Yrjö Väisälä


Yrjö Väisälä was a Finnish astronomer and physicist.
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, and there is a book with the same title in Finnish describing his works. His discoveries include 128 minor planets and 3 comets.
His brothers were mathematician Kalle Väisälä and meteorologist Vilho Väisälä. His daughter Marja Väisälä was also an astronomer and discoverer of minor planets.
Väisälä was also a fervent supporter of Esperanto, presiding the Internacia Scienca Asocio Esperantista 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 Contemporary to Bernhard Schmidt's design, but unpublished was also Prof.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 . The resulting system is known as the Schmidt-Väisälä camera or sometimes as the Väisälä camera. 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 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 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.

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.
Yrjö Väisälä is credited by the Minor Planet Center with the [|discovery of 128 asteroids] 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 comets. 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 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

1391 Carelia16 February 1936
1398 Donnera26 August 1936
1405 Sibelius12 September 1936
1406 Komppa13 September 1936
1407 Lindelöf21 November 1936
1421 Esperanto18 March 1936
1424 Sundmania9 January 1937
1446 Sillanpää26 January 1938
1447 Utra26 January 1938
1448 Lindbladia16 February 1938

1473 Ounas22 October 1938
1477 Bonsdorffia6 February 1938
1478 Vihuri6 February 1938
1479 Inkeri16 February 1938
1480 Aunus18 February 1938
1483 Hakoila24 February 1938
1488 Aura15 December 1938
1492 Oppolzer23 March 1938
1494 Savo16 September 1938
1495 Helsinki21 September 1938

1523 Pieksämäki18 January 1939
1524 Joensuu18 September 1939
1525 Savonlinna18 September 1939
1526 Mikkeli7 October 1939
1527 Malmquista18 October 1939
1529 Oterma26 January 1938
1530 Rantaseppä16 September 1938
1532 Inari16 September 1938
1533 Saimaa19 January 1939
1534 Näsi20 January 1939

1646 Rosseland19 January 1939
1656 Suomi11 March 1942
1659 Punkaharju28 December 1940
1677 Tycho Brahe6 September 1940
1678 Hveen28 December 1940
1696 Nurmela18 March 1939
1699 Honkasalo26 August 1941
1723 Klemola18 March 1936
1740 Paavo Nurmi18 October 1939
1757 Porvoo17 March 1939

2243 Lönnrot25 September 1941
2258 Viipuri7 October 1939
2292 Seili7 September 1942
2299 Hanko25 September 1941
2333 Porthan3 March 1943
2379 Heiskanen21 September 1941
2397 Lappajärvi22 February 1938
2454 Olaus Magnus21 September 1941
2464 Nordenskiöld19 January 1939
2479 Sodankylä6 February 1942

2716 Tuulikki7 October 1939
2733 Hamina22 February 1938
2737 Kotka22 February 1938
2750 Loviisa30 December 1940
2802 Weisell19 January 1939
2820 Iisalmi8 September 1942
2826 Ahti18 October 1939
2885 Palva7 October 1939
2898 Neuvo20 February 1938
2962 Otto28 December 1940

3897 Louhi8 September 1942
4181 Kivi24 February 1938
4266 Waltari28 December 1940
4512 Sinuhe20 January 1939
5073 Junttura3 March 1943
5153 Gierasch9 April 1940
18 October 1939
6572 Carson22 September 1938

Gallery