Just in case you might miss it, take note that the summer solstice will occur on Wednesday at 4:57 a.m. as the sun reaches its northernmost point of 23.26 degrees latitude in its annual journey through the sky.

As seen from our vantage point on Earth the sun appears to move along the horizon at sunrise and sunset from day to day. Over the course of a year sunrise will oscillate between northeast and southeast like a flat pendulum, while sunset does the same between northwest and southwest.

As seen from space the sun’s apparent movement would trace out the ecliptic on Earth’s surface due to the 23.26-degree tilt of Earth’s rotational axis to its orbital plane.

The movement is accompanied by changes in the sun’s arc through the sky, which is most northerly in June and most southerly in December. This corresponds with the longest and shortest days due to the arc’s greatest length in June and shortest in December.

The solstices are reversed in the Southern Hemisphere with June being the winter and December being the summer.

Like a pendulum, a time-lapse movie of the sun’s position along the horizon throughout the year would be fastest in March and September at the equinoxes as the sun overhead crosses the equator.

The word “solstice” is French, derived from Latin “solstitium.” “Sol” is Latin for sun, as in solar. Stice is a diachronic variation from the Latin “sistere,” to “stand still,” from which we also get “static,” “stasis” and “assist.”

The sun literally stands still as it sits at nearly the same point on the horizon for two weeks, like a slow pendulum at the top of its swing.

From June 14-29 it varies only one-tenth of a degree, or about one-fifth of the sun’s diameter. This compares with the daily movement at the fastest part of the movement, the equinoxes, of two-tenths of a degree per day or nearly one-half of the sun’s diameter every day.

The imperceptible daily movement at the solstice is not visible with the naked eye, which is the main reason why our ancient ancestors had a hard time figuring the exact number of days in a year. The fact that there are actually slightly less than 365-1/4 days in a year made it even more difficult.

The Gregorian calendar solved that problem by modifying the ancient Julian calendar. It took away one leap year each century and ignored one each millennium.

Without leap year the dates of the solstices and of the corresponding equinoxes would shift forward six hours each year, gaining a day every four years. With leap year the date jumps back one day, bringing the calendar in sync with the sun.

In Hawaii, we also note “Lahaina noon,” which occurs on May 26 in Honolulu as the noon sun passes overhead on its northward journey.

With less notoriety, the sun passes overhead again on July 18 as it moves southward to cross the equator at the September equinox.

The technology of timepieces and calendars masks the complexity of the sun’s annual motion such that we barely take notice its height in the sky or the location of sunrise and sunset.

Richard Brill is a retired professor of science at Honolulu Community College. His column runs on the first and third Fridays of the month. Email questions and comments to brill@hawaii.edu.