People around the world in the Northern Hemisphere will celebrate the summer solstice of 2014 on Saturday, reveling in the sunshine of what will be the year's longest day.
Druids will gather at Stonehenge in Britain, Europeans will dance around maypoles and light bonfires and Americans will fire up the barbecue for midsummer festivities as our planet, with its axis tilted 23.5 degrees, sees its Northern Hemisphere face the sun more directly than at any other time during the year.
On June 21 the sun will shine down on a straight line directly onto the Tropic of Cancer, the imaginary line in the Northern Hemisphere that marks the northernmost point facing the sun brought about by the Earth's tilt.
In the Southern Hemisphere, the line is known as the Tropic of Capricorn.
Each marks the point at which the sun will be seen highest in the sky in that hemisphere's summer and the lowest in its winter.
The world solstice is from the Latin for "sun stands still" -- "sol" and "sistere" -- and given to the day that sees the sun appear to pause, as seen from the Earth, before slowly reversing its location in the sky.
In the Northern Hemisphere after Saturday, it will appear slightly lower each day heading for the winter solstice on Dec. 21.
As the Northern Hemisphere sees the summer solstice June 21, the planet's Southern Hemisphere is seeing just the opposite, as they see their Winter Solstice -- and their shortest day of 2014.
If Saturday is the longest day of the year, with the most sunlight, why isn't it also the hottest day of they year?
The Earth's atmosphere and oceans will, of course, soak up a lot of sunlight and energy on the solstice, but is takes a while for the heating up from all that energy to occur.
The geometry of the Earth's orbit determines the dates of the summer and winter solstices and the spring and autumn equinoxes -- days when daytime and nighttime are exactly equal in length -- but our planet's seasons all lag behind those exact dates by around 6 weeks.
Many people mistakenly believe the summer solstice also moves the Earth more toward our sun.
"We're not actually closer to the sun," NASA scientist C. Alex Young says.
The solstices have nothing to do with our distance from the sun but are the result of Earth's axis being tilted more toward or more away from it, he explains.
That's the origin of our planet's seasons, he added.
"If Earth was just straight up and down, there would never be a winter or summer," he says. "It would be the same in the north and south."
