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Chapter 1

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Department
Natural Science
Course
NATS 1745
Professor
Robin Metcalfe
Semester
Fall

Description
NATS1745- History of Astronomy September 2013 Chapter 1- Living With The Sky Lesson Video: Part 1 “Archaeoastronomy” o Throughout the world, we find evidence that prehistoric mankind developed the ability to predict the cycles of the sky. o Pre historic time; time before recorded history o Put ourselves in pre historic mode; forget what you know today about space, beyond what we see. o To us, earth appears flat and motionless; one of a system of other worlds, all in orbit of the sun, (30km/second around the sun) o Mankind has always been able to see the sun; the biggest and brightest object in the sky, the moon; a large, white disk which changes shape, visible planets that move among the other stars. o Every 24 hours, moon sets westward o The stars always move in a circle around the same point in the sky o Venus, simply appears as a bright star, from night to night it follows a curved path o Clearly, Venus and the other planets are different than that of other stars o These are examples of systems of celestial bodies that could be easily identified by prehistoric people simply by watching the stars from night to night. o Three sites that contain archeological evidence of having a connection to the sky: 1. Newgrange 2. Sundagger 3. Stonehenge o The study of these sites is known as Archaeoastronomy o Most common connection to the sky between these sites is the sun, which is an easy celestial body to worship; its light and heat is so crucial to survival. o The suns path through the sky follows an easily recognizable cycle that can be used to track time, which is essential for people living off the land. o These sites have solar connection Newgrange (Ireland) o Newgrange’s roof box is aligned to the winter solstice sunrise o A large stone tomb, east coast of Ireland, over 5000 years old NATS1745- History of Astronomy September 2013 o A reconstruction made from ruins in the late 1960s o Circular stone wall, a third of a baseball stadium, rock room 20 feet above the floor (original roof) … oldest known roof structure. o Inside the mound is a 20 meter long rock passageway, which leads to a main chamber with three rooms leading off of them o On the wall is spiral carvings, rocks in rooms and the boulder that covers the main entrance o Other tombs in this sort found in Ireland, above the entrance though is a constructed square hole, known as the roof box, which faces the way the sun rises on the shortest day of the year, Dec 21 (winter solstice) o On this day, a beam of sunlight hits the roof box and the light illuminates the floor and the passageway, after 15 minutes, the main chamber is illuminated. o Precision engineering to capture the sun for a few moments every year, still works flawlessly after 5000 years. o The alignment of the tomb likely reflects a belief in rebirth or reincarnation o Shortest day of the year can be associated with rebirth, after this day, daytime starts to increase, everyday is longer and longer, more sun, warmer weather, rebirth of grass and plants o Associating a tomb with this day, the builders of Newgrange probably believed in some form of reincarnation, by illuminating the dead, the dead would be eternally reborn. o Large rocks are obviously really heavy, creating these stone structures with no machinery would require a large amount of effort by numerous people. o Therefore, Newgrange could not have been a common tomb, it was probably built to commemorate an important person or God(s), someone central to the community= eternally illuminating them on this day of the year The Sundagger of Chaco Canyon (~1000 AD) o A major settlement for the Indians of New Mexico, 1000 years old o Over 600 rooms, very important site for these people; religious or business center? o Throughout the canyon are natural rock formations, one of which is called Fajada Butte o Spiral carvings discovered on the top of this formation, two spiral carvings were found behind three large stone slabs which have two thin spaces between them, sun light went through them and cast two thin daggers of light on the slab o The daggers of light were slowly moving across the wall as the sun was moving across the sky. NATS1745- History of Astronomy September 2013 o Around noon, one dagger perfectly bisected the spiral, cut right through it o Happened to be on June 22= summer solstice. o Two spirals- one big, one small… running through the center of the large spiral is a thin beam of light o Position of the beam changes day to day, the noon sun shifts vertically on these 3 days of the year (winter sun, spring/fall sun, summer sun), also shifts horizontally throughout the year, the noon summer sun comes in through the right shaft, o In the spring and winter the sun is moving towards the left which makes it split in the shaft so you see two daggers of light on the wall o Summer solstice is the only day of the year the dagger can perfectly bisect the spiral because at noon, the sun reaches its highest point in the sky, and only in that position it can create a dagger bisecting that spiral. o The spiral was created to mark noon on the summer and winter solstice, and noon on the two equinox; the day of equal day and night o The winter solstice, the noon sun, lowest position, larger spiral is framed bu two daggers of sunlight o Equinox days, September and March, noon sun is mid point which produces a small dagger, which bisects the small spiral. o These people of New Mexico, must have discovered these beams of light, and carved these spirals in the right location and the right sizes, which means that they understood the annual position of the sun. Stonehenge (~3000 BC) o A ring of stones in southern England o Most famous monument believed to be conducted to modern astronomy due to its complex arrangement of its stones. o Constructed in stages by different waves of settlers that came to this region o The placement of the stones have been dated back to 2200 BC, o Stonehenge’s Heel Stone is aligned to the summer solstice sunrise. o Stonehenge was originally a ditch with a circle of holes dug into the ground, half the size of baseball stadium, o 500 years after this ditch, a different group of settlers came along and placed wooden stacks inside the ditch o 300 years later, another group replaced the wooden stacks into standing stones which require enormous effort as each standing stone is about the weight of a car; mass of 5 elephants. NATS1745- History of Astronomy September 2013 o The placement of the stones must have had a very significant meaning to the builders to justify them dragging these stones from about 20 miles away. o The builders of Stonehenge must have had an advanced understanding of the sky, because this did not just depict the rising sun but also the rising and setting mood, to solar and lunar eclipse. o However, a lot of this stuff would not be completely accurate today o Archeologists believe that most of Stonehenge’s features have to do with ceremonial practices not related to the sky, the holes were used to contain ashes after cremation o Stone circle thought to have healing powers, which makes sense because of the skeletons found around the site showed signs of injury or disease. o Among the principal stones, there are unmistakable alignments, solar alignments to the sun. These solar alignments could have been used to time a ceremonial event like a sacrifice, with a particular sunrise or set. o On the longest day of the year, if you were standing inside the circle, you would see the sun rising behind the Heel Stone. o Once the sun is at its highest, the Heel Stone looks like a torch, which is definitely a dramatic effect. o Sun worshippers like the society known as the Druids. For centuries, every summer solstice meet at Stonehenge to watch the sun rise behind the heel stone o Very ancient society, religious leaders of the Gallic tribe (Western Europe) o Religious practices involve worshipping the sun and moon, also involved in human sacrifices and cremations. o Historians are pretty sure that they didn’t arrive until after 2300 BC, meaning the stone structure was already there. o When Stonehenge was built, the summer solstice Sun rose beside the Heel Stone (due to the precession of the equinoxes.) o Originally, there was another Heel Stone beside the original one o The precise location of the solstice sunrise shifts by a tiny amount each year, known as the precession of the equinoxes. o That shift is too tiny to detect by eye from year to year, but over thousands of years, this shift has occurred the solstice sunrise to appear BEHIND the Heel Stone, when the original place was BETWEEN the pair of Heel Stones. o Used to be two Heel Stones to frame the sunrise o Our ability to predict the precise motion of the sun, thousands of years in the past, can give us some insight of how these NATS1745- History of Astronomy September 2013 prehistoric sights were most likely used o Druid rituals still happen today Lesson Video: Part 2 “The Sun’s Daily Cycle” o Due to Earth’s 24-hour eastward-spin around its polar axis, the Sun moves westward across the sky; it rises in the east, reaches its highest point at noon, and then sets in the west. o Sunrise= east sunset-west o Earth spins from West  East o Celestial bodies appearing on our east side and going down on the west side. o Window of sky moves westerly, as the earth moves eastward. o The earths leaning side is always the east side. o Northern Hemisphere: Sun is mostly seen on the South side of the sky, reaching due South at noon. o Southern Hempisphere: Sun is mostly seen on the North side of the sky, reaching due North at noon. o Due south: directly facing the South Pole. o In Toronto, generally have to face downtown to see the sun N-Hemisphere: East (Sunrise)  South (noon)  West (Sunset) S- Hemisphere: West (Sunset)  North (noon)  East (Sunrise) o Local Noon: when your location is facing the Sun. o Local Midnight: when your location is facing the opposite side of the sky from the Sun. o Local sunrise or sunset: when the sun’s direction is perpendicular (right angle/ 90 degrees) to your location “The Sun’s Annual Cycle” o Fall and Spring Equinox (~September 23, ~March 21): Sun rises due East and sets due West, spending equal time above and below the horizon (equal day and night) o Equinox is lain for “equal night” o After the fall equinox, the suns path changes, it shifts southward. o This shift causes the sun to rise further and further south east each day and set further and further south west each day o Unpleasant effects on us: causes the daytime length of the day (arc above horizon) to shorten = shorter and shorter days = sun at lower and lower heights in the sky o When the suns daytime arc is lower and lower, the colder it gets; NATS1745- History of Astronomy September 2013 we get indirect light (hits us at an angle rather than overhead= colder) o Winter Solstice (~December 22): Sun rises and sets at its southernmost position, traversing a short, low arc in the sky (shortest day of the year and lowest moon sun) o Solstice is Latin for “solar standstill” o As these positions of the sun continue to shift further and further south, on December 22 , they stop shifting hence the ‘solar standstill’ nd o On days following December 22 , this arc continues to shift back towards the east o Daytime is gradually starting to lengthen, begins to get warmer o Noon sun is getting higher and higher o On March 20 = first day of Spring, sun rises due east and sets due west o After, the path continues to shift further north, which causes the sun to rise further east and set further north of west. o Northward shifting= daytime is longer than nighttime; sun above our location, sun is higher so we get direct sunlight. o Summer Solstice (~June 22 ): Sun rises and sets at its northernmost position, traversing a long, high arc (longest day, highest noon sun.) o On June 22 , the rising and setting position stand still; days following the position start shifting towards the south side of the sky again. o Everything above describes what we see in the Northern Hemisphere o In the Southern Hemisphere the suns daily arcs are all tilted towards the north rather than the south o Identifying the Sun’s ri
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