Astronomy

• Universe is immense and we donot know whether the Universe has an "end" or not; we are not completely sure even of the full meaning of the question.
• The light-year is a unit of length used to express astronomical distances and measures about 9.46 trillion kilometres. It is the distance that light travels in vacuum in one year.
• The observable universe is a spherical region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time. Its Radius is 46.508 billion light years
• The Universe is probably 13.8 billion years old. The entire Universe is not static, but expanding. Universe contains objects such as Galaxies (some exploding and colliding); Neutron Stars and Pulsars; Quasars; and Black Holes
• The Universe can be closed, flat or open. The unobservable Universe, assuming there’s no topological weirdness, may be 23 trillion light years in diameter, and contain a volume of space that’s over 15 million times as large as the volume we can observe. Unobservable Universe can even be significantly bigger than that.
• Our Solar System is the "system" of planets, asteroids, and comets that orbit around our Sun. Our Solar System located at the edge of the Milky way disk, is in the Orion Arm of the Milky Way. Solar System may be 4-5 billion years old.
• The Milky way, bright band of stars is estimated to be about 50,000 light years in its diameter. There are 200 billion "Suns" in a galaxy like our own Milky Way, a spiral galaxy.
• Astronomers can see billions of galaxies. Around 10000 stars visible to our naked eye are generally within a few hundred light years around us.
• Some giant stars are located nearly 1000 light years are also visible to naked eye.

Astronomy Myths

• All heavenly bodies are assumed at different distance, based on the appearance (size seen from earth). So the order of mandalam is surya, chandra, nakshadra, pudan, sukra... Similarly, all heavenly bodies are considered close or distant based on 2D projection. Varahamira/Baskara corrected this. But our texts have not been updated.
• Water is the key element in earth. Some texts are interpreted to mean that all heavenly bodies starting with soma/chandra came from water. This may be due to the appearance of rising of heavenly bodies from ocean

Sun is centre: Helio-centric

Vedic Astronomical Values

• Twelve spokes, one wheel, navels three. Who can comprehend this? On it are placed together three hundred and sixty like pegs. They shake not in the least. (Dirghatama Rishi, Rig Veda 1.164.48)
• One of the oldest works on jyotish is the Vedanga-jyotisha, probably written by Lagadha. He most likely compiled techniques and observations from manuscripts that existed in his day. The work that survives was probably rewritten by later astronomers around 400 BCE, judging from the work's clasical (post-Vedic) Sanskrit. However, this work contains an observation that the Winter Solstice occurred when the star Shravishtha (α Delphini) was on the horizon. This dates the original work around 1400 BCE, placing it in the late Vedic period.
• A seven named horse does draw this three naved wheel… Seven steeds draw the seven wheeled chariot… Wise poets have spun a seven strand tale around this heavenly calf, the Sun. (Dirghatama Rishi, Rig Veda 1.164.1 5). Seven visible planets.
• The number seven related to the Sun has much significance when understanding the third mean solar motion. During the course of 10,000 years there are seven rotations of the third mean solar motion. For a single year the count is 0.2563795 diurnal revolutions of the earth. For two years it is .512759 and so on. One complete rotation (to equal 366.2564…) of the third motion takes 1428.571429 [10000/7] sidereal years.
• Yuga in mythology is a large number. Sun (our whole solar system) orbits around the center of the Milky Way Galaxy at 828,000 km/hr. But even at that high rate, it still takes us about 230 million years to make one complete orbit around the Milky Way
• Axial precession is the movement of the rotational axis of an astronomical body, whereby the axis slowly traces out a cone. In the case of Earth, this type of precession is also known as the precession of the equinoxes or precession of the equator. Earth goes through one such complete precessional cycle in a period of approximately 26,000 years, during which the positions of stars as measured in the equatorial coordinate system will slowly change; the change is due to the change of the coordinates. IT takes 26,471 years to come to same position. Every 2206 years, starting rasi for solar year will move by one.
• Supermassive black hole at the center of our Milky Way galaxy, known as Sgr A*, is 26,000 light-years from Earth. It's the closest black hole we can see, even if it's largely obscured by dust.

Planets - Grahas

In ancient India, all the nine planets (navagrahas) were personified as male deities. Graha is the one which moves in the sky. Around the time of Gautama Buddha, 9 graha system became popular, by including Rahu and Ketu. Rahu and Ketu denote the two points of intersection of the paths of the Sun and the Moon as they move around the celestial sphere.

• Surya (Sun) is number 1, followed by Chandra (Moon).
• Bhauma (Mars) is son of Earth, Budha (Mercury) is regarded as son of Moon.
• Guru (Jupiter) was guru of heavenly gods. Jupiter was the highest and most powerful among the Roman gods, called Jeus or Zeus by Greeks.
• Shukra (Venus) is a god or male deity was guru asuras, but Roman goddess of love.
• Shani (Saturn) is son of Sun.
• In a collective worship of all the nine planets, their idols, images or their representative figures are to be placed in a mandala (ritual diagram of a square subdivided into nine equal square cells).

Eclipse

The historical record of eclipse cycles known as the saros is by Chaldeans. Three periodicities related to lunar orbit, the synodic month, the draconic month, and the anomalistic month coincide almost perfectly each saros cycle. The Saros is a period of approximately 18 years, 11 days, 8 hours), that can be used to predict eclipses of the Sun and Moon. The eclipse season (34 days long on average) is longer than the synodic month. Rahu and Ketu passes through all the 27 Nakshatras in 18 years during its transit. It stays in one Nakshatra for about 8 months or 4 seasons (ruthu). So total 108 seasons.

Vedanga Jyotisa, supposedly composed by Rishi Lagadha makes no mention of the eclipse calculations.Rahu is nowhere mentioned in the Rig, Sama and Yajurveda. In the Atharvaveda, the description of Ketu is more suited for what we today call a comet (Dhumketu). Only in the Navagrahastotrom, Rahu and Ketu starts getting importance. 9 was the magic number. To make it 9, these two would have been added to 7 visible grahas. 28 star (7*4) of chaldeans became 27 star (9*3) of puranic astrology. Abhijit was removed from zodiac. This was also used to link it to comets in stories. Eventually added as story in Bhagvata Purana, during Golden age of Guptas.

The Surya Siddhanta gives detailed methods for making ecliptic calculations. Rahu and Ketu were astronomically defined to be the ascending and the descending nodes of the lunar orbit, intersecting the plane of the Earth's orbit.

Humans have watched eclipses since creation. Many of the popular (religious) ideas about the causes and effects of eclipses is views of small group of people (astrologers and story tellers). A lunar eclipse — an eclipse of the Moon — is perfectly safe to watch with the naked eye; you're only looking at the Moon, at night, which is quite safe. A solar eclipse is potentially dangerous, however, because viewing a solar eclipse involves looking at the Sun, which can damage your eyesight. May be good to protect eyes, if you look at Sun (any time). Total solar eclipses are terrifying and their ghostly green coronae look frightening. But is is just a natural cycle like day and night.

During a total solar eclipse when the disk of the moon fully covers the sun, the brilliant corona emits only electromagnetic radiation, though sometimes with a greenish hue. Deep in the solar interior where nuclear fusion takes place to light the sun, particles called neutrinos are born, and zip unimpeded out of the sun and into space. Every second, your body is pelted by trillions of these neutrinos no matter if the sun is above or below the horizon. The only consequence is that every few minutes a few atoms in your body are transmuted into a different isotope by absorbing a neutrino. There is no evidence that supports the idea that lunar eclipses have a physical effect on people. But it does admit that eclipses can produce “profound psychological effects” that can lead to physical effects because of the beliefs people have and the actions they take because of those beliefs. [NASA]

There will be some effect of eclipse on sea tides, climate. Science finds no physical links to eclipses and the beliefs about eclipses. Eclipses, often viewed as signs or evil omens have led ancient tribes to sacrifice animals and other humans to sway what is seen as the angry mood of the gods. Eclipses are harbingers of something very bad about to happen. Eclipses foretell major life changes and events about to happen. Every one's life follows some pattern and there is some sort of rhytm. Nature also has its own cycles and pattern. There can be some correlation between them. WE really do not know, how much. This is based on one's personal experience. We tend to remember all the occasions when two things happened together, but forget all of the other times when they did not.

In Hindu astrology, the eclipses are considered inauspicious. People in Tantric practices consider full moon day, new moon day and solar and lunar eclipse as powerful for paranormal activities. It is believed that the evil forces are appeased on these occasions.

Customs to be observed are given in many textbooks. The inauspicious period begins half a day before a solar eclipse and 3/8th day before a lunar eclipse. The water, clothes, food grains, etc., are sprinkled with the tarba or tulasi leaves. After a bath perform rituals like tarpana, sraddha, homa, prarthana and give donations. After the eclipse is over, one more bath, to erase the unholy shadow of Rahu. Some go to some sacred place or to the nearest seashore for taking a holy bath. There is a strong belief that any donation given during the eclipse hours is most auspicious. Now, MANY do not follow these TO THE DETAIL.

One can say some simple prayer or do some rituals. If you want to be on safe side, you can avoid eating couple of hours before eclipse. Pregnant women need not watch an eclipse. Do not keep food open.

Special numbers

• 7 is the highest single digit prime number. Seven grahas are visible from earth. The seven sages or saptarishis, who descended from the stars in the constellation called Ursa Major.
• 9 is a perfect square and many astronomical constants are in multiple of 9. This forms basis of navagraha syatem.
• 10 is the first double digit number formed by the coming together of one and zero. 10 is used to denote 10 directions (East, South-east, South, South-west, West, North-west, North, North-east, Up and Down. First 4 numbers totals 10 (1+2+3+4=10). This property is used for defining 4 yugas or ages.
• 12 is a composite number with four divisors (2, 3, 4 and 6)
• 18 a manifestation of 9, is a composite number, with large number of divisors being 1, 2, 3, 6 and 9. Three of these divisors (3, 6 and 9) add up to 18, hence 18 is a semi perfect number. 18 is the only number that equals twice the sum of its decimal digits. Mahabharata has been organized into 18 parvas and Geeta added to the epic was divided into 18 chapters.
• 27 stars is also a manifestation of 9. (28 stars of chaldean system by Daksha was converted in to 27 stars system by astronomer Badhra).
• 60 is convenient for division by 2,3,4,5 and 6. That way one can express fraction of 60 in whole numbers.
• 108 a manifestation of 9, which is equal to 27*4 and 12*9, is another special number. 27 constallations and each one has 4 directions or 4 parts, and 27 * 4 = 108. 108 is a Harshad (means "great joy") number, which is an integer divisible by the sum of its digits (1+0+8 = 9). The distance from the Sun to the Earth is approx 108 times the diameter of the Sun. Distance of the Moon from the Earth is approx 108 times the diameter of the Moon.
• 360 is a highly composite number, but also the smallest number divisible by every natural number from 1 to 10 except 7. A circle is divided into 360 degrees for the purpose of angular measurement. This choice of unit allows round angle to be divided into equal sectors measured in integer degrees rather than fractional degrees. one year is close to 360 days, making it equal to 12 months (30*12).
• 432 = (2^4)*(3^3). Equals 2 to the power of 4 multiplied by 3 to the power of 3. It was consifered as magic number for astronomical calculations. Kalacakra calendar in use, 60 year cycle starting with Prabhava, is by Pandita Somanatha of Kashmir/Himalayas, in 367 CE. Vernal equinox of 367 CE is Prabava Varsham. He further developed sexa decimal system. The earth's axis wobble that causes the precession of the equinoxes is approximately 25,920 years or 432 sixty year cycles.

Indian astronomers

• One of the earliest authors of Indian astrology, is said to be Pita Maha who wrote a treatise on astrology called Pita Maha Siddhant(a). He lived and wrote this book about 3,000 BCE.
• 2500 BCE another author-astrologer named Vashishtth(a) wrote several books on astrology, astronomy and philosophy. Vashishtth(a) Siddhant(a), but he wrote many other equally erudite and authoritative texts such as the Panch Siddhant(a) Kosh(a), Soory(a) Siddhant(a), Nityanand(a), Brhat Jatak(a), Aryabhat, Mansagari, Ranveer, and the Laghu Parashar.
• Aryabhata made contributions to Spherical geometry, a part of understanding the earth as a globe. Aryabhata had estimated the beginning of kaliyuga as 3102 BC. He stated that when he was 26, sixty of the 60-year cycles were completed after start of kaliyuga.
  Aryabhata was the author of the Āryabhatīya and the Aryabhatasiddhanta. 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.
• Varaha Mihira's contributions include presently used Soorya Siddhanta, (He refers to nine types of time keeping and calenders) and the fact that he proposed Prime Meridian through Ujjain in Madhya Pradesh. He knew of Earth's Precession and called it as ayanaamsha. 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.
• Brahma Gupta made contributions to Arc sin in Trigonometry. Texts from that period like Yavana Jataka, Romaka Siddahnta provide evidence of understanding of European astronomical works. Brahmagupta reinforced Aryabhata's idea of another day beginning at midnight. Brahmagupta 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.
• Baskara 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. 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. Lalla also authored the Siddhāntatilaka.
• Pandita Somanatha who developed current Kalacakra calendar of 60 year cycle
• 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 was an 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 inequlity.
• Mahendra Suri 14th century CE 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
• 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.
• Acyuta Pisārati 1550–1621 CE - Sphutanirnaya (Determination of True Planets) details an elliptical correction to existing notions. Another work, Karanottama deals with eclipses, complementary relationship between the sun and the moon, and 'the derivation of the mean and true planets'.