Yrjö Väisälä

Yrjö Väisälä [ˈyrjø ˈʋæisælæ] (listen) (6 September 1891 in[1] Utra, Kontiolahti, Grand Duchy of Finland – 21 July 1971 in Rymättylä, Finland) was a Finnish astronomer and physicist.[2]

For other uses, see Vaisala (disambiguation).
Yrjö Väisälä
Born(1891-09-06)6 September 1891
Utra, Grand Duchy of Finland, Russian Empire
Died21 July 1971(1971-07-21) (aged 79)
Rymättylä, Finland
NationalityFinnish
Scientific career
Fieldsastronomy, physics

His main contributions were in the field of optics, but he was also very active in geodetics, astronomy and optical metrology. He had even an affectionate nickname of Wizard of Tuorla (Observatory/Optics laboratory), and there is a book with the same title in Finnish describing his works. His discoveries include 128 minor planets and 3 comets.[3][2]

His brothers were mathematician Kalle Väisälä (1893–1968) and meteorologist Vilho Väisälä (1889–1969). His daughter Marja Väisälä (1916–2011) was also an astronomer and discoverer of minor planets.

Väisälä was also a fervent supporter of Esperanto, presiding the Internacia Scienca Asocio Esperantista ("International Association of Esperanto Scientists") in 1968.[4]

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 Contemporary to Bernhard Schmidt's design, but unpublished was also Prof.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".[2]

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 plates). 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
A laboratory diary of Yrjö Väisälä. The text is written in 1929. On the pages seen here Väisälä describes the principle of 'a new telescope for photography'. Väisälä never published this concept and few years later Estonian Bernhard Schmidt invented the same construction which is now known as the Schmidt camera.

In the 1920s and 1930s Finland was doing its first precision triangulation chain measurements, and to create long-distance vertices Prof. Väisälä proposed usage of flash-lights on 5 to 10 kilometres (16,000 to 33,000 ft) 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 telescopes, 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 quasars.

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 for searching asteroids and comets. 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.)

Yrjö Väisälä is credited by the Minor Planet Center with the discovery of 128 asteroids (see below) during 1935–1944.[3] 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.[5] 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 comets.[2] The parabolic comet C/1944 H1 observed in 1944 and 1945,[6] as well as the two short period comets, 40P/Väisälä, a Jupiter-family comet,[7] and C/1942 EA, a Halley-type and near-Earth comet.[8] 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 Astronomy department is known as VISPA: Väisälä Institute for Space Physics and Astronomy[9] in honour of its founder. The lunar crater Väisälä is named after him,[10] and so are the minor planets 1573 Väisälä and 2804 Yrjö.[11][12]

List of discovered minor planets
1391 Carelia16 February 1936list
1398 Donnera26 August 1936list
1405 Sibelius12 September 1936list
1406 Komppa13 September 1936list
1407 Lindelöf21 November 1936list
1421 Esperanto18 March 1936list
1424 Sundmania9 January 1937list
1446 Sillanpää26 January 1938list
1447 Utra26 January 1938list
1448 Lindbladia16 February 1938list
1449 Virtanen20 February 1938list
1450 Raimonda20 February 1938list
1451 Granö22 February 1938list
1453 Fennia8 March 1938list
1454 Kalevala16 February 1936list
1460 Haltia24 November 1937list
1462 Zamenhof6 February 1938list
1463 Nordenmarkia6 February 1938list
1471 Tornio16 September 1938list
1472 Muonio18 October 1938list
1473 Ounas22 October 1938list
1477 Bonsdorffia6 February 1938list
1478 Vihuri6 February 1938list
1479 Inkeri16 February 1938list
1480 Aunus18 February 1938list
1483 Hakoila24 February 1938list
1488 Aura15 December 1938list
1492 Oppolzer23 March 1938list
1494 Savo16 September 1938list
1495 Helsinki21 September 1938list
1496 Turku22 September 1938list
1497 Tampere22 September 1938list
1498 Lahti16 September 1938list
1499 Pori16 October 1938list
1500 Jyväskylä16 October 1938list
1503 Kuopio15 December 1938list
1518 Rovaniemi15 October 1938list
1519 Kajaani15 October 1938list
1520 Imatra22 October 1938list
1521 Seinäjoki22 October 1938list
1523 Pieksämäki18 January 1939list
1524 Joensuu18 September 1939list
1525 Savonlinna18 September 1939list
1526 Mikkeli7 October 1939list
1527 Malmquista18 October 1939list
1529 Oterma26 January 1938list
1530 Rantaseppä16 September 1938list
1532 Inari16 September 1938list
1533 Saimaa19 January 1939list
1534 Näsi20 January 1939list
1535 Päijänne9 September 1939list
1536 Pielinen18 September 1939list
1541 Estonia12 February 1939list
1542 Schalén26 August 1941list
1548 Palomaa26 March 1935list
1549 Mikko2 April 1937list
1551 Argelander24 February 1938list
1552 Bessel24 February 1938list
1567 Alikoski22 April 1941list
1631 Kopff11 October 1936list
1646 Rosseland19 January 1939list
1656 Suomi11 March 1942list
1659 Punkaharju28 December 1940list
1677 Tycho Brahe6 September 1940list
1678 Hveen28 December 1940list
1696 Nurmela18 March 1939list
1699 Honkasalo26 August 1941list
1723 Klemola18 March 1936list
1740 Paavo Nurmi18 October 1939list
1757 Porvoo17 March 1939list
1883 Rimito4 December 1942list
1928 Summa21 September 1938list
1929 Kollaa20 January 1939list
1947 Iso-Heikkilä4 March 1935list
2020 Ukko18 March 1936list
2067 Aksnes23 February 1936list
2091 Sampo26 April 1941list
2096 Väinö18 October 1939list
2194 Arpola3 April 1940list
2204 Lyyli3 March 1943list
2243 Lönnrot25 September 1941list
2258 Viipuri7 October 1939list
2292 Seili7 September 1942list
2299 Hanko25 September 1941list
2333 Porthan3 March 1943list
2379 Heiskanen21 September 1941list
2397 Lappajärvi22 February 1938list
2454 Olaus Magnus21 September 1941list
2464 Nordenskiöld19 January 1939list
2479 Sodankylä6 February 1942list
2486 Metsähovi22 March 1939list
2502 Nummela3 March 1943list
2512 Tavastia3 April 1940list
2535 Hämeenlinna17 February 1939list
2638 Gadolin19 September 1939list
2639 Planman9 April 1940list
2678 Aavasaksa24 February 1938list
2679 Kittisvaara7 October 1939list
2690 Ristiina24 February 1938list
2715 Mielikki22 October 1938list
2716 Tuulikki7 October 1939list
2733 Hamina22 February 1938list
2737 Kotka22 February 1938list
2750 Loviisa30 December 1940list
2802 Weisell19 January 1939list
2820 Iisalmi8 September 1942list
2826 Ahti18 October 1939list
2885 Palva7 October 1939list
2898 Neuvo20 February 1938list
2962 Otto28 December 1940list
2972 Niilo7 October 1939list
3037 Alku17 January 1944list
3099 Hergenrother3 April 1940list
3166 Klondike30 March 1940list
3212 Agricola19 February 1938list
3223 Forsius7 September 1942list
3272 Tillandz24 February 1938list
3281 Maupertuis24 February 1938list
3522 Becker21 September 1941list
3606 Pohjola19 September 1939list
3897 Louhi8 September 1942list
4181 Kivi24 February 1938list
4266 Waltari28 December 1940list
4512 Sinuhe20 January 1939list
5073 Junttura3 March 1943list
5153 Gierasch9 April 1940list
(6073) 1939 UB18 October 1939list
6572 Carson22 September 1938list
  • An early 20th century wooden house in Joensuu at the corner of Sepänkatu and Papinkatu streets. The building was Väisälä brothers' home in 1904–19.
  • 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".
gollark: (this was purchased by accident)
gollark: I could read my Scots copy of Harry Potter and the Philosopher's Stone without significant difficulty.
gollark: But they could *understand* it, presumably.
gollark: No, I mean imply specific rules or at least approximations for "is something in this area or not".
gollark: That seems vaguely defined and may also imply grammar rules still, if significantly weaker ones than usual.

References
  1. The birth date is a Gregorian calendar date. Although Grand Duchy of Finland was part of the Russian Empire at the time and Russia used the Julian calendar until 1918, the Gregorian calendar continued in official use in Finland because Finland had been part of Sweden when Sweden had converted to the Gregorian calendar in 1753.
  2. Öpik, Ernst (1971). "Y. Väisälä died 1971 July 21". Irish Astron. Journ. 11: 159. Bibcode:1973IrAJ...11R.159O.
  3. "Minor Planet Discoverers (by number)". Minor Planet Center. 28 October 2018. Retrieved 13 February 2019.
  4. Esperanta Finnlando numero 1/1968
  5. Schmadel, Lutz D. (2007). "(1548) Palomaa". Dictionary of Minor Planet Names – (1548) Palomaa. Springer Berlin Heidelberg. p. 123. doi:10.1007/978-3-540-29925-7_1549. ISBN 978-3-540-29925-7.
  6. "JPL Small-Body Database Browser: C/1944 H1 (Vaisala)". Jet Propulsion Laboratory. Retrieved 8 July 2016.
  7. "JPL Small-Body Database Browser: 40P/Vaisala 1". Jet Propulsion Laboratory. Retrieved 8 July 2016.
  8. "JPL Small-Body Database Browser: C/1942 EA (Vaisala)". Jet Propulsion Laboratory. Retrieved 8 July 2016.
  9. "Tuorla Observatory". Retrieved 1 October 2014.
  10. "Crater Väisälä". Gazetteer of Planetary Nomenclature. USGS Astrogeology Research Program.
  11. Schmadel, Lutz D. (2007). "(1573) Väisälä". Dictionary of Minor Planet Names – (1573) Väisälä. Springer Berlin Heidelberg. p. 125. doi:10.1007/978-3-540-29925-7_1574. ISBN 978-3-540-29925-7.
  12. Schmadel, Lutz D. (2007). "(2804) Yrjö". Dictionary of Minor Planet Names – (2804) Yrjö. Springer Berlin Heidelberg. pp. 229–230. doi:10.1007/978-3-540-29925-7_2805. ISBN 978-3-540-29925-7.
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