The Solstice…

sun

By: Michael Watson, LLB

… arrived early this morning at 05.04 GMT (01.04 EDT).  In the northern hemisphere we call it the summer solstice, and south of the equator it’s the winter solstice, so astronomers tend to call it simply the June solstice.  It is the instant during the year when planet Earth is tilted on its axis most directly in the direction of the Sun, so that the Sun appears highest in the sky at local noon in the northern hemisphere, and lowest in the sky at local noon in the southern hemisphere.

It also marks the day in the year when the Sun is above the horizon for the longest duration of the 24-hour day.  For Toronto, the Sun will be above the horizon for 15 hr, 27 min.  For Edmonton, the duration of sunlight increases to 17 hr, 3 min.  At and north of the Arctic Circle, the Sun never sets and there is 24 hours of sunlight.

The date of the June solstice is June 21 for three years in a row, and then it’s June 20 for one year, before returning to June 21 for another three years.  This is caused by the extra day that we insert into the calendar once every four years during Leap Year, in order to keep our annual calendar aligned as closely as possible to Earth’s position in its annual orbital motion around the Sun.

So what’s the etymology of the word “solstice“?  From the Online Etymology Dictionary:

mid-13c., from Old French solstice, from Latin solstitium “point at which the sun seems to stand still,” from sol “sun” (see sol) + past participle stem of sistere “to come to a stop, make stand still”

What does it mean to say that “the Sun seems to stand still”?  What this refers to is that between December and January, the Sun appears to move progressively northward in the sky, until at the solstice it reaches the most northerly point in the sky for the year (exactly on the border between the constellations Taurus and Gemini).  On June 21 the Sun comes to a stop in its northward motion, reverses direction, and from then on moves south in the sky until it reaches its most southerly point in the constellation Sagittarius on December 21.  So the “standing still” refers to the Sun ciming to a stop in its northward motion and reversing its motion from north to south in the sky.

Enjoy the start of summer, everyone!

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