Editing Yrjö Väisälä (section)

== Astronomer ==

The big [[Schmidt-Väisälä camera|Schmidt-Väisälä telescope]] he built was used at the [[University of Turku]] for searching [[asteroid]]s and [[comet]]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 comparator|"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 [[#List of discovered minor planets|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 [[comet]]s.<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".