Sky Motions. Diurnal Motion. Annual Motion. DIURNAL MOTION

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Sky Motions

• Diurnal Motion

• Annual Motion

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DIURNAL MOTION

• Daily East / West motion of the sky
• Due to the Earths rotation (15/hour)
• 360/24 hours 15/hour
• 1 in 4 minutes
• Stars fall into two groups
• Circumpolar - never rise or set
• Equatorial

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Circumpolar Stars
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Equatorial Stars
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View from the North Pole
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View from the Equator
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Coordinate System
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Celestial Meridian

• Circle going through north and south points on
  the horizon and the zenith

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Celestial Meridian

• Objects on the Meridian are at their highest
  point in the sky (transit)
• Astronomical noon is when Sun is on the Meridian.
• Does not mean the Sun is directly overhead.
• Midnight is when the Sun is on the Meridian below
  the horizon.

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Annual Motion
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Horizon Calendar
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The Sky Dome
Sunrises and Sunsets
Polaris
W
On the day of an summer solstice
On the day of an winter solstice
S
On the day of an equinox
N
E
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Polaris
W
Vernal or Autumnal Equinox
Winter Solstice
S
Summer Solstice
N
E
Starting Points for the Sun
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Sunrise in Athens
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Stonehenge
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Earths Annual Motion
Leo
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Suns Motion Tool
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Inclined Pole causes Seasons
Northern Hemisphere Summer
Northern Hemisphere Winter
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Suns motion along the Ecliptic
Suns Motion
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ANNUAL MOTION

• Constellations move westward during the year.
• Due to Earths orbital motion around the Sun
• Sun appears to moves eastward 1/day
• Path of the Sun called the ECLIPTIC
• Ecliptic inclined 23.5 to Equator
• Horizon calendar

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Annual Motion Affects the Nighttime Sky
900 PM
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Annual Motion Affects the Nighttime Sky
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Annual Motion Affects the Nighttime Sky
852 PM
Day 3
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Annual Motion Affects the Nighttime Sky
900 PM
One Year Later
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Stars

• Fixed Stars
• Modern concept of stars
• Form the Constellations
• Planets - traveling or wandering stars
• Sun, Moon, Mercury, Venus, Mars, Jupiter, and
  Saturn
• Meteors - shooting stars
• Comets - long-haired stars

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Babylonian Astronomy
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Babylonian Astronomy
Star Charts
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Babylonian Astronomy
Fatalistic Pre-determinism Everything in nature
pre-determined by the gods Doesnt lend itself to
model building Infinite time line
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End of Section