origins of astronomy

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Origins of Astronomy 1

Origins of Astronomy

Mayank Vahia

Tata Institute of Fundamental Research

Mumbai 400 005


Events that shaped human

migrations• The last ice age began about 120,000 years ago.

• The Last Glacial Maximum, occurred about 18,000 BCE.

• Between 15,000 BCE and 5,000 BCE, most of the world's glaciers melted the sea reclaimed former beaches and even valleys.

• This movement of the sea inland occurred in several steps. – 13,000 BC

– 9,000 - 8,000 BCE. 22 mm/year

– 6,000 BCE. 2 mm/year

– From 3000 BC, the rise is 7.5 mm/year.

• Myths of great floods occur in many of the world's cultures.


End of Ice Age and Human

Migration

• The last great Ice Age ended around 15,000

years ago and that must have facilitated human

migration.


AVERAGE

SNOW LINE

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Origins of Astronomy 5 Origins of Astronomy 6

1,000,000 years in a nutshell!

• Human race (Homo sapiens) first originate in Africa about million years ago.

• They remain confined to central and northern Africa for almost 900,000 years!

• Due to a mixture of reasons such as:– Sheer tireless desire to explore.

– An overflow from population growth.

– Inability of the local food sources to support a large human population.

– Internal conflicts of personality within the population.

– Differences in taste and preferred environment for settlement.

They migrate out of Africa about 100,000 years ago.


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Migration and evolution• Human race has gone through various stages of development.

– Palaeolithic – First appearance of humans to 10,000 BCE. Neanderthal Man & Homo Erectus existed until 30,000 B.C. Stone tools of increasing complexity mark this period.

– Mesolithic – 11,000 to 9,000 BCE. Metals are used in this period.

– Neolithic – pre-historic period 9,000 – 1,000 BCE. Sophisticated cultures and organised existence mark this age.

• Calolithic (Copper Stone) Age, 5500-3000 BCE.

• Bronze Age 3000 -1200 BCE.

• Iron Age 1200 BCE -

• Silicon age 2000 AD -

– Historic period.

• THESE PERIODS VARY FROM REGION TO REGION


Astronomy

• By all indications, serious astronomy begins in

late Palaeolithic age itself.

• Well accepted astronomical markings have

been dated to 15,000 BCE

• We shall show later that stone carvings of much

earlier dates also exist.

Origins of Astronomy 11prehistoric caves at

Lascaux in France.

Pleiades

Taurus

Orion


Babylonian "map of the world" It

is the earliest extant map. The

clay tablet is 12.2 cms tall. The

map was composed in

Babylonia and is the only

Babylonian map drawn on an

international scale. It is a

Persian Period, (500 BCE) copy

of an original dating to late

eighth or seventh century BCE.

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SO WHAT IS THE ROLE OF ASTRONOMY?

• Astronomy is the first ‘science’.

• Sky obviously gets noticed quickly.

• In a steady landscape, it is the fastest moving thing

(apart from animals and insects!).

• Sun rise and sunset are important for most life on

Earth.


First steps

• Astronomy begins very early in Human life

• The second thing we notice in the sky is

the Moon


Moon’s path• Moon moves only in a narrow region in the sky.

• Moon visibly drifts in the night sky.

• It follows a specific path that is marked by a series of stars.

• Moon waxes and wanes with a time period of 29/30 days.

• At Full Moon the Moon rises at Sunset and then drifts towards the Sun and after New moon it rises later and later till it rises at Sunset again.

• Full Moon occurs near of different stars each month.

• Synodic (Full moon to full moon) and Sidereal (w.r.t. distant stars) periods are different.

• Since the Sidereal period is 27 days, the sky can be divided into 27 different parts where the Moon spends 1 day. This forms the basis of Nakshatras.

• Moon gives us the concept of month, fortnight and week.


Calculation of tithis• Tithis are the dates of Lunar Calendar. It is related to the phase

of the moon.

Tithi = long. of Moon – Long. of Sun

• Tithi remains the same until the Moon in increases its distance from the Sun by 12 degrees. The complete revolution of the Moon (29.5 days) occupies 30 tithis for 3600.

• Moon does not move at constant velocity so the length of tithisvaries.

• The waning phase (from Full Moon to New Moon) is calledKrishna Paksha and the waxing phase (from New Moon to Full Moon) is called Shukla Paksha. Bhujle and Vahia, 2006

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Names of tithis: (starting with Full Moon)

PurnimaShukla30AmavasyaKrishna15

ChaturdashiShukla29ChaturdashiKrishna14

TrayodasiShukla28TrayodasiKrishna13

DwadasiShukla27DwadasiKrishna12

EkadasiShukla26EkadasiKrishna11

DasamiShukla25DasamiKrishna10

NavamiShukla24NavamiKrishna9

AshtamiShukla23AshtamiKrishna8

SaptamiShukla22SaptamiKrishna7

ShashthiShukla21ShashthiKrishna6

PanchamiShukla20PanchamiKrishna5

ChaturthiShukla19ChaturthiKrishna4

TritiyaShukla18TritiyaKrishna3

DvitiyaShukla17DvitiyaKrishna2

PratipadaShukla16PratipadaKrishna1

TithiPhaseNumberTithiPhaseNumber


Constellations

• Sky is divided into patterns that we call constellations.

• Star patterns on the path of the Moon are called Lunar Mansions (asterism) or Nakshatras.

• Sun mostly follows this path.

• The constellations on the path of the Sun are called Rashis or Zodiacal Signs.


Importance of Constellations

• Constellations help remember the sky

• They are small and easily recognisable.

• That they permit a universal definition of

directions independent of geography


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Circumpolar constellations

• Not all constellations rise and set.

• Pole star never sets and constellations close to

it also do not set.

• This gives a fixed (north) direction and

circumpolar constellations permit determination

of exact (geographic) north.


Path of the Sun• Sun mostly follows the path of the Moon. The difference is more

important than the similarity.

• Since the Sun is very bright, Sun’s path is inferred by looking at the constellations just before Sunrise or just after Sunset.

• The path of the Sun is divided into 12 Rashis or Zodiacal signs. Roughly 2.25 Nakshatras fit into a rashi.

• The Sun returns to the same Rashi when the Moon completes 12 revolutions.

• 12 months therefore make one year (approximately)


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The East

• The Sun does not rise in the exact (global) east, i.e. it does not rise exactly at the point between north and south.

• It rises in the eastern direction and sets in the western direction

• But within that, the sun rises exactly in the (local) east i.e. the line joining sunrise point and sunset point is perpendicular to the line joining the observer to the north.



Sunrise and Sunset

• The Sun rise point drifts North of East to South of East

• On Equinox (Spring or Autumn), the Sun rises exactly in the (global) East all over the world and the day and night are of equal length.

• How high the Sun rises depends on latitude.

• For regions within the Tropics, the day on which the Sun comes exactlyoverhead depends on the exact locations and 2 such days occur in a year.

• For regions in the North, Summer Solstice is the day of highest sunrise and for the South it is the Winter solstice (as experienced in the North).


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Date and Time of Solstice and Equinox

23:032102:292310:512116:57202014

17:112120:442205:042111:02202013

11:112114:492223:092005:14202012

05:302209:042317:162123:21202011

23:382103:092311:282117:32202010

17:472121:182205:452111:44202009

12:042115:442223:592005:48202008

06:082209:512318:062100:07212007

00:222204:032312:262118:26202006

18:352122:232206:462112:33202005

12:422116:302200:572106:49202004

07:042210:472319:102101:00212003

01:142204:552313:242119:16202002

timedaytimedaytimedaytimeday

Solstice

Dec

Equinox

Sept

Solstice

June

Equinox

Maryear


Sun and seasons

• Any observer will notice this drift of the Sunrise point

(against the background geography) and its relation to

seasons.

• If you reside in cold regions outside the tropics, Sun,

and its location become more important than the

Moon.

• These cultures therefore become Sun worshipers.


Winters and Summers

• For Northern Hemisphere, winter is the time the

Sun spends south of equinox.

• By this count, there are 187 days for summer

and 178.4 for winter. The winters are shorter

and colder in the northern hemisphere.


Sun and Rashis

• The constellations at Sunrise change with time.

• The constellations on the Sun’s path (Rashis) are so designed that in 1 lunar Synodic month (30 days) the Sun moves 1 Rashi. There are 12 Rashi.

• Since 360 < 365, seasons begin to drift 6 to 7 days/year and in 5 years, addition of a month is required to synchronise the calendar with the seasons.

• This is called the intercalary month.

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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 previous Full 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 is spinning in the same direction as it is rotating.

• The Sun’s plane (Orbital plane of the Earth around the Sun or the Ecliptic) is inclined to the Moon’s path by 5o.

• Point of intersection of the two planes are called the nodes. These nodes are called Rahu and Ketu. These nodes rotate with a period of 18.6 years.


Celestial Equator and Ecliptic

NCP

Ecliptic

Celestial EquatorAE

WS

SS

VE

VE = Vernal Equinox

SS = Summer Solstice

AE = Autumnal Equinox

WS = Winter Solstice

Motion of Sun

and Moon

Angle between the two is 23.5o

Hrishikesh Joglekar Origins of Astronomy 36

Ecliptic and Orbit of Moon

NCP

Lunar Orbit

Ecliptic

Celestial Equator

Rahu (Ascending Node) at VE

Ketu (Descending Node) at VE

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NCP



NCP



NCP

Rahu (Ascending Node) at WSOrigins of Astronomy 40


NCP

11



NCP



NCP

Rahu (Ascending Node) at AE



NCP



NCP

12



NCP

Rahu (Ascending Node) at SSOrigins of Astronomy 46


NCP



NCP



NCP

Rahu (Ascending Node) at VE

This complete cycle

takes 18.6 years

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Planets

• Of the ~ 6,000 stars visible at night (from ~ 1022 stars),

there are 5 objects apart from Sun and Moon which are not

stationary. They are called Planets.

• These are Mercury, Venus, Mars, Jupiter and Saturn.

• Their path is not random. They move more or less on

the 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 30o from the Sun

• Venus goes 60o from the Sun


Making calendars

• In order to keep track of time over long periods of years, a method of counting has to be devised. This is called a calendar.

• Apart from counting, special markers are introduced to ensure that the counting is correct.

• It also encourages study of rare events by pointing out their rarity.


Ancient Calendars

• Vedanga Jyotish (1200 BC) This is the oldest Lunar calendar. It contains a 5-year Yuga of 62 synodic lunar months.

• Brihaspati samvatsar (year) chakra: 60 year cycle of Jupiter. The years have names like ‘Prabhav’, ‘Vibhav’ etc.

• The Griha-parivritti cycle: It consist of 90 solar years. The length of 1 year being 365.2586 days. The year commences with sun entering Mesha (Aries sign). This type of calendar is used in southern peninsula of India especially in Tamilnadu.

• Saptarshi era: consists of cycles of 2700 years. It originated with the supposition 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 each month is synodic lunar month of 29.5 days. One year consists of 12 such months = 254 days. The remaining 11 days of the year are adjusted in Adhik maas (intercalation month) that occur generally in the 3rd, 5th, 8th,11th,14th,16th and 19 year cycle of years.

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The Saptarshi Era

• An interesting time line in the Vedic literature is the Saptarshi Era.

• It states that the Saptarshi constellation moves into different Nakshatras giving different eras. It is generally assumed to be wrong.

• However, the exact manner of the definition clearly shows that the starting date of the Era is 2300 BC and originates in southern Gujarat.

(Sule, Vahia, Bhujle, 2005)


Saptarshi Era

2100 BC 2000 AD


Yuga in Vedic Literature

• Yuga concept is introduced in Vedic astronomy to synchronise solar and lunar calendars.

• The yuga period of five years, whose constituent years are called samvatsara, parivatsara, idavatsara, anuvatsara, and idvatsara, has been in use since Vedic times.

• However, there are actually 1826.2819 days in a yuga of five solar (sidereal) years. Furthermore, there are 1830.8961 days in a period of 62 lunar months. It is suggested that ~4.5 days were dropped as ‘reset error’.


Yuga: 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. This gives 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.

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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 all-astronomical works in Sanskrit written after 500 AD.

– The Government calendar also follows the Saka era.



NORTH

South


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Rohini Shakat Bhed

• Rohini Shakat Bhed is

defined as an event where

Saturn or Mars came inside

the triangle of Rohini.

• Calculations with modern

ephemeris, its occurrence

can be dated.

• The event last occurred in

5284BC and then 9339 BE

prior to that.

(Mahajani, Vahia, Apte and Jamkhedkar,

2005)


Nakshtras• Nakshatras are the path of Moon in the night sky. Zodiacs are the path of

the 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 while Nakshatras are needed for people interested in calendar and time keeping.

• Nakshatras therefore seem to be Harappan in origin who were sea fearers.

Avg Value VS Year from 3500 BC-2000 AD

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

-4000 -3500 -3000 -2500 -2000 -1500 -1000 -500 0 500 1000 1500 2000 2500

Year

Moon's Avg Value of Dec at

peak`

THERE IS CLEAR EVIDENCE

THAT NAKSHATRAS WERE

DESIGNED AROUND 3000

BC.

Bhujale and Vahia, 2006Origins of Astronomy 64

Vernal Equinox

Summer solstice

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Outstanding issues

• Impact of astronomy on residential and burial

sites

• Origins of astrology

• Affects of precession on the seasons

• Mythologies, symbolisms and formalisation of

astronomy

• Records of comets and supernovae


Isn’t this more than enough for 1 lecture?


Acknowledgements

• I want to acknowledge all the known and unknown Web sources that I have used in the lecture.

• My special thanks to WIKIPEDIA which provided some valuable information.

• I want to thank my friends Sudha Bhujle, Kavita Gangal, Hrishikesh Joglekar, Parag Mahajani, Aniket Sule. I have stolen ideas and images from all of them!

• I want to particularly thank Dr. Jamkhedkar who has been my constant source of inspiration on this subjects.

• I want to express my apology to all those whom I may have forgotten to thank.

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