Our calendar to-day is a purely solar one; our months are twelve in number, but of purely arbitrary length, divorced from all connection with the moon; and to us, the Saros cycle does not readily leap to the eye, for eclipses of sun or moon seem to fall haphazard on any day of the month or year.
But with the Hebrews, Assyrians, and Babylonians it was not so. Their calendar was a luni-solar one—their year was on the average a solar year, their months were true lunations; the first day of their new month began on the evening when the first thin crescent of the moon appeared after its conjunction with the sun. This observation is what is meant in the Bible by the "new moon." Astronomers now by "new moon" mean the time when it is actually in conjunction with the sun, and is therefore not visible. Nations whose calendar was of this description were certain to discover the Saros much sooner than those whose months were not true lunations, like the Egyptians, Greeks, and Romans.
There are no direct references to eclipses in Scripture. They might have been used in the historical portions for the purpose of dating events, as was the great earthquake in the days of King Uzziah, but they were not so used. But we find not a few allusions to their characteristic appearances and phenomena in the books of the prophets. God in the beginning set the two great lights in the firmament for signs as well as for seasons; and the prophets throughout use the relations of the sun and moon as types of spiritual relations. The Messiah was the Sun of Righteousness; the chosen people, the Church, was as the moon, which derives her light from Him. The "signs of heaven" were symbols of great spiritual events, not omens of mundane disasters.
The prophets Joel and Amos are clear and vivid in their descriptions; probably because the eclipse of 831 b.c. was within their recollection. Joel says first, "The sun and the moon shall be dark;" and again, more plainly,—
"I will show wonders in the heavens and in the earth, blood, and fire, and pillars of smoke. The sun shall be turned into darkness, and the moon into blood, before the great and the terrible day of the Lord come."
This prophecy was quoted by St. Peter on the day of Pentecost. And in the Apocalypse, St. John says that when the sixth seal was opened, "the sun became black as sackcloth of hair, and the moon became as blood."
In these references, the two kinds of eclipses are referred to—the sun becomes black when the moon is "new" and hides it; the moon becomes as blood when it is "full" and the earth's shadow falls upon it; its deep copper colour, like that of dried blood, being due to the fact that the light, falling upon it, has passed through a great depth of the earth's atmosphere. These two eclipses cannot therefore be coincident, but they may occur only a fortnight apart—a total eclipse of the sun may be accompanied by a partial eclipse of the moon, a fortnight earlier or a fortnight later; a total eclipse of the moon may be accompanied by partial eclipses of the sun, both at the preceding and following "new moons."
Writing at about the same period, the prophet Amos says—
"Saith the Lord God, I will cause the sun to go down at noon, and I will darken the earth in the clear day,"
and seems to refer to the fact that the eclipse of 831 b.c. occurred about midday in Judæa.