 Good evening on behalf of the physics department. I welcome you all here I would like to point out that physics society is a society run by the students of the physics department, but members of course all the people who are members of the physics department Automatically become members of physics society So students have an executive committee which decides the program and implement it of course There are faculty advisors and professor Amit Dutta happens to be one of the advisors. So today I would request Professor Dutta to introduce the speaker Professor Dutta needs no introduction here Though he started his career teaching and research everything in West Bengal, Shiftoon, B college that those days now he is known as B2 Then IISC and now then he moved to IID Angur in 1971 when I was 2 and a half years old Then we spent long 36 years here, but he takes immensely to teaching, research, founding the first law center in India He published 120 papers, wrote 5 books and contributed to every aspect of the institute So and if I read his award then I am honored There is one paragraph I will just mention he is the elected member fellow of 4 academies And also his interest goes beyond mechanical engineering physics And you can see ancient and medieval artistic era That means he connects ancient history times of those days to the modern times And presents only So in a very brief account, anybody interested can just google Amit Dutta for you You will get every details in the inside I will end with some personal information When I, he has always been my father with me, happens to his elders and he is almost my age So when I joined in 2003, there was a course 5-1 to Mechanics, Clefner And I read about him in the news papers because the director of Karpura IT Is very used to appearing in the main news papers from where I get to know about him And then I realized this is the same person, because the director is sitting in the main lecture with me Taking the tutorial, no longer that I was the director of this place or that place And we used to go to the Southern lab which was a different company, different and we used to see that time We used to take in that course and those experiences and at this point I also recall Professor Malik Who was his age student, Professor Ashok Malik, same department at Mechanics So I learned many things, first I learned Mechanics Second, I learned from Professor Koukosh, what is the attitude also That here, even the person of such a stature embraces a younger colleague like this Which is well, third I would say, what is the indication to be teaching And fourth, most importantly probably, I learned what is 4-P, which no longer exists in this course It is a problem equation Thanks So, very good evening to all of you And for me, it is homecoming because I spent 30, not 36, more than 36 years And from 1970 December till 2007 December And last time I taught the course here, a science elective was also in this room I am extremely thankful to Physics Department for giving me the opportunity to come back home So when you grow old, you will realize what is the meaning of that And for all practical purposes, IIT Kanpur is my first home, not second home So I think, when I was requested by Professor Manna to spend some time I come to Lahabad for the Academy meeting Then I decided that rather than sitting idle, if I can give a series of lectures on this Very fascinating topic, which normally we do not come across Because it is nowhere in our curriculum or so But I think, when I myself worked or studied this for last 7-8 years Then what happened that Ramakrishna Mission Institute of Culture, Calcutta And the National Academy of Science, they plan to bring out an 11 volume series On history of science in India Primarily, the chief editor was Professor Sharma Who was earlier in sub-president, Nasi president, M. G. K. Menon and all such S. K. Joshi So their directive was that there are books, very, I will say Very knowledge, very important books But they are not within the reach of common students or common readers So we were told, is it possible that you write all of us That means we were quite a few authors It was on physics, mathematics, this is the part on astronomy which I wrote So it is a, the whole thing was released in the month of March I thought that since we worked, I had to work quite a lot Why not I share some of the things I read, studied and really felt Not only fascinated but also proud So therefore this lecture, five lectures which I have planned Will be primarily based on the book And I have brought one extra copy I want to give it to the P. K. Kelkar Library So that any one of you who want to read some of the things You can refer it to it So I will hand it over to Professor Choudhury You can arrange to keep it in the central library So I think the first thing, if you permit me At the age of 74, I feel more comfortable If I am allowed to sit by my audience So the first point is that Why this particular topic? We all know that the ancient astronomy Scientifically the hallows or the theories of those times Are not really tenable of not much importance now The modern astronomy Why we study this or why we listen to this So the point is why I think you should Or any Indian should do it Is that you will find it amazing The brilliance of the mind of our ancestral scientists And philosophers That is one thing Another very important point is That astronomy is something which attracts Even the primitive people, isn't it? Because every day they find sun is rising Moon is rising in a different shape They are changing All those things attract the attention And they start observing So one of the earliest branch of science Which gets developed in any civilization Is astronomy Secondly astronomy also Particularly in India It had lot of link with our cultural activities Sacrifices, various festivals All such things That means it is closely linked with the society So if you get the glimpse of The astronomy of the ancient times You get lots of ideas about the concurrent society Or the contemporaneous activities of the country It also gives you will see later That many astronomical references Can give important clue for the chronological order That means at what time this happened It is not difficult to find out If you look into the astronomical descriptions Of that particular time I gave a lecture here Next room on archaeoastronomy And the astronomical dating of the Puranic texts Only from the description It is possible to date That is of course a separate topic So another important thing is that As an Indian I find that To know about the ancient activities Is very important Not just for knowledge But for bringing back your self pride And self respect So I think that these five lectures I have planned Many of you I hope that you will enjoy Otherwise why I will expect you to spend Five wonderful evenings Of course here evenings in the month of August Not or July not that pleasant But even then I think the semester has just begun There will be many new friends And so evenings are quite useful here But I hope these five evenings You will not repent after spending here So how we have planned There will be five lectures Each one I said one and half hour Because the subject is vast Hundreds of people have worked For 4000, 5000 years So therefore it is not so easy To encapsulate everything In only five lectures of one hour duration So I suggested that Let it be one and half hours So that I have not Pressed too hard for time And go too quickly over certain Very important issues Second thing I think the level I have kept it At the high school level frankly speaking You will not require any special knowledge Or any high level Spherical trigonometry etc We are not going to go into that direction Our objective is somewhat different Those who are interested in learning How to calculate t-thes, nakshatra The book is there But here it will be primarily The basic physical concept Behind the whole thing The primary source As I mentioned will be this book Which I am keeping the copy in the central library Whenever you want you can read Because the references you will find in this book Which are quite large And some of them are very old And the complete set of references And bibliography you will get in this book The lecture topics will be The first lecture What I want to do is the story How ancient Indian astronomy Was rediscovered It was rediscovered we all forgot But it was rediscovered by the Colonial rulers who came from Europe It is a very interesting story And then of course We have to talk little about The very fundamental rudimentary aspects Of positional astronomy Because many of the terms etc And moreover as a common man As you have to learn little bit of common history So which direction sun rises Why it changes Some very basic thing Will be desirable That I hope to finish today itself Second session will be on Pre-Siddhantic astronomy You will see that our whole ancient Indian astronomy can be Divided into two periods Primarily one will be Another is Siddhantic astronomy This is explanation you will come later Pre-Siddhantic astronomy The last book which we find Is Vedanga Jatish Which is dated as 1400 BC So before that That goes to Pre-Siddhantic And then the first or second century AD onwards what we get That is called Siddhantic astronomy And third lecture will be A discussion on Siddhantic astronomy And then after that We will discuss the medieval period When the West Asian astronomers came With the new rulers From West Asia Islamic rules came And with them Something came to India Which was actually reflected back And that also I will discuss I will also discuss What is Z-astronomy And we will discuss little bit about Swai joicing Which you are quite familiar And some very tragic things Swai Jansi joicing could not be The pioneer of modern astronomy in India And the final lecture Will be on introduction of Telescopic astronomy here Survey of India And interesting stories connected The very preliminary Motivations actually Like the transit of Venus Which really started the Era of telescopic astronomy in India And finally I will have Some discussion on the Debate over the originality And antiquity of Indian astronomy So I hope that this will end And I hope to cover All these things also in this time So as these points I have already discussed And I am not going to repeat it And This also I have Discussed The structure I have also Mentioned just now The first lecture Second lecture Third, fourth and fifth lecture That also I have mentioned So the story of the rediscovery of Ancient Indian astronomy What happened you know The first hint of Ancient astronomical Knowledge in India Came to India In a very interesting manner What happened that the Government sent a team to Thailand which was Called Sam in those days To the king But there was a coup in the Paris and all the French People had to leave in a hurry They brought the 12 Centimeter telescope which They went with that also They came brought back and then Pondicherry was a French Colony at that time So they came to Pondicherry In the year 1687 And with that Those things they also brought Some fragmented tables Some charts etc So they didn't know What are those things Then I think the astronomer Cassini he examined Those tables And charts they are in very Fragmented form and showed That it was required to See their calculations for Positions of the sun and the moon But you have to subtract 3 minutes From the sun's position And 40 minutes of earth From the moon's position And then he decided that it means That all the reference Merian for these tables Was 18 degrees west of Sam and That was found that it is It matches with the meridian Of Varanasi and so India of that ancient Tables was established And the Another person also Found some more such Tables in the Karnataka state of Karnataka and so on But nothing much Happened till When Lajen till returned From India in 1769 After observing a transit Of Venach at Pondicherry With amazing experience about the Stabilities of the Indian Pondich In astronomical calculations So experience of Lajen till Attracted the attention of Bailey, Laplace and Pleifere So you know what happened So The Lajen till One day Called one Pondich and Gave him some task that Can you find out these eclipse Time and position Pondich sat on the floor With some curries, curries means Some snails and Some tables in palm leaves Tables After 45 minutes He brought the whole result And Lajen till was amazed to see That they are very accurate Not only that the time Position everything is told Also the various phases Of the eclipse also that fellow Could tell Not a very educated person And he was completely Unaware of the principles On which these tables have been Made So therefore You know he was very amazed And realized that it must Be based on some ancient knowledge Which is now lost However I will not Spend too much time Then lot of researchers started Studying but there are two groups Among them one group was saying That yes there was Very extensive knowledge base In astronomy in India In the ancient times Another group was there They said that all nonsense They are all copied from Greek etc And so on The problem you see Like say Laplace originally Was very impressed But later being influenced By others you know they said They may not be very old Then A good analysis of Surya Siddhanto was In 1789 by Samuel Davis And All the calculations they found That the ancient astronomers They are excellent quality Excellent accuracy But then what happened That Surya Siddhanto Why they were having this kind of problem I am telling you That it is impossible to believe That these guys They used to call us niggers In those days they could do something Some science So many years back Which contains so much of truth It is impossible That was a perception you know But when they calculated the results Were very accurate So now see that such antagonistic Attitude I mentioned just now Towards anything Indian origin Western scholars Bentley thought That the Hindu astronomical literature Was nothing but a mass of forgeries Framed for the purpose of deceiving The world Respecting the antiquity of the Hindu people You know that was his contention That it is a complete forgery It is very recent but they have done it So that rest of the world think That yes in ancient times They were great people Similar attitude was also In the writings of Whitney He was an American astronomer When the Surya Siddhanto Was published by Burgess I believe In 1856 So he writes I have those books Actually from what we know In other respects of the character And tendencies of the Hindu mind We should not at all Look to find the Hindus In possession of an astronomical Science containing So much of truth They have been from the very beginning Distinguished by a remarkable Inactitude and discrimination To observe to collect Facts to record to make Inductive investigation So funny you see And I do not blame them because The society at that time In the 18th and 19th century You were so degenerated if you Read the history of our society At the contemporary society European scholars to fill This way In the 19th and 20th century Many western and Indian scholars Have worked on ancient but the problem Another problem was the knowledge on Sanskrit Which is the principal Source of all the knowledge on ancient Astronomy was not that good They had to depend Quite a lot on Pundits and others to translate Secondly A large amount of writing Were in allegorical form In that was a character of All our ancient texts They are in allegorical form And to extract the real meaning Requires a kind of knowledge Kind of mindset Which they did not possess That was also another difficulty they had So many others Like say in the 19th century Max Muller, Burgess Brennan, Weber, Thebaoud, Jacobi, Esbidik Along with the Indian The primary work which I have found One is Shankar Balakrishan Dixit Then Bal Gangadhar Tilak Kalinath Mukherjee And 20th century Shamsastri, P.C. Sengupta And J.R.K. That they are the 20th century people And rest are all 19th century These books are available But only thing that the best book I think is Shankar Balakrishan Dixit 1896 1930 And later in 1940 Meteorological department of India Government of India They published a translation After a lot of trouble I could trace a copy In the positional astronomy library in Calcutta And I got a copy But it is not available either in the internet Or in any library So it can be mentioned here That many studies were Facing serious difficulties to match the dates Another problem was that He hypothesized that 1500 B.C. All the Aryans came Through Khyber Pass And they started the Vedic civilization And he had an ad hoc assumption About the date of Rig Veda As 1200 B.C. Which was the first and ended at 200 B.C. So the dates were conflicting With this hypothesis and lot of scholars Who had lot of faith in this Theory so they were Finding very confused Once later and the verses of Vedanga Jyotish You will find Vedanga Jyotish when I come later To presiddhantic astronomy tomorrow It is like Rig Jyotish and Jyotish Jyotish There are in total 49 verses Very difficult But when it was Deciphered there are nothing but Algorithms for calculation And after all the things of Vedanga Jyotish is completely deciphered Now it is found that it was written Around 1400 B.C. That is accepted by all people We will come to this once later But once this work by S.B.Dixit Was over the Indian astronomy Ancient Indian astronomy Could be divided into two major parts Presiddhantic astronomy Starting with Rig Veda Ended with Jyotish Jyotish And Siddhantic astronomy started After a long dark period Also I will mention quickly later And risk maturity in the fourth And fifth century A.D. And the first great astronomer you have Heard about is R.A. Vata 1 The set of lecture is not meant As I mentioned for experts and Professionals I will not teach you The calculation procedures they are In the book but it is primarily The whole phenomena Or the physics behind the whole thing And some very basic idea About the positional astronomy Necessary even as a common man We should have these knowledges And I will take some time For that So basics of Positional astronomy What is positional astronomy you may ask It is the finding the positions Of the sun, moon and planets In the background of fixed stars For specified times Then celestial coordinate system How to use a coordinate system To identify its location Phases of the moon And predicting eclipses Identifying equinoctical And solstice These are what are the primarily Duties of positional astronomy And nowadays you know positional Astronomy is very much used Which of course far more sophisticated Software for Panchang creation By the government of India The positional astronomy centre Their main job is to create the Panchang The points to remember as I mentioned That the system is heliocentric We all know But the observations are from the earth That you have to keep in mind And study of the apparent motions Of the celestial bodies with reference To the frame that is fixed on earth Is the key issue that we have To always keep in mind To understand the matter better It is desirable to first study The real heliocentric system You see you all know these things You must have studied in That there is sun and round sun The earth is going in an elliptic path Of course the eccentricity is very small And it is also its axis is inclined To this plane of the orbit At 23 and half degrees It is spinning and at the same time It is revolving around the sun So here you will find that this plane In which earth goes round the sun Is called the plane of the ecliptic There is why it is called ecliptic That whenever moon is on this plane And it in conjunction or opposition There is an eclipse That is why this plane is called The plane of the ecliptic And then there are four important positions One position when the inclination Of the earth's axis Inclines towards the sun directly That is the summer solstice in north Northern hemisphere it is summer So this is the summer solstice When the axis is inclined towards the sun The day is the longest And opposite to that When it is tilting away from the sun That is the winter solstice Solstice word has come Sol means sun And solstice indicate it is stationary You know you will find that the sun Is going from north to south During this period now When it reaches the extreme end It appears to be stationary for few days And then it That is called the kshinayam or uttarayam And it starts going back Again it will come here and it will slowly stop And then again So therefore these are the positions When the sun's motion appears to be Stationary and so it is solstice One is summer, one is winter Two other important days are there When the inclination Sun is here and it is inclined in this way So both the hemisphere They get equal sunlight And they are called equinox Equinox word has come Equinox is Latin Nox means night When the night is equal to day That is why it is called equinox One is spring equinox And this is autumn equinox You can judge that Which direction earth is revolving And you can easily find out Can you tell me clockwise or anti-clockwise No Because you see that spring equinox And after that only summer solstice will come Then will be the autumn equinox We are approaching 22nd September Then will be the winter So it has to be like this Two other important positions are there One is called perihelion That means the position nearest to helios That is sun Another is apahelion Which is away from the sun So this is the real thing And this same thing What I have shown there Now here one thing You have to now discuss little bit Now what is our background Background is the fixed star Now you will say they are not fixed They are moving at tremendous speed Up to 100-400 km per second But their distance is so So large that even in the whole human civilization The movement is not perceptible The great bear, saptar simandal All the stars are moving With large tremendous speed just like the sun But for thousands of years it will look like the same Because the amount of distance you will see To move in few thousand years It is imperceptible So that is why apparently they are all fixed And it is called the background of the fixed star All the things and position movement You see of sun, moon and planets That backdrop is called the background of fixed star There so how do you locate Say for example you know we tell that There is a star here You find the full moon against this star So it means what that we are in this position Because full moon means moon must be opposite to sun And if full moon is against this star You know that this is the configuration So after 6 months what will happen After 6 months earth will go here And you know then that sun is against this star Though you cannot see that Because sun is so bright you cannot see that So this is the way astronomers tell Where is sun, where is moon Moon is very easy But in case of sun you have to consider What happens after 6 months So that way there are such markers in the sky To locate the position in the sky Which is other way absolutely vacant Nothing is there Now when viewed from the earth The sun along with the rest of the heaven Appears to rotate That means it was the reality The sun here and earth going like that But actually what we see That rather than sun and hour going It appears as if we are here and sun Dynamically it is equivalent you know So that is why it looks that sun is going down The whole universe is rotating And this is what is the apparent To the ancient astronomers This was the situation Earth is at the center Then moon Then Mercury Then Venus Then sun Then Mars Jupiter and Saturn These are the only planets Because sun and moon used to be As a planet So these seven planets You know they had Now you see as I mentioned That just now That now I will define few things This is the plane of the ecliptic Where earth goes But from earth it looks sun is going So it is the same thing Sun appears to go like this Around sun apparently Now and earth is at the center Spinning around its axis Which is tilted Now there will be two circles One circle Which is the equator of the earth This is this one Another one is the intersection Of the earth's surface Or earth's spherical surface With the plane of the ecliptic So this is called the ecliptic The yellow one Now so what happens You see it is interesting That sun will be always Appearing to be on the ecliptic Isn't it And so You see today you go and you find Because this is the horizon And the heaven is going like that The whole heaven is rotating Actually earth is rotating So say sun is here So sun will go like this All these stars go After a few days You will find sun will be here It will go up like this After another few days Sun will be here Again it will appear to be there So you will find If you trace the sun's location On the starry background of the sky It will draw a curve And it is nothing but the ecliptic This line is called the ecliptic Which is a very important thing Another line is very important That is if you take Consider the equator of the earth And imaginary expand it And take it to the celestial sphere So you will get another circular line That we call as the celestial equator It is nothing but the projection Of the terrestrial equator And it is also nothing but The intersection of earth's surface With the ecliptic plane That circle you have expanded that And this is nothing but the path Which is taken by the sun And since most of the planets Because of the origin of the solar system All the planets etc They are more or less located In one plane slightly this way that way So therefore all the planets Moon etc are never far away From this line which is ecliptic That is also another point to be noted So what happened that This is the earth rotating This is our horizontal plane This is the eastern direction Western direction Northern direction Southern direction And this is the zenith And so you can see That this is the ecliptic And another is the celestial equator And sun is on the ecliptic On different locations At different days of the earth And location is defined by The star against which sun is there Which you will be able to notice Or record after 6 months Locating the full moon's position Resulting observation will be With earth axis being tilted From the normal position Sun's path in the star background Is called the ecliptic Which is tilted from the celestial equator You have seen that The sun's position changes during a year And on the equinox days It is where It will be the intersection point of the ecliptic And the celestial equator There are two nodes And these are the two points Where sun is there on 21st March Nowadays and 22nd September So then what happens Sorry We find suppose if you are standing here At latitude phi You will find on the equinox days Sun comes here And goes like this Over our earth and sets On the summer solstice day You will find the sun to rise to the extreme left Or extreme north And this will be the line Which will be taken by the sun On the winter solstice day It will be rising at the extreme right Or extreme southern point And move like this So sun is always in this band Throughout the year If you are standing on the equator You will find on the equinoctical day The sun is going like this And on summer solstice It will go like this Winter solstice will go like this If you are in Australia somewhere It will appear to be something like this So you can see a photograph Taken from the same location On four days of a year On June 21st You will find That is the summer solstice day Sun you will find to rise here On the equinoctical days You will find sun to rise here And on December 21st Winter solstice you will find So you can see sun is rising here On the summer solstice And here on the winter solstice These are the photograph taken From the same location On these four days at the sunrise And so therefore now let us see This is the celestial dome Our sky This is the celestial equator It is nothing but the expanded Form of terrestrial equator And projected on the celestial dome This is the ecliptic Which is the intersection That circle of the earth Sphere with the ecliptic plane Expanded and projected on the celestial So therefore these are the Important things And these are the two equinoctical points These are the solstice points Now how do you record the position That I will discuss later in more details But you can see that you have to Locate the position of any planet or sun Or anything on the celestial dome Now say for example One way of observational astronomy Nomenclature is that How to locate the position So what you do You go along the celestial equator And then again you go along The longitude kind of thing And wherever you are it tells you So this tells you the declination Like our latitude And this one longitude is told By right ascension And since it comes back after 24 hours Right ascension is generally Given in terms of the time So many hours, minutes, seconds And declination is given in degrees Either south which is negative And north is positive Like say currently if you say serious This is the location of the serious How do you say Now this is the ecliptic And this is the celestial equator So along celestial equator you go How much 6 hours 45 minutes And then declination is Minus 16 degrees and 43 minutes So this is the way it is Now you are saying that It is going in this direction Why it is plus Can somebody tell me Actually it is You have to see any sky map You have to see this way Then only you will find It will not be confusing We will come to these things Little later again So the plane of the ecliptic I have already mentioned So you all know that And this is the celestial dome This is the celestial equator This is the ecliptic And these are the equinoctial points And these are the southeast points The south celestial pole North celestial pole Next it is important to discuss The background against which the movements Of the solar system bodies are observed So some idea about the system In which our solar system is embedded We should know that Solar system is located in a spiral galaxy Called Milky Way Galaxy As presented in the next slide So this is our Milky Way galaxy This is the galactic center And sun is somewhere here This is our solar system You know that diameter of our Milky Way galaxy Is about 100,000 light years And we are approximately at 30,000 light years away From the center This is the Milky Way you know I will not discuss You all know about Milky Way Now the Nakshatra system Or the lunar asterisms Which are very important You see You consider yourself 5000 years back Night sky you observe The moon everyday looks different So you observe that today it is Thin creation Or now it is somewhat bigger Half moon Then it is becoming thicker And ultimately a full moon So you notice it But how do you also look At the position of the moon You notice because Today the background stars are like this Tomorrow when I see I will find a different background star So what the ancient astronomers in India did What was the easiest and obvious way to do They took everyday And the moon takes 27 days To come back to the same group of stars In the background So they found 27 groups of stars Along which moon is going through the whole period They call this as Nakshatras Nakshatra is not one star A group of stars Or that is called lunar asterisms So these were the earliest markers in the sky Ancient Indian astronomers found And it is purely an Indian system So this 27 Nakshatra system Decide the whole astronomy as you will see Shown in the pre-Siddhantic period Siddhantic period we go to Science system or Rashi system That is a little thing So these groups of stars Which identify the positions of the moon Every night during a lunar month This is not a lunar month actually This is less than lunar month as we will see This is the position of the moon Takes 27 and few days And few hours to come back to the same position In the sky But the lunar month is called from One full moon to another full moon So that is little longer 29 and half days So we will see that later why it is so So therefore 27 Nakshatras Sometimes it was 28 but mostly it is 27 Nakshatra That is the defining coordinate system Or marker system in the old So you see now how do we do it Our galaxy if you see sideways It will look like this You are all modern students you all know that We are here So naked eye we cannot see beyond 500 light years Or 250 light years So obviously in those days Without telescope our universe is confined to Only this region which is 500 light years across If you expand it and you will find That the groups of stars in the galactic this region They gave names like Jestha, Mula, Purvashara You have heard all these names So these 27 groups of stars They identified as 27 Nakshatras And they were named like this So the zodiacal signs are the constellations Which span the positions of the sun During every solar month during a solar year So there will be 12 of them So we will discuss these things later So it looks like this That sun is here Earth is here And so for example Say July 21st Sun is against what? Sun is against cancer So that is the summer salt system It is very hot Then in winter say December 21st Sun is against what? Capricorn So in same days they were very surprised That why it is happening When sun is in Capricorn It is cold When it is cancer it is hot That is why astrology came into the picture As a subject But that is not our concern So the 12 zodiacal signs are these You have perhaps you are familiar With the 12 zodiacal signs And this is the relative location Of the zodiacal signs And also the nakshatra system in India So this is the R.E.S This is the Tauras and so on This is the Mesh Rashi like that Mesh, Brisha and so on There are 12 And these are the Ashini, Varani, Krittika These are the nakshatra They are relative position wise They are located in the sky like this Now observation of the periodic motions Or as you know Dural motion Heavens rotate about the celestial pole axis Day and night The basic unit of time Then slow creeping of the sun and moon Then they notice that the In the fixed background of the star Their position is shifting And they also notice some other star-like objects Or shifting or wandering That is why they are called planets In Greek language Planet means wanderer So these 5 planets Or 7 planets they ultimately Considered as the moving bodies in the sky And they are always very near the ecliptic Sun is on the ecliptic And the whole pattern repeats after and here Thus there is nothing which will Distinguish one ear to another Astronomically of course This year you are in first year Next year you will be in second year obviously And the moon phases also you know That this is the earth And sun is from this side So here it will be new moon Then as it goes This will be waxing crescent Then this is the first quarter The waxing gibbers Then this is the full moon Because sunlight will be falling completely And you can see the full circle And this is the waning gibbers Third quarter and waning crescent So these are the moon phases So coordinate systems for locating heavenly bodies There are 3 different systems which are used We will not go into details But it is better that you just follow it The systems are similar to that They are used in locating point of the earth surface Like latitude longitude kind of thing Because this is a spherical surface And celestial dome is also a spherical surface So as I showed that one is Called the equatorial system You go along the celestial equator This 1 hour, 2 hour, 3 hour That is called the right ascension Traditionally why they are doing it You can say easily they could say 1 degree is 1 degree up to 360 degrees Perfectly all right But that is the tradition in which they did And the latitude is something like that Declination that is minus and that is the class And where the origin that is very important Origin of the coordinate system Is always the vernal equinox Now you see here I will tell That in ancient Indian tradition You know the origin is a fixed place In the European or the Greek astronomy It is always the vernal equinoctial point But due to the precision of the equinox You know it is 26000 years as I will say later So the vernal equinoctial point also shifts So our system the origin is always fixed The first beginning of the rashi areas They call meshadi, adi point means beginning So this is a fixed that is why it is called nirayana system Indian system is very peculiar it is nirayana The coordinate is fixed In western system it is sayana system Where the starting point is the vernal equinoctial point Which shifts approximately 1 degree in a century kind of thing So that is different you know So these 2 terms you should be familiar with Sayana system and nirayana system In Indian astronomy we always adopt the nirayana system This is ecliptic system another system Where again you start from the vernal equinox And go along the ecliptic and that is in degrees And perpendicular direction you go Something like latitude So this is another system Another system which is very useful is That you are locating you have a vertically up East, west, north so that is another system Which is called horizontal system Where sorry you are standing here This is your zenith this is the northern direction north pole So to locate a position of a star What you do? You find out star point if you project here On your horizontal and this line you get Then this is called the azimuth And this angle which you get from horizontal to that position That is called altitude So azimuth and altitude system is very commonly Most of the telescopic things you do You can use this system it is convenient Now deviations from the periodic scheme Just now I mentioned One is precision of the equinox Due to which the equinoctial points shift In the fixed starry background Most advance of the perihelion That means again the perihelion point Aperion points also shift in the starry background And secular retardation of earth's rotation Earth is slowing down so obviously The time will gradually slow down This is another change And some other phenomena like 23 and half degrees Not constant it oscillates With a period of 44,000 years The eccentricity of our electricity Of the earth's orbit also changes Everything is actually periodic Except this secular retardation Which is not periodic So this is the axis of the earth Which is moving in a cone If it is spinning in this direction Like a top Then precision is in the opposite direction From east to west And our spinning motion Or daily rotation is from west to east So these videos were there But I think I will not waste time in this So what happened due to the precision of the equinox At this point if you draw an arrow Our rotational axis If you rotational vector So this point will trace a circle In the celestial dome And all since the whole thing is The ecliptic is there And therefore since this whole thing Is also changing like this This point, vernal equinoctial point Shifts to the west This is also that video I will not show here Now some effects of the precision of the earth's axis The intersection of the ecliptic And the celestial equator Slowly moves westward And the celestial pole Continuously rotate in a circle About 23 and half degrees Earth radius Is quite obvious So what happens Today The celestial pole is here About which our axis Is puncturing the celestial dome there And there is luckily a star here We call it what polar is But I think In zero eddy There was nothing You know there was no pole star Again when you go 3000 BC Then you get a star That is called Thuban Another pole star So 3000 Then if you find any record Of any pole star In the ancient text It has to be around that time Because after that There was a long time There was no pole star Again I think So therefore see that We are lucky to have a big pole star now But most of the time There is no pole star See the shifting of the Equinoctial point You can see it is here Today 1000 BC it was here Like that And today it is here 2000 eddy So therefore you can see The equinoctial point Is shifting So again this precision Gives a difference Because what happens Now If you look into the Eastern direction In the December Or end Beginning January When it is cold You will find A very important constellation Called Orion Is rising in the east Kalpurus we call India 13000 years Hence It will be just the opposite Peak summer You will find Kalpurus is rising in the East In a northern horizon It is summer So this is the Kind of change Which seasons The relative position Of the stars Constellations And the seasons They change Because seasons Depend on the Equinoctial point And solstice points And they change In the background Of the fixed stars Now Another thing is That moon and earth Is very important You know That moon is going Around the earth Like this And earth Is also moving Like this And moon's Orbital motion You will find This orbital plane Is about 5 degree Different You know It is not The same plane As the ecliptic Now you see Solar And sidereal Time It is another Thing Anything In this direction So sun will be Apparently again Some star here So after some time Sun will again Appear to be Again in this direction So it is this So when again This happens That is called A sidereal D Like say that It has rotated This point Has again Come And sun is Found to be again Again in the Same direction Here is better To use You will find You come back To another position Where Sun will again Appear to be Against the same Starry position Then it is called Sidereal Here They are slightly different And day is From one sunrise To another sunrise Why it becomes different Because If it is You are here When it is a sunrise It is rotating like this You are coming From the dark region Just sunrise Is here When You go to the Next sunrise Earth has moved here So you will find You will have to rotate A little bit longer Extra So day Will be slightly longer Than 360 degree rotation So that is called Mean solar day 24 hours Sunrise to sunrise Whereas sidereal day Will be slightly different 23 hours 56 minutes When Sun appears to Come back To the same Position in the sky That time is slightly different Slightly less Because of the Earth's Orbital motion Like this Say Moon Say for example Again the same thing Say here This is the moon This is Earth This is sun So it is a full moon day Now full moon is against This star So what happened The next full moon That means When it is again in opposition Whenever it is diametrically Opposite This is called opposition So Earth has moved here And moon has to go here To be in opposition So it rotates 360 degrees Plus this extra degrees So one full moon To another full moon Is somewhat a longer period Then when moon comes back To the same position On the sky To star again So therefore This is called A sidereal The Earth moon Full moon configuration It is the next Full moon configuration And that is why You can see One is called The period is called A synodic month When it goes from Here to here One full moon to Another full moon Synodic month Lunar month Another one is called Sidereal month That means When the moon comes back To the same position In the sky That means When it will be here But moon will be here So that you see It against this star Because this is Parallel of course So therefore Sun is here Earth is here And moon is here That means It has not rotated that much So it is little bit Ahead of the full moon position So that is called The sidereal month And full moon to full moon is Synodic month Again as I said That the orbital plane Of the moon Is slightly inclined 5.4 degrees With the Ecliptic plane And there are two points Where it intersects The plane of the ecliptic They are called Nodes So when it is going Like this It is called The descending node And when it is coming up Like this It is called The ascending node X and Y Now how can you Get an eclipse For eclipse Moon has to be Either in opposition Or in conjunction That means They must be in one line And moon has to be Also in the ecliptic plane Then only it will be Possible to have an eclipse So this X, Y Must be in the direction Of the earth Some direction So luckily That happened That this plane Is also rotating So this X, Y line Is also rotating And so when This is all eclipse You know So when the Ascending node Descending node And ascending node And they are in the same line Along the earth's sun Then this is the Right situation For having an eclipse Either Lunar or solar So and this period of This rotation is And it rotates at 19.4 degrees per year So this line is rotating So note that That every full moon will be An eclipse Or every new moon will be An eclipse So for example Say now This is an ecliptic situation That means this line Is that the Line of nodes Is towards the sun But it is rotating 19.4 degrees per year So when again This kind of situation will come When earth is going like this When it has come here By that time Line of nodes has rotated By 19.4 degrees And so you will find That this is The situation For having next time Then they will be Along the sun Earth Another So this particular period 346.6 days Is called an ecliptic Here kind of thing This is the Called the eclipse here So after that Again the eclipse Will start taking place So the advance of Perihelion position You know For the planets At rates are as much You know This is this So much per century For Mercury Which is quite noticeable For earth it is this And for Mars it is this So this phenomena Also you know So comets You know They are a small Clump of ice And dust They do not have Much importance Unless you are observing A periodic comets And this is very important That in ancient Indian astronomical text There are reference to comets Which are periodic And comets Periods are pretty large You know Like say Halley's comets Is 76 years or so So you can realize That the Observation of Europeans Scholars Not observant Is not correct And in those days If some says Or some astronomer Noticed a periodic comet It used to get the name After that Particular astronomer And this you know This the comets Follow large Elliptic path And how The tail comes You are all Students of science And you know that So these are Some of the The Halley's comets This is another comet So they are in different path Different Like there is another comet Which has a period Of 17,000 years Meteors They are Again You know that Has heat Earth They are called meteorite Meteoroid is a chunk Of rock or dust in space And a meteor Is the streak of light In sky Produced by burning Of a meteorite In Earth's atmosphere Asteroids You know they are the objects Revolving around the sun But too tiny To be called as Planets So these are the Meteor Meteor shower Now it should be noted That in positional astronomy Only the angle between The heavenly objects Can be seen Nothing else So this is Something very important To know That you can Only find out Angle Accuracy means that In naked eye astronomy Till the telescope It was naked eye Astronomy The highest possible accuracy Was achieved by Jaising It was One minute of Earth And currently Do you know Our present technology Can find out an angle Of nanowark second To that accuracy level So first session I will end here But not Finish I have something To discuss from here Because I kept some time For you to Ask and ask questions So few important things Which I will tell One is that The markers in the sky The nakshatras They are all named And their locations are there So therefore All the ancient Indian astronomy Which was based on Moon's position They are called Nakshatras Very interestingly You will find Something I will tell you now That when you go How they identify Suppose in the old days Calendar you have to produce How do you make a calendar Calendar means what? The particular day in a year So you have to tell the month The day And the hour At the time How do you identify a month Now the ancient Indian astronomers Has a very unique system That all those nakshatras You have seen Moon's Rigberig name Was Masha And whenever Moon becomes full Purna Masha Against a particular nakshatra That particular month Is to be given that name Like if Purna Masha Is in Visakha Nakshatra The name will be Vaisakha So they used to identify that That is how we got The name Vaisakha protest was against So on And what happened That Purna Masha Means full moon But ultimately We got that word Purna Masha Purna Masha From the same thing And then again What was the name Of the moon Masha It becomes The word for month We call Mass So ancient This situation Was that From one full moon To another full moon Was month But it was in the very ancient times Vedic period, later in Vedanga period or Puranic period it was changed from Purnimanta system to Amanta system. So from one new moon to next new moon was the month and the name of the month will be on which Nakshatra, the full moon takes place. Nowadays of course the system is not exactly this, but the names have continued from this philosophy. So you can identify the month, locating that which particular full moon is against that Nakshatra. So the month is identified. Then they divided the whole lunar month into 30 periods, 30 lunar days. Lunar days has a special name in India, do you know that is called tithi. Tithi is actually again another purely ancient Indian astronomical term. So this tithi is nothing but a lunar day when you divide a lunar month into 30 units we get tithis. So you tell the name of the month, you tell then there was a major division of paksha. So when the moon is becoming new moon to full moon it is called Sukhla paksha, another is from full moon to new moon that is called Krishna paksha. So you mention the month, you mention the paksha and mention the tithi so you identify the day. And then within a day other kinds of things that I will discuss, when I discuss your pre-siddhantic astronomy there. So that way they used to, now we say on such and such day 15th of January say 2 o'clock we will meet, you tell your friend. So he has to know when is that time. So same thing they did, they will tell you the month paksha, tithi and also tell the time. So this was the kind of basic structure which they are evolving which is very logical because observing sun is much more difficult and it was done much later. Another very interesting thing I will tell you here and you think about it, I found it in the literature and I do not know where is the connection. Because connection with the Hellenistic astronomy that is Greek astronomy was only when Alexander came that is how the people say that after Alexander came here and then there was some contract which was established with the Greek people and many things came. But another thing you will find in Rig Veda, what is the term used for Venus, it is Vena. Vena in Sanskrit Rig Vedic Sanskrit means daughter of sun and the name of Venus planet in Rig Veda is Vena. Now Vena and Venus, it cannot be a coincidence I personally think, again you will find in Rig Vedic time I will come to that in detail. The direction to exact south because South Pole was not visible from northern hemisphere, they used to connect two stars alpha canis minoris and alpha canis majoris and when you add these two stars it pointed exactly to the south in 4000 BC not now of course. Again in Hellenistic astronomy they are described in Rig Veda as dogs, red-eyed dogs and Greek astronomy again it is canis means dogs. So but how the Rig Vedic terms go into the Hellenistic astronomy is again a point I have not found any reference or any work on that, how that connection was there. So some of you can definitely really start thinking, finding literature and you can really bring out many new things which are still not known, when was the connection established, it is not just during the Greek maybe much before that. Some people have suspected that some European astronomers and they have mentioned that perhaps the connection with Indian astronomy to western astronomy is much earlier than the Greek period and many of them they feel that the flow was from east to west not the other way round. So that is one very important interesting thing you will see. Now few things I have not discussed here that is the details of the eclipse and your, the Bhaktragotty and so on, instruments also naked eye astronomy there are some very interesting things like say if you hold one adult your hand and a normal finger how much angle it will subtend to your eyes. So that they consider to be as I think one degree they consider, when it is like this they consider as 18 degrees if it is like this then it is 10 degrees in normal case and this so this is actually they said 4 degrees and this is also 4 degrees each power at arms length. So that is also very crude way of measuring angle of the angular distance between the planets you know how they did. Of course the very important other instruments they also used one was the Ganaman that is the Shanku which was used extensively and for time measurement eclipse etc. you know that there are three types of things water clock but the most commonly used was that pot kind of thing which a hole and when it gets completely filled up you know so and they designed that in such a way in a whole civil day they called Sabana day sunrise to sunrise it will I think the 60 times it will get filled up like that. Another very interesting thing I found that the division of degree into 60 is original ancient Indian astronomical thing 360 degree is very obvious can you find out the origin of 360 360 days in a year kind of thing so suns position they thought it is one 360 degree and they divided each degree into 60 minutes I will come to that later. So many of the thing what we do use but do not think that everything has come from the west many of the things which we use are actually of Indian origin. Next I think what I will start I little bit I will make use of that because here it was very simple descriptive when I start presenting Siddhantik and Siddhantik astronomy then I have to go slowly because they will be all new here I did not go slowly because most of the things are known to you you are all science students that our story will start in the prehistoric period and in India also we have found some Stonehenge kind of system in the ancient time you have seen Stonehenge and stone structures which were used in the primitive time for some very basic astronomical things like say on when you see the eastern direction what is the furthest point when the sun rises that is the summer solstice day. So the stone structures used to be made in such a way that that direction was told why they did it you can ask the reason was because the seasons were associated with the sun's position. So they needed to do that that when it is harvesting time when you have to start the showing all those things so they needed some basic clock, air clock on which you could say otherwise you do not know whether it is going to be right time for harvesting or right time for starting showing etc. So in India Hanam Sagar and I think now Telangana not Andhra Pradesh. So Hanam Sagar is the one such unit where they have stone structures and with which you can find out the direction of the sunrise at this summer solstice direction of the sunrise in winter solstice also the moons extreme northerly and southern reposition also that has been found. Then the next when you come to next prehistoric period that is your Harappa and Indus Valley civilization we call it has been now found out that the earliest settlement which has been found at Mehergarh which is dated 6500 BC that means 8500 years old and it is a full-fazetic city you know. So therefore from that people have tried to figure out whether they had astronomical observation which is quite obvious because you are so civilized society cannot do without astronomy because most of their major structures they are having very accurate north south direction just like the pyramids. And actually you know the pyramid dating has been done by considering the error they have made because in the ancient time a particular configuration of the northernly stars they used as pure because pole star was not there so you have to use other stars later it was found they use the same thing but it was wrong because things have shifted. So here also it has been found in Mahanjodara and Harappa the major structures are slightly the later Mahanjodara period they are slightly erroneous because in the very early days they used Thuban as the north star which was accurate but by it was I think 2700 I think 2700 550 where it was exact north by 2500 BC it was already 1 degree away from the north and now it is 7 and a half degrees away from the north. So therefore many of the structures in Indus valley cities they are found either exactly to the north which are the very ancient structures but slightly erroneous because they used the same Thuban star as the pole star which was not. So that is the time so the another thing they found they found some crescent side bone structures with 30 markings which meant it is a lunar month and they had to keep even now Andaman some of the aboriginals will find they maintain this kind of a calendar with 30 groups and the groups are also bigger groups smaller group which says the phase of the moon and that kind of stone not stone by bones they have been found even in and another thing which was found in Kashmir valley very interesting there is a stone structure piece with lot of markings and pictures. One picture shows that hunting deer etc with two suns it has been interpreted as one sun and one supernova and supernova must have taken place very near to the ecliptic plane because otherwise it cannot be very near sun and they have now you know now everything is possible with computer they have found out that that happened around 5000 BC there was a major supernova which took place near the ecliptic so it could be near the sun at some time and that is some of the very ancient astronomical observation thing and some Harappan seals they have shown 7 stages which majority of the archaeologists they interpret as 7 stars of the Saptar simandal but asfak thinks it is the 7 stars of Astrazim Krithika these are something so even in Harappan civilization there were evidence of astronomical observation and certain recordings are there though we have not been able to decipher the language satisfactorily but some of the records show clearly astronomical observation so these are the prehistoric period but actually we will then start discussing the basic period what astronomical difference we find that is the pre-Siddhantic astronomy which will start tomorrow so if you have any question I will just yes please Rahu and Kethu are the two nodes you know and in the ancient times many Indian astronomers considered these are also as two planets but later even Aryavatta one knew very well that the Rahu and Kethu are not planets and why eclipse takes place due to the moon that he mentioned it is yes please Prasabandha, Taikobai did 2 minutes of accuracy yeah actually you see Jai Singh I will discuss the Jai Singh wanted to improve the accuracy and he thought that you know if you make the things very big etc. using stone and machinery your accuracy will be better so he could achieve one minute of accuracy but unfortunately even three centuries before the Uluk Beg his system or his observatory produce more or less the same accuracy so Jai Singh could not achieve much even 300 years later he produced the same accuracy as Uluk Beg's observatory you know but his objective was primarily to improve accuracy just yeah please actually what we find in Siddhantic astronomy we find the 12 Rashi and Juryakal signs names are same as the Hellenistic astronomy that is why people think not only that the 7 day week in the Prisiddhantic astronomy in Vedas there are reference to Sardar that means 6 days but the 7 day week system and the same name that is actually from they say it is I will discuss it day after tomorrow that is when you discuss I will discuss in details you know how it came. Caldeans most probably they started first it went to Greece and then came to India but before there was a week but for 6 days Sardar not Saptah yes anything else I will tell you one thing here you know why astrology came as a subject as I mentioned the people thought that when sun is in cancer it is so hot here it is in Capricorn it is so cold in the moons phases and the tidal phenomena and you know the women they have their period which is also a lunar month so that way they found that when it is Purnima or Amavasya the pains joint pains increase they have all physical explanations but to believe that they also decide that when your daughter's marriage will be properly done or your husband's examination will be good this I think there is no scientific background. But the kings remember progress of astronomy was because of astrology even in Italy in Galileo's time Galileo used to earn extra money which he needed badly to pay for the dowry of his two sisters mathematics professor salary was not at all enough it was 120th of the salary of a medical doctor and law professor no so you know what he did he used to teach astrology to the medical student because it was a compulsory course doctors were required to cast a horoscope of a patient when he comes and see whether he has enough time to live and then do treatment properly otherwise do not spend too much time so he used to teach astronomy and astrology to medical students who used to pay quite a lot of private tuition fee to him so these are all old concepts because the kings were interested in whether the next war he will win and his quote astronomer he used to make predictions now to make predictions dependable and trustworthy he had to do astronomy and had to predict eclipses and other things that king on such and such day the sun will be eclipsed by and he says yes it is happening so if he says king on such and such time if you start the war with your neighbor you will win so you will do that but I personally to me astrology has no scientific basis yeah please you see Indian astronomy hints of heliocentricities they are in the late Siddhantic period and Kerala astronomy Kerala astronomy there was some hints it was something like tycho by his system but one thing remember the daily rotation of the earth was told very empathically by Arya Bhattawan he has mentioned in his book Arya Bhattiyam that the heavenly motion is due to earth's rotation sun never sets sun never rises is also told very clearly in the Vedic literature but the orbital motion of the earth it is not found anywhere yes yeah yeah yeah that started I think the ion challenge what is called the precision ion challenge start it is not found in pre Siddhantic astronomy only in Siddhantic astronomy is there ion challenge mentioned and they accurately found out the value which was much more accurate than the Greek value so that they did and they as you said that they had to have a zero precision here you know from which they will make their calculations when I bring the method of calculation so it will be seen how was their methodology where it was required to count the number of days organa so there they starting point the zero precision here quite a few different astronomers they use differently but it is yeah it is there is a difference yeah