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

December 21, 2011 version

One People … One Sky …Two Seasons

Lawrence Hall of Science, CASunstone, resent

Amaterasu appearing from the cave on the Winter Solstice

Citron hot water of the Winter Solstice Yuzuyu, Katori City Japan

Locri Pinax Persephone Opens Likon Mystikon.

Frederic Leighton-The Return of Perspephone (1891)

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, perihelionAround January 3 or 4Sun and Earth furtherest, aphelionAround July 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.

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

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

How to tell time

• http://en.wikipedia.org/wiki/Equation_of_time Using the sun and moving to uniform watch time!

• Until 1833, the equation of time was tabulated in the sense 'mean minus apparent solar time' in the British Nautical Almanac and Astronomical Ephemeris published for the years 1767 onwards. Before the issue for 1834, all times in the almanac were in apparent solar time, because time aboard ship was most often determined by observing the Sun.

Equation of Time