilei. This
remarkable wristwatch, part of a trilogy produced
in 1985, was the first to reduce the indications of a
large tower-clock like the Zytglogge to the space of
a watch dial. The mechanism designed by Ludwig
Oechslin gives you more than a pretty sky and is
said to be most accurate. Both sidereal and mean
time are indicated, but only the high-magnitude
stars appear. Oechslin chose the traditional astrolabe format with the firmament and the sun hand
going around clockwise. The sun hand shows the
time of day as well as the apparent position of the
sun on the ecliptic. The moon hand shows the position and phase of the moon. Finally the dragon
hand, which shows the lunar nodes and crosses
the ecliptic every 18.6 years, foretells the eclipses
of the sun and the moon.
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2 Christiaan van der Klaauw, CK Astrolabium
CKAL7766. Van der Klaauw, a member of the
AHCI academy of independent watch and clock
creators who lives in the Netherlands, makes
astronomical indications his speciality. His astrolabe shows the position of the brightest stars, the
sun and the moon, and the lunar nodes with a
dragon hand. The visible part of the sky is presented on the dial in the manner of an antique
astrolabe, behind the hands and the stars.
3 Patek Philippe, ref. 5102PR Celestial. The
indications derived from the Star Calibre and the
Sky Moon Tourbillon show the night sky of the
northern hemisphere on the face of this elegant
selfwinding watch. The fine celestial dome turns
anti-clockwise. The ellipse representing the horizon frames the visible portion of the sky above
Geneva and elsewhere on the same latitude.
Although the moon crosses the sky at a different
rate than the stars, its position on the dial always
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accurately reflects its place in the sky. A hidden
mechanism makes the moon wax and wane. Two
arrows mark the position of Sirius and the moon
and can be adjusted separately to set the lunar and
stellar indications.
4 Vacheron Constantin, Tour de l’Ile. In this intricate watch, which ranks among the most complicated wristwatches, the sky above Geneva is shown
through an elliptical aperture in the dial. Although it
does not show sidereal time, it does show the equation of time – the difference between solar time and
mean time. Its other complications include a second
timezone, age and phase of the moon, minuterepeater, perpetual calendar, tourbillon, the times of
sunrise and sunset and a power-reserve indicator.
5 Van Cleef & Arpels, Midnight in Paris. This
urbane watch, which has the same name as a fragrance marketed by the brand, displays a glittering
firmament in aventurine that takes up the whole
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6 Officine Panerai, L’Astronomo Luminor
1950. Panerai launched its most complicated wristwatch in 2009, the International Year of Astronomy.
The celestial vault on the back turns anti-clockwise. The clear elliptical patch in the frosted glass
reveals the sky visible at a given latitude, which
can be set to the owner’s choice.
sun is integrated in an ingenious way. It goes
around on a transparent disc and shares the
24-hour scale with the sidereal time. It moves anticlockwise in relation to the Pole Star just as it
appears to do so in the sky, but slower than the
stars by one degree a day. It is thus caught up by
the scale of the zodiacal calendar on which it
shows the date. The sun is presumably driven by a
circumference wheel, otherwise it would clash with
the tourbillon.
The other complications are the flying tourbillon
with a silicon escapement and a minute-repeater.
7 Jaeger-LeCoultre, Master Grande Tradition.
This complex masterpiece from Le Sentier is in the
same vein as the Sky Moon Tourbillon: the astronomical indications are exactly calculated but the
appearance comes first, with a dial-side tourbillon
taking up some of the sky. It is placed on the vernal equinox, turns with the stars and shows sidereal time anti-clockwise on a 24-hour scale. The
8 IWC, Portuguese Sidérale Scafusia. As its
name suggests, this major complication with a
tourbillon is dedicated to sidereal time, which is
shown in hours and minutes on a small 24-hour
dial on the front of the watch. The focus of attention however is on the back: a planisphere of some
500 stars with lines joining them into constellations
rotates once a sidereal day around the polar axis.
face. An elliptical frame reveals the position of the
stars above Paris. The star disc goes round in one
year so the stars are in their true position only once
every 24 hours at midnight.
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The special feature is that polarising filters change
the colour of the sky from day to night through
dawn and dusk. IWC takes into account its customer’s location by providing a planisphere for the
southern hemisphere. The astrophysicist, Ben
Moore, has written a program enabling planispheres to be calculated to individual requirements
so that even customers living near the equator get
the best possible representation of their night sky
at home.
As in the Master Grande Tradition model, sidereal
time is shown by a pointer on the planisphere
against a 24-hour scale turning in the opposite
direction. It’s hard to understand why the sun hand
turns clockwise, thereby requiring its own hours
scale. If it went in the same direction as the stars,
like in the Jaeger-LeCoultre watch, it could indicate
the date, and the ecliptic that Moore specified for
the star chart would at least make sense. Despite
this, the IWC engineers have incorporated another
useful astronomical complication – the times of
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sunrise and sunset – that also exists in different
guises in watches by Patek Philippe, Vacheron
Constantin and Audemars Piguet. These two times
are shown by two small red arrows against the outside scale. The cams for the indications have to be
cut and fitted individually for each client.
The other complications: constant-force tourbillon,
sunrise and sunset, and a perpetual calendar that
shows the number of days since the start of the
year rather than the dates.
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For more on astronomical watches see our website
at www.watch-around.com
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