Isaac Israeli ben Joseph or Yitzhak ben Yosef (often known as Isaac Israeli the Younger) was a Spanish-Jewish

History of the Jews in Spain

Spanish Jews once constituted one of the largest and most prosperous Jewish communities under Muslim and Christian rule in Spain, before the majority, together with resident Muslims, were forced to convert to Catholicism, be expelled or be killed when Spain became united under the Catholic Monarchs...

 astronomer

Astronomer

An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...

/astrologer

Astrologer

An astrologer practices one or more forms of astrology. Typically an astrologer draws a horoscope for the time of an event, such as a person's birth, and interprets celestial points and their placements at the time of the event to better understand someone, determine the auspiciousness of an...

 who flourished at Toledo

Toledo, Spain

Toledo's Alcázar became renowned in the 19th and 20th centuries as a military academy. At the outbreak of the Spanish Civil War in 1936 its garrison was famously besieged by Republican forces.-Economy:...

 in the first half of the fourteenth century. He was a pupil of Asher ben Yehiel, at whose request (in 1310) he wrote the astronomical

Astronomy

Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

 work Yesod Olam, the best contribution on that subject to Hebrew literature

Hebrew literature

Hebrew literature consists of ancient, medieval, and modern writings in the Hebrew language. It is one of the primary forms of Jewish literature, though there have been cases of literature written in Hebrew by non-Jews...

.
It treats of geometry

Geometry

Geometry arose as the field of knowledge dealing with spatial relationships. Geometry was one of the two fields of pre-modern mathematics, the other being the study of numbers ....

 and trigonometry

Trigonometry

Trigonometry is a branch of mathematics that studies triangles and the relationships between their sides and the angles between these sides. Trigonometry defines the trigonometric functions, which describe those relationships and have applicability to cyclical phenomena, such as waves...

 as introductory to the subject-matter; of the structure and position of the globe; of the number and movements of the celestial spheres

Celestial spheres

The celestial spheres, or celestial orbs, were the fundamental entities of the cosmological models developed by Plato, Eudoxus, Aristotle, Ptolemy, Copernicus and others...

; of the time differences in days and nights in the various parts of the earth; of the movements of sun and moon; of the solstice

Solstice

A solstice is an astronomical event that happens twice each year when the Sun's apparent position in the sky, as viewed from Earth, reaches its northernmost or southernmost extremes...

s, the neomeniæ, the eclipse

Eclipse

An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer...

s, and the leap-year

Hebrew calendar

The Hebrew calendar , or Jewish calendar, is a lunisolar calendar used today predominantly for Jewish religious observances. It determines the dates for Jewish holidays and the appropriate public reading of Torah portions, yahrzeits , and daily Psalm reading, among many ceremonial uses...

s; it contains as well astronomical tables (an ephemeris

Ephemeris

An ephemeris is a table of values that gives the positions of astronomical objects in the sky at a given time or times. Different kinds of ephemerides are used for astronomy and astrology...

) and a perpetual calendar

Perpetual calendar

A perpetual calendar is a calendar which is good for a span of many years, such as the Runic calendar.- General information :...

. It also deals (iv, § 17) with the chronological systems

Calendar

A calendar is a system of organizing days for social, religious, commercial, or administrative purposes. This is done by giving names to periods of time, typically days, weeks, months, and years. The name given to each day is known as a date. Periods in a calendar are usually, though not...

 of other nations and religions, especially Christianity

Christianity

Christianity is a monotheistic religion based on the life and teachings of Jesus as presented in canonical gospels and other New Testament writings...

; and gives (iv, § 18) in chronological order the noted personages of the Biblical, Talmud

Talmud

The Talmud is a central text of mainstream Judaism. It takes the form of a record of rabbinic discussions pertaining to Jewish law, ethics, philosophy, customs and history....

ic, and geonic

Geonim

Geonim were the presidents of the two great Babylonian, Talmudic Academies of Sura and Pumbedita, in the Abbasid Caliphate, and were the generally accepted spiritual leaders of the Jewish community world wide in the early medieval era, in contrast to the Resh Galuta who wielded secular authority...

 periods, following the Sefer ha-Qabbalah

Sefer ha-Qabbalah

Sefer ha-Qabbalah was a book authored by Abraham ibn Daud around 1161. A chronicle of the Jewish people, it contains valuable historical and philosophical information...

of Abraham ibn Daud

Abraham ibn Daud

Abraham ibn Daud was a Spanish-Jewish astronomer, historian, and philosopher; born at Toledo, Spain about 1110; died, according to common report, a martyr about 1180. He is sometimes known by the abbreviation Rabad I or Ravad I. His mother belonged to a family famed for its learning...

. This last was included by Zacuto in his Sefer ha-Yuḥasin.

The Yesod Olam was first published at Berlin, in 1777, by Jacob Shklower. A more complete edition, with a preface by David Cassel, was published by B. Goldberg and L. Rosenkranz (1848). Israeli's work was much studied in the Middle Ages

Middle Ages

The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...

. Isaac al-Hadib, Judah Bassan, and Elijah Mizrahi annotated it, and an anonymous author wrote a commentary to it (Neubauer, Cat. Bodl. Hebr. MSS. Nos. 2044, 746, 5). An abridgment was made in Arabic by the author's son Joseph Israeli ben Isaac, of which the Hebrew translation, Kitzur Yesod Olam is still extant (ib. No. 1319, 6).

Israeli was also the author of two other astronomical works, Sha'ar ha-Shamayim and Sha'ar ha-Milu'im, both extant in manuscript (ib. No. 2046).