Tomorrow we will read a wondrous page of Talmud, that includes a discussion of astronomical distances.
תמיד לא, ב
:עשרה דברים שאל אלכסנדרוס מוקדון את זקני הנגב אמר להן
[תמיד לב, א]
מן השמים לארץ רחוק או ממזרח למערב אמרו לו ממזרח למערב תדע שהרי חמה במזרח הכל מסתכלין בה חמה במערב הכל מסתכלין בה חמה באמצע רקיע אין הכל מסתכלין בה
וחכמים אומרים זה וזה כאחד שוין שנאמר (תהלים קג, יא) כגבוה שמים על הארץ [וגו'] כרחוק מזרח ממערב ואי חד מינייהו נפיש נכתוב תרווייהו כי ההוא דנפיש ואלא חמה באמצע רקיע מ"ט אין הכל מסתכלין בה משום דקאי להדיא ולא כסי ליה מידי
Alexander of Macedon asked the Elders of the Negev about ten matters.
He said to them: Is the distance from the heavens to the earth further, or is the distance from east to west further? They said to him: From east to west is a greater distance. Know that this is so, as when the sun is in the east, everyone looks at it without hurting their eyes, and when the sun is in the west, everyone looks at it without hurting their eyes. By contrast, when the sun is inthe middle ofthe sky, no one looks at it, as it would hurt their eyes. [This shows that the sun’s place in the middle of the sky is not as far from the earth as its remote positions in the extreme east and west].
But the Sages say: This distance and that distance are equal, as it is stated: “For as the heaven is high above the earth, so great is His kindness toward them that fear Him. As far as the east is from the west, so far has He removed our transgressions from us” (Psalms 103:11–12). [The verses compare the extent of God’s kindness and His removal of transgressions to vast expanses.] And if one of the distances is greater than the other, let the verse write that both of God’s enumerated attributes are like the measure that is greater. But if so, with regard to the sun in the middle of the sky, what is the reason that no one looks at it? It is because it stands exposed and nothing covers it, [whereas it is partially screened when it is in the east or the west.]
Method for measuring the distance from the Earth to the Moon. From Joseph Delmedigo’s 1629 masterpiece, Sefer Elim, p152.
Alexander on tour…
The path of the sun, based on the famous passage in Peaschim 94b.
Historians know that Alexander the Great waged a famous campaign against Gaza and Egypt in 332 BCE. That would have placed him in or near the area in southern Israel known as the Negev, and it is while he was there that he asked the local sages whether the distance to the heavens is greater than the distance from east to west. To moderns, this is a silly question, but not to Alexander and his contemporaries. They believed that the world was a flat saucer, covered with water on which the earth floated in the middle. They also believed above us lay a solid vault that contained the stars, and which the rabbis referred to as the rakia. So which was greater, the distance up to the heavenly vault that held the sun and the stars, or the distance from one side of the earth to the other? It’s a fair question.
November 11 2019 - The Transit of Mercury
November 11, 2019: Mercury transits the sun from east to west. The horizontal yellow line represents the ecliptic, and the top is North. Make sure you are using a sun-filter on your telescope, and don’t try this with hand-held binoculars (too wobbly to see). From here.
And here is how it looks in real life through a telescope. Mercury is the black dot in the lower part of the image. At top is a more blurry sunspot. From here.
On November 11, the tiny planet of Mercury will transit (that’s astronomy-speak for “passing in front of”) across the sun. These events get astronomers very excited. You may recall that back in June of 2012 Venus was in transit across the face of the sun, leading many to spend a sunny day peering into a telescope for a glimpse. (I did. It was amazing.)
Back in the nineteenth century, the transit of Venus was of huge scientific importance because by observing it from various locations and using some clever trigonometry, astronomers could calculate the distance from the Earth. Knowing this would allow the distance of other planets from the Earth to be calculated, which would then give the answer to one of the most important astronomical questions of the time: Just how big is the solar system?
Using the transit of Venus to determine the distance from the earth to the Sun. For a deep dive into how the math works see this delightful article in the December 2003 edition of Mathematics Magazine.
The transit of Venus always occurs twice in eight years, followed by a gap of 105.5 or 121.5 years. The first time it could be viewed was in 1639, but that transit was witnessed by only two observers. By the time of the paired transits of 1761 and 1769, scientific instruments were accurate enough to provide the data needed for the all-important calculations. So in 1760 and again in 1768 the major European nations including Britain, France, Spain and Russia sent teams across the globe to measure the transit times of Venus. Perhaps the most famous expedition was that led by Captain James Cook who sailed from London to Tahiti and made a series of accurate measurements that allowed the all-important calculations to be made.
Anyway, in a couple of weeks the tiny planet of Mercury will also transit the sun. In the past, this event too could have been used to calculate the size of the solar system. But it wasn’t. The planet is just too small and too far away, and the telescopes of the time were too inaccurate for any scientifically valid measurements to be taken. Instead, astronomers waited for the larger and more visible planet Venus to transit, which also caught the attention of some important Jewish authors.
Three Jewish responses to measuring the size of the universe
Sefer Haberit 1797
The first Hebrew book to discuss the transit of Venus was Sefer Haberit, The Book of the Covenant, first published in 1797 in Brno. That also makes it the first Hebrew book to discuss the measurement of astronomical distances.
The author was Pinhas Hurwitz, a self-educated Jew from Vilna. Sefer Haberit was divided in two parts; the first, consisting of some two hundred and fifty pages is a scientific encyclopedia, addressing what Hurwitz called human wisdom (hokhmat adam) and focuses on the material world. The second part, shorter than the first at only one hundred and thirty pages, is an analysis of divine wisdom (hokhmat elohim), and focuses on spiritual matters. Sefer Haberit was an encyclopedia, and contained information on astronomy, geography, physics, and embryology. It described all manner of scientific discoveries, from the barometer to the lightening rod, and gave its readers up to date information on the recent discovery of the planet Uranus, and the (not so recent) discovery of America. Sefer Haberit was also incredibly popular; it has been reprinted some thirty times, was translated into Yiddish and Ladino, and remains available today.
In a section on solar and lunar eclipses, Hurwitz recalled the transit of Venus in 1769. He described how Cook’s expedition had almost been in vain when some of their scientific instruments were stolen the night before the transit, and how, thanks to the team’s valiant efforts, the stolen instruments were returned. Here is the original text:
And I have twice witnessed a solar eclipse caused by the moon. The first was in the Hague in Holland, and the second in Vilna in Lita, the city of my birth. During my life there was also a transit of across the sun by the planet Venus, which passed in front of it as a tiny round black dot…
This transit [of 1769] became famous across the world before it had even occurred. In British universities they examined and calculated the orbits of the planets and discovered that at a specific time Venus will pass across the face of the sun. Several years prior, they published that this event would be visible at a specific time in one location and at another time in another location…So one year prior a number of wealthy adventurers left England and sailed for more than a year to reach distant shores. They reached the island of Tahiti in the Americas, together with their telescopes and equipment to see the transit under the best conditions…
On the day before the event they set up their equipment at a specific location to be ready for the transit. But overnight the locals stole all the equipment, and then denied having done so, making the entire trip almost fruitless. But after intense negotiations they returned it all, and the transit of Venus occurred at the exact time that had been predicted…
Cook eventually returned to England with his measurements, which together with those from several other observations from Lapland to California eventually allowed the Sun-Earth distance to be calculated. (Oh, and that bit about the equipment being stolen. It is mostly true. A quadrant went missing. Here is how Cook described what happened next in his journal: “… it was not long before we got information that one of the natives had taken it away and carried it to the Eastward...I met Mr Banks and Mr Green about 4 miles from the Fort returning with the Quadrant, this was about Sunset and we all got back to the Fort about 8 oClock.”)
What is of interest here is that Hurwitz did not inform his readers of the real reason that the transit was to be observed. There is no mention of the way in which the transit of Venus could be used to determine the size of the solar system or the distance from the sun to the Earth, which were of course the real reasons for all the time and effort being spent in observing it. Why did Hurwitz leave all this out, and suggest instead that the reason for sending Captain Cook all the way from London to Tahiti was to see if the predictions for the time of the transit were accurate?
The answer lies in the fact that Hurwitz was somewhat conflicted about his belief in the model suggested by Copernicus in which the Earth and all the planets revolve around a stationary sun. Although in some places in Sefer Haberit he spoke highly of the Copernican model, Hurwitz ultimately sided with the Tychonic universe in which all the planets except the Earth revolve around the Sun, while the Sun orbits a stationary Earth, dragging the planets along with it. He did this for a number of scientific and theological reasons, including a belief that the Earth was the crowning glory of creation. “All of the planets were only created for the sake of this Earth, and everything was created for the sake of mankind on the Earth...even if the purpose of these other heavenly creations is not always clear to us.”Since the Earth was the reason for creation, it was only fitting that it lay at the center of the universe.
Hurwitz described the goal of Cook’s expedition to Tahiti as testing the predictions of the timing of the transit, when in fact its mission was far more important than that. But since Hurwitz ultimately rejected the Copernican model, he chose not to discuss the real reason for Cook’s expedition, namely to provide data that would allow the size of the Copernican solar system to be calculated. Instead, Hurwitz described the mission as one to verify the times of the predicted transit, as a sort of test of the ability of astronomers to predict these kinds of events. Although he did not reveal the real goals of the expedition, he noted that is was a great success, and that transit of Venus occurred precisely the times predicted. Which it did.
“The range of solar parallax values derived from the 1769 transit, and thus the length of the astronomical unit, drew ever closer other values accepted today. ...a modern radar-based value for the astronomical unit is 92,955,000 miles.
And based on his analysis of the 1769 transit of Venus, Thomas Horsby wrote in 1771 that “... the mean distance of the Earth from the Sun will be 93,726,900 English miles.”
Eight-tenths of a percent difference. Absolutely remarkable.”
2. Kochava Deshavit 1835
We have previously discussed the Jewish scientist extraordinaire Chaim Zelig Slonimski, For our new readers here is a recap.
Chaim Zelig Slonimski. Kochava DeShavit 1835.
To coincide with the appearance of Halley's Comet in 1835, a Hebrew book called Kokhava Deshavit (The Comet) was published in Vilna. It described where and when the comet would be visible with precise coordinates for the inhabitants of Bialystok, as well as an explanation of the nature of comets and their orbits. The author was the remarkable Hayyim Zelig Slonimski, (1810-1904), the founding editor of Hazefirah (The Dawn), a weekly Hebrew-language newspaper first published in Warsaw in 1862. He also wrote Mosdei Hokhmah (The Foundation of Wisdom), a work on algebra, and struck up a friendship with the famed German naturalist and explorer Alexander von Humboldt (1769–1859). Not content with all this, Slonimski invented a method to send two telegraphs simultaneously over one wire (which was a very big deal at the time,) and developed a calculating machine that he later presented to the Imperial Academy of Sciences in St. Petersburg. It was so successful that in 1845 the Russian minister of education made Slonimski an honorary citizen, a remarkable honor given the general oppression faced by the Jews at the time. So yes, Jewish scientist extraordinaire.
Writing in Kokhava Deshavit Slonimski explained why the transit was so important: “if [Venus] happens to pass in front of the sun and we can see it, that would be the time for astronomers to measure the angle it subtends in front of the sun (solar parallax), which is a fundamental and valuable [measure] for astronomy, as those who know these things understand. This is the reason that astronomers went to such lengths at that time to measure the moment of its [Venus’] conjunctions at various locations across the Earth. In 1769, when astronomers calculated that the transit would occur, they all prepared for this time in order to provide the most precise measurements…” [Small print: Slonimski here is absolutely correct. Solar parallax is an angular measurement that is one-half of the angular size of the Earth as seen from the sun. The reason the measurement is so important is that the distance to the sun is the radius of the Earth divided by the solar parallax.]
…Germany sent three astronomers to Domingo in the Americas and to East India, and England sent them to North America, Madras, and Tahiti. The Russian Empress Catherine sent people to follow astronomers from Germany and Sweden. They brought lots of equipment from London and Paris which they sent to the four corners of her empire…
They calculated the angle of parallax with great precision, but it was not quite accurate enough. They will get a better measurement at the next opportunity. This will occur in the Jewish year 5634 [1874] on the ninth of December, when Venus will again transit the sun at 2.18pm. The transit will last 4 hours and 9 minutes.
The reader can almost see the smile on Slonimski’s face as he shared the start time of the transit. In fact Slonimski viewed these kinds of calculations as one of the great triumphs of astronomy. When in 1846 astronomers discovered the planet Neptune, they did so on the basis of a series of calculations that suggested the existence of a planet to account for irregularities in the orbit of Uranus. And Slonimski was overjoyed, imbuing the moment with a religious patina:
The findings of this amazing discovery have struck every wise person with awe. Nothing like this in the history of humanity has ever occurred since God created man on the Earth. For can a person sit at home and use his human mind to calculate and then find a completely hidden celestial object thirty-six times as far away as the Sun is from the Earth? Yet indeed he can point to the sky and say “look, aim your telescopes there. That is where you will find another planet that orbits the Sun”…
3. Nivreshet Lenez Hahamah 1898
The third Hebrew book to discuss the measurement of astronomic distance is Nivreshet Lenez Hachama (The Chandelier of the Sunrise), published in Jerusalem in 1898. Its author was the geocentric Hayah David Spitzer. He rejected Copernicus and his heliocentric model, believing instead that the entire universe revolved around the Earth, because “everything, including the Sun, was created for the Earth and for Israel who dwell on it and keep the Torah.” Spitzer’s main interest was in determining the precise times of sunrise and sunset in halakhah, and he spent hours carefully measuring these times in and around Jerusalem.
Spitzer rejected all the calculations about the size of the solar system and the distance to the nearest stars that had been calculated using the observations of the transit of Venus, as well as estimates of the speed of light that had been made in the nineteenth century. He did so on both ‘scientific’ and religious grounds. For example, if as astronomers claimed, some stars were 24,000 light years away from Earth, their light could not have reached the Earth that had only existed for some 6,000 years. In addition, what purpose would there have been in creating such remote stars, whose light served no purpose for those on Earth? Finally, since the speed of light is not mentioned in the Talmud, the notion that light has a finite speed cannot be correct. Here is the original text.
Hayah David Spitzer, Nivreshet Lenez Hahamah(Jerusalem: Blumenthal, 1898). 35a.
We find various discussions in out Talmud about the size of the universe, and the distance to and the size of the stars. But we there is no mention at all about the idea that sunlight or light from the stars takes a finite time to reach us. If there was even the remote possibility that this was so our sages would certainly have discussed it in detail…
Spitzer claimed that anyone could perform a simple experiment that would refute the notion that light took a finite time to travel vast distances. If, during the day, the door to a house was suddenly closed, it should still be possible to see an image of the sun for some time since the light would take time to travel from the site of the now closed door across the room and into the eye of the observer. Similarly,
if we open a closed door or window…we should not be able to see sunlight for some time, and we should be forced to sit in darkness as if the doors had not been opened. What can be said of this idiocy and stupidity, at which any person would laugh? Rather, as soon as a person opens his eyes he stops seeing nothing and when he opens his eyes at night he immediately sees all the stars, both those nearby that need sixteen years for their light to travel, and those far away whose light takes one hundred and twenty years to reach us.
Sptizer 34b.
Oy. Even when judged by the scientific standards of his own time, Spitzer’s work was astonishingly naive. To explain why he adopted this extreme (and extremely uninformed) position, you need to understand that Spitzer believed that the entire scientific process had but one goal in mind - to destroy the fundamentals of Jewish belief: “Their entire aim is to deny God’s Torah, to destroy religion, to confuse those who would disagree with them and to embarrass and belittle the sages of Israel.”
These three rabbinic authors had three quite different ways of approaching both the history of the transit of Venus and the measurement of distances that was deduced from it. Hurwitz was certainly inquisitive about all things scientific, but did not reveal the real goals of the expeditions to observe the transit, because they would raise further questions about the model of the solar system in which he believed- a model in which the Earth was the unmoving center. Slonimski informed his readers of the real goals of the observations and had no issues – religious or scientific - with accepting a universe in which the Earth was not the center. But for Spitzer, the enterprise of astronomy was a vast conspiracy to undermine Torah values. He therefore stretched to reject any science that the transit of Venus bequeathed to future generations.
“Alexander was not just another conqueror in the ancient world. He severed that world from its past. He hellenized it, and at the same time he delivered a lethal blow to its traditions.”
Humanity has been intrigued by the heavens for as long as recorded history. The answer Alexander the Great received from the Elders of the Negev was not based any mathematical principles or measurements of the planets or stars. It was based on a more important and more trustworthy source: the word of God. Over a millennia later, the Temple in Jerusalem was interpreted as a model of the solar system, with its gates representing the planets. That’s next time, on Talmudology.
[Partial repost from a here.]
