Pyxis, constellation in the southern sky at about 9 hours right ascension and 30° south in declination. Its brightest star is Alpha Pyxidis, with a magnitude of 3.7. The French astronomer Nicolas Louis de Lacaille formed this constellation in 1754 from stars near what was considered the mast of

Finland: Theatre, opera, and music: …in the country is the Pyynikki Open Air Theatre of Tampere, the revolving auditorium of which can be moved to face any of the natural sets. There are innumerable institutions connected with the theatre in Finland, including the Central Federation of Finnish Theatrical Organizations. There is a wide repertory of…

tank: Gun calibre: …gun was adopted for the Pz. 61 and Pz. 68 tanks produced in Switzerland, the West German Leopard 1, the Swedish S-tank, the Japanese Type 74, and the Mark 1 and 2 versions of the Israeli Merkava. It was also retained in the original version of the U.S. M1 Abrams…

panzer: Pz. I: The Pz. I was a light tank intended as a training vehicle for the new panzer divisions until the more powerful Pz. II, III, and IV tanks could be put into service. The Pz. I went into production in 1934. It was lightly…

panzer: Pz. I: …and an improved version, the IB, was used in large numbers by the German army in the invasions of Poland (1939) and France (1940). The lightly armed and armoured IB performed adequately in these campaigns because it was used in massed formations and because opposing forces made poor use of…

panzer: Pz. II: The Pz. II was larger and more heavily armed and armoured than the Pz. I, but it was still a light tank. It was nevertheless the mainstay of the panzer divisions in the first two years of the war, because of delays encountered…

tank: Interwar developments: …cruiser tanks, and the German Pz. III also required support from more heavily armed tanks if they were to engage in fighting of any intensity. The need for tanks with more powerful 75-mm guns was clearly recognized in Germany, leading in 1934 to the design of the Pz. IV. The…

tank: World War II: The German Pz. IV and Soviet T-34 were rearmed in 1942 with longer-barreled, higher-velocity guns; soon afterward these began to be displaced by more powerfully armed tanks. In 1943 the Germans introduced the Panther medium tank with a long 75-mm gun having a muzzle velocity of 936…

tank: World War II: …1943 the Germans introduced the Panther medium tank with a long 75-mm gun having a muzzle velocity of 936 metres (3,070 feet) per second, compared with 384 metres (1,260 feet) per second for the original Pz. IV and 750 metres (2,460 feet) per second for its 1942 version. The 43-ton…

Ferdinand Porsche: …designed military vehicles, notably the Tiger tank. After the war the elder Porsche was imprisoned by the French for a time. In 1950 the Porsche sports car was introduced. The Porsche Museum opened in Zuffenhausen, a suburb of Stuttgart, in 2009.

Poland: Political process: …Poland was governed by the Polish United Workers’ Party (PUWP; Polska Zjednoczona Partia Robotnicza), the country’s communist party, which was modeled on the Communist Party of the Soviet Union. The postwar government was run as a dual system in which state organs were controlled by parallel organs of the PUWP.…

time: Time determination: The photographic zenith tube (PZT) is a telescope permanently mounted in a precisely vertical position. The light from a star passing almost directly overhead is refracted by the lens, reflected from the perfectly horizontal surface of a pool of mercury, and brought to a focus just…