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Yrjö Väisälä

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Yrjö Väisälä
Born(1891-09-06)6 September 1891[a]
Utra, Grand Duchy of Finland, Russian Empire
Died21 July 1971(1971-07-21) (aged 79)
Rymättylä, Finland
NationalityFinnish
Scientific career
Fieldsastronomy, physics

Yrjö Väisälä (Finnish: [ˈyrjø ˈʋæi̯sælæ] ⓘ; 6 September 1891[a] – 21 July 1971) was a Finnish astronomer and physicist.[1]

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.[2][1]

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.[3]

Optician

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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 Contemporary to Bernhard Schmidt's design, but unpublished was also Prof.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".[1]

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

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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

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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.[2] 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.[4] 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.[1] The parabolic comet C/1944 H1 observed in 1944 and 1945,[5] as well as the two short period comets, 40P/Väisälä, a Jupiter-family comet,[6] and C/1942 EA, a Halley-type and near-Earth comet.[7] 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

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The University of Turku Astronomy department is known as VISPA: Väisälä Institute for Space Physics and Astronomy[8] in honour of its founder. The lunar crater Väisälä is named after him,[9] and so are the minor planets 1573 Väisälä and 2804 Yrjö.[10][11]

List of discovered minor planets

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1391 Carelia 16 February 1936 list
1398 Donnera 26 August 1936 list
1405 Sibelius 12 September 1936 list
1406 Komppa 13 September 1936 list
1407 Lindelöf 21 November 1936 list
1421 Esperanto 18 March 1936 list
1424 Sundmania 9 January 1937 list
1446 Sillanpää 26 January 1938 list
1447 Utra 26 January 1938 list
1448 Lindbladia 16 February 1938 list
1449 Virtanen 20 February 1938 list
1450 Raimonda 20 February 1938 list
1451 Granö 22 February 1938 list
1453 Fennia 8 March 1938 list
1454 Kalevala 16 February 1936 list
1460 Haltia 24 November 1937 list
1462 Zamenhof 6 February 1938 list
1463 Nordenmarkia 6 February 1938 list
1471 Tornio 16 September 1938 list
1472 Muonio 18 October 1938 list
1473 Ounas 22 October 1938 list
1477 Bonsdorffia 6 February 1938 list
1478 Vihuri 6 February 1938 list
1479 Inkeri 16 February 1938 list
1480 Aunus 18 February 1938 list
1483 Hakoila 24 February 1938 list
1488 Aura 15 December 1938 list
1492 Oppolzer 23 March 1938 list
1494 Savo 16 September 1938 list
1495 Helsinki 21 September 1938 list
1496 Turku 22 September 1938 list
1497 Tampere 22 September 1938 list
1498 Lahti 16 September 1938 list
1499 Pori 16 October 1938 list
1500 Jyväskylä 16 October 1938 list
1503 Kuopio 15 December 1938 list
1518 Rovaniemi 15 October 1938 list
1519 Kajaani 15 October 1938 list
1520 Imatra 22 October 1938 list
1521 Seinäjoki 22 October 1938 list
1523 Pieksämäki 18 January 1939 list
1524 Joensuu 18 September 1939 list
1525 Savonlinna 18 September 1939 list
1526 Mikkeli 7 October 1939 list
1527 Malmquista 18 October 1939 list
1529 Oterma 26 January 1938 list
1530 Rantaseppä 16 September 1938 list
1532 Inari 16 September 1938 list
1533 Saimaa 19 January 1939 list
1534 Näsi 20 January 1939 list
1535 Päijänne 9 September 1939 list
1536 Pielinen 18 September 1939 list
1541 Estonia 12 February 1939 list
1542 Schalén 26 August 1941 list
1548 Palomaa 26 March 1935 list
1549 Mikko 2 April 1937 list
1551 Argelander 24 February 1938 list
1552 Bessel 24 February 1938 list
1567 Alikoski 22 April 1941 list
1631 Kopff 11 October 1936 list
1646 Rosseland 19 January 1939 list
1656 Suomi 11 March 1942 list
1659 Punkaharju 28 December 1940 list
1677 Tycho Brahe 6 September 1940 list
1678 Hveen 28 December 1940 list
1696 Nurmela 18 March 1939 list
1699 Honkasalo 26 August 1941 list
1723 Klemola 18 March 1936 list
1740 Paavo Nurmi 18 October 1939 list
1757 Porvoo 17 March 1939 list
1883 Rimito 4 December 1942 list
1928 Summa 21 September 1938 list
1929 Kollaa 20 January 1939 list
1947 Iso-Heikkilä 4 March 1935 list
2020 Ukko 18 March 1936 list
2067 Aksnes 23 February 1936 list
2091 Sampo 26 April 1941 list
2096 Väinö 18 October 1939 list
2194 Arpola 3 April 1940 list
2204 Lyyli 3 March 1943 list
2243 Lönnrot 25 September 1941 list
2258 Viipuri 7 October 1939 list
2292 Seili 7 September 1942 list
2299 Hanko 25 September 1941 list
2333 Porthan 3 March 1943 list
2379 Heiskanen 21 September 1941 list
2397 Lappajärvi 22 February 1938 list
2454 Olaus Magnus 21 September 1941 list
2464 Nordenskiöld 19 January 1939 list
2479 Sodankylä 6 February 1942 list
2486 Metsähovi 22 March 1939 list
2502 Nummela 3 March 1943 list
2512 Tavastia 3 April 1940 list
2535 Hämeenlinna 17 February 1939 list
2638 Gadolin 19 September 1939 list
2639 Planman 9 April 1940 list
2678 Aavasaksa 24 February 1938 list
2679 Kittisvaara 7 October 1939 list
2690 Ristiina 24 February 1938 list
2715 Mielikki 22 October 1938 list
2716 Tuulikki 7 October 1939 list
2733 Hamina 22 February 1938 list
2737 Kotka 22 February 1938 list
2750 Loviisa 30 December 1940 list
2802 Weisell 19 January 1939 list
2820 Iisalmi 8 September 1942 list
2826 Ahti 18 October 1939 list
2885 Palva 7 October 1939 list
2898 Neuvo 20 February 1938 list
2962 Otto 28 December 1940 list
2972 Niilo 7 October 1939 list
3037 Alku 17 January 1944 list
3099 Hergenrother 3 April 1940 list
3166 Klondike 30 March 1940 list
3212 Agricola 19 February 1938 list
3223 Forsius 7 September 1942 list
3272 Tillandz 24 February 1938 list
3281 Maupertuis 24 February 1938 list
3522 Becker 21 September 1941 list
3606 Pohjola 19 September 1939 list
3897 Louhi 8 September 1942 list
4181 Kivi 24 February 1938 list
4266 Waltari 28 December 1940 list
4512 Sinuhe 20 January 1939 list
5073 Junttura 3 March 1943 list
5153 Gierasch 9 April 1940 list
(6073) 1939 UB 18 October 1939 list
6572 Carson 22 September 1938 list
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  • 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.
    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".
    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

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  1. ^ a b 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.

References

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  1. ^ a b c d Öpik, Ernst (1971). "Y. Väisälä died 1971 July 21". Irish Astron. Journ. 11: 159. Bibcode:1973IrAJ...11R.159O.
  2. ^ a b "Minor Planet Discoverers (by number)". Minor Planet Center. 28 October 2018. Retrieved 13 February 2019.
  3. ^ Esperanta Finnlando numero 1/1968
  4. ^ 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.
  5. ^ "JPL Small-Body Database Browser: C/1944 H1 (Vaisala)". Jet Propulsion Laboratory. Retrieved 8 July 2016.
  6. ^ "JPL Small-Body Database Browser: 40P/Vaisala 1". Jet Propulsion Laboratory. Retrieved 8 July 2016.
  7. ^ "JPL Small-Body Database Browser: C/1942 EA (Vaisala)". Jet Propulsion Laboratory. Retrieved 8 July 2016.
  8. ^ "Tuorla Observatory". Retrieved 1 October 2014.
  9. ^ "Crater Väisälä". Gazetteer of Planetary Nomenclature. USGS Astrogeology Research Program.
  10. ^ 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.
  11. ^ 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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