The longest sunrise-to-sunset daylight period of the year in the Northern Hemisphere occurs June 21, which is the summer solstice (sun standing still) and the first day of summer. Then, at noon LST (local sundial time) the sun will appear in zenith (directly overhead) on earth's Cancer line (23 1/2oN latitude). Due to earth's rotation, the sun reaches its highest position in the sky every 24 hours precisely at noon LST, but it can never appear in zenith from any latitude north of Cancer because our planet's axis is tilted 23 1/2o from a hypothetical line perpendicular to the Ecliptic (earth's orbital plane around the sun). The Southern Hemisphere's summer solstice, longest daylight period, and beginning of summer is Dec. 21. Its zenith-sun can never appear south of the Capricorn Line (23 1/2oS latitude). Dec. 21 is the Northern Hemisphere's winter solstice, shortest daylight period, and first day of winter.

Earth's zenith-sun undergoes two different, simultaneous, apparent motions: a daily, westward, round-the-earth relatively-fast (15o/hour) movement, and a much slower (0.01o/hour) average annual movement from earth's Capricorn line on Dec. 21 - north for six months to the Cancer line by June 21, and back south for another six months to Capricorn by next Dec. 21. The total apparent motion is 94o per year; from Capricorn to Cancer, and then from Cancer back to Capricorn. It is fastest near the Equinoxes and slowest near the solstices; so slow, that it seems to "stand still" (the meaning of "solstice") on June 21 and Dec. 21.

"Sun, stand thou still!" Joshua is supposed to have ordered when the Israelites needed more daylight to defeat the Canaanites at the Battle of Jericho. The apparent zenith sun does halt its northward motion when it reaches its maximum northern latitude over Cancer on June 21 and pauses for an instant before heading slowly south back to Capricorn - where it again stops before heading back north to reach Cancer again on June 21. Of course, it is earth that is actually moving and giving us earthlings the false impression that the celestial objects are moving around us.

Interestingly, the 2002 Summer Solstice - longest day of the year, which falls as usual on June 21 in the Northern Hemisphere, is neither the year's earliest sunrise day nor the latest sunset day. The earliest sunrise this year occurs on or about June 14, one week prior to the solstice; while the latest sunset takes place on or about June 27, almost a week after the Summer Solstice occurs. After the June 21 solstice, the daylight portion (sunrise to sunset) of successive 24-hour days actually begins to shorten daily throughout the entire summer and fall. This trend ends only when earth has reached an orbital and axial tilt position which makes its Northern Hemisphere experience the shortest day of the year, Dec. 21 (or 22 on some years.)

Inasmuch as summer is the Northern Hemisphere's warmest and longest season (lasting 94 1/4 days, compared with fall's 89 1/2 days, winter's 88 1/2 days, and spring's 93 days, it is interesting to note that the length of diurnal daylight (sunrise to sunset) begins to shorten on June 22, one day after the solstice's longest daylight period, and continues shortening every day throughout the entire summer and fall until the winter solstice's shortest sunrise to sunset day on Dec. 21. Thereafter, the daily sunrise to sunset time begins to lengthen throughout the entire winter and spring until the 2003 longest day summer solstice is reached.

Finally, Earth rotates 361o/24 hours: 360o for a complete rotation about the axis, plus 1o more to compensate for having orbited 1o during that 24 hours.