Motion of Heavenly Objects

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Motion of Heavenly Objects

• Observations and Explanations

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Sun

• Observation
• rises in East, sets in West
• daily (diurnal)
• Explanations
• Sun moves through the sky (old)
• Earth rotates on axis once per day (accepted)

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Sun

• Observation
• moves west to east wrt to stars
• yearly (annual)

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June 20
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July 20
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Sun

• Observation
• moves west to east wrt to stars
• yearly (annual)
• Explanation
• Earth orbits Sun
• Ecliptic
• apparent path of the Sun through sky

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Sun

• Observation
• sunrise and sunset move north and south
• hours of daylight increase and decrease
• annual
• Explanation
• Earths rotation axis is tilted with respect to
  plane of orbit

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Seasons

• Northern Hemisphere
• summer solstice
• rotational axis points toward Sun
• most hours of daylight
• Sun rises northernmost along eastern horizon
• vernal equinox (Spring)
• equal hours of day and night
• Sun rises directly East
• moving north

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Seasons

• Northern Hemisphere
• winter solstice
• axis points away from Sun
• fewest hours of daylight
• Sun rises southernmost along eastern horizon
• fall equinox
• equal hours of day and night
• Sun rises directly East
• moving south

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Keeping Time

• Solar Day
• time between two successive crossings of the
  meridian by the Sun
  
• 24 hours
• Sidereal Day
• time between two successive crossings of the
  meridian by a star
  
• 23 hrs 56 min

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Day 2
Day 1
difference between sidereal day and solar day
sidereal day is shorter
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Keeping Time

• Tropical Year
• time for sun to complete one trip around
  ecliptic
  
• 365.242 solar days
• Sidereal Year
• time for constellations to complete one trip
  around the sky
  
• 365.256 solar days
• Difference due to Precession
• Difference due to precession time between two
  successive crossings of the meridian by a star
  
• 23 hrs 56 min

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North Star

• Observation
• different stars play the role of north star
• difficult observation to make
• time scale of 26,000 years
• Explanation
• Earths rotation axis wobbles
• precession

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Planets (wanderers)

• Observation
• five visible to naked eye
• Mercury, Venus, Mars, Jupiter, Saturn
• east to west
• daily
• west to east
• move in zodiac (narrow band surrounding
  ecliptic)
  
• retrograde (east to west)
• Explanation
• heliocentric

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Planetary Configurations

• Conjunction
• lies in same direction of the sky as the Sun
• Superior
• Sun between planet and us
• Inferior
• planet between Sun and us
• only occurs for Mercury and Venus

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Planetary Configurations

• Opposition
• planet lies directly opposite the Sun in the sky
• only occurs for Mars, Jupiter Saturn

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Planetary Configurations

• Transit
• object moves across the Suns disk
• occurs only for inferior planets
• Greatest Elongation
• greatest angular separation of a planet from Sun
• Mercury - 28o
• Venus - 47o
• superior planets - 180o

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Moon

• Observation
• rises in East, sets in West
• daily
• Explanation
• Earth rotates

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Moon

• Observation
• changes appearance
• approximately monthly
• West to East with respect to background stars
  and Sun
  
• Explanation
• Moon orbits the Earth

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Explaining Phases
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Keeping Time

• Sidereal Month
• time to complete one trip with respect to stars
• 27.3 days
• Synodic Month
• time to complete one cycle of phases
• 29.5 days

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Eclipses

• Solar Eclipse
• Moon casts shadow on Earth
• Moon between Sun and Earth
• New Moon
• Lunar Eclipse
• Earth casts shadow on Moon
• Earth between Sun and Moon
• Full Moon

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Solar Eclipse

• Total Eclipse
• Sun completely obscured
• umbra
• Partial Eclipse
• Sun partially obscured
• penumbra
• Annular Eclipse
• Moon farther away than usual
• ring around Sun

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Lunar Eclipse

• visible everywhere Moon is visible
• partial
• shadow does not completely cover Moon
• total
• shadow completely covers Moon
• reddish color - refracted light

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Eclipses

• Why dont eclipses occur every month?
• 5.5 o tilt between Moons orbit and ecliptic
• Conditions not always right at full and new moons