by John Harper
There are two : The Summer and the Winter Solstices.
This year, the Summer Solstice is at 14h 03m Daylight Saving Time ( Pacific Coast - Western USA ) on June 21st. The Winter Solstice is at 17h 56m on Dec.21st.
The times of the solstices, like the times of the equinoxes vary from year to year due to the extra 0.25639 of a day we have to save each year because the earth does not orbit the sun in exactly 365 days.
The word "solstice" means in essence "stationary" and on just two occasions in the year the sun reaches a couple of points where it seems to stop in its apparent "up and down" movements in the sky. These are the two solstices.
During the first half of the year the sun slowly climbs higher and higher in the sky and the length of daylight increases. On each successive day, at noon, it is fractionally higher in the sky. At the Summer Solstice the sun has reached its very highest point north in the sky. At noon it is just over 70 degrees above the horizon in L..A. & everyone's shadow is very short. It is the longest day (the sun is above the horizon longer on this day than any other !).
Having reached its highest point there is only one direction it can now go, and that is down ! So for the rest of the year, the sun gets lower and lower in the sky as the year grows old, daylight length begins to shorten and the length of night increases until Dec.21st., the day of the Winter Solstice when the sun has sunk to its furthest point south in the sky. From L.A., at noon, it is now only 33 degrees above the horizon at noon and shadows are very long! Day length is short, the night is long and this day is what we call the Shortest Day. The sun has reached its second stationary point, the Winter Solstice, and then begins to climb once again towards the next summer !
This apparent rising and falling of the sun in the sky is due to the tilt of the earth's axis of rotation. At the Summer Solstice, the north pole of earth is tilted as much towards the sun as it can ever get. At the Winter Solstice it is pointing as far away from the sun as it can ever get.