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What are the unique aspects of astronomy?
- It is observational, not experimental.
- It is a historical science.
- The scope of the field. (it studies the largest and smallest things in nature.)
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Units in Metric and English System
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Stellar evolution
changes in the stars caused by pulls of gravity.
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Milky Way Gallaxy
a cloud of several hundred billion stars with a flattened dislike shape somewhat like that of the solar system.
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Light Year
- 300,000 km/second
- 186,000 miles/second
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superclusters
collections of groups and clusters.
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Constellations
How many?
- a recognized grouping of stars
- 88
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Asterisms
- Unofficial groupings of stars.
- Still remain in common use.
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Zenith
point directly overhead
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celestial sphere
- a distant starscape on the interior (of earth) with earth as its center.
- Used to study stars from earth.
- Stars are viewed as being the same distance away.
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Nadir
- Point directly bellow you.
- Opposite of the zenith.
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North and South CELESTIAL POLES.
two points that do not more as the celestial sphere turns overhead.
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Celestial Equator
- imaginary line directly above the earth's equator.
- constellations on the celestial equator rise due east and set due west.
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local celestial meridian
- line that runs from the north celestial pole to the south celestial pole.
- divides earth east and west.
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ecliptic
the path the sun traces across the celestial sphere.
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zodiac
the collective group of constellations that the ecliptic crosses.
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Vernal equinox
- when the sun is crossing the celestial equator.
- March 20. from southern hemisphere to northern hemisphere
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autumnal equinox
- september 22.
- sun is crossing the celestial equators from north to south.
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Solstices
- June 21, December 21
- the sun stops it's northward or southward motion and begins to reverse direction.
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Short Term Motions in the sky.
Sun
- Solar Day
- 1 cycle
- 24h00m00s
- 360 degrees in 24h = 15 degrees/hr
- 1 degree/4mins
- appear to move eastward
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Short Term Motions in the sky
Moon
- One cycle
- lunar day
- 24h50m00s
- appear to move eastward
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Short Term Motions in the sky
Stars
- 1 cycle
- SIDEREAL DAY
- 23h56m00s
- appear to move westward
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Short Term Motions in the sky
Planets
each diurnal cycle varies in duration.
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Diurnal Motion
Daily motions
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True Motions of the Earth:
Rotation
Apparent Motions:
- Spinning of the earth on its axis...
- rising/setting of the sun, moon, stars and planets
- *diurnal/short term motions*
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True Motions of the Earth:
Revolution
- motion of earth around the sun...
- 1 degree motion of the sun along ecliptic
- 1 westward motion of the stars
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True Motions of the Earth:
Precession
- change in orientation of earth's axis...
- Polaris moving away from the NCP, no longer will be 'north stat'
- changes in equatorial coordinates of stars
- changes in seasons and constellations
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True Motions of the Earth:
Nutation
- wobbling of eath's axis...
- celestial sphere wobbles N-S
- 9'' per 18.6 years
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True Motions of the Earth:
Barycenter Motion
- true motion!!!
- earth-moon motions...
- moon revolves around earth
- earth revolves around moon
- they revolve about center of mass of system
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siderial day
- day length, measured with respect to the stars.
- siderial time.
- 23h56m00s
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angular size
how large things appear in the sky
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angular separation
how far appart things appear in the sky
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arc minutes
1 degree = 60' arc minutes
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arc second
1' arc minute = 60'' arc seconds
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synodic period
the amount of time it takes a body in the solar system to make an orbit relative to earth.
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sidereal period
the length of time a body takes to make an orbit relative to the stars.
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Geographic coordinate system (earth)
- Latitude (N-S)
- Longitude (W-E)
- geographic equator
- NGP,SGP
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Thates of Miletus
- predicted solar eclipse
- invented astronomical navigation
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Pythagoras
- presented model of the universe
- central fire (sun) and 10 objects
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Aristotle
- earth centered universe
- earth didn't rotate, it was static
- envisioned a spherical earth (shadow on moon)
- correctly explained the phases of the moon
- everything made from 4 elements (air, fire, water, earth)
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Aristarchus
- measured sizes and distances of both sun and moon.
- -moon smaller than sun, moon closer than sun
- first to consider sun centered universe
- argued that daily motions were a result of a rotating earth.
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Eratosthenes
acurately deduced the circumference of the earth
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hipparcus
- devised the first star catalogue
- it included 800-1000 stars
- estimated moon's distance and size accurately
- measured the length of a year- plotted sun on ecliptic over this year
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Claudius Ptolemy
- "Great Syntaxes of Greek Astronomy"
- 13 volume book that says everything we know about greek astronomy.
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Anaxagoras
- first person to explain eclipses
- pictured moon and planets as earthlike.
- -solid crusty surfaces shinning by reflected sun light.
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retrograde motion
when planets move west with respect to the stars.
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cosmology
- study of the origin and nature of the universe.
- geocentric-earth centered
- heliocentric- sun-centered
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planets move in an epicycle and a deferent.
the epicycle is a smaller cycle which in turn moves along a bigger circle, deferent.
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direct motion v. retrograde motion of planets
- direct motion is counter clockwise. (actual motion-west)
- retrograde motion is clockwise. (eastward)
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theory
well developed or well rested hypothesis or set of hypotheses that have been verified.
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hypothesis
single assertion or conjecture that must be tested.
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model (law)
theory that accounts for a set of observations in nature.
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scientific model
- hypothesis > theroy > model
- must fit data (observations)
- must make predictions (can be tested)
- aesthetically pleasing.
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prolemaic cosmological system
- flat system
- geocentric - earth in the center
- explained the motion of the planets using epicycles and deferents
- planets move counter clockwise in both.
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copernican cosmological system
- flat system
- put the sun rather than earth at the center
- planets closer to the sun move faster than those further away
- argued that retrogade motion was because of the motions of the combined motions of the earth and other planets
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Tycho Brahe
- "castle in the sky"
- best naked-eye observer of his time
- worked with Kepler to make his own model of the universe.
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Johannes Kepler
- employed by Brahe
- 3 laws of planetary motion
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Kepler's Law:
Law of Elipses
planets orbit the sun in elliptical orbits (cone example- oval shape ellipses) with the sun located at the center (focus)
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Kepler's cosmology:
major axis
largest diameter of ellipse
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Kepler's cosmology
minot axis
smallest diameter of ellipse
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kepler's cosmology
semi-major axis
half of the major axis
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kepler's cosmology
semi-minor axis
half of the minor axis
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Kepler's Law:
Law of Areas-Speeds in orbit
- planets move in equal areas in equal time around the sun.
- in order to do this, they must move faster when they are closer to the sun and slower when further away.
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Kepler's Law:
Harmonic Law- yardstick of the solar system
- 8 musical notes (sun, moon, earth and 5 naked eye planets)
- able to measure relative distace of all naked eye planets from the sun.
the square of a sidereal period of a planet is directly proportional to the cube of its semi-major axis.
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Galileo Galilei
- first naked-eye astronomer to look at the heavens with an astronomical telescope.
- published "the starry messenger"
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Galileo Observation:
Milky way
it was made of thousands of stars
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Galileo Observation:
Moon
has craters, mountains, valleys and seas
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Galileo Observation:
sun
has dark blotches on it which he called sunspots
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Galileo Observation:
Saturn
wasn't round, it had ears.
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Galileo Observation:
Venus
went through a series of phases just like our moon.
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Galileo Observation:
Jupiter
had four star-like objects revolving around it.
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