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Vernal Equinox, the First Day of Spring

Vernal Equinox, the First Day of Spring. By Dr. Harold Williams of Montgomery College Planetarium http://montgomerycollege.edu/Departments/planet/. The Sky Dome. Sunrises and Sunsets. Polaris. On the day of an summer solstice…. W. On the day of an winter solstice…. S.

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Vernal Equinox, the First Day of Spring

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  1. Vernal Equinox, the First Day of Spring By Dr. Harold Williams of Montgomery College Planetarium http://montgomerycollege.edu/Departments/planet/

  2. The Sky Dome Sunrises and Sunsets Polaris On the day of an summer solstice… W On the day of an winter solstice… S On the day of an equinox… N E

  3. Polaris W Vernal or Autumnal Equinox Winter Solstice S Summer Solstice N E Starting Points for the Sun

  4. 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

  5. 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.

  6. Equinoxes and Solstices • The Vernal (Spring) Equinox(about March 21): The location where the Sun crosses the equator when going from south of the equator to north of the equator. • Position of the Sun: R.A. 0h, Dec 0o • The Summer Solstice(about June 21): The location where the Sun is at its furthest north. • Position of the Sun: R.A. 6h, Dec +23.5o

  7. The Autumnal (Fall) Equinox(about September 21): Where the Sun crosses the equator when going from north to south. Position of the Sun: R.A. 12h, Dec 0o The Winter Solstice(about December 21): The location where the Sun is at its furthest south. Position of the Sun: R.A. 18h, Dec –23.5o Equinoxes and Solstices

  8. Some Resources on Seasons • Seasons in the Wikipedia http://en.wikipedia.org/wiki/Seasons • Spring Seasons in the Wikipedia http://en.wikipedia.org/wiki/Spring_%28season%29 • Tropical Year in the Wikipedia http://en.wikipedia.org/wiki/Tropical_year

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