Astronomy – planets and craters

the Rambam writes that by his time the incredible astronomical wisdom given to us at Har Sinai had largely been forgotten. He emphasizes that his calculations of the reappearance of the new moon are based on the science of his time and not the wisdom of Chazal. Nevertheless, Chazal give us glimpses of their vast secret knowledge.

The Gemara (Horayos 10a) mentions a star which reappears every seventy years, “Rabban Gamliel and Rabbi Yehoshua went together on a voyage at sea. Rabban Gamliel had bread, Rabbi Yehoshua had bread and flour. Rabban Gamliel’s bread was used up and he used Rabbi Yehoshua’s flour. He asked him, ‘Did you know that this trip would last longer than usual, that you brought flour?’ He answered, ‘A star rises every seventy years and leads sailors astray. I said, it might appear and lead us astray.’ [Rabban Gamliel] further asked, ‘You have so much [knowledge] and nevertheless have to go on a boat [to make a living]?’ [Rabbi Yehoshua] responded, ‘If you are surprised at me, be surprised at your own students on dry land, Rabbi Eliezer ben Chisma and Rabbi Yochanan ben Gudgada, who know how to estimate how many drops there are in the ocean yet have neither bread to eat nor clothes to wear!’”

The unusual “star” to which Rabbi Yehoshua refers is Halley’s Comet. His remark that “it might appear” was obviously an attempt at humility – no reasonable person would take extra rations on a sea voyage on the off chance that a comet which appears once in a lifetime should suddenly make a surprise visit. It is quite obvious that Rabbi Yehoshua calculated the exact orbit of the comet and realized it would appear in the sky during their voyage.

Over two thousand years elapsed between the days of Rabban Gamliel until Edmund Halley finally recalculated the comet’s exact orbit, a scientific feat for which he gained world acclaim.

Another astounding Gemara discusses the number of stars in existence. Because relatively few stars are visible to the naked eye the Greek astronomer, Hipparchus, claimed that there were 1,022 stars. Ptolemy raised the figure to 1,026. Their opinion held sway throughout history, despite an opposing idea that there are an infinite number of stars and worlds. By and large, the world accepted the opinion of Aristotle that “There cannot be more worlds than one.”

The Gemara’s (Berachos 32b) discussion on the verse (Yeshayahu 49:14), “And Tzion says Hashem has forsaken me,” is unique for its time. The Gemara says that Tzion complains of having been forsaken, to which Hashem replies that He “created twelve constellations; for each constellation, thirty chayil; for each chayil, thirty legions; for each legion, thirty rehaton; for each rehaton, thirty karton; for each karton, thirty gastera; and for each gastera, 365,000 times 10,000 stars, all for the sake of [Tzion].” Hashem says, “How can you say I have forsaken you?” This number of stars comes out to about 1018.

A recent estimate calculates the number of stars at 7 x 1022, which is about 70,000 times larger than Chazal’s number. However, we do not know what criteria Chazal use to define heavenly body as a star and what they excluded. They may have calculated the number only of stars of a certain magnitude.

Perhaps the most radical astronomical discovery of modern times is Copernicus’s (died 5303/1543) theory that the world is a spinning globe. He was preceded by the Zohar (Vayikra p. 10a), “The whole earth spins in a circle like a ball; the one part is up when the other part is down; the one part is light when the other is dark; it is day in the one part and night in the other.” Talk about rediscovering the wheel!

Medieval Rabbonim continued studying the heavens and dozens of them became well-known astronomers. Perhaps the greatest of them all was Rav Levi ben Gershom, the Ralbag. He was one of the first people to dare speak out against the Greek Ptolemy’s astronomical theories, which had been accepted as dogmatic truth for centuries.

The Ralbag insisted that “no argument can nullify the reality that is perceived by the senses, for true opinion must follow reality though reality need not conform to opinion.”

He wrote extensively about astronomy in his philosophical work, Milchemes Hashem. He built new theories based on hundreds of his own astronomical observations.

The Ralbag refused to rely on information handed down by astronomers over the centuries.

“We did not find among our predecessors, from Ptolemy to the present day, observations that are helpful for this investigation except our own,” he declared (Milchemes Hashem V.1.3).

His new data discredited many outdated theories and helped pave the path for modern ideas developed by Copernicus and Galileo.

In about 3511/250 BCE Eratoshenes computed the earth’s diameter with over 99½ percent accuracy. A century later, Hipparchus worked out the correct distance to the moon. But ancient scientists were unable to calculate the distance to the stars. They believed that the stars were just beyond the moon, a mere 105 light years away.

The Ralbag calculated the first realistic distance which was ten billion times more. He reckoned that stars lie about 105 light years away. In the course of his research the Ralbag invented an important instrument, subsequently used by generations of explorers. Sailors calculate the distance of their ships from the equator by measuring the angle of the sun at noon. At the equator, the sun is straight overhead at noon while further north or south it inclines lower in the sky.

Until the Ralbag’s time, this angle was measured with a quadrant, which is basically a triangle with a plumb-line attached. In Milchemes Hashem, the Ralbag describes his new invention which he calls the Megalleh Amukos. Sailors called it “Jacob’s Staff.”

The Ralbag was also deeply interested in astrology, though he pointed out that intellect and free will “have the power to move us contrary to that which is determined by the heavenly bodies” (Milchemes II.2). One of his predictions was that the conjunction (meeting) of Saturn and Jupiter in 5105/1345 would precipitate “extraordinary evil with many wars, visions and miraculous signs… Diseases and death, and the evil will endure for a long time.”

Intriguingly, the Black Death epidemic struck in 5107/1347, wiping out a third of Europe’s population. In honor of the Ralbag’s accomplishments, the Levi Crater on the moon is named after him.

Four other Jews have been honored in the same way. They are Rav Avraham Ibn Ezra, Rav Avraham Zacuto, Albert Einstein and Sir Frederick William Herschel. Rav Avraham Zacuto, author of Sefer HaYuchsin, was one of the Spanish exiles of 5252/1492. He is famous for developing improved astronomical tables, which were used by Christopher Columbus on his voyages to the New World. The tables were especially useful when hostile natives in Jamaica refused to provide Columbus’s starving crew with food after a storm. Noticing that Zacuto’s tables predicted a lunar eclipse on February 29, 5364/1504, Columbus threatened the hostile Indian chiefs with a dire punishment – he would darken the moon and sun as punishment for their stinginess. When the moon began darkening at the appointed time, the natives begged Columbus to forgive them.

Columbus magnanimously agreed to restore the moon’s light.

Sir Frederick William Herschel (whose father was Jewish) after moving to England from Germany, developed a mania for building bigger and better telescopes. He boasted, “I have looked further into space than ever human being did before me.”

Herschel began scrutinizing every inch of the sky with his giant toys.

“When I had carefully and thoroughly perfected the great instrument in all its parts,” he proclaimed, “I made a systematic use of it in my observation of the heaven, first forming a determination never to pass by any, even the smallest, portion of them without due investigation. This habit, persisted in, led to the discovery of the new planet!”

On March 13, 5541/1781 he was examining a familiar patch of stars when he noticed a newcomer he had never seen there before. At first he thought it was a comet. Then he realized that he had discovered the eighth planet of our solar system, Uranus. For thousands of years it had been axiomatic that only seven planets existed.

Although Herschel named his new planet Georginian Sidus (George’s Star) after King George III of England, the French named it “Herschel”. Thus a planet had a Jewish name  for a few decades until an objection was made that the eighth planet should be named after a Greek god like the others.

Herschel was humble enough to realize that his discoveries were only the beginning of man’s quest. “Among opticians and astronomers,” he wrote, “nothing now is talked of but what they call my great discoveries. Alas! This shows how far they are behind when such trifles as I have seen and done are called great!”

Ma rabu ma’asecha Hashem!

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