1) Origin of Astronomy

Events that shaped human migrations • The last ice age began about 120,000 years ago. Origins of Astronomy • 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 Mayank Vahia – 9,000 - 8,000 BCE. 22 mm/year Tata Institute of Fundamental Research – 6,000 BCE. 2 mm/year – From 3000 BC, the rise is 7.5 mm/year. Mumbai 400 005 • Myths of great floods occur in many of the world's cultures. Origins of Astronomy 1 Origins of Astronomy 2 End of Ice Age and Human Migration • The last great Ice Age ended around 15,000 AVERAGE years ago and that must have facilitated human SNOW LINE migration. Origins of Astronomy 3 Origins of Astronomy 4 1 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. Origins of Astronomy 5 Origins of Astronomy 6 Origins of Astronomy 7 Origins of Astronomy 8 2 Migration and evolution Astronomy • Human race has gone through various stages of development. • By all indications, serious astronomy begins in – Palaeolithic – First appearance of humans to 10,000 BCE. Neanderthal Man & Homo Erectus existed until 30,000 B.C. Stone tools of increasing late Palaeolithic age itself. 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. • Well accepted astronomical markings have • Calolithic (Copper Stone) Age, 5500-3000 BCE. been dated to 15,000 BCE • Bronze Age 3000 -1200 BCE. • Iron Age 1200 BCE - • Silicon age 2000 AD - – Historic period . • We shall show later that stone carvings of much • THESE PERIODS VARY FROM REGION TO REGION earlier dates also exist. Origins of Astronomy 9 Origins of Astronomy 10 Pleiades Babylonian "map of the world" It Taurus is the earliest extant map. The clay tablet is 12.2 cms tall. The map was composed in Babylonia and is the only Orion 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. Origins of Astronomy prehistoric caves at 11 Origins of Astronomy 12 Lascaux in France. 3 SO WHAT IS THE ROLE OF ASTRONOMY? First steps • Astronomy is the first ‘science’. • Astronomy begins very early in Human life • Sky obviously gets noticed quickly. • The second thing we notice in the sky is • In a steady landscape, it is the fastest moving thing the Moon (apart from animals and insects!). • Sun rise and sunset are important for most life on Earth. Origins of Astronomy 13 Origins of Astronomy 14 Moon’s path • Moon moves only in a narrow region in the sky. Calculation of tithis • Moon visibly drifts in the night sky. • Tithis are the dates of Lunar Calendar. It is related to the phase of the moon. • It follows a specific path that is marked by a series of stars. Tithi = long. of Moon – Long. of Sun • 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. • Tithi remains the same until the Moon in increases its distance from the Sun by 12 degrees. The complete revolution of the • Full Moon occurs near of different stars each month. Moon (29.5 days) occupies 30 tithi s for 360 0. • Synodic (Full moon to full moon) and Sidereal (w.r.t. distant stars) periods are different. • Moon does not move at constant velocity so the length of tithis • Since the Sidereal period is 27 days, the sky can be divided into 27 varies. different parts where the Moon spends 1 day. This forms the basis of Nakshatras . • The waning phase (from Full Moon to New Moon) is called Krishna Paksha and the waxing phase (from New Moon to Full • Moon gives us the concept of month, fortnight and week. Moon) is called Shukla Paksha. Bhujle and Vahia, 2006 Origins of Astronomy 15 Origins of Astronomy 16 4 Names of tithis: (starting with Full Moon) Constellations Number Phase Tithi Number Phase Tithi 1 Krishna Pratipada 16 Shukla Pratipada 2 Krishna Dvitiya 17 Shukla Dvitiya • Sky is divided into patterns that we call 3 Krishna Tritiya 18 Shukla Tritiya constellations . 4 Krishna Chaturthi 19 Shukla Chaturthi 5 Krishna Panchami 20 Shukla Panchami 6 Krishna Shashthi 21 Shukla Shashthi • Star patterns on the path of the Moon are called 7 Krishna Saptami 22 Shukla Saptami Lunar Mansions (asterism) or Nakshatras . 8 Krishna Ashtami 23 Shukla Ashtami 9 Krishna Navami 24 Shukla Navami 10 Krishna Dasami 25 Shukla Dasami 11 Krishna Ekadasi 26 Shukla Ekadasi • Sun mostly follows this path. 12 Krishna Dwadasi 27 Shukla Dwadasi 13 Krishna Trayodasi 28 Shukla Trayodasi 14 Krishna Chaturdashi 29 Shukla Chaturdashi • The constellations on the path of the Sun are 15 Krishna Amavasya 30 Shukla Purnima called Rashis or Zodiacal Signs. Origins of Astronomy 17 Origins of Astronomy 18 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 Origins of Astronomy 19 Origins of Astronomy 20 5 Circumpolar constellations Path of the Sun • Sun mostly follows the path of the Moon. The difference is more • Not all constellations rise and set. 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. • Pole star never sets and constellations close to it also do not set. • 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 • This gives a fixed (north) direction and 12 revolutions. circumpolar constellations permit determination • 12 months therefore make one year (approximately) of exact (geographic) north . Origins of Astronomy 21 Origins of Astronomy 22 Origins of Astronomy 23 Origins of Astronomy 24 6 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. Origins of Astronomy 25 Origins of Astronomy 26 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 exactly overhead 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). Origins of Astronomy 27 Origins of Astronomy 28 7 Date and Time of Solstice and Equinox Equinox Solstice Equinox Solstice Sun and seasons year Mar June Sept Dec day time day time day time day time 2002 20 19:16 21 13:24 23 04:55 22 01:14 • Any observer will notice this drift of the Sunrise point 2003 21 01:00 21 19:10 23 10:47 22 07:04 (against the background geography) and its relation to 2004 20 06:49 21 00:57 22 16:30 21 12:42 2005 20 12:33 21 06:46 22 22:23 21 18:35 seasons. 2006 20 18:26 21 12:26 23 04:03 22 00:22 2007 21 00:07 21 18:06 23 09:51 22 06:08 2008 20 05:48 20 23:59 22 15:44 21 12:04 • If you reside in cold regions outside the tropics, Sun, 2009 20 11:44 21 05:45 22 21:18 21 17:47 and its location become more important than the 2010 20 17:32 21 11:28 23 03:09 21 23:38 Moon. 2011 20 23:21 21 17:16 23 09:04 22 05:30 2012 20 05:14 20 23:09 22 14:49 21 11:11 2013 20 11:02 21 05:04 22 20:44 21 17:11 • These cultures therefore become Sun worshipers. 2014 20 16:57 21 10:51 23 02:29 21 23:03 Origins of Astronomy 29 Origins of Astronomy 30 Winters and Summers Sun and Rashis • For Northern Hemisphere, winter is the time the • The constellations at Sunrise change with time. Sun spends south of equinox. • The constellations on the Sun’s path ( Rashis ) are so designed that in 1 lunar Synodic month (30 days) the Sun moves 1 Rashi .

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