European astronomy would not be world leading without the action of Lodewijk
Woltjer over several decades.

Lodewijk –Lo- Woltjer started his scientific life as a chemist. The world of
chemistry and geology, however, seemed too narrow for his ambitions. The
Universe was to be the scientific ground where he would exercise his intellectual

His first outstanding contribution was an analysis of the polarisation of the Crab
nebula and its implication for the magnetic fields within the nebula. From there
his interest moved to the dynamic importance of magnetic fields for the
structures of the Crab nebula, but also for those of the Galaxy. Since then
supernova remnants and neutron stars remained one subject of constant interest
to him, culminating in the large observation programmes swiftly put in place at
ESO when supernova 1987A exploded.

When quasars and active galactic nuclei were discovered, and the redshift of 3C
273 was measured revealing it’s enormous the luminosity, disputes about the
origin of the redshifts erupted. Some doubted that objects as extreme as those
suggested by observations could exist; a viewpoint that Lo Woltjer very quickly
dismissed. His interest in quasars led him to the realm of high energy
astrophysics and radio astronomy, domains that were to help him to interact
later very fruitfully with colleagues in space sciences. Cosmology became one of
his active interests when he suggested, with Giancarlo Setti, that the
cosmological “diffuse” X-ray background could be produced by the
superposition of the emission of faint Active Galactic Nuclei. Interestingly, each
new field of work led to a new thread in Lo Woltjer’s work that winds its way
from it’s nascence through his whole bibliography. Together these threads build
into a broad bundle, a sign of the breadth of his contributions and scientific
culture. Reading through some of his papers while writing this text I am
confirmed in that Lo Woltjer’s contributions are not only broad, they are also
deep and they impress by the intelligence and clarity of the arguments

Lo Woltjer’s contributions to science would be enough to cast his name among
those who leave a memorable contribution to astronomy. But he also shaped
astronomy through his institutional contributions. He led the astronomy
department of Columbia university in New York from 1964 to 1974, when he
became Director General of ESO the European Southern Observatory, first in
Geneva and then in Garching bei München. When Lo Woltjer took his function,
European astronomy was still struggling to emerge from the deep depression in
which the Second World War left European science. Instruments on the
continent were no match to their US equivalents. Under Lo Woltjer’s leadership
the situation reversed completely. He developed in ESO a strong scientific group
despite tensions between ESO and national communities fearing that they would
lose the little leadership they may have had to a strong, supra-national
institution. It is largely due to Lo Woltjer’s personality and diplomatic skills that
these tensions were eased little by little for the benefit of all. Lo Woltjer also had
the foresight to form a group of first rate engineers and to encourage them to
explore and experiment with a number of novel technologies and solutions to
design original telescopes. The success of this approach became clear when the
New Technology Telescope came into operation in 1989. This was paving the
way to the Very Large Telescope (VLT), which was to become one of the world
most successful astronomical instruments. The political skills of Lo Woltjer were
of fundamental importance – together with the originality of the concept of four
telescopes that could be configured for interferometry, and the preparation
work done by ESO’s scientists and engineers - in securing the approval of the
project by ESO’s Council in 1987. All aspects of the VLT definition and
preparation bear his mark.

When Lo Woltjer left ESO in 1987 he continued contributing to the development
of the astronomical community through his involvement in the International
Astronomical Union, of which he was President 1994-1997 and through the
founding of the European Astronomical Society (EAS) in the wake of the fall of
the Soviet empire. It is also then that he served as chair of ESA’s Space Science
Advisory Committee, a position through which he contributed decisively to the
design of ESA’s Horizon 2000 programme. This programme was instrumental in
successfully structuring the scientific ambitions of the European Space Agency
and of the associated space science community. He served, among many other
functions as chair of the INTEGRAL Science Data Centre‘s Science Advice
Committee in Geneva in the 1990’s, a much appreciated support in a difficult
local environment.

Lo Woltjer’s action for the European astronomical community was
complemented by that of his wife of many years, Ulla Demierre Woltjer (1944-
2019). Ulla had a thorough knowledge of key individuals in the astronomical
community, along with their strengths and sometimes weaknesses. She gave
many opportunities for the social contacts without which a community cannot
develop, thus complementing Lo’s activities. She organised formal and less
formal events in Chile, Garching, Geneva, Saint-Michel l’Observatoire and
elsewhere, where exchanges on many levels also contributed to shape European

Lo Woltjer was a distinctly distinguished European personality, always elegant,
cultivated, and a musical connoisseur. This notwithstanding, he went several
times camping in the Canadian wilderness alone with his daughter Leonore. His
desk was always clear, an image of his mind. He had a strong natural authority, a
sharp mind and little patience with nonsense. He left a strong impression on
those who came across his path, and a lasting mark on those who shared a
segment of their careers with him.

Thierry J.-L. Courvoisier
EAS President (2010 – 2017)