The Shulchan Arukh (Orah Chayyim 229:2) rules that when the sun is at its turning point every 28 years on the night of the fourth day of the week (Tuesday night), on the following morning (Wednesday) when seeing the sun one says the blessings, oseh (maaseh) bereshit. This turning point is the vernal equinox, and this is thought to be the location of the sun when it was created. This ruling is based on the Talmud, Berakhot 59b, but the blessing is puzzling for at least four reasons.
One, the Rambam (1963, Guide, 3:45) writes with regard to the Bet ha-Mikdash that, “Avraham defined the direction towards which one would turn in prayer, fixing it exactly in the west. For the Holy of Holies is in the west… In my opinion, the reason for this is as follows: inasmuch as at that time the opinion generally accepted in the world was to the effect that the sun should be worshipped, and that it is the deity, there is no doubt that all men turned when praying towards the east. Therefore, Avraham turned when praying on Mount Moriah – I mean in the Sanctuary – towards the west, so as to turn his back upon the sun.” Yet, with the blessing of the sun we turn towards the sun.
The usual understanding of the blessing is that it is to show that we recognize G-d's control of the natural world, yet the blessing could give the impression that we are praying to the sun, G-d forbid. In our prayers, many of us face east but this in order to face Jerusalem, and only incidentally do we face the sun. Even by our prayers, the Rama (Orah Chayyim, 94:2) writes that the aron in the synagogue should not be directly in the line of the rising sun in order not to face the sun. In fact, the Tosefta (Berakhot 7:10) first records that one is to recite a blessing on seeing the sun, but then quotes R. Yehuda that saying a blessing on the sun is a form of paganism.
The Talmud Yerushalmi (Berakhot 65a, 9:2) and Vayikra Rabbah 23:8 quote the Tosefta, but leave out R. Yehuda's opinion not to say any blessing on the sun. Instead, they quote Rav Huna that the blessing on the sun is only in the rainy season when the sun had not been seen for three days. The Talmud Bavli (59b) quotes the Tosefta but does not quote either R. Yehuda's or Rav Huna's opinion. However, it quotes Abaye's explanation that the blessing is to be said once every twenty eight years.
The Rambam does not quote Rav Huna's opinion, which might be because it was not quoted in the Bavli, but also maybe he was uncomfortable with this blessing which could have been relatively frequent according to Rav Huna. However, he quoted (Mishneh Torah, Laws of blessings, 10:18) Abaye's opinion to say the blessing on the sun once every twenty eight years. The Rif did not quote this law, so why would he codify the law? Furthermore, Michael Morris has pointed out to me that the Rambam (Laws of the New Moon, 10:5) was aware that the calculation of the twenty eight year cycle was problematic (see below). Did the Rambam quote the law since it is said so infrequently? Yet, if it is problematic it should never be said. Maybe the reason why the Rambam quoted the law was because he thought one does not recite a blessing only the phrase baruch oseh bereshit.
The Mishnah (Berakhot 9:1) when referring to all the blessings on unique occasions, just refers to them by the final phrase of the blessing, as for example, oseh maaseh bereshit. Tosfot (Haroeh, 54a) quotes R. Shemayah (France, 11th century, student of Rashi) that all the blessings in the Mishnah and presumably the chapter in the Talmud are to be made with G-d's name (shem u-malchut), "Blessed be you, G-d, our G-d, King of the world," and that Rashi recited the full blessing with G-d's name by lighting. However, the Raavad (1120-1197, pages of Rif Berakhot 44a, comments on the Baal ha-Maor) writes that all the blessings recorded in chapter nine of Berakhot are said without G-d's name. Meiri (1249-1306, on Berakhot 54a, pp.202-205) writes that while the blessing of birkat ha-gomel is recited with G-d's name, the blessing of oseh (maaseh) bereshit is said without mentioning G-d's name. The Meiri also writes that the Rambam believes that all the blessings are said with G-d's name, but this is not clear.
When the Rambam records these blessings he writes the full form of the blessing, "Blessed be you, G-d, our G-d, King of the world..….," as for example by the blessing when a person sees a place where G-d did a miracle to the Jewish people (Laws of blessings, 10:9) or upon seeing the Mediterranean Sea (10:15). However, by the blessings oseh maaseh bereshit and shekocho u-gevurato malei olam, in reference to lighting, thunder, and the sun, the Rambam does not record the full blessing, just the last phrase of the blessing. (The Rambam also omits the word maaseh from the phrase, but this is a separate question.) It is assumed that the Rambam means for one to recite the full blessing with G-d's name even by these blessings, but why did the Rambam not spell this out as he did by the other blessings? Does the Rambam believe that one just says the phrase, oseh maaseh bereshit, without G-d's name? If yes, then one has emasculated the blessing, as Rebi Zera and Rebi Yehuda state in the name of Rav that any blessing that does not include G-d's Kingship is not a blessing, Yerushalmi Berakhot 62b, 9:1. Thus, maybe the Rambam was not bothered by the blessing on the sun since this was not a real blessing because he thought that one does not recite the full blessing with G-d's name on seeing the sun or for that matter by lightning and thunder.
Interestingly, the Tur and the Shulchan Arukh when referring to the blessing, oseh maaseh bereshit by comets, earthquakes, lighting, thunder, great winds (hurricanes?), oceans, rivers and mountains (Orah Chayyim 227:1, 228:1) record specifically that one recites the blessing by invoking G-d's name. However, when they record the blessing by the sun they just record that one says the phrase oseh maaseh bereshit without mentioning that one says the full blessing with G-d's name. Do they also limit the blessing since they are uncomfortable with it or just by the blessing of the sun they felt there was no need to spell out the full blessing?
Two, the Talmud and the Shulchan Arukh record this blessing in conjunction with other astronomical events, such as the movement of the moon, planets with regard to the stars, but we do not recite a blessing for these events, see Mishneh Brurah, 229:9. Rabbi Bleich, in a wonderful book on the blessing, (Bircas haChammah, Brooklyn, NY: Mesorah Publications, 1980, p.67) notes that this discrepancy is curious and he suggests that we bless the sun since the sun in its turning point "is an occasion which readily lends itself to calculation, whereas the others can be determined only with great difficulty." Yet, as we discuss below our calculation of the movement of the sun is incorrect.
Three, we say the blessing in Nisan (see Rambam, above, Mishneh Brurah 229:7) and this is based on the idea that the world was created in Nisan since the timing of the blessing is when it is thought that the sun returns to its location when it was created. However, on our prayers on Rosh Hashanah we state that the world was created in Tishrei and not Nisan. This question is an argument in the Talmud (Rosh Hashanah 10b,11a) that R. Eliezer states that the world was created in Tishrei while R. Yehoshua says it was created in Nisan. It is odd that we are inconsistent with regard to this question, and R. Bleich (pp.63-65) quotes several answers to this question.
Four, the calculation that the blessing is based on is incorrect since the reckoning of twenty eight years is based on the Julian calendar. According to the Julian calendar, the year is 52 weeks and 30 hours, which means that with each passing year, the calendar advances one day and six hours. For example, if the sun was created at 6PM on Tuesday night, then the sun would "return" to that same location the following year at 12AM (midnight) Wednesday/Thursday, and in the following year, 6AM Friday morning. After four years, the sun would "return" to initial location at 6PM, but it would be off by five days, 6PM Sunday instead of 6PM Tuesday. We need seven cycles of four years, twenty eight years, until the sun returns to its initial location both with regard to the hour and to the date, 6PM Tuesday night. Yet, we know that the Julian calendar is wrong since it adds an extra eleven minutes and fourteen seconds to the year. Thus, after twenty eight years the sun is not returning to its initial location, as even within one 28 year cycle there is a discrepancy of 310.57 minutes.
This year the discrepancy is even more apparent than usual since the blessing on the sun is on erev Pesach, while the blessing is meant to be on Rosh Chodesh Nisan, which is supposed to be on the vernal equinox. This discrepancy is because the Jewish calendar is not based on the Julian calendar while the blessing of the sun is still based on the Julian calendar. The Julian calendar was established in 46 BCE, with March 25th being the vernal equinox. This means that the blessing was to be said on March 26th because we start the day at night. The sun was created on the fourth day, which is believed to have begun on Tuesday night (not like the Rashbam on Bereshit 1:4,5), and it is believed that the sun was created at the vernal equinox, which means that Tuesday night was March 25th. We do not say the blessing at night since we cannot see the sun, but wait until the morning which would be March 26th.
March 26th was the day of the blessing until 1582 when the Gregorian calendar was instituted. This calendar fixed the Julian calendar by skipping ten days in 1582 to make the vernal equinox on March 21st and omitting the leap year three times out of 400 years (the years 1700, 1800, 1900, 2100, 2200,…). Of course, we would not accept this change which was declared by a Pope, and hence we had to add ten days to the new Gregorian calendar to return to the "true" Julian calendar. This means that after 1582, the blessing was said on April 5th, which would have been March 26th if the calendar had not been changed. In addition, in the years 1700, 1800 and 1900, the Gregorian calendar was missing three leaps years or three days, and again we have to add three days to our Gregorian calendar, which means that in the 20th and 21st century, the blessing is said on April 8th. In the 22nd century, they will have to add another day, and then the blessing will be said on April 9th.
In conclusion, R. Bleich (p.76) notes that while there is no requirement to say the blessing with a minyan, it is preferable to recite the blessings in the company of a large assemblage since "the glory of the King is in the multitude of the populace," see Mishneh Brurah 229:8. Thus, many are planning to make large gatherings on April 8 to say the blessing, but it seems to me that in view of all the problems with the blessing that it should be said in a low key manner. Furthermore, the Rambam and the Shulchan Arukh only record to say the blessing in the morning but do not specify when in the morning. The Magen Avraham (229:5) writes that one should say the blessing exactly at sunrise, but I think that one should specifically not say the blessing at sunrise to minimize the impression that one is praying to the sun. Finally, further research is needed whether one should say the full blessing with G-d's name or just the phrase oseh maaseh bereshit which is the view of the Raavad, the Meiri and most likely the Rambam, Tur and Shulchan Arukh.