Contemporary Hindu Astronomy & Astrology is based on our Research with texts like Surya Siddhanta, Narakantheerava, Aryabhatiya, Brhatjataka, Sripathi, Ganakananda, Graha Laaghava, Krishnamisriya, Kaala Maadhaviya, Kaala Saadhana Koumudi, Kaala Nibandha, Pratyabdaphala Panchanga Sarali, Poorva Kalamrutham, Uttara Kalamrutham, Muhurtadarpanam, Muhurta Maartandam and other texts.
Since ancient times, all over World, there was great interest in the development of Astronomy. Serious scientific attempts were made to investigate and explain the various celestial phenomenon happening above us in the skies by observing them at different times and places on Earth. Surprisingly, ancient Hindu Astronomers devised some fundamental rules much earlier independently. As per Surya Siddhanta, it was said that at the end of each Manvantara, Earth sinks into the Oceans loosing all knowledge and habitat. And, at the New Begining of the next Manvantara, past knowledge is transcended to the new Manvantara. This point is worth noting. Thus, Inventions, Debates, and Refinements continued among Hindu Astronomers and Astrologers till the 12th century AD. This was the period, Astronomy attained its maximum development and improvement in India. Even today, Hindu Astrologers by practicing these fundamental rules, helped Hindu Astronomy to survive with whatever limitations these theories may be having. Tri-skandha Shashtra has the three constituents namely, Siddhantha, Jyotisha, and Muhurtha. All the three are closely inter-related in the Hindu system of living and life, that evolved since Vedic-Puranic times.
The celestial phenomena observed by the ancients were the same as those of today. The Sun progressed steadily westward in the course of a day, and the stars and the five visible planets did the same at night. The asterisms (Star complexes) were believed to beat these planets in their attempt to forge ahead, causing planets to move eastward. This Hindu view prevailed throughout the world then. The Sun was observed at sunset to have moved eastward by about one degree a day against the background of stars, and in course of a year it had completely traversed the 360 degree path of constellations that came to be known as the zodiac. Thus, a complete revolution is meant that it had trvelled fully through all the star constellations. So, planets generally moved eastward along the zodiac, with Sun's apparent annual path (ecliptic). But some times, they moved with a puzzling reverse-motion phenomenon in the sky before resuming their normal eastward motion. The Moon moved across the ecliptic in about 27 & 1/3 days and went through several phases, called "Kala" in Hindu scriptures. Earliest civilisations around the world did not realise that these phenomena were in part a product of motion of Earth itself. And, they wanted to predict the apparent motions of these celestial bodies, which interest caused the birth of Astronomy.
An early attempt to devise a Calendar based on Moon's phases (Kala) was abandoned as incresingly becoming too complex to synchronize. Chinese those days did not systematically attempt determining celestial motions, and did not show much interest in Astronomy. Surprising evidence of a more substantial interest in Astronomy was found with the presence of ancient stone alignments and stone circles found throughout Europe and Great Britain. As early as 3000 BC, the collection of massive stones at Stonehenge revealed that a functional ancient observatory prevailed at that time, where every morning its priests followed the annual motion of Sun along the horizon to notice and note beginnings of the seasons. By about 2500 BC, Stonehenge was known to have started predicting eclipses of the Moon. Similar activities were undertaken till 1000 AD.
In ancient India, before 12th century AD, development of Hindu Astronomy originated with Vedic and Puranic background materials & Hindu Mythology. A large number of Scriptures, Treatises, and Formulas were devised quite independent of others across the Globe. No doubt we all must wonder at ancient Rishis (Sages) enormous capability of understanding and reasoning in their Astronomical works. The way Planetary behaviour was explained, simply by observation and logical thinking, and that too with ordinary simplistic instruments (like Sankhu, Yantra) coupled with their mental prowessess is nothing but God's blessing on them.
Among all the various Siddhanthas, Surya Siddhanta is even today widely known as the best & first elaborate mathematical work in Hindu Astronomy. Many commentaries and critics were written by both followers & critics. It is unfortunate that today we have no easy access to many of these Siddhantas/works to testify with modern methods and means. Few traces and parts are known to exist in some form here or there, lying without any body's notice or perusal.
Study of motions of these celestial bodies required only that they are regarded as points of light (Jyothi). In 4th century BC, Aristotle proposed a theory of physical nature of these bodies. He postulated properties of perfection and unchangeability in these celestial bodies, in contrast to the ever-changing Earth. Next centuries came up with an observation-based estimate of sizes of Sun & Moon. These estimates were universally admired as landmarks even though they are seriously under-estimates.
Physical similarities of Earth & Planets became a matter of significant inquiry, that Earth and all planets are in continuous circular motion around Sun. This question of circular motion was resolved with the advent of Telescope in 1609 AD exploring the skies. The results in 1610 AD were that Moon was found to be a mountainous body "much like Earth”. Further, the moons of Jupiter, and the phases of Venus, were discovered. This was great evidence that the planets had Earth-like characteristics.
Such important discoveries verifying physical reality accumulated throughout the 17th & 18th centuries. The nature of Moon was discussed in increasing detail. In the 17th century, rings of Saturn were correctly interpreted. Further, dark markings on Mars, and belts of clouds on Jupiter, speculating that Venus was hidden in clouds, became real-wonders. With more refined telescopes, the details of the solar system became better known. Discovery of the planet Uranus in 1781 AD, Neptune in 1846 AD, were the result of actual observations at Observatories, a grand victory for theory and observational developments.
In India, besides the fundamental works mentioned earlier, Aryabhatiya by Aryabhat-I in 499 AD, Romaka & Paulasa Siddhanta by Latadeva in 505 AD, Pancha Siddhanta by Varahamihira in 550 AD, Brahmasphuta Siddhanta, Khandakhadyaka by Brahmagupta in 628 AD, Sishyadhi vruddhida by Lalla in 748 AD, Laghumanasa & Brhanmanasa by Manjula in 932 AD, Siddhanta Sekhara by Sripati in 1028 AD, Siddhanta Siromani by Bhaskara-II in 1150 AD are some important foot-prints and landmark scriptures in Hindu Astronomy and Astrology. I will not go into details of these works here. Let us understand Astronomy that is useful in Astrology and for our prediction purposses. It is our own understanding of Astronomy from the point of view of Astrological necessities and niceties.
But we all must honestly admit that a serious and sincere work of substantial standard in Astronomy did not take place in this Hindu land after the 12th century AD, whereas other countries showed much greater interest and exploited their rich knowledge taking cues and hints from Hindu thoughts. Hindus may have valid reasons for total neglect of Astronomy due to external phenomenon like continuous wars, invasions, calamities, foreign-rule etc., but even scholars were demoralised so much that they abondoned development of Hindu Astronomy. Hindus who took to studying Astronomy first, having laid foundations in Astronomy, enthralling and enlightening other countries, and promoting spread of interest and ideas in Astronomy throughout the entire world, finally lost its own rich heritage today at its own behest.
In the skies above us, are the vast number of small and big Stars (Nakshatra). Nakshatra means "Na" + "kshata" i.e not dying or permanent. This entire stardom called Asterism is grouped into 27 clusters and given names. Of course, some call the "Abhijit" the 28th Nakshatra, but its composition is for some other convenience. Within this 27 Star Asterism, our planets Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn (Rahu and Ketu) appear moving continuously and repeatedly in a systematic fashion as viewed from Earth which too is revoving on its axis.
Hindu Astronomy with roots in Vedas & Puranas was continuously refined as a knowledge reservoir of fundamental rules according to changes and developments that took place in the developing Astronomy all over the Globe. To begin with, Hindu Astronomy is primarily based upon different systems of time-measurements (Maana) for different purposses. These are, time-modes of Brahma (Creator), of Gods (for Festivals etc.), of Fathers (for rituals, customs), of Prajapati, of Jupiter (Brhaspati), of Solar (Saura), of Civil (Savana), of Lunar (Chandra), and of Siderial (Stars). The time-modes of Brahma, Gods, and Fathers have little significance in Astrology, but they are for purposses of reckoning time from the begining of creation of universe, for Hindu Festivals, rituals and customs and the like.
According to Kaala Nibandha of Vidyaranya muni, Jupiter's time-mode (Brhasptya maana of 361 days) is useful for the 60 years-cycle determination (an extra year sometimes comes called the Adhi vatsara), and each year is given a name. Solar time-mode (Saura maana of 365 days) is instrumental in calculations for day-night cycles, the solstices, the equinoxes, and Sun's entry into Cancer & Capricorn (kranti). Civil time-mode (Savana maana of 360 days) is instrumental for the period between Sun-rise to next Sun-rise (Ahas) for calculating time of Sunrise, Noon, Sunset, and midnight. Lunar time-mode (Chandra maana of 354 days) is instrumental for calculating each Lunar day (tithi), Half-month (Paksha), Lunar junction with Asterisms (Nakshatra), Lunar Conjunctions (yoga), and day-halves (Karana). Siderial time-mode (Nakshatra maana of 324 days) needs no explanation as it is basic for both Astronomical calculations and Astrological purposses as the referral backdrop screen for all planetary motions. Such differential treatment of time-measures complicated matters for synchronising them all together, and balancing them argueably and purposefully. This is essentially the most striking and most-intelligent feature peculiar to Hindu System. It is a wonder that our ancient scholars earned universal acclaim & appreciation.
In this backdrop, change from totally lunar system to Luni-Solar-Civil-Siderial system gave rise to some more radical refinements in explaining planetary behaviour, in line and tune with its earlier developments. Every Hindu Astronomical calculation starts with Ahargana which means the number of civil days passed from the day of reckoning taken as kaliyug (Iron Age) as the recent reference point. Kaliyug was thought to be about 1,970,784,000 solar years. Naturally, Ahargana will become a large number as centuries roll over since commencement of Kaliyug. So, any small negligible fraction ignored in early years, will soon get accumulated to become alarmingly big because of largeness of the resulting Ahargana and effects all other Astronomical calculations based on it. This is why a different reckoning point which is most recent is taken instead of Kaliyug. One such is Salivahana era (Solar) which refers to a lapse of 3179 complete revolutions (Solar years) in Kaliyug at Salivahana era start (April 12, 1859 to April 11, 1860). The other is Vikramaditya era (Luni-Solar) which refers a lapse of 3044 complete revolutions (Luni-Solar years) in Kaliyug at Vikramaditya era start (April 4, 1859 to March 22, 1860) . Salivahana era became popular among Hindu Astronomers and Astrologers. Ujjain (in Rajasthan state of India), a mideveal Hindu seat of Hindu scholarly excellence (23N10 Lattitude, 75E47 Longitude), as reference place on completion of 588465th civil day (between 17th and 18th February, 3102 BC) in all Astronomical calculations by Hindu Scholars merits mention here.
Another important feature in Hindu Astronomy for Astrology is that a siderial day extends from Sun-rise to the next Sun-rise, a Siderial Month composed of 30 such siderial days, and a siderial year composed of 12 such siderial Months. Lateron, it was discovered that a siderial year was exceeding 12 siderial Months by about one quarter of a siderial day. Hindu Astronomers revised their theories by adjusting siderial day/month/year with the 27 Nakshatras (for accomodating tithis etc.), using an intercalary month (by Adhika Masa, and balancing the resulting excess with Sunya Masa). These were needed for determining Lords of the Months, yet conforming to the already developed fundamental-rules in Hindu Astronomy. Next, the tropical solar year (Savana samvatsara) had to be equated with the siderial year by the addition of precession of the equinoxes (Ayanamsa) to accommodate the starting and ending of Seasons. And the time begining with that Asterism (each star formulated to have a definite longitude) must coincide with the vernal equinox to explain the coincidence with (Ugadi) the first point of Aswini Nakshatra among Stars. These became necessary in view of Astrological importance to Uttarayana, Dakshinayana, Masadhipathi, Varshadhipathi, and many other Nayakas (Lords). These factors are often cited in Hindu Almanacs (Panchang) for many Hindu rituals and customs, besides Astrology. In this manner, not only concordance has been achieved between Astrology, Astronomy, Hindu Rituals and Customs, but also concordance between the different Time-modes (Kala maana) as explained earlier. This uniform and universal concordance bringing all systems on par is an excellent ingenuinity of Hindus, which are proved true and valid even today.
The exciting part of Hindu Astronomy is the aspect of rotations (Swa-bhrmana or spinning on its axis) and revolutions (Bhrmana around an external central point) of the planets Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn. Par-excellence of Hindu Astronomers lies in their minutest attention given to aspects like tilt of Earth’s axis of rotation, ayanamsa, maintaining the 27 Star chart as background referral scene, among many such considerations. Most Hindu treatises upto the 12 th century AD, especially Aryabhatiya, contain these intricate but widely accepted principles as per Geometry and Trignometry. The Hindu Sines and Versed Sines (Bhujajya, Kotijya) are acknowledged all over the world even today as miraculous approximations, and are found exact to the fourth decimal place. Today’s Higher level Mathematicians must stand wonder-struck at such Geometrical postulates at such an ancient past.
Planetary orbits (paths of revolution) were assumed to be that planets & Earth were orbitting round Sun. Initially circular orbits for the planets were thought of. But soon accurate astronomical observations showed that this was not strictly accurate. In 1600 AD, it was discovered that planets move round Sun in elliptical orbits having Sun in one of their two foci individually. It was argued that the line joining any planet to Sun sweeps out equal areas in equal times as the planet describes its orbit. Both these laws were first formulated in 1609 AD for Mars. In 1619 AD, the argument that squares of the periods of planets are proportional to the cubes of the mean radii of their orbits became widely accepted.
Newton explained his own idea that the rotation of Earth. Newton provided a sketch of the path the particle, dropped from a height, would follow, quite incorrectly showing it as perfectly spiral towards the centre of Earth. Theory of planetary motion led to the elliptical path of the particle, extended to that of planets similarly.
Aryabhatta introduced the same concept as Epicycles (some kind of spiral motion) and explained the theory of planetary speeds, motions, orbits, and eventually their positions at any point of time. Although a complex calculation, his theory earned Hindu applause as well as the World over. Aryabhatta was the one who refined Sighra and Manda (elliptical declination and inclination). It re-established ancient theory that Budha (Mercury) and Sukra (Venus) being planets between Earth and Sun, are dragged along by Sun. This led to refining Hindu calculations by positioning these two planets always around Sun, because they can not deviate from their orbiting path set at a definite distance from Sun. Of course, these two planets’ motion was so adjusted to their times of Risings (Udaya) and Settings (Astamaya), and Retrograde (Vakra) settings. These refinements, on par with other developing theories all over World, were essentially to maintain Hindu Astrological-Astronomy intact without sacrificing Hindu Systems of living and life having roots in Vedas and Puranas.
I personally think (I have other valid postulates to integrate into a cohesive theory) that Aryabhatta's epicycles theory is a static concept (planetary position calculated at an interval drawing a perfect circle at that point) instead of a dyanamic concept (explaining planetary continuous motion). This distinguishing feature is like that between differentiation and integration we all study in Graduate level Calculus in Mathematics. Infact, planets move only continuously and not step-after-step as prescribed in procedures for making the Hindu Almanac (Panchang) and Astrological (Horoscope) calculations.
Hindu Astrology is primarily meant for future predictions. Tri-skandha shashtra (three-part) include Siddhanta, Astrology, Muhurtas for orderly Social and Human behaviour with traditions rituals & customs. The fundamental reference point in Hindu Astrology is always the place of Birth on Earth, which introduces further correctives in Astrology for Horoscope-based future predictions.