8 Let us return to the words which follow. “Let them be for signs and for seasons and for days and years.” We have spoken about signs. By times, we understand the succession of seasons, winter, spring, summer and autumn, which we see follow each other in so regular a course, thanks to the regularity of the movement of the luminaries. It is winter when the sun sojourns in the south and produces in abundance the shades of night in our region. The air spread over the earth is chilly, and the damp exhalations, which gather over our heads, give rise to rains, to frosts, to innumerable flakes of snow. When, returning from the southern regions, the sun is in the middle of the heavens and divides day and night into equal parts, the more it sojourns above the earth the more it brings back a mild temperature to us. Then comes spring, which makes all the plants germinate, and gives to the greater part of the trees their new life, and, by successive generation, perpetuates all the land and water animals. From thence the sun, returning to the summer solstice, in the direction of the North, gives us the longest days. And, as it travels farther in the air, it burns that which is over our heads, dries up the earth, ripens the grains and hastens the maturity of the fruits of the trees. At the epoch of its greatest heat, the shadows which the sun makes at mid-day are short, because it shines from above, from the air over our heads. Thus the longest days are those when the shadows are shortest, in the same way that the shortest days are those when the shadows are longest. It is this which happens to all of us “Hetero-skii” (shadowed-on-one-side) who inhabit the northern regions of the earth. But there are people who, two days in the year, are completely without shade at mid-day, because the sun, being perpendicularly over their heads, lights them so equally from all sides, that it could through a narrow opening shine at the bottom of a well. Thus there are some who call them “askii” (shadowless). For those who live beyond the land of spices see their shadow now on one side, now on another, the only inhabitants of this land of which the shade falls at mid-day; thus they are given the name of “amphiskii,” (shadowed-on-both-sides). All these phenomena happen while the sun is passing into northern regions: they give us an idea of the heat thrown on the air, by the rays of the sun and of the effects that they produce. Next we pass to autumn, which breaks up the excessive heat, lessening the warmth little by little, and by a moderate temperature brings us back without suffering to winter, to the time when the sun returns from the northern regions to the southern. It is thus that seasons, following the course of the sun, succeed each other to rule our life.
“Let them be for days” says Scripture, not to produce them but to rule them; because day and night are older than the creation of the luminaries and it is this that the psalm declares to us. “The sun to rule by day...the moon and stars to rule by night.” How does the sun rule by day? Because carrying everywhere light with it, it is no sooner risen above the horizon than it drives away darkness and brings us day. Thus we might, without self deception, define day as air lighted by the sun, or as the space of time that the sun passes in our hemisphere. The functions of the sun and moon serve further to mark years. The moon, after having twelve times run her course, forms a year which sometimes needs an intercalary month to make it exactly agree with the seasons. Such was formerly the year of the Hebrews and of the early Greeks. As to the solar year, it is the time that the sun, having started from a certain sign, takes to return to it in its normal progress.
Source: Nine Homilies of Hexaemeron (New Advent)