簡介
爾約·維薩拉（芬蘭語：Yrjö Väisälä， [ˈyrjø ˈʋæisælæ]，1891年9月6日－1971年7月21日）是一位芬蘭天文學家和物理學家。
維薩拉的主要貢獻是光學方面，但他在大地測量學、天文學和光學氣象學也有相當貢獻。他因此獲得綽號“Tuorla（天文台/光學實驗室）的魔術師”。另有一本同名的芬蘭書籍就是描述他的光學成就。
他的兩位兄弟分別是數學家卡利·維薩拉（Kalle Väisälä）和氣象學家維爾霍·維薩拉（Vilho Väisälä）。
維薩拉也是相當狂熱的世界語支持者。並曾在1968年擔任國際世界語科學家協會（世界語：Internacia Scienca Asocio Esperantista）會長。
光學設計
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Contemporary to Bernhard Schmidts design, but unpublished was also Prof.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. (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
大地測量學
In the 1920s and 1930s Finlandwas doing its first precision triangulation chain measurements, and to create long-distance vertices Prof. Väisälä proposed usage of flash-lights on 5（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. A Väisälä interferometry baseline 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.)
天文學
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.)
維薩拉還以發現兩顆周期彗星維薩拉彗星（40P/Väisälä）和維薩拉－奧特瑪彗星（139P/Väisälä-Oterma）而聞名。後者是和芬蘭首位獲得天文學博士的女性天文學家利斯·奧特瑪（Liisi Oterma）共同發現，起初被賦予小型星臨時編號 1939 TN。
發現小行星
維薩拉總共發現了128顆小行星。他使用知道生日的朋友命名這些小行星，其中一位朋友是馬蒂·帕洛馬（Matti Palomaa）教授的名字被用在小行星1548的命名。因為目前沒有小行星以美國加州的帕洛馬山天文台（Palomar Observatory），且有一個字母不同，因此符合小行星不得名稱重複的規則。
命名事物
月球上的維薩拉環形山
小行星1573和小行星2804
圖爾庫大學天文系全稱“維薩拉太空物理與天文研究所”表示對他的尊敬。
