Astronomy is a natural science that deals with the study of celestial objects (such as stars, planets, comets, nebulae, star clusters and galaxies) and phenomena that originate outside the Earth's atmosphere (such as the cosmic background radiation). It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the formation and development of the universe.
Astronomy is one of the oldest sciences. Prehistoric cultures left behind astronomical artifacts such as the Egyptian monuments and Stonehenge, and early civilizations such as the Babylonians, Greeks, Chinese, and Indians performed methodical observations of the night sky. However, the invention of the telescope was required before astronomy was able to develop into a modern science. Historically, astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, the making of calendars, and even astrology, but professional astronomy is nowadays often considered to be synonymous with astrophysics.
During the 20th century, the field of professional astronomy split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of celestial objects, which is then analyzed using basic principles of physics. Theoretical astronomy is oriented towards the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain the observational results, and observations being used to confirm theoretical results.
Amateur astronomers have contributed to many important astronomical discoveries, and astronomy is one of the few sciences where amateurs can still play an active role, especially in the discovery and observation of transient phenomena.
Early History
Early cultures identified celestial objects with gods and spirits. They related these objects (and their movements) to phenomena such as rain, drought, seasons, and tides. It is generally believed that the first "professional" astronomers were priests (such as the Magi), and that their understanding of the "heavens" was seen as "divine", hence astronomy's ancient connection to what is now called astrology. Ancient structures with possibly astronomical alignments (such as Stonehenge) probably fulfilled both astronomical and religious functions.
Calendars of the world have usually been set by the Sun and Moon (measuring the day, month and year), and were of importance to agricultural societies, in which the harvest depended on planting at the correct time of year. The most common modern calendar is based on the Roman calendar, which divided the year into twelve months of alternating thirty and thirty-one days apiece. In 46 BC Julius Caesar instigated calendar reform and adopted a calendar based upon the 365 1/4 day year length originally proposed by 4th century BC Greek astronomer Callippus.
Babylonian astronomy
The Babylonians were the first to recognize that astronomical phenomena are periodic and apply mathematics to their predictions. Tablets dating back to the Old Babylonian period document the application of mathematics to the variation in the length of daylight over a solar year. Centuries of Babylonian observations of celestial phenomena are recorded in the series of cuneiform tablets known as the Enûma Anu Enlil — the oldest significant astronomical text that we possess is Tablet 63 of the Enûma Anu Enlil , the Venus tablet of Ammisaduqa, which lists the first and last visible risings of Venus over a period of about 21 years. It is the earliest evidence that planetary phenomena were recognized as periodic.
The MUL.APIN contains catalogues of stars and constellations as well as schemes for predicting heliacal risings and settings of the planets, and lengths of daylight as measured by a water clock, gnomon, shadows, and intercalations. The Babylonian GU text arranges stars in 'strings' that lie along declination circles and thus measure right-ascensions or time intervals, and also employs the stars of the zenith, which are also separated by given right-ascensional differences. There are dozens of cuneiform Mesopotamian texts with real observations of eclipses, mainly from Babylonia.
The first civilisation known to possess a functional theory of the planets were the Babylonians. The oldest surviving planetary astronomical text is the Babylonian Venus tablet of Ammisaduqa, a 7th century BC copy of a list of observations of the motions of the planet Venus that probably dates as early as the second millennium BC. The Babylonian astrologers also laid the foundations of what would eventually become Western astrology. The Enuma anu enlil, written during the Neo-Assyrian period in the 7th century BC, comprises a list of omens and their relationships with various celestial phenomena including the motions of the planets.
Egyptian Astronomy
Egyptian astronomy begins in prehistoric times. The presence of stone circles at Nabta Playa dating from the 5th millennium BCE show the importance of astronomy to the religious life of ancient Egypt even in the prehistoric period. The annual flooding of the Nile meant that the heliacal risings, or first visible appearances of stars at dawn, was of special interest in determining when this might occur, and it is no surprise that the 365 day period of the Egyptian calendar was already in use at the beginning of Egyptian history. The constellation system used among the Egyptians also appears to have been essentially of native origin.
The precise orientation of the Egyptian pyramids affords a lasting demonstration of the high degree of technical skill in watching the heavens attained in the 3rd millennium BCE. It has been shown the Pyramids were aligned towards the pole star, which, because of the precession of the equinoxes, was at that time Thuban, a faint star in the constellation of Draco. Evaluation of the site of the temple of Amun-Re at Karnak, taking into account the change over time of the obliquity of the ecliptic, has shown that the Great Temple was aligned on the rising of the midwinter sun. The length of the corridor down which sunlight would travel would have limited illumination at other times of the year.
Astronomy played a considerable part in religious matters for fixing the dates of festivals and determining the hours of the night. The titles of several temple books are preserved recording the movements and phases of the sun, moon and stars. The rising of Sirius (Egyptian: Sopdet, Greek: Sothis) at the beginning of the inundation was a particularly important point to fix in the yearly calendar.
From the tables of stars on the ceiling of the tombs of Rameses VI and Rameses IX it seems that for fixing the hours of the night a man seated on the ground faced the Astrologer in such a position that the line of observation of the pole star passed over the middle of his head. On the different days of the year each hour was determined by a fixed star culminating or nearly culminating in it, and the position of these stars at the time is given in the tables as in the centre, on the left eye, on the right shoulder, etc. According to the texts, in founding or rebuilding temples the north axis was determined by the same apparatus, and we may conclude that it was the usual one for astronomical observations. In careful hands it might give results of a high degree of accuracy.
Greek Astronomy
The development of astronomy by the Greek and Hellenistic astronomers is considered by historians to be a major phase in the history of astronomy. Greek astronomy is characterized from the start by seeking a rational, physical explanation for celestial phenomena. Most of the constellations of the northern hemisphere derive are taken from Greek astronomy, as are the names of many stars and planets. It was influenced by Babylonian and, to a lesser extent, Egyptian astronomy; in turn, it influenced Indian, Arabic-Islamic and Western European astronomy.
References to identifiable stars and constellations appear in the writings of Homer and Hesiod, the earliest surviving examples of Greek literature. In the Iliad and the Odyssey, Homer refers to the following celestial objects:
- the constellation Boötes
- the star cluster Hyades
- the constellation Orion
- the star cluster Pleiades
- Sirius, the Dog Star
- the constellation Ursa Major
Hesiod, who wrote in the early 7th century BCE, adds the star Arcturus to this list in his poetic calendar Works and Days. Though neither Homer nor Hesiod set out to write a scientific work, they hint at a rudimentary cosmology of a flat earth surrounded by an "Ocean River." Some stars rise and set (disappear into the ocean, from the viewpoint of the Greeks); others are ever-visible. At certain times of the year, certain stars will rise or set at sunrise or sunset.
Speculation about the cosmos was common in Pre-Socratic philosophy in the 6th and 5th centuries BCE. Anaximander (c.610 BC–c. 546 BC) described a cylindrical earth suspended in the center of the cosmos, surrounded by rings of fire. Philolaus (c. 480 BC–c. 405 BC) the Pythagorean described a cosmos with the stars, planets, Sun, Moon, Earth, and a counter-Earth (Antichthon)--ten bodies in all--circling an unseen central fire. Such reports show that Greeks of the 6th and 5th centuries were aware of the planets and speculated about the structure of the cosmos.
The planets in early Greek astronomy
The name "planet" comes from the Greek term πλανήτης, planētēs, meaning "wanderer", as ancient astronomers noted how certain lights moved across the sky in relation to the other stars. Five planets can be seen with the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn. Sometimes the luminaries, the Sun and Moon, are added to the list of naked eye planets to make a total of seven. Since the planets disappear from time to time when they approach the Sun, careful attention is required to identify all five. Observations of Venus are not straightforward. Early Greeks thought that the evening and morning appearances of Venus represented two different objects, calling it Hesperus ("evening star") when it appeared in the western evening sky and Phosphorus ("light-bringer") when it appeared in the eastern morning sky. They eventually came to recognize that both objects were the same planet. Pythagoras is given credit for this realization.
The planets eventually received names drawn from Greek mythology. The equivalent names in Roman mythology are the basis for the modern English names of the planets.
n classical Greece, astronomy was a branch of mathematics; astronomers sought to create geometrical models that could imitate the appearances of celestial motions. This tradition began with the Pythagoreans, who placed astronomy among the four mathematical arts (along with arithmetic, geometry, and music). The study of number comprising the four arts was later called the quadrivium.
Although he was not a creative mathematician, Plato (427-347 BCE) included the quadrivium as the basis for philosophical education in the Republic. He encouraged a younger mathematician, Eudoxus of Cnidus (c. 410 BCE-c. 347 BCE), to develop a system of Greek astronomy. According to a modern historian of science, David Lindberg:
- In their work we find (1) a shift from stellar to planetary concerns, (2) the creation of a geometrical model, the "two-sphere model," for the representation of stellar and planetary phenomena, and (3) the establishment of criteria governing theories designed to account for planetary observations. (Lindberg 1992, p. 90)
The two-sphere model is a geocentric model. It divides the cosmos into two regions:
- A spherical Earth, central and motionless (the sublunary sphere).
- A spherical heavenly realm centered on the Earth, which may contain multiple rotating spheres made of aether
Plato's main books on cosmology are the Timaeus and the Republic. In them he described the two-sphere model and said there were eight circles or spheres carrying the seven planets and the fixed stars. He put the celestial objects in the following order, beginning with the one closest to Earth:
- Moon
- Sun
- Venus
- Mercury
- Mars
- Jupiter
- Saturn
- Fixed stars
According to the "Myth of Er" in the Republic, the cosmos is the Spindle of Necessity, attended by Sirens and spun by the three daughters of the Goddess Necessity known collectively as the Moirae or Fates.
According to a story reported by Simplicius of Cilicia (6th century CE), Plato posed a question for the Greek mathematicians of his day: "By the assumption of what uniform and orderly motions can the apparent motions of the planets be accounted for?" (quoted in Lloyd 1970, p. 84). Plato proposed that the seemingly chaotic wandering motions of the planets could be explained by combinations of uniform circular motions centered on a spherical Earth, apparently a novel idea in the 4th century.
Eudoxus rose to the challenge by assigning to each planet a set of concentric spheres. By tilting the axes of the spheres, and by assigning each a different period of revolution, he was able to approximate the celestial "appearances." Thus, he was the first to attempt a mathematical description of the motions of the planets. A general idea of the content of On Speeds, his book on the planets, can be gleaned from Aristotle's Metaphysics XII, 8, and a commentary by Simplicius on De caelo, another work by Aristotle. Since all his own works are lost, our knowledge of Eudoxus is obtained from secondary sources. Aratus's poem on astronomy is based on a work of Eudoxus, and possibly also Theodosius of Bithynia's Sphaerics. They give us an indication of his work in spherical astronomy as well as planetary motions.
Callippus, a Greek astronomer of the 4th century, added seven spheres to Eudoxus' original 27 (in addition to the planetary spheres, Eudoxus included a sphere for the fixed stars). Aristotle described both systems, but insisted on adding "unrolling" spheres between each set of spheres to cancel the motions of the outer set. Aristotle was concerned about the physical nature of the system; without unrollers, the outer motions would be transferred to the inner planets.
Planetary models and observational astronomy
The Eudoxan system had several critical flaws. One was its inability to predict motions exactly. Callippus' work may have been an attempt to correct this flaw. A related problem is the inability of his models to explain why planets appear to change speed. A third flaw is its inability to explain changes in the brightness of planets as seen from Earth. Because the spheres are concentric, planets will always remain at the same distance from Earth. This problem was pointed out in Antiquity by Autolycus of Pitane (c. 310 BCE).
Apollonius of Perga (c. 262 BC–c. 190 BC) responded by introducing two new mechanisms that allowed a planet to vary its distance and speed: the eccentric deferent and the deferent and epicycle. The deferent is a circle carrying the planet around the Earth. (The word deferent comes from the Latin ferro, ferre, meaning "to carry.") An eccentric deferent is slightly off-center from Earth. In a deferent and epicycle model, the deferent carries a small circle, the epicycle, which carries the planet. The deferent-and-epicycle model can mimic the eccentric model, as shown by Apollonius' theorem. It can also explain retrogradation, which happens when planets appear to reverse their motion through the zodiac for a short time. Modern historians of astronomy have determined that Eudoxus' models could only have approximated retrogradation crudely for some planets, and not at all for others.
In the 2nd century BCE, Hipparchus, aware of the extraordinary accuracy with which Babylonian astronomers could predict the planets' motions, insisted that Greek astronomers achieve similar levels of accuracy. Somehow he had access to Babylonian observations or predictions, and used them to create better geometrical models. For the Sun, he used a simple eccentric model, based on observations of the equinoxes, which explained both changes in the speed of the Sun and differences in the lengths of the seasons. For the Moon, he used a deferent and epicycle model. He could not create accurate models for the remaining planets, and criticized other Greek astronomers for creating inaccurate models.
Hipparchus also compiled a star catalogue. According to Pliny the Elder, he observed a nova (new star). So that later generations could tell whether other stars came to be, perished, moved, or changed in brightness, he recorded the position and brightness of the stars. Ptolemy mentioned the catalogue in connection with Hipparchus' discovery of precession. (Precession of the equinoxes is a slow motion of the place of the equinoxes through the zodiac, caused by the shifting of the Earth's axis). Hipparchus thought it was caused by the motion of the sphere of fixed stars.
Heliocentrism and cosmic scales
In the 3rd century BCE, Aristarchus of Samos proposed an alternate cosmology (arrangement of the universe): a heliocentric model of the solar system, placing the Sun, not the Earth, at the center of the known universe (hence he is sometimes known as the "Greek Copernicus"). His astronomical ideas were not well-received, however, and only a few brief references to them are preserved. We know the name of one follower of Aristarchus: Seleucus of Seleucia.
Aristarchus also wrote a book On the Sizes and Distances of the Sun and Moon, which is his only work to have survived. In this work, he calculated the sizes of the Sun and Moon, as well as their distances from the Earth in Earth radii. Shortly afterwards, Eratosthenes calculated the size of the Earth, providing a value for the Earth radii which could be plugged into Aristarchus' calculations. Hipparchus wrote another book On the Sizes and Distances of the Sun and Moon, which has not survived. Both Aristarchus and Hipparchus drastically underestimated the distance of the Sun from the Earth.
Astronomy in the Greco-Roman and Late Antique eras
Hipparchus is considered to have been among the most important Greek astronomers, because he introduced the concept of exact prediction into astronomy. He was also the last innovative astronomer before Claudius Ptolemy, a mathematician who worked at Alexandria in Roman Egypt in the 2nd century CE. Ptolemy's works on astronomy and astrology include the Almagest, the Planetary Hypotheses, and the Tetrabiblos, as well as the Handy Tables, the Canobic Inscription, and other minor works.
Ptolemaic astronomy
The Almagest is one of the most influential books in the history of Western astronomy. In this book, Ptolemy explained how to predict the behavior of the planets, as Hipparchus could not, with the introduction of a new mathematical tool, the equant. The Almagest gave a comprehensive treatment of astronomy, incorporating theorems, models, and observations from many previous mathematicians. This fact may explain its survival, in contrast to more specialized works that were neglected and lost. Ptolemy placed the planets in the order that would remain standard until it was displaced by the heliocentric system and the Tychonic system:
- Moon
- Mercury
- Venus
- Sun
- Mars
- Jupiter
- Saturn
- Fixed stars
The extent of Ptolemy's reliance on the work of other mathematicians, in particular his use of Hipparchus' star catalogue, has been debated since the 19th century. A controversial claim was made by Robert R. Newton in the 1970s. in The Crime of Claudius Ptolemy, he argued that Ptolemy faked his observations and falsely claimed the catalogue of Hipparchus as his own work. Newton's theories have not been adopted by most historians of astronomy.
A few mathematicians of Late Antiquity wrote commentaries on the Almagest, including Pappus of Alexandria as well as Theon of Alexandria and his daughter Hypatia. Ptolemaic astronomy became standard in medieval western European and Islamic astronomy until it was displaced by Maraghan, heliocentric and Tychonic systems by the 16th century. However, recently discovered manuscripts reveal that Greek astrologers of Antiquity continued using pre-Ptolemaic methods for their calculations (Aaboe, 2001).
Indian Astronomy
Indian astronomy—the earliest textual mention of which is given in the religious literature of India (2nd millennium BCE)—became an established tradition by the 1st millennium BCE, when Jyotiṣa Vedānga and other ancillary branches of learning called Vedangas began to take shape.[1] During the following centuries a number of Indian astronomers studied various aspects of astronomical sciences and global discourse with other cultures followed.
| Name | Year | Contributions |
|---|---|---|
| Lagadha | 2nd–1st millennium BCE | The earliest astronomical text—named Vedānga Jyotiṣa—dates back to around 1200 BC, and details several astronomical attributes generally applied for timing social and religious events. The Vedānga Jyotiṣa also details astronomical calculations, calendrical studies, and establishes rules for empirical observation.Since the texts written by 1200 BCE were largely religious compositions the Vedānga Jyotiṣa has connections with Indian astrology and details several important aspects of the time and seasons, including lunar months, solar months, and their adjustment by a lunar leap month of Adhimāsa. Ritus and Yugas are also described.Tripathi (2008) holds that ' Twenty-seven constellations, eclipses, seven planets, and twelve signs of the zodiac were also known at that time. |
| Aryabhata | 476–550 CE | Aryabhata was the author of the Āryabhatīya and the Aryabhatasiddhanta, which, according to Hayashi (2008): 'circulated mainly in the northwest of India and, through the Sāsānian dynasty (224–651) of Iran, had a profound influence on the development of Islamic astronomy. Its contents are preserved to some extent in the works of Varahamihira (flourished c. 550), Bhaskara I (flourished c. 629), Brahmagupta (598–c. 665), and others. It is one of the earliest astronomical works to assign the start of each day to midnight.' Aryabhata explicitly mentioned that the earth rotates about its axis, thereby causing what appears to be an apparent westward motion of the stars. Aryabhata also mentioned that reflected sunlight is the cause behind the shining of the moon. Ayrabhata's followers were particularly strong in South India, where his principles of the diurnal rotation of the earth, among others, were followed and a number of secondary works were based on them. |
| Brahmagupta | 598–668 CE | Brahmasphuta-siddhanta (Correctly Established Doctrine of Brahma, 628 CE) dealt with both Indian mathematics and astronomy. Hayashi (2008) writes: 'It was translated into Arabic in Baghdad about 771 and had a major impact on Islamic mathematics and astronomy.'In Khandakhadyaka (A Piece Eatable, 665 CE) Brahmagupta reinforced Aryabhata's idea of another day beginning at midnight. Bahmagupta also calculated the instantaneous motion of a planet, gave correct equations for parallax, and some information related to the computation of eclipses. His works introduced Indian concept of mathematics based astronomy into the Arab world. |
| Varāhamihira | 505 CE | Varāhamihira was an astronomer and mathematician who studied and Indian astronomy as well as the many principles of Greek, Egyptian, and Roman astronomical sciences. His Pañcasiddhāntikā is a treatise and compendium drawing from several knowledge systems. |
| Bhāskara I | 629 CE | Authored the astronomical works Mahabhaskariya (Great Book of Bhaskara), Laghubhaskariya (Small Book of Bhaskara), and the Aryabhatiyabhashya (629 CE)—a commentary on the Āryabhatīya written by Aryabhata.Hayashi (2008) writes 'Planetary longitudes, heliacal rising and setting of the planets, conjunctions among the planets and stars, solar and lunar eclipses, and the phases of the Moon are among the topics Bhaskara discusses in his astronomical treatises. Baskara I's works were followed by Vateśvara (880 CE), who in his eight chapter Vateśvarasiddhānta devised methods for determining the parallax in longitude directly, the motion of the equinoxes and the solstices, and the quadrant of the sun at any given time. |
| Lalla | 8th century CE | Author of the Śisyadhīvrddhida (Treatise Which Expands the Intellect of Students), which corrects several assumptions of Āryabhata. The Śisyadhīvrddhida of Lalla itself is divided into two parts:Grahādhyāya and Golādhyāya.Grahādhyāya (Chapter I-XIII) deals with planetary calculations, determination of the mean and true planets, three problems pertaining to diurnal motion of Earth, eclipses, rising and setting of the planets, the various cusps of the moon, planetary and astral conjunctions, and complementary situations of the sun and the moon.The second part—titled Golādhyāya (chapter XIV–XXII)—deals with graphical representation of planetary motion, astronomical instruments, spherics, and emphasizes on corrections and rejection of flawed principles. Lalla shows influence of Āryabhata, Brahmagupta, and Bhāskara I. His works were followed by later astronomers Śrīpati, Vateśvara, and Bhāskara II.Lalla also authored the Siddhāntatilaka. |
| Bhāskara II | 1114 CE | Authored Siddhāntaśiromaṇi (Head Jewel of Accuracy) and Karaṇakutūhala (Calculation of Astronomical Wonders) and reported on his observations of planetary positions, conjunctions, eclipses, cosmography, geography, mathematics, and astronomical equipment used in his research at the observatory in Ujjain, which he headed. |
| Śrīpati | 1045 CE | Śrīpati was a astronomer and mathematician who followed the Brhmagupta school and authored the Siddhāntaśekhara (The Crest of Established Doctrines) in 20 chapters, thereby introducing several new concepts, including moon's second ineuqlity. |
| Mahendra Suri | 14th century CE | Mahendra Suri authored the Yantra-rāja (The King of Instruments, written in 1370 CE)—a Sanskrit work on the astrolabe, itself introduced in India during the reign of the 14th century Tughlaq dynasty ruler Firuz Shah Tughluq (1351–1388 CE).Suri seems to have been a Jain astronomer in the service of Firuz Shah Tughluq. The 182 verse Yantra-rāja mentions the astrolabe from the first chapter onwards, and also presents a fundamental formula along with a numerical table for drawing an astrolabe although the proof itself has not been detailed. Longitudes of 32 stars as well as their latitudes have also been mentioned.Mahendra Suri also explained the Gnomon, equatorial co-ordinates, and elliptical co-ordinates.The works of Mahendra Suri may have influenced later astronomers like Padmanābha (1423 CE)—author of the Yantra-rāja-adhikāra, the first chapter of his Yantra-kirnāvali. |
| Nilakanthan Somayaji | 1444–1544 CE | In 1500, Nilakanthan Somayaji of the Kerala school of astronomy and mathematics, in his Tantrasangraha, revised Aryabhata's model for the planets Mercury and Venus. His equation of the centre for these planets remained the most accurate until the time of Johannes Kepler in the 17th century. Nilakanthan Somayaji, in his Aryabhatiyabhasya, a commentary on Aryabhata's Aryabhatiya, developed his own computational system for a partially heliocentric planetary model, in which Mercury, Venus, Mars, Jupiter and Saturn orbit the Sun, which in turn orbits the Earth, similar to the Tychonic system later proposed by Tycho Brahe in the late 16th century. Nilakantha's system, however, was mathematically more effient than the Tychonic system, due to correctly taking into account the equation of the centre and latitudinal motion of Mercury and Venus. Most astronomers of the Kerala school of astronomy and mathematics who followed him accepted his planetary model. He also authored a treatise titled Jyotirmimamsa stressing the necessity and importance of astronomical observations to obtain correct parameters for computations. |
| Acyuta Pisārati | 1550–1621 CE | Sphutanirnaya (Determination of True Planets) details an elliptical correction to existing notions. Sphutanirnaya was later expanded to Rāśigolasphutānīti (True Longitude Computation of the Sphere of the Zodiac).Another work, Karanottama deals with eclipses, complementary relationship between the sun and the moon, and 'the derivation of the mean and true planets'.In Uparāgakriyākrama (Method of Computing Eclipses), Acyuta Pisārati suggests improvements in methods of calculation of eclipses. |
Astronomy in China
Astronomy in China has a very long history, and historians consider that, 'they were the most persistent and accurate observers of celestial phenomena anywhere in the world before the Arabs'. Star names later categorized in the twenty-eight mansions have been found on oracle bones unearthed at Anyang, dating back to the middle Shang Dynasty (Chinese Bronze Age), and the 'mansion' (xiù:宿) system's nucleus seems to have taken shape by the time of the ruler Wu Ding (1339-1281 BCE).
Detailed records of astronomical observations began during the Warring States period (4th century BC) and flourished from the Han period onwards. Chinese astronomy was 'equatorial', centered as it was on close observation of circumpolar stars, was based on different principles from those prevailing in traditional Western astronomy, where heliacal risings and settings of zodiac constellations formed the basic 'ecliptic' framework.
Some elements of Indian astronomy reached China with the expansion of Buddhism during the Later Han dynasty (25–220 CE), but the most detailed incorporation of Indian astronomical thought occurred during the Tang Dynasty (618-907) when numerous Indian astronomers took up residence in the Chinese capital, and Chinese scholars like the great Tantric Buddhist monk and mathematician Yi Xing mastered its system. Islamic astronomers, collaborated closely with their Chinese colleagues during the Yuan Dynasty, and, after a period of relative decline during the Ming Dynasty, astronomy was revitalized under the stimulus of Western cosmology and technology after the Jesuits established their missions. The telescope was introduced in the 17th century. In 1669, the Peking observatory was completely redesigned and refitted under the direction of Ferdinand Verbiest in 1669. Today, China continues to be active in astronomy, with many observatories and its own space program.
History of Chinese constellations
The divisions of the sky began with the Northern Dipper and the 28 mansions.
In early 1980s, a tomb was found at Xishuipo (西水坡) in Puyang, Henan Province. There were some clamshells and bones forming the images of the Azure Dragon, the White Tiger and the Northern Dipper. It is believed that the tomb belongs to the Neolithic Age, about 6,000 years ago.
Star names relating to the 28 lunar mansions were found on oracle bones dating back to the Wuding Period, about 3,200 years ago.
In 1977, a lacquer box was excavated from the tomb of Yi, the marquis of Zeng, in Suixian, Hubei Province. Names of the 28 lunar mansions were found on the cover of the box, proving that the use of this classification system was made before 433 BC.
As lunar mansions have such an ancient origin, the meaning of most of their names have become obscure. Even worse, name of each lunar mansion consists of only one Chinese word, and the meaning of which could vary at different times in history. So the meaning of the names are still under discussion.
Besides 28 lunar mansions, most constellations are based on the works of Shi Shen-fu and Gan De, who were astrologists during the period of Warring States (481 BC - 221 BC) in China.
In the late period of the Ming Dynasty, the agricultural scientist and mathematician Xu Guangqi (1562 - 1633 AD) introduced 23 additional constellations which are near to the Celestial South Pole, which are based on star catalogues from the West.
Star catalogues
In the 4th century BC the two Chinese astronomers responsible for the earliest information going into the star catalogues are Shi Shen and Gan De of the Warring States period.
| Author | Transliterated name | Chinese Catalogue name | Pinyin |
|---|---|---|---|
| Shi Shen | Shi Shen astronomy | 石申天文 | Shi Shen tienwen |
| Gan De | Astronomic star observation | 天文星占 | Tianwen xingzhan |
These books appeared to have lasted till the 6th century, but are lost after that. A number of books share similar names, often quoted and named after them. These texts should not be confused with the original catalogues written by them. Notable works that helped preserve the contents include:
| Author | Transliterated name | Chinese name | Pinyin | Comments |
|---|---|---|---|---|
| Sima Qian | Book of Celestial Offices | 天官書 | Tianguan shu | This is the astronomical chapter of the Records of the Grand Historian, a massive history compiled during the late 2nd century BC by the Han-era scholar and official Sima Qian. This chapter provides a star catalogue and discusses the "schools" of Gan De and Shi Shen. |
| Ma Xian (馬顯) | Star Manual of the Masters Gan and Shi | 甘石星經 | Gan Shi Xingjing | Despite having the name credited to Shi and Gan, it was lost and actually compiled circa 579 AD as an appendix to the Treatise on Astrology of the Kaiyuan Era, and summarized in a book "郡齋讀書志". |
| Book of Jin | 晉書 | Jin shu | In the Astronomical chapters of the text | |
| Book of Sui | 隋書 | Sui shu | ||
| Gautama Siddha | Treatise on Astrology of the Kaiyuan Era | 開元占經 | Kaiyuan Zhanjing | During the reign of Emperor Xuanzong of Tang (712 - 756 AD). After analyzing and providing summary on the work of Gan De and Shi Shen, Tang era astronomers mentioned the names of more than 800 stars that were found.121 of them marked with positions. The astronomical table of sines by the Indian astronomer and mathematician, Aryabhata, were also translated into the Kaiyuan Zhanjing. |
| The Great Firmament Star Manual Common to Astrology | 通占大象曆星經 | Tongzhan taxiangli xingjing | This renamed star manual is incorporated in the Taoist book Daozang. |
Wu Xian (巫咸) has been one of the astronomers in debate. He is often represented as one of the "Three Schools Astronomical tradition" along with Gan and Shi.The Chinese classic text "Star Manual of Master Wu Xian" (巫咸星經), and its authorship is still in dispute because it mentioned names of Twelve Countries, which did not exist in the Shang Dynasty, the era of which it was supposed to have been written. Moreover, it was customary in the past for the Chinese to forge works of notable scholars, as this could lead to a possible explanation for the inconsistencies found. Wu Xian is generally mentioned as the astronomer who lived many years before Gan and Shi.
The Han Dynasty astronomer and inventor Zhang Heng (78 - 139 AD) not only catalogued some 2500 different stars, but also recognized over 100 different constellations. Zhang Heng also published his work Ling Xian, a summary of different astronomical theories in China at the time. In subsequent period of the Three Kingdoms (220 - 280 AD), Chen Zhuo (陳卓) combined the work of his predecessors, forming another star catalogue. This time 283 constellations and 1464 stars were listed. The astronomer Guo Shoujin of the Yuan Dynasty (1279 - 1368 AD) created a new catalogue which was believed to contain thousands of stars. Unfortunately, many of documents at that period were destroyed, including that of Shoujin. Imperial Astronomical Instruments (儀象考成) published in 1757 containing 3083 stars exactly.
Copernican Astronomy
The renaissance came to astronomy with the work of Nicolaus Copernicus, who proposed a heliocentric system, in which the planets revolved around the Sun and not the Earth. His De revolutionibus provided a full mathematical discussion of his system, using the geometrical techniques that had been traditional in astronomy since before the time of Ptolemy. His work was later defended, expanded upon and modified by Galileo Galilei and Johannes Kepler.
Galileo was among the first to use a telescope to observe the sky, and after constructing a 20x refractor telescope he discovered the four largest moons of Jupiter in 1610. This was the first observation of satellites orbiting another planet. He also found that our Moon had craters and observed (and correctly explained) sunspots. Galileo noted that Venus exhibited a full set of phases resembling lunar phases. Galileo argued that these observations supported the Copernican system and were, to some extent, incompatible with the favored model of the Earth at the center of the universe.
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