Reference for Eruvin 111:11

ואמר שמואל אין לך תקופת ניסן שנופלת בצדק שאינה משברת את האילנות ואין לך תקופת טבת שנופלת בצדק שאינה מייבשת את הזרעים והוא דאיתליד לבנה או בלבנה או בצדק:

and sometimes turns about.<span class="x" onmousemove="('comment',' Sc. hidden from view as if it turned about behind the North.');">²⁰</span> R'Mesharsheya stated: These rules<span class="x" onmousemove="('comment',' On the points of sunrise and sunset.');">²³</span> should be disregarded for it was taught: The sun has never exactly risen in the North East and set in the North West, nor has it ever risen precisely in the South East and set in the South West. Samuel stated: Thee vernal equinox occurs only at the beginning of one of the four quarters of the day<span class="x" onmousemove="('comment',' Sc. the solar day of twenty-four hours, which includes both day and night.');">²⁴</span> viz. , either at the beginning of the day or at the beginning of the night or at midday or at midnight.<span class="x" onmousemove="('comment',' The year consists of three hundred and sixty-five days and six hours approx., representing fifty-two weeks and one and a quarter solar day's. The first vernal equinox which, according to tradition, occurred on the first of Nisan, which was then a Wednesday at the beginning of the first quarter of the solar day, i.e., at the 'beginning of the night' (solar days in the Heb. calendar beginning with nightfall) was consequently followed in the second year by a vernal equinox that began at the beginning of a second quarter of the solar day which was the 'midnight' of Thursday');">²⁵</span> The summer solstice only occurs either at the end of one and a half, or at the end of seven and a half hours of the day or the night.<span class="x" onmousemove="('comment',' The period intervening between an equinox and the following solstice and between a solstice and the following equinox is, as stated infra, ninety-one days and seven and a half hours approx., representing thirteen weeks and seven and a half hours. When the first vernal equinox occurred at the beginning of a Wednesday (cf. prev. n.) the following summer solstice must have occurred thirteen weeks later at the end of seven and a half hours after the beginning of the night belonging to that Wednesday. When the second vernal equinox occurred at the midnight of Thursday the summer solstice must have occurred thirteen weeks later at the end of one and a half hours after the beginning of the day also a Thursday. Since the third vernal equinox occurred on a Friday at the beginning of the day the following solstice must have occurred thirteen weeks later at the end of seven and a half hours of the day also a Friday. Finally when the fourth vernal equinox occurred at midday on Saturday, the following solstice must have occurred at the end of one and a half hours of the night of the Sunday thirteen weeks later.');">²⁶</span> The autumnal equinox only occurs at the end of three, or nine hours of the day or the night,<span class="x" onmousemove="('comment',' This is obtained by dropping the thirteen complete weeks (cf. prev. n.) which do not affect the weekday or the hour, and by adding the seven and a half hours to the respective summer solstices (cf. prev. nn.) .');">²⁷</span> and the winter solstice only occurs at the end of four and a half, or ten and a half hours of the day o the night.<span class="x" onmousemove="('comment',' These calculations are arrived at by dropping the weeks and adding the hours (cf. prev. n.) to the respective times of the autumnal equinoxes, the same process as in the previous cases being repeated every four years.');">²⁸</span> The duration of a season of the year<span class="x" onmousemove="('comment',' I.e., the lapse of time between an equinox and a solstice that follows it, and between a solstice and an equinox that follows it.');">²⁹</span> is no longer than ninety-one days and seven and a half hours; and the beginning of one season is removed from that of the other by no more than one half of a planetary hour.<span class="x" onmousemove="('comment',' Every hour of the day is assumed to be governed by the sun, the moon or one of the undermentioned planets in the following order: Mercury, Moon, Saturn, Jupiter, Mars, Sun and Venus. It follows that every eighth hour is under the influence of the same heavenly body. Since, for instance, Mercury is in ascendancy in the first hour of the first day of the week, it is also in ascendancy in the eighth, the fifteenth and the twenty-second hour and so on ad infinitum. Similarly Venus who is in ascendancy in the seventh hour of the first day of the week is also in ascendancy in the fourteenth and the twenty-first hour etc. Now since the beginning of one season is removed from that of the next season (as stated supra) by thirteen weeks and seven and a half hours and since in every week (consisting of 7 X 24 hours) the same relative order and succession of the heavenly bodies is invariably repeated, the weeks may be entirely disregarded in the calculations that determine what heavenly body would exercise its influence at the beginning of a season. The seven and a half hours only having to be taken into consideration, and the number of heavenly bodies concerned being seven, it follows that the same heavenly body that was in ascendancy at the beginning of a season is again in ascendancy during the last half hour of that season and during the first half hour of the season that follows. Every season thus begins 'one half of a planetary hour' later than the preceding one.');">³⁰</span> Samuel further stated: The vernal equinox never begins under Jupiter<span class="x" onmousemove="('comment',' Sc. the hour under the influence of this planet (cf. prev. n.) .');">³¹</span> but it breaks the trees, nor does the winter solstice begin under Jupiter but it dries up the seed. This, however, is the case only when the new moon occurred in the moon-hour or in the Jupiter-hour.<span class="x" onmousemove="('comment',' Sc. the hour under the influence of this planet (cf. prev. n.) .');">³¹</span>

Jastrow