Yrjö Väisälä

Template:Short description {{#invoke:other uses|otheruses}} Template:Infobox scientist

Yrjö Väisälä ({{#invoke:IPA|main}}; 6 September 1891Template:Efn – 21 July 1971) was a Finnish astronomer and physicist.<ref name="Obituary-by-Öpik" />

His main contributions were in the field of optics. He was also active in geodetics, astronomy and optical metrology. 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.<ref name="MPC-Discoverers" /><ref name="Obituary-by-Öpik" />

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

Väisälä was a fervent supporter of Esperanto, presiding over the Internacia Scienca Asocio Esperantista ("International Association of Esperanto Scientists") in 1968.<ref>Esperanta Finnlando numero 1/1968</ref>

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 Contemporary to Bernhard Schmidt's design, but unpublished was also Prof.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".<ref name="Obituary-by-Öpik" />

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

File:Vaisala diary.JPG

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 Template:Convert 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.<ref name="MPC-Discoverers" /> 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.<ref name="springer-1548-Palomaa" /> 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.<ref name="Obituary-by-Öpik" /> The parabolic comet C/1944 H1 observed in 1944 and 1945,<ref name="jpldata-C/1944 H1" /> as well as the two short period comets, 40P/Väisälä, a Jupiter-family comet,<ref name="jpldata-40P/Vaisala 1" /> and C/1942 EA, a Halley-type and near-Earth comet.<ref name="jpldata-C/1942 EA" /> 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<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> in honour of its founder. The lunar crater Väisälä is named after him,<ref>Template:GPN</ref> and so are the minor planets 1573 Väisälä and 2804 Yrjö.<ref name="springer-1573-Väisälä" /><ref name="springer-2804-Yrjö" />

List of discovered minor planets

1391 Carelia	16 February 1936	Template:LoMP
1398 Donnera	26 August 1936	Template:LoMP
1405 Sibelius	12 September 1936	Template:LoMP
1406 Komppa	13 September 1936	Template:LoMP
1407 Lindelöf	21 November 1936	Template:LoMP
1421 Esperanto	18 March 1936	Template:LoMP
1424 Sundmania	9 January 1937	Template:LoMP
1446 Sillanpää	26 January 1938	Template:LoMP
1447 Utra	26 January 1938	Template:LoMP
1448 Lindbladia	16 February 1938	Template:LoMP

1449 Virtanen	20 February 1938	Template:LoMP
1450 Raimonda	20 February 1938	Template:LoMP
1451 Granö	22 February 1938	Template:LoMP
1453 Fennia	8 March 1938	Template:LoMP
1454 Kalevala	16 February 1936	Template:LoMP
1460 Haltia	24 November 1937	Template:LoMP
1462 Zamenhof	6 February 1938	Template:LoMP
1463 Nordenmarkia	6 February 1938	Template:LoMP
1471 Tornio	16 September 1938	Template:LoMP
1472 Muonio	18 October 1938	Template:LoMP

1473 Ounas	22 October 1938	Template:LoMP
1477 Bonsdorffia	6 February 1938	Template:LoMP
1478 Vihuri	6 February 1938	Template:LoMP
1479 Inkeri	16 February 1938	Template:LoMP
1480 Aunus	18 February 1938	Template:LoMP
1483 Hakoila	24 February 1938	Template:LoMP
1488 Aura	15 December 1938	Template:LoMP
1492 Oppolzer	23 March 1938	Template:LoMP
1494 Savo	16 September 1938	Template:LoMP
1495 Helsinki	21 September 1938	Template:LoMP

1496 Turku	22 September 1938	Template:LoMP
1497 Tampere	22 September 1938	Template:LoMP
1498 Lahti	16 September 1938	Template:LoMP
1499 Pori	16 October 1938	Template:LoMP
1500 Jyväskylä	16 October 1938	Template:LoMP
1503 Kuopio	15 December 1938	Template:LoMP
1518 Rovaniemi	15 October 1938	Template:LoMP
1519 Kajaani	15 October 1938	Template:LoMP
1520 Imatra	22 October 1938	Template:LoMP
1521 Seinäjoki	22 October 1938	Template:LoMP

1523 Pieksämäki	18 January 1939	Template:LoMP
1524 Joensuu	18 September 1939	Template:LoMP
1525 Savonlinna	18 September 1939	Template:LoMP
1526 Mikkeli	7 October 1939	Template:LoMP
1527 Malmquista	18 October 1939	Template:LoMP
1529 Oterma	26 January 1938	Template:LoMP
1530 Rantaseppä	16 September 1938	Template:LoMP
1532 Inari	16 September 1938	Template:LoMP
1533 Saimaa	19 January 1939	Template:LoMP
1534 Näsi	20 January 1939	Template:LoMP

1535 Päijänne	9 September 1939	Template:LoMP
1536 Pielinen	18 September 1939	Template:LoMP
1541 Estonia	12 February 1939	Template:LoMP
1542 Schalén	26 August 1941	Template:LoMP
1548 Palomaa	26 March 1935	Template:LoMP
1549 Mikko	2 April 1937	Template:LoMP
1551 Argelander	24 February 1938	Template:LoMP
1552 Bessel	24 February 1938	Template:LoMP
1567 Alikoski	22 April 1941	Template:LoMP
1631 Kopff	11 October 1936	Template:LoMP

1646 Rosseland	19 January 1939	Template:LoMP
1656 Suomi	11 March 1942	Template:LoMP
1659 Punkaharju	28 December 1940	Template:LoMP
1677 Tycho Brahe	6 September 1940	Template:LoMP
1678 Hveen	28 December 1940	Template:LoMP
1696 Nurmela	18 March 1939	Template:LoMP
1699 Honkasalo	26 August 1941	Template:LoMP
1723 Klemola	18 March 1936	Template:LoMP
1740 Paavo Nurmi	18 October 1939	Template:LoMP
1757 Porvoo	17 March 1939	Template:LoMP

1883 Rimito	4 December 1942	Template:LoMP
1928 Summa	21 September 1938	Template:LoMP
1929 Kollaa	20 January 1939	Template:LoMP
1947 Iso-Heikkilä	4 March 1935	Template:LoMP
2020 Ukko	18 March 1936	Template:LoMP
2067 Aksnes	23 February 1936	Template:LoMP
2091 Sampo	26 April 1941	Template:LoMP
2096 Väinö	18 October 1939	Template:LoMP
2194 Arpola	3 April 1940	Template:LoMP
2204 Lyyli	3 March 1943	Template:LoMP

2243 Lönnrot	25 September 1941	Template:LoMP
2258 Viipuri	7 October 1939	Template:LoMP
2292 Seili	7 September 1942	Template:LoMP
2299 Hanko	25 September 1941	Template:LoMP
2333 Porthan	3 March 1943	Template:LoMP
2379 Heiskanen	21 September 1941	Template:LoMP
2397 Lappajärvi	22 February 1938	Template:LoMP
2454 Olaus Magnus	21 September 1941	Template:LoMP
2464 Nordenskiöld	19 January 1939	Template:LoMP
2479 Sodankylä	6 February 1942	Template:LoMP

2486 Metsähovi	22 March 1939	Template:LoMP
2502 Nummela	3 March 1943	Template:LoMP
2512 Tavastia	3 April 1940	Template:LoMP
2535 Hämeenlinna	17 February 1939	Template:LoMP
2638 Gadolin	19 September 1939	Template:LoMP
2639 Planman	9 April 1940	Template:LoMP
2678 Aavasaksa	24 February 1938	Template:LoMP
2679 Kittisvaara	7 October 1939	Template:LoMP
2690 Ristiina	24 February 1938	Template:LoMP
2715 Mielikki	22 October 1938	Template:LoMP

2716 Tuulikki	7 October 1939	Template:LoMP
2733 Hamina	22 February 1938	Template:LoMP
2737 Kotka	22 February 1938	Template:LoMP
2750 Loviisa	30 December 1940	Template:LoMP
2802 Weisell	19 January 1939	Template:LoMP
2820 Iisalmi	8 September 1942	Template:LoMP
2826 Ahti	18 October 1939	Template:LoMP
2885 Palva	7 October 1939	Template:LoMP
2898 Neuvo	20 February 1938	Template:LoMP
2962 Otto	28 December 1940	Template:LoMP

2972 Niilo	7 October 1939	Template:LoMP
3037 Alku	17 January 1944	Template:LoMP
3099 Hergenrother	3 April 1940	Template:LoMP
3166 Klondike	30 March 1940	Template:LoMP
3212 Agricola	19 February 1938	Template:LoMP
3223 Forsius	7 September 1942	Template:LoMP
3272 Tillandz	24 February 1938	Template:LoMP
3281 Maupertuis	24 February 1938	Template:LoMP
3522 Becker	21 September 1941	Template:LoMP
3606 Pohjola	19 September 1939	Template:LoMP

3897 Louhi	8 September 1942	Template:LoMP
4181 Kivi	24 February 1938	Template:LoMP
4266 Waltari	28 December 1940	Template:LoMP
4512 Sinuhe	20 January 1939	Template:LoMP
5073 Junttura	3 March 1943	Template:LoMP
5153 Gierasch	9 April 1940	Template:LoMP
Template:Mp	18 October 1939	Template:LoMP
6572 Carson	22 September 1938	Template:LoMP

Gallery

• Väisälä brothers childhood home (elliptic cut).jpg

  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.

• 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".

External links

• Turun Ursa, Template:In lang