The Week Not Marked by Nature.—Only the week, measured by divine command, has no landmark.
The three independent celestial motions—the daily rotation of our globe on its axis, the monthly circuit of the earth by the moon, and the yearly revolution of earth and moon about the sun—mark off our time, but there is no astronomical cycle connected with the seven-day week.
The Year Measured by the Sun.—As our spinning earth, circled continuously by the moon, traverses its vast course around the sun, it makes the circuit of the four seasonal landmarks—the summer and winter solstices and the spring and autumnal equinoxes—to complete what we call a year.
These points do not mark off the year as visibly as the moon does the lunar month, yet even relatively primitive peoples can recognize them by repeated observation of the shadows cast by the sun at rising, setting, and noon throughout the year.
At the summer and winter solstices occur the days of longest and shortest sunlight, when the sun is seen farthest north and farthest south in the sky; at the spring and fall equinoxes, when day and night over the whole globe are equal, the sun rises directly in the east and sets directly in the west.
Today the astronomers in the great observatories train their telescopes on the stars to regulate the time signals that set our clocks.For “God called the light Day, and the darkness he called Night” (Genesis 1:5).As we, on any given spot on this spinning globe, are carried eastward, out of the sunlight and into the shadow, we say that the sun is setting in the west.The ancients needed no clocks to tell them when they passed the boundary line between day and night—sunrise began the day and sunset ushered in the night. Therefore a day in the calendar is measured by one complete rotation of the earth on its axis, including a day and a night. Each full day ran evening-morning, dark-light, night-day (Leviticus ; 22:6, 7; Mark , 32).Also certain other ancient peoples, like the Babylonians, began their day at sunset, although the Egyptians counted from sunrise.The harmony of the time statements in the Scripture strengthens our confidence in the accuracy of the inspired Word, but chronology is not essential to salvation.