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The Day of the Sun's Return, The Winter Solstice

The Day of the Sun's Return, The Winter Solstice. Montgomery College Planetarium at Takoma Park/Silver Spring http://montgomerycollege.edu/Departments/planet By Dr. Harold Williams. One People … One Sky …Two Seasons. Length of Seasons. Summer 93 days 15 hours 29 minutes

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The Day of the Sun's Return, The Winter Solstice

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  1. The Day of the Sun's Return, The Winter Solstice Montgomery College Planetarium at Takoma Park/Silver Spring http://montgomerycollege.edu/Departments/planet By Dr. Harold Williams

  2. One People … One Sky …Two Seasons

  3. Length of Seasons • Summer 93 days 15 hours 29 minutes • Autumn 89 days 20 hours • Winter 88 days 23 hours 54 minutes • Spring 92 days 18 hours 26 minutes Sun and Earth closest, perihelion Around January 3 or 4 Sun and Earth furtherest, aphelion Around July 4

  4. Obliquity of the ecliptic • 23 ½ degrees, approximately, between day axis of rotation and year axis of revolutionary orbit about the sun • Causes the seasons • Seasons are not caused by the fact that the earths orbit is not a perfect circle, but its orbit is slightly elliptical. • This ellipticity of the earths orbit does cause the seasons which are caused by the tilt, obliquity of the ecliptic, to be slightly unequal in length.

  5. Seasonal Years • Mean tropical year is 365.242 189 670 SI days • vernal equinox: 365.24237404 + 0.00000010338×a days • northern solstice: 365.24162603 + 0.00000000650×a days • autumn equinox: 365.24201767 − 0.00000023150×a days • southern solstice: 365.24274049 − 0.00000012446×a days • Average tropical year is 365.2422 currently. • a in Julian years from 2000

  6. Winter Solstice Links • http://en.wikipedia.org/wiki/Shortest_day

  7. How to tell time • http://en.wikipedia.org/wiki/Equation_of_time

  8. Equation of Time

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