ASTRONOMY

-In the Bible Although the Bible contains no explicit mention of the science of astronomy, it nevertheless has many references to topics such as the laws of the heavens (Jer. 31:34 (35); 33:25; Job 38:33) and the movements of the sun and the moon (Josh. 10:13; Ps. 19:6–7; Job 31:26; Eccles. 1:5–6). The Israelites did not study the stars as did the Babylonians, Egyptians, and Greeks. They may have refrained from too close observation of the celestial bodies out of a fear of idolatry – "When you look up to the sky and behold the sun, and the moon, and the stars, the whole heavenly host, you must not be lured into bowing down to them or serving them…" (Deut. 4: 19). Nevertheless, some basic knowledge of astronomy was essential to fix the dates of festivals and holidays. THE STARS AND THE PLANETS The firmament or heavenly vault, the abode of the two "great lights" and the stars, was stretched between the waters above and the waters beneath (Gen. 1:14–18), and was rigid and strong "as a molten mirror" (Job 37:18). The stars of the heaven are as numerous "as the sands on the seashore" (Gen. 22:17); they are also frequently called "the host of heaven." The planets (mazzalot; II Kings 23:5) are, according to most biblical interpreters, in the twelve regions of the firmament which are later referred to as the signs of the zodiac . Other constellations, the five planets, the sun and the moon, and various individual stars are referred to in the Bible (e.g., cf. Job 38:31–32). THE SUN AND THE MOON The sun and the moon are frequently mentioned: the sun is referred to as shemesh (Ex. 22:2; Deut. 24:15), ḥammah (Isa. 24:23; Job 30:28), and ḥarsah (Judg. 14:18). The usual term for the moon (yare'aḥ) was also used to designate the lunar cycle (e.g., Ex. 2:2; Deut. 21:13; I Kings 6:37). The moon is also called levanah (Isa. 24:23; Song 6:10), and the full moon is called kese(h) (Ps. 81:4; Prov. 7:20). The   word ḥodesh ("month") originally meant "the renewal of the moon," and described the day of the new moon (I Sam. 20:24, 34; Ezek. 26:1) and the length of its cycle (Gen. 29:14). THE PLANETS SATURN AND VENUS It is generally agreed that Chiun (Amos. 5:26) refers to Saturn (called kaiwānu, kai(a)mānu in Assyrian, and kaivana in Syrian). Lucifer (Heilel), the "son of the morning" is, according to most interpreters, the planet Venus that is visible at dawn (Isa. 14:12). In Arabic, Venus is called al-Zuhara ("the bright one."). THE FIXED STARS In the Bible kesil is mentioned four times (Isa. 13:10; Amos 5:8; Job. 9:9; 38:31). Views on its interpretation vary, but it is sometimes taken to represent Orion, which was considered to be one of the giant angels (Gen. 6:4). The Targum Jonathan rendered kesil, the "giant" (nefila; Job 9:9; 38:31); and in Isaiah 13:10 reference is made to "the stars of the heavens and their titans (kesileihem)." Kimah is, according to several interpreters, the constellation of the Pleiades. Other commentators identify it as Aldebaran, Arcturus, or Sirius. Ash (or ayish; Job 38:32) is mentioned with kesil and kimah (Job 9:9), and R. Judah b. Ezekiel claimed that it is the star called Yuta, "the lamb's tail," in Aramaic (Ber. 58b), which is probably Aldebaran. In the Vulgate, ash is translated as the Hyades, while the Septuagint gives it as "the Evening Star," i.e., Venus. Ḥadrei-Teiman (Job 9:9) is thought to represent the twinkling stars of the Southern firmament – the ship Argo, the Southern Cross, Centaurus and others – which could be observed in the land of Israel in the time of Job but cannot now, because of the precession of the equinoxes (that is, the slow westward movement of the earth's axis which makes the position of the stars change continuously), and thus the zodiac seems to change its position in relation to the horizon over hundreds of years. Mezarim in Job 37:9 is possibly a nickname for mazzalot, though according to some modern interpreters the mezarim are the Great Bear and the Little Bear. -In the Apocrypha In the Book of Enoch several chapters are devoted to the courses of the heavenly bodies, to the fixing of the length of day and night in the different months, to the moon's course during the month, and to the difference between the solar and lunar years. These astronomical ideas, often inaccurate, were interspersed with legends about angels and spirits. Thus, the angels elevate Enoch through the various spheres of the heavens, and at the fourth he perceives the sun and the moon and a multitude of stars. -In the Talmud and Midrash It is difficult to discuss fully the knowledge of astronomy in the talmudic period on the basis of the limited material in the Talmud and Midrashim. The knowledge of astronomy possessed by the tannaim and amoraim was not committed to paper, and only was recorded after its compilation by the geonim. The talmudic sages viewed astronomy – the computing of seasons and planets – and knowledge of the month order and the calendar (intercalation) as important adjuncts to the study of the Torah. They attributed these studies to the ancients of the Bible, and interpreted the verse "And of the children of Issachar that had understanding of the times, to know what Israel ought to do" (I Chron. 12:33) as meaning that the children of Issachar knew how to compute the cycles of the planets in order to learn how Israel would determine the months and leap years. The study of this science was even considered an obligation for the talented person (Shab. 75a). Many of the tannaim and amoraim were experts in astronomy as, for example, johanan b. zakkai (Suk. 28a), gamaliel II, and Joshua b. Hananiah. The last named knew of the existence of a comet which appeared once every seventy years and led mariners astray (Hor. 10a). This was probably Halley's Comet. Among the Babylonian amoraim, samuel was important in the field of astronomy. He claimed that he could calculate and adjust the festival calendar of the Diaspora, without recourse to an eyewitness' report of the new moon in Israel (RH 20b), and he even made intercalary calculations covering a period of years. The first generations of the amoraim were acquainted with a baraita called "Secrets of Intercalation," in which were written precepts for the sanctification and intercalation of the month (RH 20b). In general, this knowledge was rarely committed to paper, being "secrets of the Torah not to be passed on to all and sundry" (Ket. 112a). In the eyes of the talmudic sages the earth was the center of creation, with heaven as a hemisphere spread over it. The Midrash conceived the heavens as being made up of several spheres or vaults – the sun, moon, stars, and planets being fixed in the second one (Ḥag. 12b). Nevertheless, a knowledge of the order of the celestial bodies, their path and distances from the earth, existed alongside of the above mythological picture. At the horizon, the heaven and earth "kiss each other," and the earth's diameter from east to west is equivalent to the height of the heavens above the earth (Tam. 32a). The earth is usually described as a disk encircled by water. In the Midrash it is pictured as standing on twelve columns, for the tribes of Israel, or seven columns, for the pillars of wisdom. The columns rest upon water, the water upon mountains, the mountains upon the wind, the wind upon the storm, and the storm is dependent on the arm of the Almighty. Yet with all this there existed a clear recognition of the earth as a sphere (TJ, Av. Zar. 3:1, 42C; Num. R. 13; 14). MOTIONS OF THE CELESTIAL BODIES In one baraita (Pes. 94b) there are differing opinions regarding the circles of rotation and the planets. "The Jewish sages say 'The sun moves by day beneath the firmament, and by night above the firmament'; the learned of the nations say, 'The sun moves by day beneath the firmament and by night beneath the earth.'" This baraita is most important, as it is evidence of a serious interest in celestial mechanics, of an early knowledge of scientific concepts, and of an objective approach to the solution of astronomical problems. The daily changes in the positions of sunrise and sunset in the annual cycle of the sun were well   known. These phenomena are explained by the existence of 365 windows in the firmament – 182 in the east, where the sun rises; and 182 in the west, where it sets; and one in the center of the firmament, the place of its first entrance at the time of the Creation (TJ, RH 2:5, 58a; Ex. R. 15:22). The distance traversed in 30 days by the sun, is traversed by the moon in two and one-half days. The sun is called the "Greater Light" and the moon, the "Lesser Light" because the solar year is longer than the lunar year by 11 days (Ex. R. ibid.). As for the courses of the planets, it is said (Gen. R. 10:4) " there is a planet that finishes its cycle in 12 years – that is Jupiter; and there is a planet which finishes its cycle in 30 years – that is Saturn; except for Venus and Mars that do not finish their cycles for 480 years." The figures given for Jupiter and Saturn are correct, according to the geocentric system of the motion of the planets, but the figures relating to Venus and Mars were wholly inaccurate and they seem to have been regarded as doubtful in quite early times. A concept of the solar motions is found in the baraita (Ber. 59b), which is explained by a great cycle of 28 years, at the end of which the sun returns to its original position relative to the stars and planets. The aggadah even accurately works out the time of the start of both the solar and lunar cycles (Targ. Jon., Gen. 1:16). The great cycle of the moon is also mentioned, being 21 years (Pd–RE 7); there is also a possible hint of a cycle of 19 years (Targ. Jon., Gen. 1:14). This length of time is the basis for calendar calculation, having been fixed at a much later period, and it remains valid up to the present day. The monthly changes in the shape of the moon are also well described (Ex. R. 15:26), and it is clear that various writers on this problem were not too far from the truth. THE FOUR SEASONS (Tekufot). The change of season and the comparison of day and night are fairly well described: "there are four seasons of the year, from the Nisan season to the Tammuz season the day borrows from the night, and from the Tammuz season to the Tishri season the day repays the night; from the Tishri season to the Tevet season the night borrows from the day, and from the Tevet season to the Nisan season the night repays the day; during the Nisan season and Tishri season, neither one owes anything to the other" (Mid. Ps. 19:3). Samuel gives reasonably accurate figures regarding the periods between the seasons (Er. 56a), but when he discusses the fixing of the dates of the seasons, he allows imaginary bases to be included. THE PLANETS, THE ZODIAC, STARS, AND COMETS The names of the planets – Saturn, Jupiter, the Sun, Mars, Venus (or Kokhevet), Mercury (or Kokhav Hammah), and the Moon – are referred to collectively in an acrostic as שצ״מ הנכ״ל. The 12 signs of the Zodiac and their relation to the months of the year are Aries (Nisan), Taurus (Iyyar), Gemini (Sivan), Cancer (Tammuz), Leo (Av), Virgo (Elul), Libra (Tishri), Scorpio (Marheshvan), Sagittarius (Kislev), Capricorn (Tevet), Aquarius (Shevat), and Pisces (Adar). From the astrological viewpoint, the 12 signs of the Zodiac have different influences on the "four winds of heaven," and sometimes there is a symbolic connection with the 12 tribes of Israel (Yal., Ex. 418; Yal., I Kings 185). In addition to the stars mentioned in the Bible, there is also a reference to the Milky Way (Ber. 58b). The meteors mentioned in the Mishnah (Ber. 9:2) are comets (Ber. 58b), and Samuel admitted that he did not know their nature. The "Baraita of Samuel," which was traditionally written by the amora Samuel, is ascribed by some to the ninth century (see below). -Astronomy in the Middle Ages The principal contributions of medieval Jewry to astronomy were the calculation of the hebrew calendar ; the translation of Arabic works and the diffusion of knowledge from the Arabic world; and the compilation of astronomical tables for scientific and navigational purposes. ptolemy , the Alexandrian astronomer of the second century C.E., compiled the Almagest (Syntaxis Mathematica), a long work in 13 books systematizing the structure of the universe and Greek astronomy. The Almagest dominated astronomical and astrological thought for 14 centuries, becoming the authority on astronomy and the major source for astronomical commentaries and translations in the medieval period. The Jews were of major importance to scholastic Europe and the beginning of the Renaissance, in that they provided a link between the Arabic translations, commentaries, and compilations of the Almagest and the Christian astronomers, mostly by means of their own translations and commentaries in Hebrew or Latin. One of the first Hebrew translations of the Arabic version of the Almagest was made by jacob anatoli between the years 1231 and 1235 as Ḥibbur ha-Gadol ha-Nikra al-Magesti. Anatoli also translated Averroes' summary of the Almagest under the title Kiẓẓur al-Magesti, and Kitāb fial-Ḥarakāt al-Samāwiyya ("The Book on the Heavenly Movements") by the ninth-century Arabic astronomer al-Farghānī (Alfraganus) under the title Yesodot ha-Tekhunah. The compendium of Ptolemy's Almagest in Arabic by Ibn Aflaḥ ha-Ishbili (the 12th-century Spanish astronomer), known also as Abu-Muhammad Jābir ibn Aflaḥ, is mentioned by maimonides in the Guide of the Perplexed (2:9). Ibn Aflaḥ's book (Kitāb al-Hayʾd, "The Book of Astronomy") is important for its critical appraisal of the Ptolemaic system of the universe, and was translated into Hebrew in two versions: one by Moses ibn tibbon (the 13th-century French physician and translator in 1274), and another, apparently, by Jacob b. Machir ibn tibbon (Don Profiat), which was abridged by Samuel b. Judah of Marseilles (the 14th-century French physician) in 1335. Moses ibn Tibbon also translated Eisagōgē eis ta Phainomena ("Introduction to Celestial Phenomena") of the first-century B.C.E. Greek philosopher, Geminus, under the title of Ḥokhmat ha-Kokhavim or Hokhmat Tekhunah ha-Kaẓar or Sefer ha-Ḥokhmah ha-Kaddurit, in 1246 at Naples. He also translated Kitâb al-Hay'a ("The Book on Astronomy") by the Arab astronomer al-Biṭrūjī of Seville (d. 1185) under the title Ma'amar bi-Tekhunah in 1259. The latter work had a great influence on Jewish scholars up to the 16th   century. Jacob b. Machir translated around 1271 Fi-Hay'at al- ʿÂlam ("On the Astronomy of the Universe" as Sefer ha-Tekhunah) by Abuʿali ibn al-Haytham (11th century), describing the quadrant and astronomy. Samuel b. Judah of Marseilles translated the treatise on the movement of the fixed stars (Ma'amarbi-Tenuʾat ha-Kokhavim ha-Kayyamim), by Abu Ishaq Ibrahim ibn Yaḥya al-Zarqālī (also known as Zarqāla or Zarqallah) of Cordova (second half of the 11th century). Moses b. Elijah the Greek (probably the 15th-century Moses Galeno) translated a study of astronomy by Omar ibn Muhammad under the title, Sefer Mezukkak. The Christian Jacob Christmann translated into Latin the Hebrew translations of the summary of the Almagest by Jacob Anatoli and al-Farghānī's book on astronomy (Frankfurt, 1590). abraham de balmes (d. 1524) translated into Latin Moses ibn Tibbon's Hebrew translation of Geminus' work on astronomy (see above), under the mistaken title Isagogicon Astrologiae Ptolemaei, as well as Jacob b. Machir's Hebrew translation of the above work by Ibn al-Haytham, under the title Liber de Mundo. The following are among those who published commentaries on the Almagest: Samuel ben Judah of Marseilles (14th century), David ibn Naḥmias of Toledo (beginning of 14th century), and Elijah Mizraḥi (d. 1525). Commentaries on the Hebrew translation of al-Farghānī's work were composed by Moses Handali (possibly 13th century), Isaac b. Samuel abu al-Khayr (c. 1340), Maimon of Montpellier (of unknown date; see montpellier ), and Judah ibn Verga (1457). There exists a shortened version of the Almagest which was possibly written by Ḥayyim Vital . At the end of the Middle Ages books in Latin were also translated into Hebrew. The essay by the German astronomer, Johannes de Gamundia (1380–1442), "De ratione componendi et usu novi instrumenti" was translated by David Kalonymus b. Jacob Meir Kalonymus under the title Marot ha-Kokhavim (1466). Theorica Planetarum of Georg Peuerbach (1423–1461) was translated twice: once by Ephraim Mizraḥi, and a second time by moses b. baruch almosnino (1510–1580). John de Sacrobosco (John of Holywood, the Parisian mathematician and astronomer who died in 1256) wrote the famous Tractatus de Sphaera, which elucidated and incorporated Ptolemy's Almagest and the work of al-Farghānī (see above) and which soon replaced both these books. It was translated into Hebrew around 1399 by solomon b. abraham (Avigdor) of Montpellier as the Mareh ha-Ofannim. Several Arabic essays were translated into European languages, especially Latin and Spanish. These translations were, in fact, the main channels for the progress of astronomy in medieval Europe. In 1256 Judah b. Moses ha-Kohen of Toledo translated into Spanish the Kitāb al-Kawākib ("Book of the Stars") of 'Abd al-Raḥmān al-Sūfi (tenth century) under the title Libro de las figuras and the astrological treatise Kitāb al-Bārie by Ibn Abu al-Rijāl (11th century) under the title Librocomplido. Commentaries on the Tractatus de Sphaera by Johnde Sacrobosco were published in the 16th and 17th centuries by Moses b. Baruch Almosnino, mattathias delacrut (1550), and Manoah Handil b. Shemariah (Polish author who died in 1612). A commentary on Georg Peuerbach's Theorica Planetarum was written by moses isserles in the early 17th century. In the Middle Ages Jews compiled most of the astronomical tables. Among these, the heretic Jew Sind ibn Ali (829–33) was a principal contributor to the astronomical tables of Caliph Maimun. abraham b. Ḥiyya ha-Nasi compiled (before 1136) tables called "Luḥot ha-Nasi" ("The Tables of the Prince or al-Battānī's Tables"), named after the Arab who died in 929, on whose calculations they were based. Al-Battānī had a great influence on astronomy; Maimonides relied on his tables for computing the sun's path, and his works were also mentioned by judah halevi (12th-century), abraham ibn ezra (1092–1167), isaac israeli (ninth to tenth century), and several other Hebrew authors. Abraham ibn Ezra compiled astronomical tables on the movements of the seven planets, and translated in 1160 the "Reasons for the al-Khwārizmī Tables" by Ahmad b. Elmenthi. Twelve Jewish astronomers, under the leadership of the Cordovan astronomer, Ibn Arzarkāli (Azarchel), helped to compile the "Toledo Tables" in the 12th century. In 1263 these were translated into Latin by John of Brescia and Jacob b. Machir ibn Tibbon, and later served as a basis in a Spanish version for the famous "Alphonsine Tables." These were prepared in 1272 by a group of astronomers, headed by Isaac Ibn Sa'id (also Sid). The Latin Tables were translated into Hebrew in 1460 by Moses b. Abraham of Nimes, while a new corrected edition was made by Solomon Davin of Rodez. Commentaries were written by Moses Botarel Farissol in 1465 and Mattathias Delacrut in the 16th century. Specially significant to the Hebrew astronomers were the "Persian Tables" in Greek, which were compiled late in the 14th century by Georgios Krisokaka. Solomon b. Elijah drew up (in about 1374) a set of astronomical tables with notes, the first section according to the Ptolemaic system and the second "in the manner of the Persians." Before 1525 Elijah Mizraḥi wrote a commentary on the tables "drawn up by the Persian sages." Astronomical tables were also devised by levi b. gershom (1288–1344), based on sources found in Persia, Egypt, etc. Isaac b. Solomon ibn Elhada (14th to 15th century) prepared tables for periods and seasons based on Ibn al-Raqqān, al-Battāni, and Ibn al-Kammād. Joseph b. Isaac b. Moses ibn waqar , writing in Arabic in 1357, drew up tables for the years 720–840 of the Muslim calendar (i.e., 1342–1462) and in 1396 he translated his book into Hebrew with additions and alterations. Other tables were compiled by Jacob b. Machir (1300), Jacob b. David b. Yom Tov (1361), and abraham zacuto , whose tables and Almanach Perpetuum in Latin and Spanish were used by Columbus on his voyages. EARLY JEWISH ASTRONOMERS There were comparatively few original works by medieval Jewish astronomers, but of these a number were equal to works of contemporary non-Jewish writers. Of importance was the group of men in the eighth and ninth centuries who took up astronomy professionally. Generally, they practiced as astrologers and their   knowledge was derived from Greek and ancient Indian writers. Unfortunately, comparatively few of their writings have been preserved. Some were translated into Latin, and a few works have been found in Hebrew. Māshaʾallāh, whose Hebrew name was possibly Joab or Joel, lived during the second half of the eighth and the beginning of the ninth century, and served in the courts of the caliphs in Baghdad. His essay, "Sefer be-Kadrut ha-Levanah ve-Ḥibbur ha-Kokhavim u-Tekufat ha-Shanim" has been preserved in Hebrew. The Persian Jewish astronomer Andruzager b. Zadi Faruch, who lived in the ninth century, is often identified with the expert in intercalation Eliezer b. Faruch, to whom the Arab chronologist al-Bīrūnī (early 11th century) attributed the fixing of the Jewish calendar. The "Baraita of Samuel" which dealt with the secrets of intercalation, dates from the ninth century but was attributed to the amora Samuel; it is regarded by some as the first original Hebrew work on astronomy in the Middle Ages. During the late tenth century Ḥasan ibn Ḥasan wrote three books on intercalation; unfortunately they have not been preserved, but reference to their contents was made by Abraham ibn Ezra and Isaac Israeli. shabbetai donnolo (tenth century) wrote a commentary on the Sefer Yeẓirah . Although they demonstrate the author's knowledge of the subject, the astronomical terms are confused with concepts belonging to astrology and mysticism. A calendar is given, showing the location of the heavenly bodies in 4706 (summer of 956). This work is important in that it constitutes the main source of rashi 's astronomy. The greatest of the Jewish astronomers who wrote in Hebrew at the beginning of the Spanish period was Abraham b. Ḥiyya ha-Nasi, whose works influenced generations of Jewish writers. Those of his works which were translated into Latin had an important influence on the development of European science. Apart from his astronomical calendars and Arabic astrological work which he translated into Latin, Abraham b. Ḥiyya wrote the following important works: Ẓurat ha-Areẓ, an astronomical-geographical text; Sefer ha-Ibbur, which included series of calculations of years, and determinations of new moons and cycles; Ḥeshbon Mahalakhot ha-Kokhavim, a book to which comments were added by Abraham ibn Ezra. In his hymn, "Keter Malkhut" solomon ibn gabirol describes the structure of the universe according to Aristotle and Ptolemy. This work contains detailed calculations of the length of the cycle of each star and its size in relation to the size of the earth. Abraham Ibn Ezra, in addition to his works on astrology and his calendars and commentaries, wrote the following texts on theoretical astronomy: Sefer ha-Ibbur which is on the subject of cycles, new moons, seasons, and signs of the Zodiac; Shalosh She'elot, replies to three questions on intercalation posed by David b. Joseph of Narbonne (c. 1139); and Kelei Neḥoshet an explanation of the use of the instruments of the astrolabical type. This last was followed by Kelei Neḥoshet ha-Sheni which analyzes the fundamentals of intercalation and the sources of astronomy. It has been passed on by Maimonides who also gives a detailed description of the laws of the spheres (Yad. Yesodei ha-Torah, 3). He maintains (ibid., 4:10) that it was to this that the talmudists referred in their commentaries on the creation (ch. 1). Maimonides' writings show him to have been a foremost astronomer of his time, and demonstrate a scientific approach in his analysis of apparent contradictory data. The main Jewish astronomers of the 13th century were Judah b. Solomon ha-Kohen ibn Matkah of Toledo, the author of an encyclopedia, Midrash ha-Ḥokhmah, part of which consists of summaries of the great Greek and Muslim astronomers; gershom b. solomon , whose work Sha'ar ha-Shamayim contains a section on the works of Ptolemy, Aristotle, Avicenna, and Averroes. This book was held in high esteem in the Middle Ages, and meir aldabi (c. 1360) used it extensively in the astronomical section of his Shevilei Emunah. In the zohar – probably a 13th-century Spanish composition – there is a passage which gives as a cause of the day's changing into night the revolution of the earth. Some 250 years before Copernicus the Zohar stated that "the whole earth spins in a circle like a ball; the one part is up when the other part is down; the one part is light when the other is dark, it is day in the one part and night in the other." Of great importance is Yesod Olam by isaac b. joseph israeli . This work, written in 1310, includes a study of astronomy and cosmography. The author deals with the system of intercalation and with laws of the sanctification of the month according to Maimonides. He gives a method for calculating the parallax of the moon, the importance of which was appreciated up to the time of Kepler. This was the leading textbook on astronomy written during the Middle Ages, and was held in high esteem for hundreds of years. Commentaries and explanations to it were written by Isaac Alhadib, Elijah Mizraḥi, and others. In the yeshivot of the 19th century it was the main text for the study of the calendar. Isaac ben Solomon Israeli translated a summary of it into Hebrew entitled Kiẓẓur Yesod Olam. Isaac Israeli also wrote Sha'ar ha-Shamayim which dealt with the subject of periods and seasons and Sefer Sha'ar ha-Millu'im on the movement of the planets, their order, and positions. The greatest of the Jewish astronomers of the Middle Ages was undoubtedly Levi b. Gershom. Curtze, the historian of astronomy, numbers him among the forerunners of Copernicus in that he pioneered new methods of research, from which evolved his own original system of astronomy. Levi b. Gershom was an independent and original scholar, and although he did not produce a work specifically devoted to astronomy, his knowledge of astronomy is clearly brought out in the first section of the fifth book of his Milḥamot Adonai. This section of the work was known to later generations as Sefer ha-Tekhunah. Levi b. Gershom explains in detail: a) his discovery, or improvement, of the cross-staff, a device for measuring angles and spherical distances. The inventor called it "the depth finder," while it became known in Europe   as "Jacob's staff " (baculus Jacobi) b) his method of passing a light ray from a star through a small aperture in a darkened chamber on to a board. This is the first recorded use of the camera obscura. By these methods Levi b. Gershom carried out numerous measurements and rectified many erroneous conceptions regarding the position of the stars. Among his achievements was the measurement of the relationship of the diameters of the sun and the moon to the lengths of their apparent orbits, and the relationship between the parts of the surfaces covered during an eclipse, and the size of the total area. As a result of his corrections of the originally accepted distances and data, he was able to arrive at a new conception of the distances separating the bodies of the universe and their position in space, and hence (in ch. 9) at a rejection of the basic assumptions of the astronomy of Ptolemy and al-Biṭrūjī. Chapter 99 of the text contains his "Astronomical Tables" (Luḥot) on which commentaries have been written by Moses Botarel Farissol. The importance of the work may be gauged from the fact that part of the book was translated into Latin during the author's lifetime (in 1342). The entire book was not translated until the 15th century. Other Jewish inventors of astronomical instruments in the later Middle Ages were Jacob b. Machir, who invented an angle measuring device, a quadrant, which he described in his work Rova Yisrael; Isaac b. Solomon b. ẒaddikAl Hadib (also al-Aḥdab) wrote Keli ha-Miẓẓu'a about his invention of a new instrument which was a combination of astrolabe and quadrant; Jacob (Bonet) de lattes (15th to 16th centuries) designed a device in the shape of a ring for measuring the height of the sun and the stars. His work on this was written in Latin (De annuli astronomii utilitate) and was reprinted no less than six times within 50 years. immanuel b. jacob bonfils (the 14th-century physician and astronomer of Tarascon) wrote many works on astronomy including one on the construction of the astrolabe, as well as tables of the determination of Venus from 1300 to 1357, and tables for the declination of the sun, etc. Abraham Zacuto was an influential astronomer of the 16th century. His main work was originally written in Hebrew, but was very soon translated into Spanish, and the Latin synopsis of it, Almanach Perpetuum ("The Continual Almanac") was translated into Spanish and Arabic. All of Zacuto's works, his improved astrolabe, and his astronomical tables were of great importance, particularly in the voyages of discovery of the Spanish and Portuguese explorers. Knowledge of Jewish medieval astronomy is limited to a very small part of the extensive writings on the subject. Much material remains undiscovered and most of what is available has yet to be studied carefully. Yet, over 250 Jewish astronomers are known to have lived before 1500. -Jewish Astronomy in the late Renaissance The Jewish contribution to astronomy after Copernicus was relatively small. Most writers concerned themselves with transcriptions from old writings or with summarizing these. Thus, the writings on astronomy of the 18th century and in the rabbinical literature of the 19th century are basically derived from the Ptolemaic school. In the 16th century judah loew b. bezalel had a high reputation as an astronomer. However, apart from his few astrological discussions, nothing can be found in his few writings to support this. Moses Isserles (d. 1573) showed a real knowledge of astronomy, particularly in his books Torat ha-Olah (Prague, 1569) and his commentary on Theorica Planetarum. david gans was well acquainted with the development of astronomical knowledge. He was a colleague of Kepler and Tycho Brahe; for the latter he translated parts of the "Alphonsine Tables" into German. His most important astronomical work was Nehmad ve-Na'im written in 1613 and published in Jessnitz, 1743, which presented the first Hebrew exposition of the Copernican system, but the author rejected it because of his traditional Ptolemaic outlook. Mordecai b. Abraham Jaffe wrote Levush Eder ha-Yakar in Levush Or Yekarot (Lublin, 1594), which contains a commentary on Maimonides' laws of the sanctification of the month as well as a lesson on astronomy; his Be'urei Yafeh is a commentary on Ẓurat ha-Areẓ by Abraham b. Ḥiyya. joseph solomon delmedigo was a pupil of Galileo. In his Elim two chapters are devoted to astronomy: the first, "The Laws of the Heavens" is an exposition of the first two chapters of the Almagest, the second, "The Mightiness of God," is devoted to an explanation of other parts of the Almagest and of writings by Copernicus and al-Battānī. Delmedigo was the first outstanding exponent of the Copernican theory in Hebrew literature within the framework of traditional Judaism. His method was to reply to questions from the viewpoint of the ancients, and from that of the astronomers who followed Copernicus. tobias cohn , the physician, remained faithful to the ancients, although he was quite familiar with the astronomy of Copernicus. In his Ma'aseh Tuviyyah (Venice, 1707–8) he analyzed the geocentric conception in its classic form, and in the one revised by Tycho Brahe. The heliocentric view is analyzed and rejected, mainly on religious and traditional grounds. jonathan b. joseph from ruzhany , another commentator on Ẓurat ha-Areẓ, wrote Yeshu'ah be-Yisrael ("Salvation in Israel," Frankfurt, 1720), an explanation of Maimonides' laws of the sanctification of the month. Raphael ha-Levi of Hanover (1685–1788) wrote Tekhunatha-Shamayim (Amsterdam, 1756), a study of astronomy as related to Maimonides' law, and "Tables of Intercalation" (pt. 1, Leiden, 1756; pt. 2, Hanover, 1757). Israel b. Moses ha-Levi of Zamosc in his book, Nezah Yisrael (Frankfurt on the Oder, 1741), classified certain obscure parts of the Talmud which dealt with engineering and astronomy. He also wrote a commentary on Yesod Olam by Isaac Israeli, and a textbook called Arubbot ha-Shamayim. Shevilei de-Raki'a (Prague, 1785) by Elijah b. Hayyim of Hochheim is devoted to an explanation of Maimonides' laws of the sanctification of the month. In it the author distinguishes between the geocentric assumptions of Maimonides, and the theories of the   new astronomy. In the 19th century, israel david b. mordecai jaffe-margoliot wrote Ḥazon Mo'ed (Pressburg, 1843), dealing with astronomy, the mathematics of intercalation, as well as with the additional day of festivals in the Diaspora. -Jews in Modern Astronomy The frequently repeated statement that Sir William Herschel, astronomer to King George III and his sister Caroline, were of Jewish origin has been shown to be not in accordance with the facts. Among those who contributed to the development of astronomy in the 19th century were Wilhelm Beer (1797–1850), specialist in the mapping of the features of the moon; hermann goldschmidt is especially noted for his work from 1852 to 1861 in discovering 14 new asteroids between Mars and Jupiter; Rudolph Wolf (1816–1893), at the turn of the century, organized systematic solar work at Zurich; Adolph Hirsch (1830–1901) conducted mainly geophysical work in Switzerland; maurice loewy invented, at the Paris Observatory, the Coudé telescope; Edmund Weiss (1837–1917), was director of the Vienna Observatory in the mid-19th century; Friedrich Simon Archenhold (1861–1939) was a well-known writer of popular books on astronomy; Adolph Marcuse (1860–1930), participated in several astronomical expeditions; Fritz Cohen and Samuel Oppenheim conducted important work in celestical mechanics; as did Erwin Finlay freundlich , first in Berlin and then at St. Andrews in Scotland. During this century, richard prager , at first at the University Observatory, Berlin, and from 1938 at the Harvard Observatory, worked on variable stars through the continuation of the Geschichte und Literatur der Veraenderlichen Sterne. sir arthur schuster , in England, founded in 1919 the forerunner of the International Astronomical Union, to whose subsequent rapid development was due much of the well-organized effort and success of present-day astronomy. Frank schlesinger , in the U.S.A., was the first to devise photographic methods for a large scale derivation of stellar distances ("parallax-determinations"). karl schwarzschild , director of the Astrophysical Observatory in Potsdam, did fundamental work in many fields; for example, the laws of stellar motions, photometry, optics, the astrophysical application of atomic physics, and the theoretical exploration of stellar atmospheres. His son Martin schwarzschild , who taught at Princeton, U.S.A., was an expert in stellar evolution, and the design of satellite-borne telescopes. albert einstein was noted also for his researches in astrophysics. Other contemporary American astronomers of Jewish origin were Luigi Jacchia (1911–1996), on solar-terrestrial relationships, and David Layzer (1925– ), who researched in theoretical atomic astrophysics, both at Harvard University. At the University of Texas, Gerard de Vancouleurs (1918–1995) was involved in research into the structure and systems of extragalactic nebulae. Rudolph Minkowski (1895–1976) up to 1934 at Hamburg University, investigated at Pasadena the intricate problems of supernovae. herbert a. friedman , at the U.S. Naval Research Laboratory in Washington, was a leader in the new field of outer-space spectroscopy. At Rochester University, Emil Wolf (1922– ) was concerned with optical research with astrophysical applications. Leo Goldberg (1913–1987), at the Smithsonian Astrophysical Observatory, organized teamwork for the initiation of new solar and stellar space research. At the California Institute of Technology, Jesse L. Greenstein (1909–2002) carried out fundamental astrophysical work, particularly in high-dispersion spectroscopy. Before going to Israel, George Alter (1890–1972) was at the University of Prague, and at the Sidmouth Observatory in England, where he was mainly concerned with problems of star clusters. Arthur Beer (1900–1980), formerly at Breslau and Hamburg, and, from 1934, at the Universities of London and Cambridge, investigated problems of spectroscopic binaries, new stars, stellar photometry, large-scale spectrophotometric determination of distances of stars in the outer regions of our galaxy, its spiral structure, and problems in the history of astronomy. At the Royal Greenwich Observatory, stellar evolution and the abundance of chemical elements in the stars were investigated by Bernard Pagel (1929– ). Modern cosmological theories, which began in the 1920s, have been developed by Thomas Gold (1920–2004), hermann bondi , Dennis Sciama (1930– ), Leon Mestel (1930– ), and Franz Kahn (1926–1998). Cosmological and other astronomical work of great originality and ingenuity was developed in Soviet Russia; outstanding among the researchers were Vitoli Lazarevich Ginzburg and Joseph S. Shklovski (d. 1985). Leading French astronomers included: the former general secretary of the International Astronomical Union, Jean-Claude Pecker (Observatoire de Paris), and Evry Schatzman (Institut d'Astrophysique, Paris), both active in studies of stellar evolution. See also physics . -BIBLIOGRAPHY: G. Sarton, Introduction to the History of Science, 5 vols. (1927–48), indexes; C. Roth, The Jewish Contribution to Civilisation (19382), 67, 76, 80–81, 189–90; Legacy of Israel (19282), 173–314; G. Forbes, History of Astronomy (1909); M. Steinschneider, in: JQR, 13 (1900/01), 106–10; idem, Jewish Literature from the 8th to the 18th Centuries (1857); W.M. Feldman, Rabbinical Mathematics and Astronomy (1931), includes bibliography; O. Neugebauer, in: HUCA, 22 (1949), 321–63; J.B.J. Delambre, Histoire de l'astronomie du moyen-âge (1819, repr. 1965); C. Roth, in: JQR, 27 (1936/37), 233–6; A. Marx, in: Essays and Studies… Linda R. Miller (1938), 117–70; S. Gandz, Studies in Hebrew Astronomy and Mathematics (1970). (Arthur Beer)