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I don't know if this question is a good fit for here - it probably wants the non-existent "History of Astronomic Navigation SE", or maybe just "History SE" - but I'll start here:

As described in this article here by Dr Mario Livio: The Talmud (an 1500-2000 year-old Jewish book of laws and traditions) describes how a Rabbi anticipated hs ship getting lost, because “There is a star that appears every 70 years and induces navigation errors. I thought it might appear and cause us to go astray.”.

Various theories are put forward to the identity of this star - with the 70-year period suggesting Halley's comet, although another theory posits that it was a variable star (see article for details).

My question is one that the article doesn't seem to address: How could a comet or a variable star confuse sailors? Comets don't even look like stars, so as long as they don't cover up the Pole Star or any other important navigational bodies why should they confuse sailors?

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  • $\begingroup$ I'm voting to close this question as off-topic because this is not even demonstrated to be a fact of history $\endgroup$ – Carl Witthoft Apr 3 '20 at 13:36
  • $\begingroup$ @CarlWitthoft fair enough... though it's a demonstrable fact that someone 1700 years ago believed that stars appear and confuse navigators - maybe the question could be rephrased as "is it even plausible that such a thing could occur, comet, variable or otherwise" $\endgroup$ – AKA Apr 3 '20 at 14:51
  • $\begingroup$ The site is not over-run with questions about navigation, I don't think this one hurts because we have both a history and a navigation tag, and the answer seems close enough to Astronomy. It's hard for me to imagine how the appearance of one additional star could confuse anyone who already knows how to navigate using stars though. So I think the mystery in this story is not an Astronomical mystery, there's something else going on. Now, if the question was "Are there any variable stars that suddenly appear to the naked eye every 70 years in a confusing way?" the answer is probably no. $\endgroup$ – uhoh Apr 3 '20 at 15:40
  • $\begingroup$ Might get more answers on "History of Science & Maths SE". It doesn't just need knowledge of astronomy, but mostly historical knowledge too. How exactly was navigation done at the time (techniques and instruments varied)? Also how much of this was actually common knowledge that rabbis (not being professional sailors) would be familiar with? Livio assumes they must be interested in astronomy as they mention a star, but it could just be a vague notion that navigation has something to do with stars, so they talk of a star. Just like modern movies can use vague science ideas for the plot. $\endgroup$ – Stephan Matthiesen Apr 5 '20 at 11:10
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Comets can look like stars. Sometimes the outside of the coma and tail of the comet are too faint to see with the naked eye, and only the central part of the coma is bright enough to be seen. In this case the comet will appear like a (slightly fuzzy) star. Look at the Great Nebula in Orion. It appears star-like, perhaps a little fuzzy. Other clusters and nebulae were initially classified as "stars".

Moreover in the language of the first century AD (and until relatively recently) the word "star" meant "any heavenly light" and included comets, planets, and meteors. A navigator at that time would consider a comet to be just a "hairy star", while the learnéd debated whether comets were astronomical or meteorological stars.

At the time, many people also believed in "astrology" (the belief that the stars could have magical influences on life on Earth). It would seem quite reasonable, then, to think a star that appears every 70 years could affect navigation in mysterious ways.

As with many such ancient texts, the correct interpretation is probably lost. I'd consider it to be a parable: A man may be knowledgable and wise (as evidenced by his knowledge of the stars) but still be poor. I see no reason to try to identify the "star", no more that I would try to identify the farm in Isaiah 28. Trying to prove the story is "scientifically correct" seems to miss the point.

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