Circle of Illumination, dividing day from night

Sun-Earth Relationships



The axis tilts 23.5 degrees from the perpendicular to the orbital plane but remains
pointing towards Polaris (North Star).

A Fall (Autumnal) Equinox (approx. Sept 22)
     Vertical Ray over Equator at noon, 12 hour (equal) days and nights everywhere
      between the poles
B Winter Solstice (approx. Dec 21)
    Vertical Ray over Tropic of Capricorn (23.5 degrees south latitude), longest day of
     the year for Southern Hemisphere, 24 hour night for Arctic Circle (66.5 deg. north)
     24 hours daylight within the Antarctic Circle (66.5 deg. south)
C Spring (Vernal) Equinox (approx. March 21)
    Vertical Ray over Equator at noon, 12 hour (equal) days and nights everywhere
      between the poles
D Summer Soltice (approx. June 21)
    Vertical Ray over Tropic of Cancer (23.5 degrees north latitude), longest day of
     the year for Northern Hemisphere, 24 hour night for Antarctic Circle
     24 hours daylight within the Arctic Circle