Origins of Astronomy - Tata Institute of Fundamental Research

year2002200320042005200620072008200920102011201220132014Date and Time of Solstice and Equinoxday20212020202120202020202020EquinoxMartime19:1601:0006:4912:3318:2600:0705:4811:4417:3223:2105:1411:0216:57day21212121212120212121202121SolsticeJunetime13:2419:1000:5706:4612:2618:0623:5905:4511:2817:1623:0905:0410:51day23232222232322222323222223EquinoxSepttime04:5510:4716:3022:2304:0309:5115:4421:1803:0909:0414:4920:4402:29day22222121222221212122212121SolsticeDectime01:1407:0412:4218:3500:2206:0812:0417:4723:3805:3011:1117:1123:03Sun and seasons• Any observer will notice this drift of the Sunrise point(against the background geography) and its relation toseasons.• If you reside in cold regions outside the tropics, Sun,and its location become more important than theMoon.• These cultures therefore become Sun worshipers.Origins of Astronomy 29Origins of Astronomy 30Winters and Summers• For Northern Hemisphere, winter is the time theSun spends south of equinox.• By this count, there are 187 days for summerand 178.4 for winter. The winters are shorterand colder in the northern hemisphere.Sun and Rashis• The constellations at Sunrise change with time.• The constellations on the Sun’s path (Rashis) are sodesigned that in 1 lunar Synodic month (30 days) theSun moves 1 Rashi. There are 12 Rashi.• Since 360 < 365, seasons begin to drift 6 to 7days/year and in 5 years, addition of a month isrequired to synchronise the calendar with the seasons.• This is called the intercalary month.Origins of Astronomy 31Origins of Astronomy 328

Sun and Moon together• When the Moon returns to a Nakshatra it doesn’t have the same phase• Phase of the Moon is decided by its distance from the Sun• At each of Full Moon, the Moon is 2.25 Nakshatras away from the previousFull Moon, and the Sun is 1 Rashi ahead (Rashis are defined that way)• Sun and Moon move in the same direction suggests that the Earth isspinning in the same direction as it is rotating.• The Sun’s plane (Orbital plane of the Earth around the Sun or the Ecliptic) isinclined to the Moon’s path by 5 o.• Point of intersection of the two planes are called the nodes. These nodes arecalled Rahu and Ketu. These nodes rotate with a period of 18.6 years.Origins of Astronomy 33 Origins of Astronomy 34Celestial Equator and EclipticEcliptic and Orbit of MoonNCPEclipticKetu (Descending Node) at VENCPLunar OrbitEclipticSSAECelestial EquatorCelestial EquatorWSVEAnglebetween thetwo is 23.5 oMotion of Sunand MoonVE = Vernal EquinoxSS = Summer SolsticeAE = Autumnal EquinoxWS = Winter SolsticeOrigins of Astronomy 35Rahu (Ascending Node) at VEHrishikesh Joglekar Origins of Astronomy 369

Ecliptic and Orbit of MoonEcliptic and Orbit of MoonNCPNCPOrigins of Astronomy 37Origins of Astronomy 38Ecliptic and Orbit of MoonEcliptic and Orbit of MoonNCPNCPRahu (Ascending Node) at WSOrigins of Astronomy 39Origins of Astronomy 4010

Planets• Of the ~ 6,000 stars visible at night (from ~ 10 22 stars),there are 5 objects apart from Sun and Moon which are notstationary. They are called Planets.• These are Mercury, Venus, Mars, Jupiter and Saturn.• Their path is not random. They move more or less onthe same path as the Sun and the Moon.• Mercury moves the fastest and Saturn the slowest.Planet periods• Mercury goes around the Sun 88 (earth) in days.• Venus takes 0.61 (earth) years• Mars takes 1.88 (earth) years• Jupiter takes 11.9 (earth) years• Saturn takes 29.4 (earth) years• Mercury goes 30 o from the Sun• Venus goes 60 o from the SunOrigins of Astronomy 49Origins of Astronomy 50Making calendars• In order to keep track of time over long periodsof years, a method of counting has to bedevised. This is called a calendar.• Apart from counting, special markers areintroduced to ensure that the counting iscorrect.• It also encourages study of rare events bypointing out their rarity.Origins of Astronomy 51Ancient Calendars• Vedanga Jyotish (1200 BC) This is the oldest Lunar calendar. Itcontains a 5-year Yuga of 62 synodic lunar months.• Brihaspati samvatsar (year) chakra: 60 year cycle of Jupiter. The yearshave names like ‘Prabhav’, ‘Vibhav’ etc.• The Griha-parivritti cycle: It consist of 90 solar years. The length of 1year being 365.2586 days. The year commences with sun enteringMesha (Aries sign). This type of calendar is used in southern peninsulaof India especially in Tamilnadu.• Saptarshi era: consists of cycles of 2700 years. It originated with thesupposition that seven Rishis stay in each Nakshatra for 100 years.This era was in use in Kashmir.• The currently used calendar is Luni-solar calendar in which eachmonth is synodic lunar month of 29.5 days. One year consists of 12such months = 254 days. The remaining 11 days of the year areadjusted in Adhik maas (intercalation month) that occur generally inOrigins of Astronomy 52the 3rd, 5th, 8th,11th,14th,16th and 19 year cycle of years.13

The Saptarshi EraSaptarshi Era• An interesting time line in the Vedic literature isthe Saptarshi Era.• It states that the Saptarshi constellation movesinto different Nakshatras giving different eras. Itis generally assumed to be wrong.• However, the exact manner of the definitionclearly shows that the starting date of the Era is2300 BC and originates in southern Gujarat.(Sule, Vahia, Bhujle, 2005)2100 BC 2000 ADOrigins of Astronomy 53Origins of Astronomy 54Yuga in Vedic Literature• Yuga concept is introduced in Vedic astronomyto synchronise solar and lunar calendars.• The yuga period of five years, whoseconstituent years are called samvatsara,parivatsara, idavatsara, anuvatsara, andidvatsara, has been in use since Vedic times.• However, there are actually 1826.2819 days ina yuga of five solar (sidereal) years.Furthermore, there are 1830.8961 days in aperiod of 62 lunar months. It is suggested that~4.5 days were dropped as ‘reset error’.Origins of Astronomy 55Yuga: Recent interpretation• There are 4 Yugas the duration scale of 4:3:2:1• Satya Yuga or Krita Yuga (1,728,000 years),• Treta Yuga (1,296,000 years) ,• Dvapara Yuga (864,000 years)• Kali Yuga (432,000 years)• Satya Yuga or Krita Yuga - dhyana (meditation)• Treta Yuga - yajna (sacrifice)• Dvapara Yuga - archana (worship)• Kali Yuga - daana (alms)• More acceptable interpretation is that they are Daivik years or days. Thisgives Yugas to be 1200: 2400: 3600: 4800 years (total 12,000 years).• It is believed to have begun with the death of Krishna in 3102 BC?????.• This reference of time is still used in religion and literature.Origins of Astronomy 5614

Calendars in use• The Vikram era:– Begins with the coronation of King Vikramaditya.– The year 1900 AD corresponds to 1958 of the Vikram era,– It is popular in northern India and Gujarat.• The Saka era:– Begins with King Salivahana's accession to the throne.– The year 1900 AD would be 1823.– Popular in southern India, this reference in almost allastronomicalworks in Sanskrit written after 500 AD.– The Government calendar also follows the Saka era.Origins of Astronomy 57Origins of Astronomy 58NORTHSouthOrigins of Astronomy 59Origins of Astronomy 6015

Rohini Shakat Bhed• Rohini Shakat Bhed isdefined as an event whereSaturn or Mars came insidethe triangle of Rohini.• Calculations with modernephemeris, its occurrencecan be dated.• The event last occurred in5284BC and then 9339 BEprior to that.Origins of Astronomy 61 (Mahajani, Vahia, Apte and Jamkhedkar, Origins of Astronomy 622005)Nakshtras• Nakshatras are the path of Moon in the night sky. Zodiacs are the path ofthe Sun in the night sky.• Zodiacs were designed in Babylonia before 3000 BC.• Nakshatras appeared fully defined in Babylonia after 1000 BC.• Zodiacs are needed for people preoccupied with Seasons whileNakshatras are needed for people interested in calendar and time keeping.• Nakshatras therefore seem to be Harappan in origin who were seafearers.Vernal EquinoxSummer solsticeAvg Value VS Year from 3500 BC-2000 ADTHERE IS CLEAR EVIDENCETHAT NAKSHATRAS WEREDESIGNED AROUND 3000BC.Moon's Avg Value of Dec atpeak`5.004.504.003.503.002.502.001.501.000.500.00-4000 -3500 -3000 -2500 -2000 -1500 -1000 -500 0 500 1000 1500 2000 2500YearBhujale and Vahia, 2006Origins of Astronomy 63Origins of Astronomy 6416

Outstanding issues• Impact of astronomy on residential and burialsites• Origins of astrology• Affects of precession on the seasons• Mythologies, symbolisms and formalisation ofastronomy• Records of comets and supernovaeIsn’t this more than enough for 1lecture?Origins of Astronomy 65Origins of Astronomy 66Acknowledgements• I want to acknowledge all the known and unknown Websources that I have used in the lecture.• My special thanks to WIKIPEDIA which provided some valuableinformation.• I want to thank my friends Sudha Bhujle, Kavita Gangal,Hrishikesh Joglekar, Parag Mahajani, Aniket Sule. I have stolenideas and images from all of them!• I want to particularly thank Dr. Jamkhedkar who has been myconstant source of inspiration on this subjects.• I want to express my apology to all those whom I may haveforgotten to thank.Origins of Astronomy 6717