AST101- chp 3 notes.docx

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Astronomy & Astrophysics
Michael Reid

AST101 THE SCIENCE OF ASTRONOMY CHAPTER 3 (3.1) In what ways do all humans use scientific thinking? - comes naturally to us - science is a way of learning about nature through careful observation and trial-and-error experiments - we all learn something new and witness the unexpected - modern scientists trained to organize their thinking in a way that makes it easier for them to share their discoveries How did astronomical observations benefit ancient societies? -Central Africa: people learned to predict the weather with reasonable accuracy by making careful observation of the moon -discovered that the orientation of the crescent “horns” relative to the horizon is closely tied to local rainfall patterns -used changing positions of the sun, moon, and stars to keep track of time and seasons (crucial skills for those who depended on agriculture) - length of our day is the time it takes the sun to make one full circuit of the sky - length of the month comes from the moon’s cycle of phases - our year is based on the cycle of the seasons - the 7 days a week were named after the 7 naked eye objects that appear to move among the constellations: the sun, moon, and the 5 planets’ recognized in ancient times What did ancient civilizations achieve in astronomy? Determining the Time of Day: - during daytime told the time by observing the suns path through the sky - At night, could estimate time from the position and phase of the moon - Egyptians divided daylight into 12 equal parts and we still break the 24 hour day into 12 hours each of A.M. and P.M. - Egyptians also divided the night into 12 equal parts - By 1500 b.c., Egyptians abandoned star clocks (specific stars that appear in sky on specific days or times) and used clocks that measure time by the flow on water through an opening of a particular size - 1600s mechanical clocks Marking the Seasons: - Stonehenge: oldest standing human made structures; kept track of the seasons and was a social and religious gathering place - Templo Mayor: the run rose through the notch between the two temples on the equinoxes - The Sun Dagger: three large slabs of rock in front of the spiral produce different patterns of light and shadow throughout the year Lunar Calendars: - lunar cycle (one new moon to the next) as the basis of a calendar - Metonic Cycle: lunar phases repeat on the same solar dates about every 19 years (precisely 235 lunar months) Ancient Structures and Archaeoastronomy - the study of ancient structures in search of astronomical connections - many cultures made careful observations of planets and stars - scientists engage in archaeoastronomy evaluate ancient structures to see if they served astronomical purposes (any particular alignments) - however the mere existence of astronomical alignments is not enough to establish that a structure has an astronomical purpose; the alignments may be coincidental - Navigator: a person who had acquired the knowledge necessary to navigate great distances among the islands (patterns of waves, directions and guidance of s
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