Wednesday, October 26, 2011

Sailing the Friendly Skies

Perhaps it was the fact that this week’s Parsha discusses a boat, but there was some interesting astronomical news this week that got me thinking about a certain passage from the Gemara in Horiyos (10a). There, the Gemara relays a story in which Rabban Gamliel and Rebbi Yehoshua were traveling on a ship. Rebbi Yehoshua had packed extremely durable food, whereas Rabban Gamliel packed meals befitting a standard seafarer. The ship was delayed and Rabban Gamliel’s supply was exhausted. Rabban Gamliel was only able to be sustained due to Rebbi Yehoshua’s careful planning. Rabban Gamliel inquired of Rebbi Yehoshua how he knew the journey would take so long. Rebbi Yehoshua responded:

".[כוכב אחד לשבעים שנה עולה ומתעה את (הספינות) [הספנים] ואמרתי שמא יעלה ויתעה [אותנו"

“There is a star that appears in seventy years and tricks the sailors. I said to myself that perhaps it will rise and trick us.”

It is common knowledge that ancient sailors were extremely dependent on astronomical knowledge in order to navigate. Without modern equipment such as GPS devices, the most accurate method of determining one’s position is based on the stellar positions. The stars move through the sky in very specific patterns. Some are always in the north and others in the south. With this knowledge, sailors can navigate the seas. Additionally, apparent celestial position changes based on latitude, so one can determine his latitude with extreme precision based on how high specific stars are from the horizon. Thus, if a “tricky” star were to “appear” it could be disastrous to the sailors because it could send them way off course.

Rashi explains that the celestial object mentioned refers to a star that rises once every seventy years. This star sometimes appears in the north and sometimes in the south. If the sailor, unaware of this star’s nature, were to see it in the north at the beginning of the journey and later, unbeknownst to him, it would change position then he would think he was traveling in one direction but would actually be going in the opposite direction. Rebbi Yehoshua was nervous that this would occur to them while they were on their journey so he packed extra durable food.

While much has been written throughout the ages expressing the symbolic meaning behind this passage, it is very unclear as to the identity of this “star” in the plain meaning of the text. “Regular” stars have set positions in the sky and cannot change from north to south, so it seems unlikely that it could be a regular star. The planets’ orbits do not have them rising once every seventy years and switching from north to south during that time so they are also not viable options.

At first glance one may think that this star is a comet. Comets move across the sky and could theoretically be good candidates for what is being discussed. There is only one comet that has a short orbital period that is easily seen by the naked eye and interestingly it happens to appear once every 75-76 years, Comet Halley (Halley’s Comet). This comet has been recorded by ancient astronomers at least as far back as 240 BCE, so it had been sighted prior to the time of Rebbi Yehoshua. If Rebbi Yehoshua was rounding the 75-76 years and referencing it as 70, then perhaps he was discussing this comet. This would be exceptionally fantastic because history gives credit to Edmund Halley as figuring out that the various comets recorded throughout history at 75-76 year intervals were all the same object and that this is that comet’s periodicity was 75-76 years. This “discovery” would not occur until over 1,500 years after Rebbi Yehoshua in the year 1705 CE!!!

There is one major problem with this assertion, though. The only arrival of Comet Halley during Rebbi Yehoshua’s lifetime would have been in 66 CE. Rabban Gamliel would have been an extremely young child at this time and in the ensuing parts of the story he is displayed as being older. (See Rashash, Pesachim 74a) Additionally, it would seem that he already achieved the title Rabban meaning that he was the Nasi and that did not happen until after the destruction of the second Beis Hamikdash which occurred in 70 CE. (See Gittin 56b; also see Seder Hadoros’ biographical synopsis of Rebbi Zeira for a discussion of the usage of titles in the Gemara indicating that the individual had already achieved that status at the time being referenced by the Gemara.) Thus, this story had to have happened well after Comet Halley’s appearance in 66 CE. To assert that Rebbi Yehoshua did not remember that the last appearance was in 66 CE and, therefore, was nervous that it would appear during the journey; or that he thought it would come sooner than 75 years this particular instance is unlikely. Rebbi Yehoshua mentions the 70 year interval in his statement; thereby displaying that he was aware of the orbital period. If he was aware of this fact, then it is unreasonable that he would not have remembered the last magnificent appearance of this comet which would have happened in his own lifetime and that he felt its periodicity was not subject to change.

I concede that I do not know what the identity of the object that Rashi is describing, however, I would like to suggest another approach to this passage. As I will explain, it would appear that Rashi had a variant text of this passage and I would like to offer a suggestion based on the text present in the standard editions of Gemara that we currently have. Perhaps, Rebbi Yehoshua was not stating that there is a star that appears every seventy years, rather, he was stating that there will be a star to appear in seventy years. He was not discussing a recurring event; he was mentioning that there was going to be a one time event that would happen in seventy years from the time being discussed in the Gemara. If this is, in fact, the case then one may ask why was Rebbi Yehoshua concerned that this star would appear prior to its seventy year date of arrival? The answer is that although based on Rebbi Yehoshua’s calculations the star would be coming in seventy years, nevertheless he may have realized that there was a margin of error in his calculations that would allow for this star to appear prior to that time. Therefore, he stated that there is a star destined to appear in seventy years, but because it was possible that it would appear sooner, he brought along extra provisions. The reason why this suggestion seems more likely based on the text in our Gemara is because the language used is:

"כוכב אחד לשבעים שנה."

and not:

"כוכב אחת לשבעים שנה."

The difference is that the text we have has the word “אחד” “one” in the masculine form and not “אחת” in the feminine. While this may seem like a minor variance, in truth it makes a world of a difference. If in the feminine it would indicate that the “one” is referring to the implicit, “פעם” “occurrence” and it is as if it says, “פעם אחת” “one occurrence.” Note that Rashi has this word in the feminine in his commentary to this passage. This reading of the text would be stating that the star appears once every seventy years and is a recurring event. Since in our text “one” is in the masculine form, it is clearly referring to the star and not referring to the periodicity of the star being seventy years. Thus, the translation of the entire sentence becomes, “One star will appear in seventy years, etc.” and is no longer, “A star appears once every seventy, etc.”

If this is the case, what then could this “star” be? We have ruled out regular stars, planets, and comets already, so what is left to be considered? Perhaps, Rebbi Yehoshua was referring to a new star appearing out of nowhere. Although uncommon, this has happened in extremely rare instances. When this has occurred it has not been that a brand new star was formed, rather, there was a star that was too faint to be seen by the naked eye which then brightened and became visible. At the end of large stars’ lives they experience an event called a supernova. Supernovae are essentially massive explosions during which time tremendous energy and radiance is emitted from dying stars. Supernovae that have become visible to the naked eye have occurred only a handful of times through recorded history.Over several months, these new stars then faded away and disappeared, only to be seen via telescope. Interestingly, the very first known one recorded in history happened in 185 CE. This is now referred to as SN 185 and made the news this week as observations by NASA’s Spitzer and WISE telescopes uncovered many more of the dynamics of how this supernova unfolded. Although Rebbi Yehoshua did not live until 185 CE, he would certainly have been alive and well 70 years prior to this and could easily have been aboard a ship with Rabban Gamliel in 115 CE. Keep in mind that the Gemara does not state that the actual reason for the delay of journey was because the star actually appeared, just that that was the reason Rebbi Yehoshua was prepared for such a delay. Supernovae are very unpredictable, perhaps leaving Rebbi Yehoshua doubting his accuracy and leaving a margin of error. In fact, if Rebbi Yehoshua was able to predict this one, his seventy year margin of error is far more accurate than even today’s predictions for supernovae!!! If this is the case, it is also astounding because even the ability to predict or understand supernovae is not considered to be known by man until the twentieth century and as previously mentioned, the accuracy with which Rebbi Yehoshua predicted this one is still not attainable by contemporary scientists!!!

The question then arises, why could such a star cause such confusion as to mislead a sailor. The rest of the sky would still have the same appearance and the sailor would just see an extra star, but would not head in the wrong direction. Upon further review, however, one can see that SN 185 may have actually been a little more confusing than just appearing as an additional star. The North Star and nearby Big Dipper are integral to celestial navigation as they are always positioned in the north. SN 185 occurred in the ancient constellation of Centaurus. In ancient times most people were not as familiar with those southern constellations since they can only be seen from more southerly parts of Earth. The area of Centaurus where SN 185 appeared would normally not be able to be confused with the Big Dipper and North Star, however, because they appear to have different configurations. The difference in configuration seems so apparent, but in fact is only so striking because this region of Centaurus is missing one bright star that appears in the Big Dipper. SN 185 flared up and appeared in that region so it is possible that a sailor would have glanced to the south quickly and mistaken this constellation for the Big Dipper!

The Big Dipper and North Star in the north:

Centaurus (prior to SN 185's appearance and post its disappearance) in the south:

Centaurus as it would appear with SN 185 in the year 185CE:

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