Tales from the Golden Age: Wilhelm Struve (1793-1864)

Wilhelm Struve; founder of an astronomical dynasty.

Wilhelm Struve; founder of an astronomical dynasty.

 

 

 

 

 

 

 

 

 

 

Dedicated to Mike 4242

 

Do the words of a poem lose their poignancy once its author departs this world?

Can the limp of ‘progress’ outshine the ‘grand procession’ of great accomplishment?

Can a culture, basking in the glory of its own achievement, be made mute by a faithless generation of technocrats?

Can an optical bench test inspire more than a night spent behind the eyepiece of a grand old telescope?

Let us venerate that which is deserving of veneration!

Whose crown shall we adorn with a laurel wreath?

Let us sing again of old dead men

 And clear the cobwebs from their medals.

For they have no equal in the present age

No muse to light their way.

 

In the last years of the eighteenth century, the socio-political map of Europe was rapidly changing. In France, Napolean Bonaparte had risen to power and his armies had overrun Germany, plunging it into political and economic upset, a time where the world’s great empires – British, French, Dutch and Russian – jockeyed for power. Yet, amidst this turmoil, a new centre of learning was established at Dorpat Observatory in Russia, the brainchild of the great astronomer Wilhelm Struve (1793-1864), which soon became the envy of the astronomical world.

Uncertain beginnings

Like many great astronomers from the golden age, the career of Wilhem Struve was more accidental than preordained. He was born at Altona, Duchy of Holstein (then a part of the Denmark–Norway kingdoms), near Hamburg, the youngest of 18 siblings of Jacob Struve (1755–1841), a trained mathematician and principal of the local school attended by his son. There, the boy quickly gained a reputation both as an accomplished athlete and a student of great academic promise sic mens sana in corpore sano sit.

In 1808, so the story goes, Struve was taking a stroll along a street in the Hamburg suburb of St. Pauli, when he fell into the hands of a French press gang seeking to enrol army recruits. He soon escaped though and Struve’s father moved the family away from the French occupation to Dorpat (modern Estonia) in Imperial Russia, to avoid military service, equipped with Danish passports.

The same year, the 15 year old entered the Imperial University of Dorpat, where he first studied philology, but soon tired of it, turning his attention instead to mathematics and astronomy. He began to support himself by offering his tutelage to wealthy patrons.

He received his doctorate at age 20, on a thesis on the latitude and longitude of Dorpat observatory. Between 1813 to 1820, Struve secured a permanent post there and taught at the university. With his position secured at Dorpat, Struve returned to Altona to visit his parents and became engaged to his sweetheart, Emilie Wall (1796–1834), whom he married in 1815. Their matrimony was long and happy and she bore him 12 children, eight of which survived childhood. His handsome appearance and cordial personality won him many notable friends. During his period away from Dorpat, Struve visited the established German observatories, forging friendships with the prominent astronomers of the age including Friedrich Wilhelm Bessel, Heinrich Olbers, Johann Schroter and the great mathematician, Carl Friedrich Gauss.

 The observatory at Dorpat was first erected in 1810 and was originally topped with a dome which was replaced by a more elaborate, cylindrical structure by 1822. It was equipped with a large transit instrument by the famous English telescope maker, Dollond, a Baumann repeating circle for the determination of star altitudes as well as a  Herschelian reflector of 8-foot focus. Its director, Professor Johann Huth, suffered chronic ill health and by 1820 Struve became a full professor and director of the observatory. Developing a keen interest in double stars, Struve became pre-occupied with their research, using both the transit instrument and a smaller refractor of 5-foot focus in their pursuit.

The sweetest of telescopes

As his interest in double star astronomy and geodesy deepened, Struve began to seek out a larger instrument that would do justice to the university and establish Dorpat as a major centre of world-class astronomical research. In 1820, Struve paid the great German optician, Joseph Fraunhofer, a visit in Munich to find out how large a telescope he could make. Thanks to a generous grant from the university – which had the Romanov imperial family as its patron – Struve was able to place an order for the largest and most modern refracting telescope to grace the world. Its aperture was to be 9 Paris inches (9.6 modern inches), to be mounted on a sturdy, clock-driven equatorial mount. 

The 9.6" Dorpat refractor; iconic of an age.

The 9.6″ Dorpat refractor; iconic of an age.

In 1824, Fraunhofer had completed the instrument and painstakingly shipped it in 22 crates from Munich. Eager to ensure a safe transit, Struve despatched one of his students to serve as an escort. Finally, on the faithful day of November 10, 1824, a grand procession of horse-drawn carts arrived at the observatory, where the instrument and its fine accoutrement of optical and micrometrical accessories, was carefully unpacked. Curiously, Fraunhofer had failed to include instructions on its assembly but that didn’t deter Struve, who, using only a drawing he received from Fraunhofer earlier, managed to put the grand instrument together in just five days!

The Dorpat 9.6 inch achromatic refractor had a relative aperture of f/18 and was mounted on a beautiful wooden pier. Its tube was fashioned from fir wood covered with mahogany veneer which gleamed like polished copper and its declination and hour circles had a silvery gleam. A couple of long, slender rods were mounted on either side of the instrument to minimise tube flexure. This was not only the most powerful telescope on Earth, it was also the most beautiful. The telescope was temporarily located in the western hall of the observatory, where a high, south-facing window provided an unobstructed view of the heavens up to an altitude of 45 degrees above the horizon.

Schematic of the Great Dorpat refractor.

Schematic of the Great Dorpat refractor.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As magnificent as the telescope looked astride its state-of-the-art equatorial mount, its optical evaluation was still forthcoming. That opportunity arrived on November 16, during a clear spell in the wee small hours. Examining the moon and a suite of double stars, Struve proclaimed, “This magnificent work of art was doubly astonishing both for the excellence of its design and construction, and for its great optical power and the quality of its images.” In the words of Dr. Joseph Ashbrook, former editor of Sky & Telescope, “Wilhelm Struve’s first use of the Dorpat refractor marked a major milestone in astronomical history. The great, clumsy, altazimuth reflectors of the Herschels’ became obsolete on that date, for Struve had begun to measure double stars with the first modern telescope.”

Ardent and faithful with the telescope

With the Great Dorpat refractor, Struve discovered 3,134 double stars publishing his work in his magnum opus, Catalogus Novus Stellarum Duplicium (1827), which was refined over the decades until his retirement. The great telescope was also use to measure the angular sizes of the major planets and their satellites and made important observations of comets.

The mechanical excellence of the telescope enabled Struve to work with extraordinary efficiency. 400 objects could be viewed at very high powers (typically 700 diameters); or one object every nine seconds! In just three years, he had examined an astonishing 20,000 objects, discovering a new double star for every 38 single ones examined.

Struve remained at Dorpat until 1839, after which he founded and became director of the new Pulkovo Observatory near St Petersburg which had an even larger refractor installed (15-inch). Here Struve’s son, Otto, continued his father’s work, discovering a further 500 pairs. The recipient of many honours, the Elder Struve won the Gold Medal of the Royal Astronomical Society in 1826. He was elected a Fellow of the Royal Society in March, 1827 and was awarded their Royal Medal the same year and was elected a member of the Royal Swedish Academy of Sciences in 1833. In 1843 Wilhelm formally adopted Russian nationality. The collective work of the Struves was responsible for establishing the orbits of some 20 per cent of all the binary star systems known to date.

Struve carefully measured the “constant of aberration” in 1843. He was also the first to measure the parallax of Vega, although Friedrich Bessel had been the first to measure the parallax of a star (61 Cygni). He was also one of the pioneering astronomers to identify the effects of interstellar extinction (though he provided no mechanism to explain the effect). His estimate of the average rate of visual extinction – 1 magnitude per kpc – is remarkably close to modern estimates (0.7-1.0 magnitude per kpc).

Struve was also interested in geodetic surveying, and in 1831 published Beschreibung der Breitengradmessung in den Ostseeprovinzen Russlands. He initiated the Struve Geodetic Arc, which was a chain of survey triangulations stretching from Hammerfest in Norway to the Black Sea, through ten countries and over 2,820 kilometres, in order to establish the precise dimensions of the Earth.  He retired in 1862 due to failing health and died two years later on the morning of November 23, 1864.

Struve founded a dynasty of astronomers, with his sons from his marriage to Emilie Wall and, after her passing, further children from his remarriage to Johann Bartels (1807–1867), daughter of the mathematician Martin Bartels, who bore him a further six children. His name and that of his sons, Otto and Karl, is immortalised by the naming of asteroid 768 Struve and a lunar crater was named for another three astronomers of the Struve family: Friedrich Georg Wilhelm, Otto Wilhelm and Otto.

It is difficult to summarise the achievements of this great astronomer from the golden age. Perhaps it is fitting to quote the words of the Reverend C. Pritchard, who wrote a short biography of the man in the Astronomical Register (1865).

Whatever is mortal of Wilhelm Struve, rests in the churchyard attached to the beloved institution which he so long adorned. His  grave lies under the shadow of its domes and was selected by himself: yet it is not these domes alone which constitute its monument; the spirit of the man still breathes in the zeal, the labours the unanimity, which survive the master, and reign within them. That spirit will be reproduced again and again in future ages, when other men, animated by the story of his example, shall endeavour to follow in his steps.”

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Thank you for reading.

Eye.

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