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Nats 1745 History of Astronomy notes sept- dec.docx

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Department
Natural Science
Course
NATS 1745
Professor
Mary- Helen Armour
Semester
Fall

Description
Nats 1745 History of Astronomy Sept 11, 2013. What are we looking at in the sky? Motions in the sky- how these objects are moving? There wasn’t the same understanding that these were other worlds. Astronomy before the telescope was about what kind of motions there are in the sky. What are these motions in the sky? Telescope is a recent discovery; humans have watched the night sky thousands of years before. Prior to 1600 1700s astronomy was what are these motions? Everything moves, orbits amongst each other (moon, sun) it was hard to understand these motions when they (early astronomers) believed that the earth was standing still. Within the solar system up until Isaac Newton (late 1700’s) most of what were observing is the motions of the sky moons constellations etc. All of these individual motions added up cause what we see in the sky, not one single motion. The language pretends the sun is in motion, we still say the sun rises even though it’s the earth that is moving not the sun. Earth is always in motion, how is it moving? It spins on its axis (causes day, night) Orbits the sun (causes our year) Earth wobbles around subtly as it’s moving (thousands of years) in observation you can see the affects of this wobbling. If we look down from the north pole everything spins counter clockwise (causes everything to rise in the east and set in the west) Synodic vs. Syberial Earth takes 23 hours and 56 minutes to rotate on its axis (syberial day) (how long it takes an object to rotate on its axis) Earths synodic day is 24 hours (standing at noon the sun is directly south of me, 24 hours later the sun is directly south of me again but I’ve turned 361 degrees because earth is moving around the sun as I’m turning on my axis, the earth takes a little longer to come back) • The sidereal day is actually about 4 Minutes shorter than the synodic day. • We find this situation arises in many Instances. • Synodic periods are generally the more Easily observable Sidereal periods take more careful Observations again background stars • it is a mark of more sophisticated Observers to be able to differentiate Between the two. Orbit around the sun is also CCW. • These motions combined with the Earth’s axial tilt produces the characteristic patterns we see in the night sky. • Another motion of Earth is precession. This is a very slow wobble of the Earth’s axis. Over 26,000 years the direction which the poles point to change. • This means the current North star was not the north stars a few thousand years ago. Changing with time • This cycle is quite significant when studying the changes with time. • The position above the horizon of stars will change with time due to this cycle. • This means when studying ancient monuments we need to think about what the sky looked like THEN not now. There are many different ways to measure a year. Generally we use the vernal year 365.2424 days to measure a year. Precession is the last motion on earth… earth is tilted on its axis that is what creates the seasons, but this axis doesn’t stay pointed on the same axis… over the cycle of precession the earth wobbles through the sky. Right now the earths axis points to Polaris Motions -SUN Sometimes the earth is closer to the sun sometimes it is farther away The sun appears to move across the sky every day, rising in the east and setting in the west due to the rotation of Earth However this changes due to - time of year - where you are on Earth Since Earth’s rotation is actually tilted relative to the sun • Time of the year changes the angle of sunlight because the Earth is tilted, so as it goes around the sun, the angle of the sunlight changes. Monday, Sept 16 2013. Motions - MOON • most visible object in night sky • orbits once through zodiac in 27.3 days (sidereal period) (orbits earth and rotates on its axis in 27.3 days) • same face always points toward Earth • moves east to west through sky • goes through phases • from full moon to full moon 29.5days (synodic period) Motions – MOON Phases • moon is visible due to reflected sun light • as moon circles Earth, changes alignment with sun, so amount of moon visible changes, and where it appears in sky changes • new moon when moon between sun and Earth. • full moon when moon on opposite side of Earth from sun. • during ‘quarters’ half of moon is actually visible, it is either 1 or 3 quarters around full circle of orbit Tides: • When we look at the moon, the same side is always turned towards Earth. The moons rotation on its axis is the same as its orbit around Earth. (This is called a tidal lock and is a common situation between planets and their moons) • Tides are also caused by the moons gravity and the sun also exerts a force. The moon causes the Earth’s water to bulge in the direction of the moon. As Earth spins, the solid surfaces move through this bulge, giving us the rising and falling tides. The moon contributes 70% to the tides and the sun has 30% effect on the tides When the moon is full the tides get higher • During a new and a full moon, since the Earth – Sun – Moon are aligned the effect is at its maximum. • During the quarters, since Moon- Earth – Sun are at right angles, the moon and sun working against each other and it results in a far lesser effect. • Spring tides are when you have the greatest change in water height (new or full moon) • Neap tides are when you have the least change in water height (quarters). • To any civilization living where tides occur, this relation between the tides and the appearance of the moon is quickly obvious Motions –Eclipses • One of the more spectacular phenomenon we see in the sky in the eclipse of the moon or sun • The term ‘Eclipse’ generally refers to when two objects align in the sky so one blocks the other. • (i.e., the moon can also eclipse a planet, one star can eclipse another etc..) The path the moon take around the Earth occasionally crosses the ecliptic (path of Earth around the sun). When this happens either the sun is blocked by the moon (solar eclipse) or the moon is blocked by Earth (lunar eclipse) The moon, which is orbiting Earth at about a 5 degree tilt actually passes directly across the Earth – sun line at either a new moon or a full moon At a new moon, the moon can block the view of the sun either totally (total solar eclipse) or only a part of the sun (partial eclipse). These eclipses happen as the Earth passes through a shadow cast by the moon on the Earth. The shadow is only however at most a couple of hundred kilometers wide. This is the path of totality where we will see a total solar eclipse. Since the moon is smaller that Earth – this type of eclipse lasts at most a few minutes. One variation on this – the moon changes distance from Earth. If it is at one of its further parts of the its orbit during an eclipse it may not be big enough to totally cover the sun – annular eclipse. For a lunar eclipse the shadow is bigger so it lasts longer (hours) and tends to be more frequent! Why don’t eclipses happen every new and full moon? -This is because the moon’s orbit around Earth is tilted at about 5 degrees from the Earth’s orbit around the sun. Only when the moon cuts across the Earth – Sun line exactly at a new or full moon can an eclipse happen. Generally the time between possible eclipse alignments is every 5-6 months. A series of eclipses will occur, moving from one pole to another over the space of a few years, and then it will repeat over again. Saros Cycle • The path of the sun and moon and the pattern of eclipses as they move around actually produces a regular repeated pattern called the Saros cycle. • This is a cycle of just over 18 years. This is occurring as the different ways to measure the moons cycle over lap Synodic – new moon to new moon Anomalistic – perigee to perigee (closest approach to earth to closest approach to earth) Draconic - Node to node (the point where the moon passes the earths sun line to the point where the moon passes the earths sun line) Eclipses will occur at the same latitude, but not quite the same longitude, as the periods are fractions, so there is an extra 8 hours. Every 54 (and a bit) years, and eclipse should occur again in exactly the same location since it will have cycled through a full day – this is the triple Saros cycle. Because eclipses at any one location happen infrequently, these are one of the hardest of astronomical events to predict. It takes a high level of astronomical sophistication to get a handle on the cycles in which eclipses occur. Only two ancient civilizations seemed to have a grasp of this eclipse cycle – these were the Mayans and Babylonians (Chaldeans) These two groups were also the only two ancient civilizations to develop a place keeping number system… Monday, September 23, 2013. Planet, Stars and Other objects: Mercury, Venus, (Earth), Mars, Jupiter, Saturn. These 5 are visible with the naked eye and have been known for millennia. The outermost 2 are Uranus, and Neptune. (Pluto’s designation has recently changed) have only been discovered with the invention of the telescope. • To the ancients there were seven large bodies as the sun and moon were usually lumped into the same category with the 5 visible planets. Motions -PLANETS • Because these seven objects are all on the same plane in the solar system, they will seem to follow a similar path against the background of stars. We call this line the ecliptic. • All of the planets orbit around the sun in the same direction, so their motion in the sky will appear to travel in the same direction. Venus and Mercury have orbits that are nearer to the sun. Because of this, they are never seen very far from the sun – this means we see them only for at most a couple of hours before sunrise or after sunset. • Venus will never appear higher than about 46 degrees above horizon, while Mercury, which is even closer to the sun, appears at most 23 degrees above the horizon. Can only see planets that reflect sunlight. Venus is considered either morning or evening star whether it is visible in the morning or evening it is the brightest star Inner Planets: These planets also have a cycle of phases. Venus in particular is easy to observe with a telescope as they align from earth. Planet sun so that only a part of the sunlit face is visible. These phases however cannot be seen without a telescope. The total venus cycle lasts about 534 days. The outer planets follow a complete path through the night sky- they seem to rise in the east and set in the west. B/c they are further from the sun than earth, we will also catch up and pass them at regular intervals. As we pass the outer planets we see the optical illusion we call retrograde motion: In retrograde motion the planets will appear to slow down and reverse direction for a short period then turn around and resume their path in the sky. At the middle of the retrograde loop the planets will be at their closest approach to earth and will be brightest in the sky. Particular with mars which undergoes this loop about every 26 months, this brightening is very noticeable. We don’t see phases of mars because its outside of our orbit therefore we only see one sunlit face constantly. TERMS: Conjunction: occurs when the planets appear closest in the sky Opposition: occurs as objects appear at 180° in the sky from the sun, this means they will rise as the sun sets. When the planets outside of Earths orbit are in opposition they are in the middle of their retrograde loop. At the point of opposition, the planet will appear to be brightest as its at its closest approach to earth. For the planets inside earths orbit, they are never in opposition. They appear as either an evening star or a morning star. They reach a maximum elongation from the sun. As they switch from being an evening star to a morning star (moves from east to west of sun) they undergo their retrograde motion. Ancient Astronomy Key Points • How far back do we have records of astronomical observations? • What objects did different civilizations record? • How did ancient builders relate their buildings to the sky? • How did ancients use the knowledge they had of the sky? The earliest example of an astronomical record may be the Blanchard bone. This is a short piece of bone on which a carver may have recorded the phases of the moon. This record is something like 30,000 years old. The study of archeoastronomy is the study of the relation between the orientation of a building, tomb or monument and the alignments with objects in the sky. • Even today there are examples of the how more primitive cultures use the sky to help predict events like seasons and weather. The Nga tribe of Africa use the orientation of the moon to tell when the rainy season is. • Another example of astronomical knowledge are the solar alignments we see in many ancient monuments. One example is a tomb at Newgrange in Ireland • the sun shines through an opening in the top of tomb above the entrance at the midwinter solstice sunrise. Many ancient monuments show these alignments to sunrises, midday or sunset at either a solstice or an equinox. • Another example of astronomical knowledge are the solar alignments we see in many ancient monuments. One example is a tomb at Newgrange in Ireland • the sun shines through an opening in the top of tomb above the entrance at the midwinter solstice sunrise. Many ancient monuments show these alignments to sunrises, midday or sunset at either a solstice or an equinox. • Two major ancient monuments whose astronomical alignments are fairly well established are the pyramids in Egypt and Stonehenge. For the pyramids there are extensive written records surrounding this culture, even though not for the precise time of the pyramid building. • For Stonehenge the situation is far less clear, as there is no written record, and we are not even entirely sure as to who were the builders. Stonehenge was actually built in several stages, which complicates the interpretation. Stonehenge • In the 18th century William Stukeley first recognized that Stonehenge marks the summer solstice sunrise. He is the founder of the modern druids to mark this event each year at Stonehenge. • This monument however is much older than the druids. Construction started somewhere around 2700 B.C., which makes it even older than the pyramids. • The oldest part of Stonehenge is the outer bank and ditch which contain the Aubrey holes. These had some sort of ritualistic purpose, and there were 56 of them. Speculation suggests these holes could have been used as an eclipse predictor, but there is no evidence to support this view. • Later a ring of bluestones – brought from Wales was added in the interior. After a couple of centuries these were removed and replaced with the large upright trilithons and sarsen stone ring in the post and lintel construction. After the bluestones were brought back in again. • The station stones are four stones set along the outer bank and ditch. The Heel stone sits on the causeway and it is looking across this stone from the inner ring along which the solstice summer sunrise is seen. • Many other different possible alignments relating to the positions of moon and sun rises and sets have been postulated as being marked by the various stone in the circles. • The problem with ANY of these interpretations of Stonehenge, and many other ancient monuments is a lack of records. • We don’t KNOW what the ancients had in mind in building these type of monuments, all we can see is the LIKELY alignments built into them. October 2, 2013 Nabta Playa • One of the earliest know monuments even before pyramid building • Seems to have been a Neolithic civilization that built this ring. (circa 6000 B.C.) • Alignments seem to mark summer solstice as well as N-S and E-W alignment. • Additional alignments to bright stars like Sirius have been suggested, but only weak evidence for these. • The largest pyramid at giza is the great pyramid of Khufu (Cheops – the greek name). this was built in the fourth dynasty around 2600 B.C. This pyramid is unusual in a number of features. In most pyramids the burial chamber is still subterranean. In this pyramid however, it is up in the structure of the pyramid. • There are also four shafts coming out of the two chambers. Although other pyramids have been found to have these shafts, the ones in the great pyramid seem to have been much more precisely constructed • From the upper or kings chamber the southern shaft seems to point towards the bright stars in Prions belt. Orion is thought to be associated with the god Orious • The northern shaft from this chamber appears to point towards Thuban, which would have been the north star at the time of construction of these monuments. The northern circumpolar constellations where considered immortals by the Egyptians, and the north star is the center around which the heavens would appear to revolve. • From the lower or queens chamber there are also two shafts one points towards Sirius (south) the other towards the little dipper (North). Sirius was thought to be associated with Isis the wife of Osirus, and Sirius also at this time had its heliacal rising at the same time the river Nile would start to flood. One version of the Egyptian calendar is based on the rising of this star associated with the flood • When looking at the 3 pyramids on the plateau, it also appears as if they have been constructed to represent the image of the Orions belt. There are some inconsistencies in this theory. It may have been that the 3 andd smallest pyramid that was built later took advantage of the earlier alignment of the larger two • It has been suggested that in Khafre (son of Khufu) time, there was a cult of sun worshippers, and that his pyramid was built in relation to his father’s in order to frame the sunrise or sunset at a particular alignment • Another aspect of the great pyramid of Khufu, is that it is very accurately aligned on the compass directions. This could have been done using the stars. You would mark the rising and setting points of a number of stars. (the sun or moon could not have been used as they are too wide for this kind of accuracy). The half way point between rising and setting where the star is exactly at it’s highest point above the horizon would be exactly south. • The Egyptians also used the stars as timekeepers. They had a basically lunar calander of 12 months of 30 days, with five added extra god days to keep the year at the right length. These months were each divided into weeks of 10 days (decans). • The start of each week throughout the year was marked with the helical rising of one of the 36 decan constellations. Another religious calendar was also used that was basically lunar, but an extra month was added occasionally to keep the religious year in sync with the seasonal year, and it was the rising of the Sirius that was used to keep the year in sync with the seasons • On the image on the next slide we see a representation of the temple ceiling at dendera. The decans are numbered. The constellations of the zidiac are also present but this temple ceiling date from the time of the greek kings of Egypt and these are an incorporation of the Greek astrology into the Egyptian 4 • Americas • Anthony Aveni has written extensively about the Central and South American cultures. (see webpage for references) • Teotihuacan is a city of temples laid out in a very precise N-S, E-W alignment. This city dates to around the time of Christ. It seems that the astronomical alignments of this city were influential on later cultures. (such as the Maya and Aztec) • Around this city there are markers for sunrises and sunsets at particular times, as well as markers for the constellation of the Pleiades. The Pleiades seem to have been a significant constellation to this and later cultures since at the time this city was built, this group of stars had its heliacal rising, on the day the sun passed the zenith. The Pleiades also pass directly overhead at the location of this city. • Mayans • They were probably the most sophisticated astronomers and mathematicians of the region. • The mayans had a positional number system like our own, however they used a base 20 system rather than a base 10. • Our records of Mayan astronomy come from a few documents called Codices, and some surviving stellae. • The most important of these is the Dresden Codex. • The Dresden codex contains three main tables describing the cycles of the moon, Venus and Mars. • The Mayans seemed to have kept time with two separate calendars. One was a religious calendar of 260 days – called a tzolkin. This was based on a combination of the base 20 day names with a count of 13. This number matches to several natural cycles – including the growing season in this region of the world and the time Venus spends as either a morning or evening star. • The second calendar – called the Haab, was a 365 day calendar (bases on the solar year). It had 20 months of 18 days, will five extra or ‘empty’ days at the end. • For there to be an even number of tzolkin and years would take a count of 52 years. (sometimes referred to as a calendar round) • The lunar table in the Dresden Codex runs for 405 lunations (synodic periods), this was equivalent to 46 tzolkin. • In this lunar table the record of lunations is grouped into 6 (177 day) and 5 (148) lunations. Using this type of grouping it is possible to predict lunar eclipses. • The Mayans seemed to have been obsessed with the planet Venus that is the second table in the Codex. Venus represented the god of war to the Mayans, and conflicts were often only initiated if Venus was in the right place in the sky. • • Mayans also incorporated many astronomical alignments into their various architectures. In the city of Chichen Itza there are many examples of this. Caracol is a temple to venus with it’s major door and several windows aligned to catch certain risings and positions of Venus during the planets cycles. • The inca • The Inca did not have a language the way the Maya did, but they do seem to have had a certain level of astronomical knowledge. Many of their monuments were destroyed by the Spanish conquerors, but records of their buildings and cities do exist. • The Inca saw the world as an interwoven whole and did not separate astronomy from nature or religion. The Inca also saw things in patterns of 2. They were also a very strictly organized society. This appears in their architecture and interpretation of the world. • For the Inca, like other civilizations in this part of the world the Pleiades would have been an important constellation that marked the regular seasons of the year. • The capital city of the Inca was Cuzco - their name for the city was Tahunatinsuyu, this refers to the four quarter. The city sat at the joining of 2 rivers, and was divided into four quarters. Where these rivers joined was their main temple to the sun called Coricancha (Qoricancha) - the correct Inca relation was the Temple of the ancestors • There are two buildings one dedicated to the sun and one to the moon. The city plan would have radiated out from this central temple. Associated with the sun would have been Venus (Chasca) and associated with the moon would have the stars, particularly Pleiades. From Ancient Astronomer by Anthony Aveni • From this central temple the city is divided radially by lines. The main divisions cut the city in four parts (though not equal parts). In the upper or upstream part of the city we find the quarters called Chinchasuyu and Antisuyu, while in the lower or downstream part of the city, will be the Cuntisuyu and Collasuyu quarters. • The quarters were further subdivided by ceque lines. 3 of the quarters had 9 lines, while 1 had 14. this total of 41 lines may have been related to the lunar sidereal cycle. • These ceque lines were marked out with a markers called huacas. These could be some sort of geographical feature, or an astronomical alignment. In total there seem to have been 328 of these markers. This corresponds to the number of days the Pleiades were visible in the sky at this location. The Pleiades would have been significant since they first appear just before the summer solstice at the beginning of the planting season, and disappear around the time of the harvest for 37 days • From this central temple the city is divided radially by lines. The main divisions cut the city in four parts (not equal parts) In the upper part • The quarters were further subdivided by ceque lines. 3 of the quartres had 9 lines while 1 had 14. This total of 41 lines might have been related to the lunar syderial cycle India • The earliest refrences to indian astronomy date back to 2000bc and are foung in the Rig Veda. Vedic Aryans defined Sun Stars and Comets • In fact there are many quotes from various religious and astrological texts that seem to suggest that they thought that stars were also suns, or the sun was also a star • India also developed an interesting cosmology, their calanders and years of Brahma is the only one of the many time scales for the age in the universe that comes anywhere near the times cosmologist now suggest for the age of the universe A day and night of Brahma constitute approximately 4 millions years, and after a lifetime, the Brahma enters a sleep/death period, destroying the universe • When the god is reawakened the universe is reborn to begin another cycle this is similar to the current theory of the universe ‘big bang’ to ‘big crunch’ and is very different from the worlds view of most other cultures th th • In the late 5 and early 6 centuries one of the major figures in astronomy in india was aryabhatta his major work was the aryabhattiya. Translations of his text made it to renaissance Europe and would have been made the mathematical techniques available to the European mathematicians and astronomers. This book has heliocentric model of the universe (sun is at the center of the solar system) he also tries to explain a gravitational force that holds the bodie
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