Birkat Hachama
Birkat Hachama (ברכת החמה, "Blessing of the Sun") refers to a rare Jewish blessing that is recited to the Creator, thanking Him for creating the sun. The blessing is recited when the sun completes its cycle every 28 years on a Tuesday at sundown. Jewish tradition says that when the Sun completes this cycle, it has returned to its position when the world was created. Because the blessing needs to be said when the sun is visible, the blessing is postponed to the following day, on Wednesday morning. According to Judaism, the Sun has a 28-year solar  cycle known as "machzor gadol" (מחזור גדול, "the great cycle"). A solar year is estimated as 365.25 days and the "Blessing of the Sun", being said at the beginning of this cycle, is thus recited every 10,227 (28 times 365.25) days. The last time that it was recited was on April 8, 2009 (14 "Nisan" 5769 on the Hebrew calendar.) From an astronomic point of view, there is nothing special to these dates; e.g. the sun, moon, planets and stars will not be aligned in any specific pattern. The text of the blessing itself is as follows: Source of the  practice. The primary source for the institution of "Birkat Hachama" is a "Beraita" mentioned in the "Talmud": The middle of this clause in the "beraita" (elided here) speaks of other astronomical phenomena, the interpretation of which is ambiguous. The "Gemara" clarifies when the 'turning point' (תקופה) mentioned in the "beraita" occurs: Next, the "gemara" explains the basis of the 28 years: This explanation provided by Abaye is based on a ruling of Shmuel also mentioned in the "Talmud": Shmuel stated: The vernal equinox occurs only at the beginning of one of the four quarters of the day, either at the  beginning of the day or at the beginning of the night, or midday or midnight. The summer solstice only occurs either at the end of 1.5 or at the end of 7.5 hours of the day or the night. The autumnal equinox only occurs at the end of 3 or 9 hours of the day or the night. The winter solstice only occurs at the end of 4.5 or 10.5 hours of the day or the night. The duration of a season of the year is no longer than 91 days and 7.5 hours. Shmuel's calculations, however, are imprecise  because the earth does not travel around the sun with a constant speed. His imprecision, according to Abraham ibn Ezra, was a function of the desire of the time to avoid the necessity of manipulating fractions. Codification in Jewish law. The Shulchan Aruch states that this blessing, generally said upon experiencing natural phenomena, should also be recited upon witnessing the "chammah bi-tkufatah" ( = sun at its turning point). This term, quoted from the above-mentioned Beraita, is explained by the Chofetz Chaim as referring to the point in time at which the Sun returns to the start of its  cycle, similar to when it was created. As explained below, the blessing is recited on the morning after the Sun completes its cycle; ideally, it should be recited at sunrise, referred to in Jewish law as "haneitz hachammah". It is preferred to recite the blessing with a multitude of people, in keeping with the principle of "b'rov am hadrat melech". The "Magen Avraham" and the "Levush" insist that it be recited within the first three hours after sunrise. The "Mishnah Brurah", however, states on behalf of numerous "Achronim" that it is permitted the blessing to be recited until "halachic" noon . According to most opinions, the blessing may only be recited if the Sun can be seen. However, if the Sun is completely blocked by clouds, there is a minority view that allows the blessing to be recited nevertheless, because essentially the blessing is on the concurrence of the Sun's physical position with the timing of the day. Overview. According to the Babylonian Talmud, the Sun makes a 28-year cycle to return to the position that it was in when the Universe was first created at the time (Tuesday evening) it was created. According to Jewish tradition, the Sun  was created on the fourth day (, "yom revi'i") of the week of Creation. Because Jewish law considers the time unit of a day to span from evening to evening, the beginning of the "halachic" fourth day, so to speak, is on Tuesday evening at sundown. The 28-year cycle therefore begins and ends at the point in time when the Sun was created, this being sundown on Tuesday. The Sun only returns to this exact position at sundown on a Tuesday once every 28 years. Despite the rigorous calculations that follow, there is no synchronization of this prayer and the  actual astronomical point in time when the sun crosses the celestial equator; the symbolism is no different from a situation in which the "molad" for "Tishrei" would fall out by day on a Sunday and "Rosh Hashanah" falls out on Monday. The vernal equinox. As explained in the Talmud, there is a tradition that the Sun was created in its vernal equinox position at the beginning of the springtime Jewish lunar month of "Nissan". The sages of the Talmud settled disputes over the "halachic" definition of the vernal equinox by establishing it on March 25 of the Julian calendar. Because  both the Julian calendar and Jewish tradition define a solar year as exactly 365.25 days, the "halachic" vernal equinox historically fell out on March 25 every year. This halachic equinox now falls about 17 days after the true equinox, with the error increasing by about 3/4 of a day per century. In summary, "Birkat Hachama" is recited when the halachic vernal equinox (the position at which the Sun was created) occurs at sundown on a Tuesday (the time at which the sun was created). The solar calendar. This method of marking the cycle of "machzor gadol" (that is, using the  25th of March) was invalidated in 1582 when the Julian calendar was replaced by the Gregorian calendar by decree of Pope Gregory XIII. The calendar was adjusted to allow for Easter to be celebrated in the appropriate time according to an agreement reached at the First Council of Nicaea in 325 CE. To recalibrate the calendar, two adjustments were made: The last day of the Julian calendar was Thursday, 4 October 1582 and this was followed by the first day of the Gregorian calendar, Friday, 15 October. Thus, while the halachic vernal equinox occurred on March 25 until 1582, in  1583 it occurred on April 4 of the new Gregorian Calendar. However, the Jewish calendar was in no need of such a modification, and remained uninfluenced by it. As a result, the "halachic" vernal equinox has been shifting slightly forward in the Gregorian year ever since 1582. The "halachic" equinox usually jumps a day every century because the algorithm that established the Gregorian calendar dictates that leap years do not occur in years divisible by 100, unless also divisible by 400. Jewish law, however, provides no means for changing the established calendar until such a time as the Sanhedrin might  be reconvened, and compensates for it by moving the date of the equinox almost every century. There was no shift between 1909 and 2009, however, because of the exception regarding years divisible by 400; thus, the year 2000 did contain a February 29 and no compensation was necessary. The table at right depicts all the vernal equinoxes from 1981 to 2009, two years in which "Birkat Hachama" occurs; note that the equinox does not occur at sunset (time=0) on the fourth day (Tuesday) any other years in the entire 28-year cycle. The "halachic" year of 365.25 days is equivalent  to 52 weeks, 1 day and 6 hours. This means that any given date will, three times out of four, appear a day later in the calendar week in a subsequent year. For example: July 3, 1936, however, was on a Friday and not a Thursday because the six hours that accrued over each of the four years effectively adds another calendar day (i.e. 6 hours × 4 years = 24 hours = 1 day). "Halacha" maintains that the Sun was created in the position of the vernal equinox immediately after sundown on the fourth day of the week of  Creation, which is equivalent to sunset on Tuesday of that week. If that is considered time zero (t=0), and subsequent years' vernal equinoxes occur one day and six hours later, it would appear as follows: Every four years sees a jump of an additional day because the four six-hour periods sum to a full day. This is somewhat similar to a solar leap year occurring every 4 years to account for the four quarter days that accrued at a rate of a quarter day per year. Although the proper time for the blessing would be at sundown on Tuesday  April 7, the Sun is no longer visible at sundown; the blessing is therefore delayed until the following morning. The 28-year cycle is based on a solar year of 365.25 days, which is only nearly precise. The Hebrew calendar itself uses a solar year of 365.2468222 days, but utilizes the less precise approximation of 365.25 for Birkat Hachama so that the blessing might occur with some frequency. See also Hebrew calendar: Accuracy. How the date is calculated. This table represents a week with all the 24 hours marked and labeled by the "planet", actually a celestial light in direct  translation, which corresponds to them according to the ancient geocentric model of "planet" order. It is based on Rashi's commentary to "Eruvin" 56a. We create this table by noting that in the Bible the stars were created on Wednesday at twilight so we place Saturn (the first "star") at hour 1 (or 6:00 p.m.). Then we follow with all the six other "planets" (Jupiter, Mars, Sun, Venus, Mercury, and Moon) and repeat the order until all the hours of the week have a "star" assigned to them. We assume the world was created in the Hebrew month of "Nissan , not Tishrei". So hour 1 (sunset) on Wednesday on this chart represents the beginning of "Tekufat Nissan" (Spring) in the first year of creation, the Hebrew year 1. For the purpose of "Birkat Hachama", the calculation of Samuel of Nehardea for the length of a tropical year is used not the more accurate calculation of "Adda bar Ahavah". Therefore, a year is assumed to be 52 weeks and one day and six hours (365.25 days). This means that a year after creation "Tekufat Nissan" will occur one day and six hours later on this chart, or on Thursday at the  sixth hour, Jupiter. Each year this will shift another day and six hours. It will take 28 years for "Tekufat Nissan" to return to being on Wednesday at twilight. It is worth noting that the true spring equinox occurs on March 21 yet "Birkat Hachama" is said 18 days later. This inaccuracy accrued over thousands of years as a result of using the inexact calculation of Samuel for the length of the year. Order of the service. The service generally includes: The "Shehecheyanu" blessing is not recited. There is no obligation to say "Birkat Hachama": it is an opportunistic blessing  recited only if one happens to see the sun in this state; such blessings (another example is the annual blessing upon seeing flowering fruit trees in Nisan) receive no "Shehecheyanu". Those who do recite "Shehecheyanu" should take care to wear a new garment or have a new fruit close by, to remove all doubt. Occurrences of "Birkat Hachama". Occurrences in the last 120 years: "Birkat Hachama" will occur next on Note: Because the dates for "Birkat Hachama" assume a 365.25-day solar year and the Julian calendar also assumes a 365.25-day solar year, "Birkat Hachama" will always fall on  March 26 in the Julian calendar. While "Birkat Hachama" usually occurs in the Jewish lunar month of "Nissan", this is not always the case; it will occur on 29 "Adar" II (April 10) in the year 2233. Lerman's thesis. Moshe Lerman suggested a background to "Birkat Hachama" by pointing out a possible connection between the traditional Hebrew dating and the two "machzorim" ("cycles") that are observed in Jewish tradition—the "small" 19-year cycle which is the basis of the Jewish calendar, and the "big" 28-year cycle which determines the year in which "Birkat Hachama" is recited. Mathematically , if one knows the position of a certain year in both cycles, one can compute the number associated to the year modulo 532 (19 times 28), given that the starting point of both cycles is year 1. Because the astronomical year is slightly shorter than 365.25 days, the date of "Birkat Hachama" shifts away from the spring equinox as history proceeds. A simple astronomical calculation shows that 84 cycles of 28 years before 5769, in the Jewish year 3417, the spring equinox was in the beginning of the night before the fourth day of the week as stipulated by the  Talmud. Lerman takes this as a hint that the astronomically astute Jewish sages of the time concluded that the Jewish year 3417 was a first year in the cycle of 28 years. Moreover, Lerman suggests that these same Jewish sages would have reasoned that year 3421 was a first year in the 19-year cycle, in accordance with an ancient tradition that the world was created in the first week of the month of "Nissan", and thus the sun was created on the fourth day of "Nissan". Since every 19 years the solar and lunar calendars align, and the Spring  equinox of 3421 occurred early in the night leading to the fourth day of the Jewish month of "Nissan", it follows that 3421 was the first year of a 19-year cycle. Lerman surmises that the Jewish sages at the time could argue for a determination of the position of their years in both cycles and could therefore compute the absolute year-count modulo 532 years. They were left with a number of options, 532 years apart from each other, and Lerman suggests that they chose the dating closest to what seemed to be the truth according to a literal  interpretation of biblical accounts. The sages legally defined future equinox times by instituting the 28-year cycle, to protect the Hebrew dating against future change, and to leave a remembrance to what they had done.