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Jyotirvidya (Astronomy) science of motion and nature of stars, planets and other cosmic bodies in the universe. Jyotirvidya is one of the oldest branches of science. In many old civilisations, methodical and well-regulated movements of the stars and divine bodies were a subject of utmost curiosity to the men of sciences. Scholarly people of the ancient time used to note down their observational studies on the reciprocal interchange of places of the sun, moon and planets and tried to forecast about future events on the basis of these experiences. In the time of purana, pundits introduced the science of enumeration of time (days, months and years) through observation of movements and rotations of cosmic bodies and on the basis of this the mode of adjusting the natural divisions of time in a calendar was evolved. Afterwards the knowledge procured from the study of astronomy became essential in navigation particularly in determining direction.

The Chinese used calendar for their daily necessities as early as 13th century BC. Chinese scholar Shih Shen formulated an almanac back about 350 BC embodying descriptions of 800 stars. This is considered to be the earliest calendar in the history of astronomy. Most of the ancient astronomers were priests. Many of them gradually started to opine that there is a relation between men's destiny and position and movements of stars and planets. Thus astronomy by and by transferred into astrology. But since the 18th century, astrology has been kept separate from astronomy. At present scientific deliberations relating to the distance, gravity, materialistic compositions, formation etc of stars and planets have been incorporated in the study of astronomy. In modern astronomical science there is no acceptance of astrology. Consequently, physics, mathematics and astronomy are inseparably linked today.

There are evidences of astronomical studies in India since the Vedic period. However, movements of only sun and moon were observed during the time. Years were divided into months on the basis of new moon and full moon. The state of the study of ancient Indian astronomy can he traced from a few books and scriptures of ancient time, of them, the Veda is the oldest. The Veda has six accompanying branches, which are known as Vedanga. The 5th Vedanga is on Jyotiska where a narration of stars and planets is available. Due to the necessity of the stellar positions in all-Hindu religions and social rituals, mention of astronomy is there in all Hindu treatises and also astronomy has been practised in all ages. Indian astronomy is divided into three branches: Ganit (mathematics), Hora and Samhita. The branch that deals with planets is called Ganit. The Hora scripture helps determine the good or bad signs of journey, marriage etc in accordance with the positions and auspicious moment of planets and also cast one's horoscope by looking into the stellar positions at the time of one's birth. The mathematical branch of astrology is again of two kinds: Siddhanta or deduction and Karan or act of performing. In Siddhanta result of each enumeration was determined after applying proofs and evidences. In Karan method of enumeration only is narrated. Position of the planets can be determined by applying related formulas, but there is no reference in Karan as to how would that formula be evolved. Owing to total dependence on Karan culture of astrology instead of astronomy began to get upperhand in India with the passage of time. Astrologers engaged themselves only in casting horoscopes and various calculations with the help of Karan.

In Hindu religion the place of Purana, ie myths and mythologies is next to the Veda. Purana is composed of ancient tales and hearsay. Puranas are eighteen in number. There are references of astronomy in the Puranas but those are pervaded with metaphors and stories. Various allegories have been resorted to in describing the motions of the sun, moon and planets. Amusing tales have been concocted while discussing the stellar region. In the Purana every star has been personified with a human figure. For example the sun travels, but since no person as strong and majestic as the sun could travel on foot, image of a chariot has been contrived. Likewise, horses have also been imagined for pulling the chariot. According to the Puranas, the sun and planets observe the happenings on earth while travelling in the space at amazing speeds, and thereby cast their spell on human beings and events in the earth.

As stated in the Puranas, there was only water all over at the dawn of creation. This water gradually began to circumambulate in a circular motion, which in turn produced bubbling foams. Besides, one kind of white element emanated from the water out of which the creator created an egg. This egg bisects into two parts and the Brahmma appeared out of this egg from where the name Brahmanda or the Universe is derived. One part of this broken egg constituted the earth and the other space. According to the Purana, the tiny parts that scattered all over at the time of bursting of the egg produced rains. As to the area of the Universe, it has been said that at the lowest part of the Universe there is a layer of pitch darkness expanding 1 crore 85 lac yojana (one yojana or jojan is about 8 km). The hell follows just after this. Its expanse is 13 crore 12 lac yojon. After this there is again 1 lac yojon wide darkness. On top of this darkness there are 34,000 yojana width of thunderbolt. On this rests the matrix or middle world stretching 60,000 yojana. On top of the matrix is the Swarna Prthivi or Golden World. Above this are the 7 worlds, each expanding 10,000 yojana.

According to Visnu Purana, there are seven nether worlds in the globe. These are Atal, Bital, Nital, Gavastimata, Mahatal, Shrestha Sutal and Patal. Each of these nether worlds is 10 thousand yojana in expanse. One lac yojana above the earth is sun sphere, one lac yojana above of it is moon sphere while one lac yojana above this is the stellar region. Two-lac yojana above this is Mercury, Venus, Mars, Jupiter and Saturn spheres respectively. Above one lac yojana of the Saturn sphere is the Great Bear constellation. Another one lac yojana upward is the Pole Star. And around this Pole Star or North Star revolves all the stars. Indian astronomers belonging to the Purana era or Pre-Purana era believed that sun is nearer than the moon and the stellar region is nearer than the mercury sphere. In the ancient Indian astronomy the sun and the moon were called planets like the Mercury, the Venus, the Mars, the Jupiter, and the Saturn. Besides, two other planets namely Rahu and Ketu were also imagined.

The codes and edicts of all Hindu rituals are compiled in a book called Samhita and it may be divided into two parts. One is the practical part and the other is the action part. The practical part comprises codes and regulations for work as per lunar and stellar calculations while in the action part good or bad omen of a work is determined by observing the physical and surrounding state of things. The professional group of fortune-tellers sprang out basing on the action part. One has to attain special dexterity in astronomy for mastering the practical part. The entire knowledge of Indian astronomy was compiled in the Samhita since antiquity. But no traces of these ancient Samhitas are available today.

The book of Indian astronomy is called Siddhanta Grantha. Aryabhattya authored by Aryabhatta (476 AD?-550 AD?), Pancha Siddhantika compiled by barahmihir (499 AD?- 587?), Brahmmosfut Siddhanta written by Brahmagupta (598 AD-665 AD?) and Ganitadhyaya and Goladhyaya authored by Bhaskaracharya are some of the best specimens of Siddhanta Grantha. Besides these works, more lucid and complete book on the subject is Surya Siddhanta authored by an anonymous astronomer (or Moydanava).

The astronomers belonging to the Siddhanta era tried much to find congruency of the knowledge they earned through research with the accounts of the Puranas. In the case of any dispute between Purana and research, they held on to their arguments humbly ignoring the Puranas. According to the proponents of the Siddhanta, the earth is round; its northern half is land and the southern half is water. Poulish Siddhanta has acknowledged that the earth is situated in the centre of the universe and that its shape is round. It has further stated that its one half is land and the other half is water.

The mythological Arctic Mountain is situated on the land portion and that deity lives there. On top of it is the northern pole. The mythological sea-horse mouth (Badab) is situated in the watery half where demons and nagas (snakes) live. The line bifurcating the earth into two parts is called the equator. There were four famous cities in its four sides. They were Jamkoti in the east, Rome in the west, Lanka in the south and Siddhapur in the west. The earth is bounded by axis at the two poles. When the sun rises on the joining line between the Arctic Mountain and Lanka, it is noontime then at Jamkoti, evening at Siddhapur and midnight at Rome.

Barah Mihir the compiler of Siddhanta was aware of gravitation He opined that all people are attached to the surface of the earth as the petals of Kadamba (Anthocephalus indicus) flower are attached to the body of the Kadamba. Not that some body's legs are grounded on the soil and of others heads. Everybody stands with his head high, keeping the legs firmly grounded. The earth attracts everything towards its centre. That is why the centre of the earth from all places is down below and the sky up above. Likewise, all subjects of modern day astronomy including rotation of sun and moon, position and motion of stars and planets, calculations of sun and moon eclipses, calculations of rising and setting of heavenly bodies etc are available in these Siddhanta books. However, they could not determine that the sun is the centre of the Solar system. The Siddhanta treatise are based on the theory that the earth is the centre point and every thing move round the earth.

Study of astronomy in Bangladesh In Bangladesh the history of the study of astronomy is of very recent origin and is assumed to have begun since the middle of the 20th century. Study in astronomy in the country, particularly during the Pakistan period, was mainly theory based. Since observational astronomy or space technology was extremely costly, no organised efforts were accomplished in this field at the time. Astronomical study therefore was confined during the Pakistan period as a branch of Mathematics.

In the post-independent period a few eminent personalities and organisations rendered significant contribution to observational astronomy study, of them eminent mathematician Md Abdul Jabbar is noteworthy who could be dubbed as the pioneer of astronomical science in independent Bangladesh. The first ever Celestial Globe or C-Globe was compiled and drawn up under his overall supervision and planning. He authored a number of books to popularise the study of astronomy in Bangla language. Among those Tara Parichiti, Khagol Parichoya and Prachin Jyotirvidya are worth mentioning.

The Bangladesh Science Museum initiated astronomy-related activities since 1980. It started with a 4-inch reflex telescope to make opportunities for interested public to observe the sky. Besides, a ten seat capacity mini-planetarium was provided to impart knowledge of the night sky to the amateur astronomers.

Some organised pursuits in the observational astronomy commenced in the country with the setting up of bangladesh astronomical association in 1988 by a group of young men interested in the study of astronomy. They generally observed various astronomical events, viz eclipse of the sun or the moon, appearance of any new bright comet, meteor-storm, planetary antipathy etc and kept their camp open for general public. Though another predecessor organisation entitled Bangladesh Astronomical Society began functioning since 1985, but their organisational activities were very limited and mostly science museum based. The Bangladesh Astronomical Association has been performing a yeoman's service to popularise astronomical matters to general people through regular publication of their space related magazine Mahakash Barta. Despite all these, the practice and study of astronomy in Bangladesh is very limited and rightly said to be in its primary stage. [Masud Hasan Chowdhury, Md Mahbub Murshed and Sifatul Quader Chowdhury]