The University of Tartu (Estonian: Tartu Ülikool) is a public research university in Tartu, Estonia. It is the national university of Estonia, as well as the largest and oldest university in the country.
The university was founded in 1632 by Gustavus Adolphus, at the time the king of Sweden. Its first chancellor was Baron Johan Skytte, the governor-general of the Swedish province of Livonia.
The Tartu Observatory (Estonian: Tartu Observatoorium) is the largest astronomical observatory in Estonia. On 1 January 2018, Tartu Observatory was joined again to the University of Tartu, and the observatory is now an institute of the university. It is located on the Tõravere hill, about 20 km south-west of Tartu in Nõo Parish, Tartu County. The old Tartu Observatory, located in Tartu city centre, is known internationally for its connection to Friedrich Georg Wilhelm von Struve and the Struve Geodetic Arc, of which it is the first reference point.
In fields such as epidemiology, social sciences, psychology and statistics, an observational study draws inferences from a sample to a population where the independent variable is not under the control of the researcher because of ethical concerns or logistical constraints. One common observational study is about the possible effect of a treatment on subjects, where the assignment of subjects into a treated group versus a control group is outside the control of the investigator. This is in contrast with experiments, such as randomized controlled trials, where each subject is randomly assigned to a treated group or a control group. Observational studies, for lacking an assignment mechanism, naturally present difficulties for inferential analysis.
Tartu is the second largest city in Estonia after Tallinn. Tartu has a population of 97,759 (as of 2024). It is 186 kilometres (116 miles) southeast of Tallinn and 245 kilometres (152 miles) northeast of Riga, Latvia. Tartu lies on the Emajõgi river, which connects the two largest lakes in Estonia, Lake Võrtsjärv and Lake Peipus. From the 13th century until the end of the 19th century, Tartu was known in most of the world by variants of its historical name Dorpat.
Tartu, the largest urban centre of southern Estonia, is home to the nation's oldest and most renowned university, the University of Tartu (founded in 1632). Tartu also houses the Supreme Court of Estonia, the Ministry of Education and Research, the Estonian National Museum, and the oldest Estonian-language theatre, Vanemuine. It is also the birthplace of the Estonian Song Festivals.
Hydroxyapatite (IMA name: hydroxylapatite) (Hap, HAp, or HA) is a naturally occurring mineral form of apatite with the formula Ca5(PO4)3(OH), often written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities. It is the hydroxyl endmember of the complex apatite group. The OH ion can be replaced by fluoride or chloride, producing fluorapatite or chlorapatite. It crystallizes in the hexagonal crystal system. Pure hydroxyapatite powder is white. Naturally occurring apatites can, however, also have brown, yellow, or green colorations, comparable to the discolorations of dental fluorosis.
Up to 50% by volume and 70% by weight of human bone is a modified form of hydroxyapatite, known as bone mineral. Carbonated calcium-deficient hydroxyapatite is the main mineral of which dental enamel and dentin are composed. Hydroxyapatite crystals are also found in pathological calcifications such as those found in breast tumors, as well as calcifications within the pineal gland (and other structures of the brain) known as corpora arenacea or "brain sand".
Ernst Christoph Friedrich Knorre (11 December 1759 – 1 December 1810) was a German-born astronomer who lived and worked in present-day Estonia as a founding professor of mathematics at the Universität Dorpat and chief observator for the Dorpat Observatory. His son Karl Friedrich Knorre and grandson Viktor Knorre were also notable astronomers. Recently NASA named an asteroid in honor of the three generations of Knorre astronomers.
Juri Lotman (Russian: Ю́рий Миха́йлович Ло́тман; 28 February 1922 – 28 October 1993) was a prominent Russian-Estonian literary scholar, semiotician, and historian of Russian culture, who worked at the University of Tartu. He was elected a member of the British Academy (1977), the Norwegian Academy of Science and Letters (1987), the Royal Swedish Academy of Sciences (1989) and the Estonian Academy of Sciences (1990). He was a founder of the Tartu–Moscow Semiotic School. The number of his printed works exceeds 800 titles. His extensive archive (now kept at the University of Tallinn and at the Tartu University Library) includes his correspondence with a number of Russian and Western intellectuals.