Hellenistic astrology in the context of "Arab and Persian astrology"

Babylonian astronomy was the study or recording of celestial objects during the early history of Mesopotamia. The numeral system used, sexagesimal, was based on 60, as opposed to ten in the modern decimal system. This system simplified the calculating and recording of unusually great and small numbers.

During the 8th and 7th centuries BC, Babylonian astronomers developed a new empirical approach to astronomy. They began studying and recording their belief system and philosophies dealing with an ideal nature of the universe and began employing an internal logic within their predictive planetary systems. This was an important contribution to astronomy and the philosophy of science, and some modern scholars have thus referred to this approach as a scientific revolution. This approach to astronomy was adopted and further developed in Greek and Hellenistic astrology. Classical Greek and Latin sources frequently use the term Chaldeans for the philosophers, who were considered as priest-scribes specializing in astronomical and other forms of divination. Babylonian astronomy paved the way for modern astrology and is responsible for its spread across the Graeco-Roman empire during the 2nd-century Hellenistic Period. The Babylonians used the sexagesimal system to trace the planets' transits, by dividing the 360 degree sky into 30 degrees, they assigned 12 zodiacal signs to the stars along the ecliptic.

Western astrology is the system of astrology most popular in Western countries. It is historically based on Ptolemy's Tetrabiblos (2nd century CE), which in turn was a continuation of Hellenistic and ultimately Babylonian traditions.

Western astrology is largely horoscopic, that is, it is a form of divination based on the construction of a horoscope for an exact moment, such as a person's birth as well as location (since time zones may or may not affect a person's birth chart), in which various cosmic bodies are said to have an influence. Astrology in western popular culture is often reduced to sun sign astrology, which considers only the individual's date of birth (i.e. the "position of the Sun" at that date).

Some medieval Muslims took a keen interest in the study of astrology, partly because they considered the celestial bodies to be essential, partly because the dwellers of desert-regions often travelled at night, and relied upon knowledge of the constellations for guidance in their journeys.

After the advent of Islam, the Muslims needed to determine the time of the prayers, the direction of the Kaaba, and the correct orientation of the mosque, all of which helped give a religious impetus to the study of astronomy and contributed towards the belief that the heavenly bodies were influential upon terrestrial affairs as well as the human condition. The science dealing with such influences was termed astrology (Arabic: علم النجوم Ilm an-Nujūm), a discipline contained within the field of astronomy (more broadly known as علم الفلك Ilm al-Falak 'the science of formation [of the heavens]'). The principles of these studies were rooted in Arabian, Persian, Babylonian, Hellenistic and Indian traditions and both were developed by the Arabs following their establishment of a magnificent observatory and library of astronomical and astrological texts at Baghdad in the 8th century.

In Western astrology, astrological signs are the zodiac, twelve 30-degree sectors that are crossed by the Sun's 360-degree orbital path as viewed from Earth in its sky. The signs enumerate from the first day of spring, known as the First Point of Aries, which is the vernal equinox. The astrological signs are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces. The Western zodiac originated in Babylonian astrology, and was later influenced by the Hellenistic culture. Each sign was named after a constellation the sun annually moved through while crossing the sky. This observation is emphasized in the simplified and popular sun sign astrology. Over the centuries, Western astrology's zodiacal divisions have shifted out of alignment with the constellations they were named after by axial precession of the Earth while Hindu astrology measurements correct for this shifting. Astrology (i.e. a system of omina based on celestial appearances) was developed in Chinese and Tibetan cultures as well but these astrologies are not based upon the zodiac but deal with the whole sky.

Astrology is a pseudoscience. Scientific investigations of the theoretical basis and experimental verification of claims have shown it to have no scientific validity or explanatory power. More plausible explanations for the apparent correlation between personality traits and birth months exist, such as the influence of seasonal birth in humans.

Traditional Chinese astronomy has a system of dividing the celestial sphere into asterisms or constellations, known as "officials" (Chinese: 星官; pinyin: xīng guān).

The Chinese asterisms are generally smaller than the constellations of Hellenistic tradition. The Song dynasty (13th-century) Suzhou planisphere shows a total of 283 asterisms, comprising a total of 1,565 individual stars.The asterisms are divided into four groups, the Twenty-Eight Mansions (二十八宿; Èrshíbā Xiù) along the ecliptic, and the Three Enclosures of the northern sky. The southern sky was added as a fifth group in the late Ming dynasty based on European star charts, comprising an additional 23 asterisms.

Vettius Valens (February 8, 120 – c. 175) was a 2nd-century Hellenistic astrologer, a somewhat younger contemporary of Claudius Ptolemy.

Valens' major work is the Anthology (Latin: Anthologia), ten volumes in Greek written roughly within the period 150 to 175. The Anthology is the longest and most detailed treatise on astrology which has survived from that period. A working professional astrologer, Valens includes over a hundred sample charts from his case files in the Anthology.