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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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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

One People … One Sky …Two Seasons


Length of seasons

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


Obliquity of the ecliptic

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.


Seasonal years

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


Winter solstice links

Winter Solstice Links

  • http://en.wikipedia.org/wiki/Shortest_day


How to tell time

How to tell time

  • http://en.wikipedia.org/wiki/Equation_of_time


Equation of time

Equation of Time


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