Friday, June 22, 2018

Summer Solstice Splendor

Recall your personal response to the “first day of summer” when you were a school student. Children greet this day with happiness and fervor. By this date in June some midwestern school children have been on summer vacation for several weeks. Other schools, primarily in the mostly non-agricultural east, have school calendars extending until mid or late June. Eastern snowstorms wreaked havoc this school year making closing dates even later than usual.

One day appears on printed annual calendars every year. It is called the summer solstice or the first day of summer. This special astronomical event is unaffected by our efforts to postpone scheduled activities to conform with the vagaries of daily weather. Among many special days on our annual calendars, the summer solstice has special appeal for science minded folk—in particular the astronomy minded.

Most people realize the date on or close to June 21 is the longest day of the year—longest in terms of daylight. But it is the longest day of the year only for people in the Northern Hemisphere. At the Equator, 12-hour days and nights persist all year long. The longest Northern Hemisphere day is longer than the second or third longest day by only a few seconds. Sunrise and sunset times change very little for several days. After a few weeks we may take note of the slowly diminishing day length.

The Summer Solstice is the date on which the sun seems to “stand still.” We know that our Sun, when viewed each day at noon, appears to creep higher and higher in the sky between December and March. The sun appears to ascend from south to north on the ecliptic, the apparent annual path of the sun. Between March and June, the sun continues to ascend northward in the sky, beyond the celestial equator, an imaginary line formed in the sky by extension of Earth’s equator. The sun ascends to its farthest northward position on June 21. On that date the Sun appears to stand, or stop moving farther north. Technically, the sun “stands still” only momentarily, and the sun’s apparent movement slowly begins to resume its slow southward journey. Daylight begins to shorten.

We may derive literal meanings from the Latin. Sol means “sun.” Stice means to “make stand” or “to stop.” Literally, solstice means “the sun stands still,” but only briefly when its northernmost or southernmost position has been reached. During December, “winter solstice” is also noted on our printed calendars when the sun reaches its southernmost distance from the celestial equator, a permanent reference point in the sky based on the plane of Earth’s Equator. For Southern hemisphere residents, the sun stands still for a brief time on December 21 this year. It will be their summer solstice!

Viewed from any spot on Earth, the Sun seems to advance northward in the sky, then southward, a total range of 47º during the calendar year. If Earth’s axis were tilted 0º instead of 23.4º, the Sun would appear at the same noontime elevation above the horizon daily. The lengths of day and night would be virtually identical all year long, assuming the Earth’s orbit was perfectly circular. There would be no seasons on our planet. Last year we included a discussion of seasons. For your reference, we link…

The Northern Hemisphere’s winter solstice occurs on December 21 in 2018. Three months later the Vernal Equinox occurs on March 20, 2019, while the Autumnal Equinox will occur on September 22, 2018. On Equinoxes, day and night lengths are exactly the same all over the world. Astronomy enthusiasts become enthralled with the majestic subtleties of our grand Solar System. From a theological perspective, we propose that these majestic subtleties provide countless divine benefits to humanity as well as an opportunity to stretch our understanding of how the cosmos works.