Yrjö Väisälä (; 6 September 1891 – 21 July 1971) was a
Finnish astronomer
An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...
and
physicist
A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate cau ...
.
His main contributions were in the field of
optics
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of optical instruments, instruments that use or Photodetector, detect it. Optics usually describes t ...
. He was also active in
geodetics,
astronomy
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...
and optical
metrology
Metrology is the scientific study of measurement. It establishes a common understanding of Unit of measurement, units, crucial in linking human activities. Modern metrology has its roots in the French Revolution's political motivation to stan ...
. He had an affectionate nickname of ''Wizard of
Tuorla'' (Observatory/Optics laboratory), and a book with the same title in Finnish describes his works. His discoveries include 128 asteroids and 3 comets.
His brothers were mathematician Kalle Väisälä (1893–1968) and meteorologist
Vilho Väisälä
Vilho Väisälä (; September 28, 1889 – August 12, 1969) was a Finnish meteorologist and physicist, and founder of Vaisala Oyj.
After graduation in mathematics in 1912, Väisälä worked for the Finnish Meteorological Institute in ''ae ...
(1889–1969). His daughter
Marja Väisälä (1916–2011) was an astronomer and
discoverer of minor planets.
Väisälä was a fervent supporter of
Esperanto
Esperanto (, ) is the world's most widely spoken Constructed language, constructed international auxiliary language. Created by L. L. Zamenhof in 1887 to be 'the International Language' (), it is intended to be a universal second language for ...
, presiding over the ''Internacia Scienca Asocio Esperantista'' ("International Association of Esperanto Scientists") in 1968.
Optician
He developed several methods for measuring the quality of optical elements, as well as a lot of practical methods of manufacturing said elements. This allowed the construction of some of the earliest high-quality
Schmidt cameras, in particular a "field-flattened" version known as
Schmidt-Väisälä camera. Contemporary to
Bernhard Schmidt's design, but unpublished was also Prof. Yrjö Väisälä's identical design which he had mentioned in lecture notes in 1924 with a footnote: "problematic spherical focal surface".
Once he saw Schmidt's publication, he promptly went ahead and "solved" the field flattening problem by placing a doubly convex lens slightly in front of the film holder – back in the 1930s, astronomical films were glass plates ''(also see
photographic plate
Photographic plates preceded film as the primary medium for capturing images in photography. These plates, made of metal or glass and coated with a light-sensitive emulsion, were integral to early photographic processes such as heliography, d ...
s)''. The resulting system is known as the Schmidt-Väisälä camera or sometimes as the ''Väisälä camera''. (This solution is not perfect, as images of different colour end up at slightly different places.) Prof. Väisälä made a small test unit of 7 mirrors in a mosaic on stiff background steel frame, however it proved to be impossible to stabilize as "just adjust and forget" structure, and next time anybody tried it, was with active controls on
Multiple Mirror Telescope.
Geodesy

In the 1920s and 1930s
Finland
Finland, officially the Republic of Finland, is a Nordic country in Northern Europe. It borders Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of Bothnia to the west and the Gulf of Finland to the south, ...
was doing its first precision triangulation chain measurements, and to create long-distance vertices Prof. Väisälä proposed usage of flash-lights on altitude balloons, or on some big fireworks rockets. The idea was to measure the exact position of the flash against background stars, and by precisely knowing one camera location, to derive an accurate location for another camera. This required better wide-field cameras than were available, and was discarded.
Later, Prof. Väisälä developed a method to multiply an optical length reference using
white light interferometry to precisely determine lengths of baselines used in triangulation chains. Several such baselines were created in Finland for second high-precision triangulation campaign in 1950s and 1960s.
Later GPS made these methods largely obsolete. The
Nummela Standard Baseline established by Väisälä is still maintained by the
Finnish Geodetic Institute in
Nummela for the calibration of other distance measurement instruments.
Prof. Väisälä also developed excellent tools to measure earth rotational axis position by building so called
zenith telescope
A zenith telescope is a type of telescope that is designed to point straight up at or near the zenith. They are used for precision measurement of star positions, to simplify telescope construction, or both.
A classic zenith telescope, also known ...
s, and in the 1960s Tuorla Observatory was in the top rank of North Pole position tracking measurements.
In the 1980s radioastronomy was able to replace Earth rotation tracking by referring things against "non-moving background" of
quasar
A quasar ( ) is an extremely Luminosity, luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by accretion onto a supermassive black hole with a mass rangi ...
s.
For these Zenith Telescopes, Prof. Väisälä made also one of the first experiments at doing mirrors of liquid mercury. (Such mirror needs extremely smooth rotational speeds which were achieved in the late 1990s.)
Astronomer
The big
Schmidt-Väisälä telescope he built was used at the
University of Turku
The University of Turku (, shortened ''UTU'') is a multidisciplinary public university with eight faculties located in the city of Turku in southwestern Finland. The university also has campuses in Rauma and Pori and research stations in Kevo ...
for searching
asteroid
An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...
s and
comet
A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...
s. His research group discovered 7 comets and 807 asteroids.
For this rather massive photographic survey work, Prof. Väisälä developed also a protocol of taking two exposures on same plate some 2–3 hours apart and offsetting those images slightly. Any dot-pairs that differed from background were moving, and deserved follow-up photos. This method halved the film consumption compared to method of
"blink comparing", where plates get single exposures, and are compared by rapidly showing first and second exposures to human operator. (Blink-comparing was used to find e.g.
Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...
.)
Yrjö Väisälä is credited by the
Minor Planet Center
The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory.
Funct ...
with the
discovery of 128 asteroids ''(see below)'' during 1935–1944.
He used to name them with the names of his personal friends that had birthdays. One of them was the professor Matti Herman Palomaa, after whom an asteroid
1548 Palomaa was named.
For this reason the
Palomar Mountain Observatory in California has never had an asteroid bearing its name – the rules for naming asteroids state that the names have to differ from each other with more than one letter.
Besides minor planets, he has also discovered 3
comet
A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...
s.
The parabolic comet
C/1944 H1 observed in 1944 and 1945,
as well as the two
short period comets,
40P/Väisälä, a Jupiter-family comet,
and
C/1942 EA, a Halley-type and
near-Earth comet.
Together with
Liisi Oterma he co-discovered the Jupiter-family comet
139P/Väisälä–Oterma, which was first classified as asteroid and received the provisional designation "1939 TN".
Honors and awards
The University of
Turku
Turku ( ; ; , ) is a city in Finland and the regional capital of Southwest Finland. It is located on the southwestern coast of the country at the mouth of the Aura River (Finland), River Aura. The population of Turku is approximately , while t ...
Astronomy department is known as ''VISPA: Väisälä Institute for Space Physics and Astronomy'' in honour of its founder. The lunar crater ''
Väisälä'' is named after him,
and so are the minor planets
1573 Väisälä and
2804 Yrjö.
List of discovered minor planets
Gallery
File:Väisälä brothers childhood home (elliptic cut).jpg, An early 20th century wooden house in Joensuu
Joensuu (; ; ) is a city in Finland and the regional capital of North Karelia. It is located in the eastern interior of the country and in the Finnish Lakeland. The population of Joensuu is approximately , while the sub-region has a population ...
at the corner of Sepänkatu and Papinkatu streets. The building was Väisälä brothers' home in 1904–19.
File:Väisälä lapsuuskoti muistolaatta.jpg, A commemorative plaque attached to the building in 1976. The text reads: "At this place was Väisälä scientist brothers, Vilho, Yrjö and Kalle's, home in 1904–1919. Joensuu Lyceum ex-students".
Notes
References
External links
Turun Ursa
{{DEFAULTSORT:Vaisala, Yrjo
1891 births
1971 deaths
20th-century astronomers
Finnish astronomers
Discoverers of asteroids
Discoverers of comets
*
Finnish Esperantists
Finnish geodesists
Optical engineers
People associated with the University of Turku
People from Joensuu
Astronomy-optics society
Astronomical instrument makers