IWC Schaffhausen reaches for the stars

Portugiese Sidérale Scafusia



Paranal, Chile, 27 August 2011 – Today, in the middle of the Atacama Desert in Chile, IWC Schaffhausen presented a technological masterpiece of Haute Horlogerie to journalists from all over the world. After ten years of intensive research, the Swiss watch manufacturer has succeeded in uniting solar time with sidereal time, together with astronomical displays, in a single watch. The result is a fascinating universal work of art which comes with a wealth of surprising complications and new technical features. The Portuguese Sidérale Scafusia is the most complex timepiece ever created by IWC.

“With a history already stretching back over 140 years, IWC sets a new benchmark with this watch,” says Georges Kern, CEO of IWC Schaffhausen. “The development of the Portuguese Sidérale Scafusia was an exciting challenge for everyone involved and called for enormous commitment and interdisciplinary cooperation. It is an unparalleled distillation of pioneering work, craftsmanship, engineering and exclusivity. The result is overwhelming and fills us with immense pride.” Reason enough, then, to invite media professionals from all over the world to the unveiling of the new star in IWC’s firmament at a venue just as unusual as the watch itself: at Paranal, in the middle of the Chilean desert. Paranal, built and operated by the European Southern Observatory (ESO) flagship of European astronomy and the most advanced optical instrument of its kind. The Portuguese Sidérale Scafusia was designed to bring together astronomical displays and to show them with absolute precision. The most conspicuous feature of this new and highly complex timepiece is the constant-force tourbillon, which dominates the dial. But the reverse side of the watch is no less impressive. Neatly packed into the tiny space are a celestial chart, horizon, geographical coordinates, solar time, sidereal time, sunrise and sunset display as well as a display showing daytime, night-time and twilight. And behind the display showing the number of day, of course, is a completely integrated perpetual calendar. While the astronomers on Mount Paranal used their gigantic telescopes to probe billions of light years into the universe, journalists from all over the world gathered at the Residencia – home to approximately 150 scientists working with ESO – to learn all about the history and development of the Portuguese Sidérale Scafusia. No wonder IWC decided to premiere this watchmaking milestone in such unusual surroundings: after all, ESO’s world-leading astronomical research facilities located here provide nightly views of deepest space which no human eye has ever seen before.

Two ways to measure time on a single watch
Here on earth, our time is based on the length of the average solar day; but for observation of the stars, the factor that counts is the sidereal day, from the Latin sidus, for star. The two types of day, however, differ in length. The average solar day lasts exactly 24 hours and measures the average time between the sun’s passage over a given meridian. The reference for a sidereal day is an infinitely distant star, which is exactly perpendicular to the observation point at the beginning and the end of the period during which it is observed. It therefore measures the time taken for the earth to complete a rotation around its own axis. And because the earth not only turns around its own axis but also describes an arc around the sun, a sidereal day is about four minutes shorter than an average solar day. The 24-hour display located at the “12 o’clock” position on the dial has hour and minute hands, which show sidereal time with breathtaking accuracy. The train created by IWC’s engineers tracks sidereal time with such precision that it deviates by a maximum of just 11.5 seconds in the course of an entire year: yet another example of technological achievement at its best from Schaffhausen.

—The current time of day (or average solar time) is shown on a classical 12-hour display with central hour and minute hands. The seconds hand is mounted on the titanium cage of the tourbillon at “9 o’clock” and advances in one-second intervals in constant power mode

An impressive tourbillon
Thanks to the Portuguese Sidérale Scafusia, it is now possible to see two different methods of measuring time side by side on a single watch. Average solar time – in other words the scale against which we measure the course of our daily lives – is displayed on the central hour and minute hands. The seconds are shown by a tourbillon mounted on a ball bearing at the “9 o’clock” position. Taking up almost a quarter of the entire bottom plate, the tourbillon is impressive for its sheer size alone. But the connoisseur will take even greater pleasure in the unusual design: it features a constant power mechanism, which compensates for the continuous depletion of energy in the barrels and transmits a steady trickle of energy to the balance. This boosts the precision of the newly designed hand-wound 94900 calibre to an even higher level. Two barrels aligned in parallel guarantee a minimum of two days’ constant power. All this time, the seconds hand mounted on the titanium cage of the tourbillon advances in one-second intervals. Throughout the remaining time of the four-day power reserve, the tourbillon continues to run evenly, following the rhythm of the balance, which oscillates at the rate of 2.5 hertz, or 18,000 beats per hour.

A celestial chart of a special kind
The Portuguese Sidérale Scafusia is not only an impressive sight from the front, but also from the reverse side, with its imprinted night sky and perpetual calendar. The calendar is shown in the form of a circular cut-out and counts the days of the year continuously: the 1st of January is day 1, the 31st of December day 365; or, in the case of a leap year – indicated by the letters LY, number 366. This is joined, on the edge of the case back, by a further display that shows the current time of day, the sidereal time as well as sunrise and sunset with arrows in a 24-hour rhythm. Finally, at the centre, is the night sky. The horizon, engraved in yellow, shows the night sky as the owner himself sees it at a location of his choice. IWC’s engineers use the coordinates of the individual location to calculate the angle of the horizon and then machine the cams which control the sunrise and sunset display. This means that the customer is not only the owner of an extraordinary watch but also has his own personalized constellation showing the night sky at the geographical position of his choosing. Also linked to this is the background formed by the night sky, which has a polarization filter that makes it appear grey by day and blue by night.

—The first thing that strikes the viewer is the centrally positioned celestial chart which, thanks to a polarization filter, appears grey during the day and blue at night. The yellow horizon line is individually calculated for a location specified by the watch’s owner

Every watch is unique
For all its precision and attention to detail, the Portuguese Sidérale Scafusia is eminently suitable for everyday use. It is water-resistant to 3 bar and, considering that the mechanism is so delicate, astonishingly impervious to shocks. A winder designed specially for the Portuguese Sidérale Scafusia ensures that this masterpiece from Schaffhausen continues to show precise times even if the owner chooses not to wear it for a prolonged period. As you might expect, the watch is also accompanied by a magnifying glass to facilitate precise examination of the night sky on the watch as well as comprehensive astronomical documentation. Every Portuguese Sidérale Scafusia is unique because, apart from the personal celestial chart on the back cover, the customer can also choose from a wide range of case materials and dial designs, as well as the colour and material of the wristband. In view of the degree of customization and the complexity of the design and mechanism this involves, buyers will have to wait approximately one year for delivery. But as we said: special features require time.

Further information

IWC Schaffhausen
Clemens von Walzel
Department Manager Public Relations
Tel. +41 (0)52 635 69 29

Portugieser Sidérale Scafusia

Ref. 5041


  • Mechanical movement, new balance with two adjustment cams and two adjustment weights, Breguet spring, two barrels, constant power tourbillon
  • Dial side displays: 24-hour display (sidereal time), sidereal time and solar time can be set separately, power reserve display
  • Rear side displays: Customized celestial chart and horizon, sunrise and sunset display, sidereal time and solar time, day, night and dusk display under celestial chart, perpetual calendar with display showing leap years and number of day


  • Calibre 94900
  • Frequency 18,000 A/ h / 2.5 Hz
  • Jewels 56
  • Power reserve 4 days (96 h)
  • Winding hand-wound


  • Materials: Case material as specified by customer (e.g. platinum or red gold), Strap as specified by customer with IWC folding clasp
  • Glass: Sapphire, convex, antireflective coating on both sides
  • Back: see-through sapphire-glass back
  • Water-resistant: 3 bar
  • Diameter: 46 mm
  • Height: 17.5 mm
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