OBSERVATORY (ASTRONOMICAL). The erection of special buildings for astronomical research is a practice of long standing. It is said by Diodorus that the great temple of Belus at Babylon was built for astronomical purposes, and, since there is indication in the Chinese records that the gnomon was used for measuring the height of the sun in the reign of the emperor Yao (2300 B.C.) it may be said that the beginning of practical astron omy was contemporaneous in Eastern and Western Asia. There is no evidence of the existence of an observatory of Greek or Alexandrine origin until the time of Ptolemy Soter, who, about 30o B.C., built one at Alexandria. The earliest records from an observatory known to be extant are those of Hipparchus (c. 140 B.c.) who has left a catalogue of stars from observations made at the island of Rhodes, repeating those made earlier at Alexandria. Three hundred years later, Ptolemy (A.D. 150) compiled a star catalogue, but it is doubtful whether this was from his own observation and, therefore, whether he had an observatory beyond that at Alexandria.
The art of astronomical observation was revived several hun dred years later in Western Asia when observatories were estab lished at Damascus and Baghdad and one at Mokatta by Caliph Hakim about A.D. moo. A splendid observatory was built at Maragha in north-west Persia by Hulagu Khan about A.D. 126o, but the most productive was that of the Persian Prince Ulugha Beigh, grandson of the great Tamerlaine, who, at Samarcand with his assistants, made a catalogue of stars from observations with a large quadrant in the first half of the 15th century. Later in that century, about 1471, John Muller of Konigsberg, better known as Regiomontanus, set up an observatory at Nuremberg, with the help of Bernard Walther of that city, furnished with instruments of his own design, and after his death in 1476, clocks, then a re cent invention, were added to the equipment, but the first observatory that may be considered a prototype of modern na tional observatories was that of Tycho Brahe on the island of Hveen. Here, on Aug. 8, 1576, there was laid the foundation stone
of a building to serve as a residence and an observatory to which he gave the appropriate name Uranibourg.
Tycho Brake's Observatory.—This building was of some magnificence and large enough to house Tycho and several young men who lived with him as students or observers. It was furnished with a large quadrant attached to a wall in the plane of the meridian, for to this astronomer is due the credit of appreciating the advantage of size in instruments of this type, and of the principle which is embodied in the mural circle. Here Tycho Brahe lived in some state, with a dwarf as jester among his small retinue, for 20 years, and with his assistants, one of whom was Longomontanus, a name well known in the science, observed the heavens and produced a catalogue of the position of more than I,000 stars. On the death of his patron, Frederick II. in 1588, Tycho was deprived of royal favour and income. In 1597 Tycho left Denmark, the observatory at Hveen having been already dismantled.
The invention of the telescope in 1609 opens a new chapter in the history of observatories, and the first of a new class may be taken to be the building at Padua from which Galileo made the first observation of Jupiter's satellites on Jan. 8, 161o, Others were created as additions to universities or similar institutions during the 17th century, an observatory called the "Tower of the Winds" having been established at the Vatican by Gregory XIII., the Pope who gave his name to the Gregorian Calendar, and an other attached in 1632 to the university at Leyden, that had been in existence for half a century. In 1637, King Christian IV of Denmark, established a permanent observatory at Copenhagen which was completed 20 years later and then placed under the direction of Longomontanus. It exists in some form at the present date.