When the Sky Falls Montgomery College Planetarium at Takoma Park/Silver Spring By Dr. Harold Williams When the Sky Falls

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 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 eliptical. This elipticity 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 SI days vernal equinox: ×a days northern solstice: ×a days autumn equinox: − ×a days southern solstice: − ×a days Average tropical year is currently.