ASTR 100 Week 4 Notes Bob Berrington
ASTR 100 Week 4 Notes Bob Berrington ASTR 100
Popular in Introduction to Astronomy: Solar System and Beyond
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This 4 page Class Notes was uploaded by Sarah Gardner on Sunday February 7, 2016. The Class Notes belongs to ASTR 100 at Ball State University taught by Dr. Bob Berrington in Fall 2016. Since its upload, it has received 39 views. For similar materials see Introduction to Astronomy: Solar System and Beyond in Astronomy at Ball State University.
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Date Created: 02/07/16
ASTR 100 Week 4 Spring 2016, MWF Section 2, The Rise of Astronomy Extremelly helpful resource for bowl diagrams and basically everything covered in class: http://astro.unl.edu/naap/ Diagrams and such The Earthbound Observer Cont. Motion of stars looking east o Stars appear to rise at an angle (90 degrees latitude) out of the east o Makes arch motions (diurnal motions) Motions of the starts looking north o Polaris located near the NCP o Appears stationary o Other stars circle Polaris Circumpolar Stars o Means around the pole o The stars that circle the pole and never set on the horizon from the viewer’s specific point are circumpolar. Aka they never “dip” below the horizon o All stars whose angular distance is less than the observer’s latitude are circumpolar o Starry Night free computer program a great way to see how this occurs (shown in class) North Pole o If standing directly on the north pole, are point are South Points o All stars are circumpolar at the north pole Determining circumpolar stars o Always find the NCP first o North Pole= all stars are circumpolar o South Pole = all stars are circumpolar o Equator = no stars are circumpolar (all stars visible over the course of 24 hrs if there was no sunlight) 0 o 30 North = ones within the viewer’s latitude of the pole are circumpolar o 30 South = all stars within 30 degrees of the SCP are circumpolar Ancient Astronomers o Stonehenge In Englande Marks the summer solstice Sun sets on heel stone 56 Aubrey holes (shows repetition of lunar cycle) o Mayans Temples used as observatories o Bighorn Medicine Wheel Wyoming – built by Native American tribes Marks solstice and several bright stars Importance of Astronomy to the Ancient peoples o One simple reason: food o Timing of planting crops a matter of life and death The heavens were sacred to ancient astronomers o Intangible o Cosmologies = stories for posterity about the stars o Constellations = gods, heroes, mythical creatures o 48 ancient constellations remain today All from civilizations in the Northern Hemisphere Modern Constellations o In 1928, the International Astronomical Union (IAU) established 88 constellations They defined a constellation as an area of the sky No more fighting over stars for constellations (some ancient constellations had one or more stars that were the same) o Asterisms An unofficial grouping of stars Examples: the Big Dipper is a subset of Ursa Major o Assigning Greek letters to the bright stars Always the lowercase greek letter Called a bayer The brightest are alpha (α) Second brightest are beta (β) And so on o A star’s bayer (greek letter) is followed by the genitive form (possessive) Example: Alpha Orionis Look of the Wikipedia page of Modern Constellations – a good reference for proper names of stars The biggest star in the sky, Sirius, is the α of the constellation Canis Major o The Brightest Stars We use a Magnitude scale Developed by Hipparchus 160 – 127 BC Divides stars by brightness into 6 classes st o Brightest called 1 magnitude o Faintest called 6 magnitude o 1 magnitude stars are 100x brighter than 6 magnitude stars o Modern Astronomers Quantified the magnitude system Difference of S magnitudes means a factor of 100 in flux Brighter objects have lower magnitudes (sun has a magnitude of -35) Allows us to extend definition greater than 1 to 6 magnitudes non integer values for very specific brightness If two stars differ by 1 magnitude… One is about 2.5x brighter than the other If magnitudes differ by two… 2 It is (2.5 ) times brighter To find the difference of brightness between 2 stars… M 1 M 2 Stars differ by 2.5 o Greek Astronomers Overview Tried to measure size of known universe Philosophy driven (not scientific) However, they did develop the scientific method Aristotle (384-322 BC) Geocentric model (earth centered) Didn’t see a parallax in the stars o A parallax is a shift in position due to a change in vantage point Didn’t detect motion (falling objects swept westward Earth = at the center and immobile o Greek Philosophy The four elements Water, Earth, Fire, Air o Long ago, the four nations lived together in harmony o Then, everything changed when the Fire Nation attacked… o Moving on o Motion of the Sun Ancient astronomers made observations of the sun, stars, and planets Sun = easterly trend (defines orbital plane of the earth) Stars = westward Sun completes its cycle every 365,25 days Traces out ecliptic o EcliptOc: sun’s orbit on the celestial sphere o 23.5 tilt compared to celestial equator o Orientation of the Celestial Sphere Earth’s axis is tilted at 23.5 degrees Earth’s rotation makes earth like a gyroscope The earth is spinning so quickly that the axis is fixed Mercator projection When looking at a flat map of the surface of the earth, the distortions get bigger as you go north Other projections possible (cylindrical, conic, azimuthal) One would need 2 projections to cover the whole sky o Cardinal Directions of the sky chart North is up, east is to the left Will continue next week
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