posted
Next week, Jews will recite Birkat HaChama, the blessing for the world being created. The idea is that the sun will return to exact same place it was created, so we give thanks for creation. This blessing is only recited every 28 years.
Now clearly, the sun is moving through space, so it's not the exact same place in a galactic frame of reference. But I'm wondering if there is any scientific evidence of a solar cycle that is 28 years, perhaps in reference to the Earth.
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The 28 year cycle is based on the assumption that it take exactly 365 days and 6 hours for the earth to complete one revolution around the sun. This might sound familiar as it is also the basis for the Julian calendar.
The idea is that the sun will be in the exact place, in relation to the earth, on the same day of the week that it was created, the fourth day (Wednesday).
But, to make it really interesting, the opinion that the world was created in Nisan/the spring is one we don't really hold by. We really think that creation happened in Tishrei, hence all the Rosh Hashana prayers that say "hayom hora'at ha'olam" (today the world was created).
quote:Originally posted by adenam: The idea is that the sun will be in the exact place, in relation to the earth, on the same day of the week that it was created, the fourth day (Wednesday).
Right. So it is only a 28-year cycle because of the interaction between the 365.25 day year (a natural phenomenon) and the 7 day week (a wholly artificial construct, or a spiritual one if you prefer).
I would not expect this to have any more relationship to a physical solar cycle than the 19-year cycle of the Jewish calendar. Maybe less.
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But the 19 year cycle of the Jewish calender is related to a physical lunar/cycle. Its known as the Metonic cycle It is the length of time that it takes for the moon to return to the same point in the sky.
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If there a solar equivalent to the Metonic cycle?
I understand that by playing with the calendar, you can get 28 years. But is there anything that an astronomer would see that would back up the idea that after 28 years the sun returns to the same spot?
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quote:Originally posted by Armoth: Wiki says the Vernal Equinox is Mar 20th...How did we get April 8th?
Birkat hachama goes according to the Julian calendar (365 days, 6 hours) but we now use the Gregorian calendar (365 days, 5 hours, 49 minutes and 12 seconds). Those 10 minutes and 48 seconds make a big difference over several thousand years.
It's also why we are way off in changing to "v'tein tal umatar l'bracha"
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is there any halachic/hashkafic literature that you know of to explain why we continue this practice even though there is a discrepancy of about 20 days?
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The only (scientific) solar cycle I know of has an 11 year cycle, or 22 years if you consider that the polarity of the sun changes at the end of every 11 year cycle. Galactically it takes I think 230 million years for the Solar System to make one revolution around the center of the galaxy, putting it back literally in the same spot in the galactic sense.
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quote:Originally posted by Minerva: If there a solar equivalent to the Metonic cycle?
I understand that by playing with the calendar, you can get 28 years. But is there anything that an astronomer would see that would back up the idea that after 28 years the sun returns to the same spot?
I'm not sure what you mean. What an astronomer would see is the position of the sun relative to stars as viewed from the earth. Of course its not actually the sun that is moving, its the earth. The movement of the sun within the galaxy is very slow in comparison to the human life span so we can neglect that. The time it takes for the sun to come to the position in the sky relative to the stars is (to a first approximation) 1 year. That's the time it takes for the earth to move back to same position.
The Metonic cycle is different because the moon is orbiting the earth as it orbits around the sun. Because the length of time it takes the earth to orbit the sun isn't evenly divisible by the length of time it takes the moon to orbit the earth, after one year the earth will have returned to its starting position, but the moon won't be in the same point in its orbit. The earth has to orbit the sun 19 times before the moon is roughly in the same position again.
So a metonic cycle is a combined cycle of both the moon and the sun (or more precisely the moon and the earth).
If you want to get more precise, the moon doesn't technically orbit the earth. The moon and earth both orbit around their combined center of mass (which is about 3/4 of the earth's radius from the center of the earth). So the earth doesn't come back to the same position in its orbit for 19 year either, but that difference is small enough it would not have been noticeable to greek astronomers.
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quote:Originally posted by Armoth: is there any halachic/hashkafic literature that you know of to explain why we continue this practice even though there is a discrepancy of about 20 days?
On the halachic side, I think you can chalk that up to the lack of a central Rabbinical authority that can do anything about it.
On the hashkafic side, I'd be tempted to answer "enough with the chumras, people; ein ladavar sof. There are supposed to be limits to how obsessive halacha gets." But take that with a pillar of salt.
["Chumras" means "stringencies"; "ein ladavar sof" literally means "there's no end to it," and is idiomatically equivalent to "that way lies madness."]
quote:The movement of the sun within the galaxy is very slow in comparison to the human life span so we can neglect that.
Eh. Even over 70 years it would likely be measureable with modern instruments. (You know, the kind used for nanosecond time differences when checking general relativity.) Over two or three thousand, a sufficiently obsessive people might well be justified in not neglecting it.
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quote:Originally posted by adenam: But, to make it really interesting, the opinion that the world was created in Nisan/the spring is one we don't really hold by. We really think that creation happened in Tishrei, hence all the Rosh Hashana prayers that say "hayom hora'at ha'olam" (today the world was created).
I wouldn't go quite that far. There's no particular reason to privilege Rosh Hashana over Birchas HaChama as evidence that "we hold" one way or the other, and you'll find authorities on both sides of this question. I'd say we actually go with both.
(I also seem to remember there being a way of dealing with that particular bit of liturgy other than simply pointing to competing bits, but alas, all my machzorim are in storage over four hours from where I currently live.)
[Also, I'm adding a link to my previous post in a moment.]
quote:Over two or three thousand, a sufficiently obsessive people might well be justified in not neglecting it.
But since no human culture (obsessive or otherwise) has persisted anywhere near that long, I stand by my original statement.
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quote:Over two or three thousand, a sufficiently obsessive people might well be justified in not neglecting it.
But since no human culture (obsessive or otherwise) has persisted anywhere near that long, I stand by my original statement.
Well. The Torah has certainly been around in roughly its current form for a millennium or so, and it's a religious ritual we are discussing.
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quote:Well. The Torah has certainly been around in roughly its current form for a millennium or so, and it's a religious ritual we are discussing.
Yes, I think there is credible evidence that the Torah is thousands of years old but we aren't talking about just the book, we are talking about the culture. And while I recognize that some Jews believe that their religious rituals are unchanged since the time of Moses (*), historic evidence does not support those claims. For example, the current Jewish calendar has only been in use since the 4th century CE.
(*) I should add that this is not a criticism of Jewish beliefs. I have a great deal of respect for Judaism but as with all religions there is a gap between the claims accepted by believers and the claims that can be substantiated independently. As a non-Jew, I am naturally skeptical as I am sure you are skeptical of many of the claims made by my religion.
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quote:Originally posted by The Rabbit: But the 19 year cycle of the Jewish calender is related to a physical lunar/cycle. Its known as the Metonic cycle It is the length of time that it takes for the moon to return to the same point in the sky.
I know. (Although I didn't know it had a name. Cool!)
Hence the "maybe less".
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quote:For example, the current Jewish calendar has only been in use since the 4th century CE.
In its final form, this is pretty much true, and relevant... but even putting aside the fact that the calendar was hardly invented from scratch at that point, I'd quibble with the assertion that more than 1600 years isn't "anywhere near" 2000. Posts: 884 | Registered: Mar 2005
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quote:In its final form, this is pretty much true, and relevant... but even putting aside the fact that the calendar was hardly invented from scratch at that point, I'd quibble with the assertion that more than 1600 years isn't "anywhere near" 2000
Once again, I'm talking about the culture, and the none of currently existing Jewish cultures are any where near that old.
Consider for example language (a central component of any culture). Yiddish is at most a thousand years old as a language, but over the last 50 years its virtually disappeared. Modern Hebrew is a language that isn't even one century old.
Yes some components of the modern Jewish cultures are very old, but others are very new. I didn't claim that no component of a human culture was ancient, my claim that no human culture has persisted for anywhere near 2 to 3 thousand years. Persistence of a part of the culture is not the samething as persistence of the culture as a whole.
Oh, and the original context of this was in regard to whether movement of our solar system within our galaxy was negligible within the context of religious ritual. Are there any Jews who feel that it would are suggesting that the fractions of a second should inserted in the calender at thousand year intervals to preserve the integrity of the Jewish holidays?
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quote:Originally posted by The Rabbit: Once again, I'm talking about the culture, and the none of currently existing Jewish cultures are any where near that old.
Yes, you can define "culture" more narrowly -- a case can be made that no culture lasts more than a generation, if you want to go down that semantic road -- but I hardly think that's at all relevant to KoM's argument. You're introducing a red herring and giving it central importance.
By your own logic, the calendar's been in use over 1600 years. This is more than enough time for its users to notice discrepancies and tinker with it if they were so inclined... and as KoM pointed out, it wouldn't have taken nearly that long. Lack of longevity is simply not a factor here.
Edited to address what you edited your post to add...
quote:Originally posted by The Rabbit: Oh, and the original context of this was in regard to whether movement of our solar system within our galaxy was negligible within the context of religious ritual. Are there any Jews who feel that it would are suggesting that the fractions of a second should inserted in the calender at thousand year intervals to preserve the integrity of the Jewish holidays?
Well, no, but that's a separate issue entirely. The claim you contested was that the difference would be observable even in a 70-year period and certainly in a longer one, and that "a sufficiently obsessive people might well be justified in not neglecting it." Sure, one might question whether the Jews are sufficiently obsessive, or whether they might opt to disregard it anyway, just as we choose to ignore even larger issues than that. But that has absolutely nothing to do with longevity.
quote:Originally posted by Armoth: Wiki says the Vernal Equinox is Mar 20th...How did we get April 8th?
Birkat hachama goes according to the Julian calendar (365 days, 6 hours) but we now use the Gregorian calendar (365 days, 5 hours, 49 minutes and 12 seconds). Those 10 minutes and 48 seconds make a big difference over several thousand years.
It's also why we are way off in changing to "v'tein tal umatar l'bracha"
But you haven't been using the calender for several thousand years. It only goes back 1600 years. By my calculation you should only be off by 12 days not 19.
I've noted that the start of passover always coincides with a full moon and never the actual vernal equinox. I suspect that the discrepancy is the result of using lunar months with some years having 12 and others 13, and has nothing to do with the difference between the Gregorian and Julian calendars.
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quote:By your own logic, the calendar's been in use over 1600 years. This is more than enough time for its users to notice discrepancies and tinker with it if they were so inclined... and as KoM pointed out, it wouldn't have taken nearly that long. Lack of longevity is simply not a factor here.
Actually, what KoM noted is that using modern technology that allows for measurement of nanosecond times scales, the movement of the sum with respect to the rest of the galaxy might be measurable in a 60 to 70 year time period. I can neither confirm nor deny this.
But the context here is how long it takes for the moon to appear in the same position relative to the stars. The other factors that make the 19 year estimate off are far far far greater than the nearly undetectable movement of our solar system through the galaxy. Even on a scale of a couple thousand years, this movement would not be big enough to cause discrepancies in the calendar. Perhaps over millions of years.
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quote:Originally posted by The Rabbit: But you haven't been using the calender for several thousand years. It only goes back 1600 years. By my calculation you should only be off by 12 days not 19.
Once again, that's when the system was finalized (arguably; some date the finishing touches even later) not when it started. Or are you really claiming Hillel II didn't draw on any precedent at all, but invented the whole thing from whole cloth?
[Edited to name the right Hillel.]
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posted
So bottom line, there is nothing to make us believe that there is a 28 cycle of any type related to the sun.
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quote:Originally posted by The Rabbit: Even on a scale of a couple thousand years, this movement would not be big enough to cause discrepancies in the calendar. Perhaps over millions of years.
Now, see, that's a better argument. Posts: 884 | Registered: Mar 2005
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quote:Originally posted by Minerva: So bottom line, there is nothing to make us believe that there is a 28 cycle of any type related to the sun.
I don't think anyone claims otherwise. And if there were, you know Aish would. They still do Codes seminars. Posts: 32919 | Registered: Mar 2003
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quote:Originally posted by Minerva: So bottom line, there is nothing to make us believe that there is a 28 cycle of any type related to the sun.
The 19 year cycle is a product of the 29.5 day lunar cycle and the 365.25 day solar cycle.
The 28 year cycle is a product of the 7 day week and the 365.25 day solar cycle. But unlike the Metonic cycle, the 7 day week is not reflective on any astronomical phenomenon (at least to my knowledge) so there is no astronomical significance to the 28 year cycle.
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quote:Originally posted by rivka: Pesach always falls on a full moon. It begins on the 15th day of the lunar month.
Is that because they didn't have electric lights back then, and needed the moonlight to travel safely?
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quote:Originally posted by rivka: Pesach always falls on a full moon. It begins on the 15th day of the lunar month.
Thanks for confirming that.
I still haven't figured out why you think it should fall on the equinox.
I didn't, but Armoth asked
quote:Wiki says the Vernal Equinox is Mar 20th...How did we get April 8th?
adenam suggested this was because of error accumulated from the inaccuracy of the Julian calendar but since Pesach begins at sundown April 8, I presumed that the you got to April 8 (rather than March 20) because the date was set based on a lunar calendar rather than a solar calendar. Hence the discrepancy had nothing to do with the minor inaccuracy of presuming the year is 365.25 days long.
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Ah. Arnoth wasn't talking about Pesach there; he was talking about Birchas HaChama. That the one falls the evening after the other on this cycle is a coincidence.
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Ah, I had incorrectly presumed that since Birchas HaChama fell on the day before Pesach, the two were connected. My mistake.
According to wikipedia, Birchas HaChama was original on March 25 and the movement to April 8 is indeed due to the differences between the Julian and Gregorian calendars.
I'm curious. Historically, it seems that it has been common to add and subtract days from the Jewish calendar to keep it in sync with the solar year. Is there some reason this hasn't been done to keep Birchas Hachama synchronized with the vernal equinox. Does this reflect some sort of rigidification of Jewish practices, greater difficulty in achieving consensus among Rabbis today or something else? If this same system had been practiced since for all 5769 years of the Jewish calendar, you'd now be off by over 43 days and be celebrating the equinox in May. If it continued for 12,000 years, you'd be celebrating the equinox at the summer solstice.
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quote:Originally posted by rivka: Pesach always falls on a full moon. It begins on the 15th day of the lunar month.
Thanks for confirming that.
I still haven't figured out why you think it should fall on the equinox.
I think there's some confusion with Easter, which more or less falls on the first Sunday after the first full moon after the vernal equinox. I looked this up online and there's a little slop there due to standardization efforts and whether you are using the Gregorian or Julian calendar or are East Orthodox. There's also some debate about whether the Last Supper was a seder, so that adds to the confusion as well.
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quote:I think there's some confusion with Easter, which more or less falls on the first Sunday after the first full moon after the vernal equinox.
No, my confusion was solely because this year "Jewish Equinox" falls the day before the beginning of Pesach this year. I presumed that two were linked and since Pesach is celebrated based on a lunar calendar and I presumed that the "Jewish Equinox" also followed a lunar calendar. It turns out it is merely coincidence that the two coincide this year.
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The confusion is not only here, I'm afraid. Many of my peers (who know little of Birkas Hachama since it has never happened in their lifetime)believe that the equinox is always supposed to fall out on the 14th of the lunar month, Nisan (the day before Pessach) every 28 years.
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quote:Originally posted by The Rabbit: According to wikipedia, Birchas HaChama was original on March 25 and the movement to April 8 is indeed due to the differences between the Julian and Gregorian calendars.
I'm curious. Historically, it seems that it has been common to add and subtract days from the Jewish calendar to keep it in sync with the solar year. Is there some reason this hasn't been done to keep Birchas Hachama synchronized with the vernal equinox. Does this reflect some sort of rigidification of Jewish practices, greater difficulty in achieving consensus among Rabbis today or something else? If this same system had been practiced since for all 5769 years of the Jewish calendar, you'd now be off by over 43 days and be celebrating the equinox in May. If it continued for 12,000 years, you'd be celebrating the equinox at the summer solstice.
It is definately harder than it was to enact changes in Jewish Law. Rabbis today do not hold the same power that rabbis 2000 years ago had. The real smicha, the direct chain of transmission started by Moses, was lost due to persecution. Now it is basically taboo to argue with any laws perscribed by the talmud as those rabbis either had real smicha or were closer in time to those who did. Since Samuel enacted that this is the way to calculate the cycle for birkat hachama in the Talmud, we cannot really change it. Similarly, those of us unfortunate enough to be living outside of Israel cannot take away the extra day that was added on to holidays celebrated outside of Israel that we must observe because it was unsure of when the new moon would have been seen over Jerusalem, even though modern astronomy could tell us exactly when it is.
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Gevalt, Armoth. I'm not sure whether to be more irritated with their Judaic teachers or their science teachers.
Birkas haChamah is not any kind of equinox. Just as one can celebrate Shabbos every seventh day without believing in a literal 7-day creation, I will say Birkas haChamah without believing in a literal 28-year cycle.
Rabbit, changing the calendar would require a Great Sanhedrin. And despite attempts in Israel, that does not currently exist. Not one that is accepted by the majority of practicing Jews, certainly.
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On a related note. Easter (in the West) falls on the first Sunday following the first full moon following the vernal equinox. Most of the time, this puts Easter on Sunday during the week of Pesach, but not always.
In looking through a table of Easter and Pesach dates, it appears that whenever the full moon occurs between March 21 and March 25, Pesach begins one lunar cycle after Easter but the data I looked at was limited. I know that Pesach is determined based on the Jewish calendar, but I'm curious. If I assume that Pesach would begin on the date of the first full moon after March 25, would I always be right?
Also, the date of March 25 caught my attention since it is the orginal date of Birkas haChamah and was the date of the Vernal Equinox when the Julian Calendar was first introduced. I'm wondering if this is just a coincidence or if there is a causal relationship.
(Not that it makes any difference, I'm just curious).
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posted
On a tangential note, why humans typically start the year with the Vernal Equinox rather than the Winter Solstice? It just seems like we'd go by when the sun reaches its minimum and starts going back the other way, rather than when it's already halfway back, you know? Even though the weather lags behind the sun.... still.... it's the SUN. Does that seem weird to anyone else?
I guess because of calendar drift, our new year starts fairly close to the solstice, but all the astronomical systems start at the vernal equinox as zero point, and most calendar years do too (including ours originally before it drifted, if I am recalling correctly).
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quote:The sources in halachah, the background mathematics, and the meaning of this blessing will be explored in the coming chapters, with the help of He who imparts understanding to man.
Did Ron help write that?
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