Denis Diderot

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Denis Diderot
Diderot, by Louis-Michel van Loo, 1767
Born	5 October 1713 Langres, Champagne, Kingdom of France
Died	31 July 1784 (aged 70) Paris, France
Alma mater	University of Paris
Era	18th-century philosophy
Region	Western philosophy
School	Encyclopédistes French materialism
Main interests	Science, literature, philosophy, art
Signature

Denis Diderot was a French philosopher, art critic, and writer, best known for serving as co-founder, chief editor, and contributor to the Encyclopédie along with Jean le Rond d'Alembert. He was a prominent figure during the Enlightenment.

Diderot began his education by obtaining a Master of Arts degree in philosophy at a Jesuit college in 1732. He considered working in the church clergy before briefly studying law. When he decided to become a writer in 1734, his father disowned him for not entering one of the learned professions. He lived a bohemian existence for the next decade. He befriended philosopher Jean-Jacques Rousseau in 1742.

Though his work was broad as well as rigorous, it did not bring Diderot riches. He secured none of the posts that were occasionally given to needy men of letters; he could not even obtain the bare official recognition of merit that was implied by being chosen a member of the Académie française. He saw no alternative to selling his library to provide a dowry for his daughter. Empress Catherine II of Russia heard of his financial troubles and commissioned an agent in Paris to buy the library. She then requested that the philosopher retain the books in Paris until she required them, and act as her librarian with a yearly salary. Between October 1773 and March 1774, the sick Diderot spent a few months at the empress's court in Saint Petersburg.

Diderot died of pulmonary thrombosis in Paris on 31 July 1784, and was buried in the city's Église Saint-Roch. His heirs sent his vast library to Catherine II, who had it deposited at the National Library of Russia. He has several times been denied burial in the Panthéon with other French notables. The French government considered memorializing him in this fashion on the 300th anniversary of his birth, but this did not come to pass.

Diderot's literary reputation during his lifetime rested primarily on his plays and his contributions to the Encyclopédie; many of his most important works, including Jacques the Fatalist, Rameau's Nephew, Paradox of the Actor, and D'Alembert's Dream, were published only after his death.

Early life

N° 9 de la place dans le centre ville de Langres: in the background on the right side the birthplace of Denis Diderot

 

Statue of Denis Diderot in the city of Langres, his birthplace

 

Denis Diderot was born in Langres, Champagne. His parents were Didier Diderot (1685–1759), a cutler, maître coutelier, and his wife, Angélique Vigneron (1677–1748). Three of five siblings survived to adulthood, Denise Diderot (1715–1797) and their youngest brother Pierre-Didier Diderot (1722–1787), and finally their sister Angélique Diderot (1720–1749). According to Arthur McCandless Wilson, Denis Diderot greatly admired his sister Denise, sometimes referring to her as "a female Socrates".

Diderot began his formal education at a Jesuit college in Langres, earning a Master of Arts degree in philosophy in 1732. He then entered the Collège d'Harcourt of the University of Paris. He abandoned the idea of entering the clergy in 1735, and instead decided to study at the Paris Law Faculty. His study of law was short-lived however and in the early 1740s, he decided to become a writer and translator. Because of his refusal to enter one of the learned professions, he was disowned by his father, and for the next ten years he lived a bohemian existence.

In 1742, he befriended Jean-Jacques Rousseau, whom he met while watching games of chess and drinking coffee at the Café de la Régence. In 1743, he further alienated his father by marrying Antoinette Champion (1710–1796), a devout Roman Catholic. The match was considered inappropriate due to Champion's low social standing, poor education, fatherless status, and lack of a dowry. She was about three years older than Diderot. The marriage, in October 1743, produced one surviving child, a girl. Her name was Angélique, named after both Diderot's dead mother and sister. The death of his sister, a nun, in her convent may have affected Diderot's opinion of religion. She is assumed to have been the inspiration for his novel about a nun, La Religieuse, in which he depicts a woman who is forced to enter a convent where she suffers at the hands of the other nuns in the community.

Diderot had affairs with Mlle. Babuti (who would marry Greuze), Madeleine de Puisieux, Sophie Volland and Mme de Maux. His letters to Sophie Volland are known for their candor and are regarded to be "among the literary treasures of the eighteenth century".

Early works

Diderot's earliest works included a translation of Temple Stanyan's History of Greece (1743); with two colleagues, François-Vincent Toussaint and Marc-Antoine Eidous, he produced a translation of Robert James's Medicinal Dictionary (1746–1748). In 1745, he published a translation of Shaftesbury's Inquiry Concerning Virtue and Merit, to which he had added his own "reflections".

Philosophical Thoughts

In 1746, Diderot wrote his first original work: the Philosophical Thoughts (French:Pensées philosophiques). In this book, Diderot argued for a reconciliation of reason with feeling so as to establish harmony. According to Diderot, without feeling there is a detrimental effect on virtue, and no possibility of creating sublime work. However, since feeling without discipline can be destructive, reason is necessary to control feeling.

At the time Diderot wrote this book he was a deist. Hence there is a defense of deism in this book, and some arguments against atheism. The book also contains criticism of Christianity.

The Skeptic's Walk

In 1747, Diderot wrote The Skeptic's Walk (French:Promenade du sceptique) in which a deist, an atheist, and a pantheist have a dialogue on the nature of divinity. The deist gives the argument from design. The atheist says that the universe is better explained by physics, chemistry, matter, and motion. The pantheist says that the cosmic unity of mind and matter, which are co-eternal and comprise the universe, is God. This work remained unpublished till 1830. The local police—warned by the priests of another attack on Christianity—either seized the manuscript, or authorities forced Diderot give an undertaking that he would not publish this work, according to different versions of what happened.

The Indiscreet Jewels

In 1748, Diderot needed to raise money on short notice. He had become a father through his wife, and his mistress Mme. de Puisieux was making financial demands from him. At this time, Diderot had stated to Mme. de Puisieux that writing a novel was a trivial task, whereupon she challenged him to write a novel. In response, Diderot wrote his novel The Indiscreet Jewels (French:Les bijoux indiscrets). The book is about the magical ring of a Sultan which induces any woman's "discreet jewels" to confess their sexual experiences when the ring is pointed at them. In all, the ring is pointed at thirty different women in the book—usually at a dinner or a social meeting—with the Sultan typically being visible to the woman. However, since the ring has the additional property of making its owner invisible when required, a few of the sexual experiences recounted are through direct observation with the Sultan making himself invisible and placing his person in the unsuspecting woman's boudoir.

Besides the bawdiness there are several digressions into philosophy, music, and literature in the book. In one such philosophical digression, the Sultan has a dream in which he sees a child named "Experiment" growing bigger and stronger till it demolishes an ancient temple named "Hypothesis". The book proved to be lucrative for Diderot even though it could only be sold clandestinely. It is Diderot's most published work.

The book is believed to be an imitation of Le Sopha.

Scientific work

Diderot would keep writing on science in a desultory way all his life. The scientific work of which he was most proud was Memoires sur differents sujets de mathematique (1748). This work contains original ideas on acoustics, tension, air resistance, and "a project for a new organ" which could be played by all. Some of Diderot's scientific works were applauded by contemporary publications of his time like The Gentleman's Magazine, the Journal des savants; and the Jesuit publication Journal de Trevoux, which invited more such work: "on the part of a man as clever and able as M. Diderot seems to be, of whom we should also observe that his style is as elegant, trenchant, and unaffected as it is lively and ingenious."

Letter on the Blind

Diderot's celebrated Letter on the Blind (Lettre sur les aveugles à l'usage de ceux qui voient) (1749) introduced him to the world as an original thinker. The subject is a discussion of the interrelation between man's reason and the knowledge acquired through perception (the five senses). The title of his book also evoked some ironic doubt about who exactly were "the blind" under discussion. In the essay, blind English mathematician Nicholas Saunderson argues that, since knowledge derives from the senses, mathematics is the only form of knowledge that both he and a sighted person can agree on. It is suggested that the blind could be taught to read through their sense of touch. (A later essay, Lettre sur les sourds et muets, considered the case of a similar deprivation in the deaf and mute.) According to Jonathan Israel, what makes the Lettre sur les aveugles so remarkable, however, is its distinct, if undeveloped, presentation of the theory of variation and natural selection.

This powerful essay, for which La Mettrie expressed warm appreciation in 1751, revolves around a remarkable deathbed scene in which a dying blind philosopher, Saunderson, rejects the arguments of a deist clergyman who endeavours to win him round to a belief in a providential God during his last hours. Saunderson's arguments are those of a neo-Spinozist Naturalist and fatalist, using a sophisticated notion of the self-generation and natural evolution of species without Creation or supernatural intervention. The notion of "thinking matter" is upheld and the "argument from design" discarded (following La Mettrie) as hollow and unconvincing. The work appeared anonymously in Paris in June 1749, and was vigorously suppressed by the authorities. Diderot, who had been under police surveillance since 1747, was swiftly identified as the author, had his manuscripts confiscated, and was imprisoned for some months, under a lettre de cachet, on the outskirts of Paris, in the dungeons at Vincennes where he was visited almost daily by Rousseau, at the time his closest and most assiduous ally.

Voltaire wrote an enthusiastic letter to Diderot commending the Lettre and stating that he had held Diderot in high regard for a long time to which Diderot had sent a warm response. Soon after this, Diderot was arrested.

Science historian Conway Zirkle has written that Diderot was an early evolutionary thinker and noted that his passage that described natural selection was "so clear and accurate that it almost seems that we would be forced to accept his conclusions as a logical necessity even in the absence of the evidence collected since his time."

Incarceration and release

Angered by public resentment over the Peace of Aix-la-Chapelle, the government started incarcerating many of its critics. It was decided at this time to rein in Diderot. On 23 July 1749, the governor of the Vincennes fortress instructed the police to incarcerate Diderot, and the next day he was arrested and placed in solitary confinement in the Vincennes. He had been permitted to retain one book that he had in his possession at the time of his arrest, Paradise Lost, which he read during his incarceration. He wrote notes and annotations on the book, using a toothpick as a pen, and ink that he made by scraping slate from the walls and mixing it with wine.

In August 1749, Mme du Chatelet, presumably at Voltaire's behest, wrote to the governor of Vincennes, who was her relative, pleading that Diderot be lodged more comfortably while jailed. The governor then offered Diderot access to the great halls of the Vincennes castle and the freedom to receive books and visitors providing he would write a document of submission. On 13 August 1749, Diderot wrote to the governor:

I admit to you...that the Pensees, the Bijoux, and the Lettre sur les aveugles are debaucheries of the mind that escaped from me; but I can...promise you on my honor (and I do have honor) that they will be the last, and that they are the only ones...As for those who have taken part in the publication of these works, nothing will be hidden from you. I shall depose verbally, in the depths[secrecy] of your heart, the names both of the publishers and the printers.

On 20 August, Diderot was lodged in a comfortable room in the Vincennes, allowed to meet visitors, and to walk in the gardens of the Vincennes. On 23 August, Diderot signed another letter promising to never leave the Vincennes without permission. On 3 November 1749, Diderot was released from the Vincennes. Subsequently, in 1750, he released the prospectus for the Encyclopédie.

Encyclopédie

Genesis

Title page of the Encyclopédie

 

André le Breton, a bookseller and printer, approached Diderot with a project for the publication of a translation of Ephraim Chambers' Cyclopaedia, or Universal Dictionary of Arts and Sciences into French, first undertaken by the Englishman John Mills, and followed by the German Gottfried Sellius. Diderot accepted the proposal, and transformed it. He persuaded Le Breton to publish a new work, which would consolidate ideas and knowledge from the Republic of Letters. The publishers found capital for a larger enterprise than they had first planned. Jean le Rond d'Alembert was persuaded to become Diderot's colleague, and permission was procured from the government.

In 1750 an elaborate prospectus announced the project, and in 1751 the first volume was published. This work was unorthodox and advanced for the time. Diderot stated that "An encyclopedia ought to make good the failure to execute such a project hitherto, and should encompass not only the fields already covered by the academies, but each and every branch of human knowledge." Comprehensive knowledge will give "the power to change men's common way of thinking." The work combined scholarship with information on trades. Diderot emphasized the abundance of knowledge within each subject area. Everyone would benefit from these insights.

Controversies

Diderot's work, however, was mired in controversy from the beginning; the project was suspended by the courts in 1752. Just as the second volume was completed accusations arose regarding seditious content, concerning the editor's entries on religion and natural law. Diderot was detained and his house was searched for manuscripts for subsequent articles: but the search proved fruitless as no manuscripts could be found. They were hidden in the house of an unlikely confederate—Chretien de Lamoignon Malesherbes, who originally ordered the search. Although Malesherbes was a staunch absolutist, and loyal to the monarchy - he was sympathetic to the literary project. Along with his support, and that of other well-placed influential confederates, the project resumed. Diderot returned to his efforts only to be constantly embroiled in controversy. 

These twenty years were to Diderot not merely a time of incessant drudgery, but harassing persecution and desertion of friends. The ecclesiastical party detested the Encyclopédie, in which they saw a rising stronghold for their philosophic enemies. By 1757 they could endure it no longer - the subscribers had grown from 2,000 to 4,000, a measure of the growth of the work in popular influence and power. Diderot wanted the Encyclopédie to give all the knowledge of the world to the people of France. However, the Encyclopédie threatened the governing social classes of France (aristocracy) because it took for granted the justice of religious tolerance, freedom of thought, and the value of science and industry. It asserted the doctrine that the main concern of the nation's government ought to be the nation's common people. It was believed that the Encyclopédie was the work of an organized band of conspirators against society, and that the dangerous ideas they held were made truly formidable by their open publication. In 1759, the Encyclopédie was formally suppressed. The decree did not stop the work, which went on, but its difficulties increased by the necessity of being clandestine. Jean le Rond d'Alembert withdrew from the enterprise and other powerful colleagues, including Anne Robert Jacques Turgot, Baron de Laune, declined to contribute further to a book which had acquired a bad reputation.

Diderot's contribution

Diderot was left to finish the task as best he could. He wrote 7,000 articles, some very slight, but many of them laborious, comprehensive, and long. He damaged his eyesight correcting proofs and editing the manuscripts of less competent contributors. He spent his days at workshops, mastering manufacturing processes, and his nights writing what he had learned during the day. He was incessantly harassed by threats of police raids. The last copies of the first volume were issued in 1765. 

In 1764, when his immense work was drawing to an end, he encountered a crowning mortification: he discovered that the bookseller, Le Breton, fearing the government's displeasure, had struck out from the proof sheets, after they had left Diderot's hands, all passages that he considered too dangerous. "He and his printing-house overseer," writes Furbank, "had worked in complete secrecy, and had moreover deliberately destroyed the author's original manuscript so that the damage could not be repaired." The monument to which Diderot had given the labor of twenty long and oppressive years was irreparably mutilated and defaced. It was 12 years, in 1772, before the subscribers received the final 28 folio volumes of the Encyclopédie, ou dictionnaire raisonné des sciences, des arts et des métiers since the first volume had been published. 

When Diderot's work on the Encyclopédie project came to a end in 1765, he expressed concerns to his friends that the twenty-five years he had spent on the project had been wasted.

Mature works

Although the Encyclopédie was Diderot's most monumental product, he was the author of many other works that sowed nearly every intellectual field with new and creative ideas. Diderot's writing ranges from a graceful trifle like the Regrets sur ma vieille robe de chambre (Regrets for my Old Dressing Gown) up to the heady D'Alembert's Dream (Le Rêve de d'Alembert) (composed 1769), a philosophical dialogue in which he plunges into the depths of the controversy as to the ultimate constitution of matter and the meaning of life. Jacques le fataliste (written in 1773, but not published until 1792 in German and 1796 in French) is similar to Tristram Shandy and The Sentimental Journey in its challenge to the conventional novel's structure and content.

Rameau's Nephew

The dialogue Rameau's Nephew (French: Le Neveu de Rameau) is a "farce-tragedy" reminiscent of the Satires of Horace, a favorite classical author of Diderot's whose lines "Vertumnis, quotquot sunt, natus iniquis" ("A man born when every single Vertumnus was out of sorts") appear as epigraph. According to Nicholas Cronk, Rameau's Nephew is "arguably the greatest work of the French Enlightenment's greatest writer."

Diderot's intention in writing the dialogue—whether as a satire on contemporary manners, a reduction of the theory of self-interest to an absurdity, the application of irony to the ethics of ordinary convention, a mere setting for a discussion about music, or a vigorous dramatic sketch of a parasite and a human original—is disputed. In political terms it explores "the bipolarisation of the social classes under absolute monarchy," and insofar as its protagonist demonstrates how the servant often manipulates the master, Le Neveu de Rameau can be seen to anticipate Hegel's master–slave dialectic.

Un dîner de philosophes painted by Jean Huber. Denis Diderot is the second from the right (seated).

 

The narrator in the book recounts a conversation with Jean-François Rameau, nephew of the famous Jean-Philippe Rameau. The nephew composes and teaches music with some success but feels disadvantaged by his name and is jealous of his uncle. Eventually he sinks into an indolent and debauched state. After his wife's death, he loses all self-esteem and his brusque manners result in him being ostracized by former friends. A character profile of the nephew is now sketched by Diderot: a man who was once wealthy and comfortable with a pretty wife, who is now living in poverty and decadence, shunned by his friends. And yet this man retains enough of his past to analyze his despondency philosophically and maintains his sense of humor. Essentially he believes in nothing—not in religion, nor in morality; nor in the Roussean view about nature being better than civilization since in his opinion every species in nature consumes one another. He views the same process at work in the economic world where men consume each other through the legal system. The wise man, according to the nephew, will consequently practice hedonism:

Hurrah for wisdom and philosophy!--the wisdom of Solomon: to drink good wines, gorge on choice foods, tumble pretty women, sleep on downy beds; outside of that, all is vanity.

The dialogue ends with Diderot calling the nephew a wastrel, a coward, and a glutton devoid of spiritual values to which the nephew replies: "I believe you are right."

The publication history of the Nephew is circuitous. Written in 1761, Diderot never saw the work through to publication during his lifetime, and apparently did not even share it with his friends. After Diderot's death, a copy of the text reached Schiller, who gave it to Goethe, who, in 1805, translated the work into German. Goethe's translation entered France, and was retranslated into French in 1821. Another copy of the text was published in 1823, but it had been expurgated by Diderot's daughter prior to publication. The original manuscript was only found in 1891.

Visual arts

Diderot's most intimate friend was the philologist Friedrich Melchior Grimm. They were brought together by their friend in common at that time, Jean-Jacques Rousseau. In 1753, Grimm began writing a newsletter, the La Correspondance littéraire, philosophique et critique, which he would send to various high personages in Europe.

In 1759, Grimm asked Diderot to report on the biennial art exhibitions in the Louvre for the Correspondance. Diderot reported on the Salons between 1759 and 1771 and again in 1775 and 1781. Diderot's reports would become "the most celebrated contributions to La Correspondance."

According to Charles Augustin Sainte-Beuve, Diderot's reports initiated the French into a new way of laughing, and introduced people to the mystery and purport of color by ideas. "Before Diderot", Anne Louise Germaine de Staël wrote, "I had never seen anything in pictures except dull and lifeless colours; it was his imagination that gave them relief and life, and it is almost a new sense for which I am indebted to his genius".

Diderot had appended an Essai sur la peinture to his report on the 1765 Salon in which he expressed his views on artistic beauty. Goethe described the Essai sur la peinture as "a magnificent work; it speaks even more usefully to the poet than to the painter, though for the painter too it is a torch of blazing illumination".

Jean-Baptiste Greuze (1725–1805) was Diderot's favorite contemporary artist. Diderot appreciated Greuze's sentimentality, and more particularly Greuze's portrayals of his wife who had once been Diderot's mistress.

Theater

Diderot wrote sentimental plays, Le Fils naturel (1757) and Le Père de famille (1758), accompanying them with essays on theatrical theory and practice, including "Les Entretiens sur Le Fils Naturel" (Conversations on The Natural Son), in which he announced the principles of a new drama: the 'serious genre', a realistic midpoint between comedy and tragedy that stood in opposition to the stilted conventions of the classical French stage. In 1758, Diderot introduced the concept of the fourth wall, the imaginary "wall" at the front of the stage in a traditional three-walled box set in a proscenium theatre, through which the audience sees the action in the world of the play.

Diderot and Catherine the Great

Journey to Russia

Diderot's travel from Paris to Saint Petersburg in 1773–1774. The blue line marks the outward from 3 June 1773 until 9 October 1773, and the red line marks the return journey 5 March 1774 to 21 October 1774.

 

When the Russian Empress Catherine the Great heard that Diderot was in need of money, she arranged to buy his library and appoint him caretaker of it until his death, at a salary of 1,000 livres per year. She even paid him 50 years salary in advance. Although Diderot hated traveling, he was obliged to visit her.

On 9 October 1773, he reached St. Petersburg, met Catherine the next day and they had several discussions on various subjects. During his five-month stay at her court, he met her almost every day. During these conversations, he would later state, they spoke 'man to man'.

He would occasionally make his point by slapping her thighs. In a letter to Madame Geoffrin, Catherine wrote:

Your Diderot is an extraordinary man. I emerge from interviews with him with my thighs bruised and quite black. I have been obliged to put a table between us to protect myself and my members.

One of the topics discussed was Diderot's ideas about how to transform Russia into a utopia. In a letter to Comte de Ségur, the Empress wrote that if she followed Diderot's advice, chaos would ensue in her kingdom.

Back in France

When returning, Diderot asked the Empress for 1,500 rubles as reimbursement for his trip. She gave him 3,000 rubles, an expensive ring, and an officer to escort him back to Paris. He would write a eulogy in her honor on reaching Paris.

In 1766, when Catherine heard that Diderot had not received his annual fee for editing the Encyclopédie (an important source of income for the philosopher), she arranged for him to receive a massive sum of 50,000 livres as an advance for his services as her librarian.

In July 1784, upon hearing that Diderot was in poor health, Catherine arranged for him to move into a luxurious suite in the Rue de Richelieu. Diderot died two weeks after moving there—on 31 July 1784.

Among Diderot's last works were notes "On the Instructions of her Imperial Majesty...for the Drawing up of Laws". This commentary on Russia included replies to some arguments Catherine had made in the Nakaz. Diderot wrote that Catherine was certainly despotic, due to circumstances and training, but was not inherently tyrannical. Thus, if she wished to destroy despotism in Russia, she should abdicate her throne and destroy anyone who tries to revive the monarchy. She should publicly declare that "there is no true sovereign other than the nation, and there can be no true legislator other than the people." She should create a new Russian legal code establishing an independent legal framework and starting with the text: "We the people, and we the sovereign of this people, swear conjointly these laws, by which we are judged equally." In the Nakaz, Catherine had written: "It is for legislation to follow the spirit of the nation." Diderot's rebuttal stated that it is for legislation to make the spirit of the nation. For instance, he argued, it is not appropriate to make public executions unnecessarily horrific.

Ultimately, Diderot decided not to send these notes to Catherine; however, they were delivered to her with his other papers after he died. When she read them, she was furious and commented that they were an incoherent gibberish devoid of prudence, insight, and verisimilitude.

Philosophy

In his youth, Diderot was originally a follower of Voltaire and his deist Anglomanie, but gradually moved away from this line of thought towards materialism and atheism, a move which was finally realized in 1747 in the philosophical debate in the second part of his The Skeptic's Walk (1747). Diderot opposed mysticism and occultism, which were highly prevalent in France at the time he wrote, and believed religious truth claims must fall under the domain of reason, not mystical experience or esoteric secrets. However, Diderot showed some interest in the work of Paracelsus. He was "a philosopher in whom all the contradictions of the time struggle with one another" (Rosenkranz).

In his 1754 book On the interpretation of Nature, Diderot expounded on his views about Nature, evolution, materialism, mathematics, and experimental science. It is speculated that Diderot may have contributed to his friend Baron d'Holbach's 1770 book The System of Nature. Diderot had enthusiastically endorsed the book stating that:

What I like is a philosophy clear, definite, and frank, such as you have in the System of Nature. The author is not an atheist on one page and a deist on another. His philosophy is all of one piece.

In conceiving the Encyclopédie, Diderot had thought of the work as a fight on behalf of posterity and had expressed confidence that posterity would be grateful for his effort. According to Diderot, "posterity is for the philosopher what the 'other world' is for the man of religion."

Appreciation and influence

Jean-Simon Berthélemy, Young man admiring Denis Diderot's bust

 

Marmontel and Henri Meister commented on the great pleasure of having intellectual conversations with Diderot. Morellet, a regular attendee at D'Holbach's salon, wrote: "It is there that I heard...Diderot treat questions of philosophy, art, or literature, and by his wealth of expression, fluency, and inspired appearance, hold our attention for a long stretch of time." Diderot's contemporary, and rival, Jean Jacques Rousseau wrote in his Confessions that after a few centuries Diderot would be accorded as much respect by posterity as was given to Plato and Aristotle. In Germany, Goethe, Schiller, and Lessing expressed admiration for Diderot's writings, Goethe pronouncing Diderot's Rameau's Nephew to be "the classical work of an outstanding man" and that "Diderot is Diderot, a unique individual; whoever carps at him and his affairs is a philistine."

In the next century, Diderot was admired by Balzac, Delacroix, Stendhal, Zola, and Schopenhauer. According to Comte, Diderot was the foremost intellectual in an exciting age. Historian Michelet described him as "the true Prometheus" and stated that Diderot's ideas would continue to remain influential long into the future. Marx chose Diderot as his "favorite prose-writer."

Contemporary tributes

Monument to Denis Diderot in Paris, 6th arrondissement, by Jean Gautherin

 

Otis Fellows and Norman Torrey have described Diderot as "the most interesting and provocative figure of the French eighteenth century."

In 1993, American writer Cathleen Schine published Rameau's Niece, a satire of academic life in New York that took as its premise a woman's research into an (imagined) 18th-century pornographic parody of Diderot's Rameau's Nephew. The book was praised by Michiko Kakutani in the New York Times as "a nimble philosophical satire of the academic mind" and "an enchanting comedy of modern manners."

French author Eric-Emmanuel Schmitt wrote a play titled Le Libertin (The Libertine) which imagines a day in Diderot's life including a fictional sitting for a woman painter which becomes sexually charged but is interrupted by the demands of editing the Encyclopédie. It was first staged at Paris' Théâtre Montparnasse in 1997 starring Bernard Giraudeau as Diderot and Christiane Cohendy as Madame Therbouche and was well received by critics.

In 2013, the tricentennial of Diderot's birth, his hometown of Langres held a series of events in his honor and produced an audio tour of the town highlighting places that were part of Diderot's past, including the remains of the convent where his sister Angélique took her vows. On 6 October 2013, a museum of the Enlightenment focusing on Diderot's contributions to the movement, the Maison des Lumières Denis Diderot, was inaugurated in Langres.

Bibliography

• Essai sur le mérite et la vertu, written by Shaftesbury French translation and annotation by Diderot (1745)
• Philosophical Thoughts, essay (1746)
• La Promenade du sceptique (1747)
• The Indiscreet Jewels, novel (1748)
• Lettre sur les aveugles à l'usage de ceux qui voient (1749)
• Encyclopédie, (1750–1765)
• Lettre sur les sourds et muets (1751)
• Pensées sur l'interprétation de la nature, essai (1751)
• "Systeme de la Nature," (1754)
• Le Fils naturel (1757)
• Entretiens sur le Fils naturel (1757)
• Le père de famille (1758)
• Discours sur la poesie dramatique (1758)
• Salons, critique d'art (1759–1781)
• La Religieuse, Roman (1760; revised in 1770 and in the early 1780s; the novel was first published as a volume posthumously in 1796).
• Le neveu de Rameau, dialogue (1763).
• Lettre sur le commerce de la librairie (1763)
• Mystification ou l’histoire des portraits (1768)
• Entretien entre D'Alembert et Diderot (1769)
• Le rêve de D'Alembert, dialogue (1769)
• Suite de l'entretien entre D'Alembert et Diderot (1769)
• Paradoxe sur le comédien (written between 1770 and 1778; first published posthumously in 1830)
• Apologie de l'abbé Galiani (1770)
• Principes philosophiques sur la matière et le mouvement, essai (1770)
• Entretien d'un père avec ses enfants (1771)
• Jacques le fataliste et son maître, novel (1771–1778)
• Ceci n'est pas un conte, story (1772)
• Madame de La Carlière, short story and moral fable, (1772)
• Supplément au voyage de Bougainville (1772)
• Histoire philosophique et politique des deux Indes, in collaboration with Raynal (1772–1781)
• Voyage en Hollande (1773)
• Éléments de physiologie (1773–1774)
• Réfutation d'Helvétius (1774)
• Observations sur le Nakaz (1774)
• Essai sur les règnes de Claude et de Néron (1778)
• Est-il Bon? Est-il méchant? (1781)
• Lettre apologétique de l'abbé Raynal à Monsieur Grimm (1781)
• Aux insurgents d'Amérique (1782)

Uranium Seawater Extraction Makes Nuclear Power Completely Renewable

By James Conca

Original link:  https://www.forbes.com/sites/jamesconca/2016/07/01/uranium-seawater-extraction-makes-nuclear-power-completely-renewable/?fbclid=IwAR1ej0epC8Acm6R7G3Ga139syEwkEBgp0nWsOW08Syz_REUvIB2Ct8P0NuM#114721d3159a

America, Japan and China are racing to be the first nation to make nuclear energy completely renewable. The hurdle is making it economic to extract uranium from seawater, because the amount of uranium in seawater is truly inexhaustible.

And it seems America is in the lead. New technological breakthroughs from DOE’s Pacific Northwest (PNNL) and Oak Ridge (ORNL) national laboratories have made removing uranium from seawater within economic reach and the only question is - when will the source of uranium for our nuclear power plants change from mined ore to seawater extraction?

Nuclear fuel made with uranium extracted from seawater makes nuclear power completely renewable. It’s not just that the 4 billion tons of uranium in seawater now would fuel a thousand 1,000-MW nuclear power plants for a 100,000 years. It’s that uranium extracted from seawater is replenished continuously, so nuclear becomes as endless as solar, hydro and wind.

Researchers around the world have been working frantically to develop an array of materials and fibers able to economically extract uranium from seawater. They have succeeded, as discussed at a conference devoted to the topic. Researchers at the Pacific Northwest National Laboratory exposed this special uranium-sorbing fiber developed at ORNL to Pseudomonas fluorescens and used the Advanced Photon Source at Argonne National Laboratory to create a 3-D X-ray microtomograph to determine microstructure and the effects of interactions with organisms and seawater. Courtesy of Pacific Northwest National Laboratory

Specifically, this latest technology builds on work by researchers in Japan and uses polyethylene fibers coated with amidoxime to pull in and bind uranium dioxide from seawater (see figure above). In seawater, amidoxime attracts and binds uranium dioxide to the surface of the fiber braids, which can be on the order of 15 centimeters in diameter and run multiple meters in length depending on where they are deployed (see figure below).

After a month or so in seawater, the lengths are remotely released to the surface and collected.  An acid treatment recovers the uranium in the form of a uranyl complex, regenerating the fibers that can be reused many times. The concentrated uranyl complex then can be enriched to become nuclear fuel.
This procedure, along with the global effort, was described in a special report in Industrial & Engineering Chemistry Research. The scientists from PNNL and ORNL led more than half of the 30 papers in the special issue, involving synthesizing and characterizing uranium adsorbents and marine testing of these adsorbents at facilities like PNNL's Marine Sciences Laboratory in Sequim, Washington.

Scientists envision anchoring hundreds of lengths of U-extracting fibers in the sea for a month or so until they fill with uranium. Then a wireless signal would release them to float to the surface where the uranium could be recovered and the fibers reused. It doesn’t matter where in the world the fibers are floating. Source: Andy Sproles at ORNL

Gary Gill, deputy director of PNNL's Coastal Sciences Division who coordinated the marine testing, noted, "Understanding how the adsorbents perform under natural seawater conditions is critical to reliably assessing how well the uranium adsorbent materials work." In addition to marine testing, PNNL assessed how well the adsorbent attracted uranium versus other elements, how durable the adsorbent was, how buildup of marine organisms might impact performance, and which adsorbent materials are not toxic.

This marine testing shows that these new fibers had the capacity to hold 6 grams of uranium per kilogram of adsorbent in only about 50 days in natural seawater. A nice video of U extraction from seawater can be seen on the University of Tennessee Knoxville website.

And later this month, July 19 to 22, global experts in uranium extraction from seawater will convene at the University of Maryland-College Park for the First International Conference on Seawater Uranium Recovery.

Stephen Kung, in DOE's Office of Nuclear Energy, says that “Finding alternatives to uranium ore mining is a necessary step in planning for the future of nuclear energy.” And these advances by PNNL and ORNL have reduced the cost by a factor of four in just five years. But it’s still over $200/lb of U3O8, twice as much as it needs to be to replace mining uranium ore.

Fortunately, the cost of uranium is a small percentage of the cost of nuclear fuel, which is itself a small percentage of the cost of nuclear power. Over the last twenty years, uranium spot prices have varied between $10 and $120/lb of U3O8, mainly from changes in the availability of weapons-grade uranium to blend down to make reactor fuel.

So as the cost of extracting U from seawater falls to below $100/lb, it will become a commercially viable alternative to mining new uranium ore. But even at $200/lb of U3O8, it doesn’t add more than a small fraction of a cent per kWh to the cost of nuclear power.

However, the big deal about extracting uranium from seawater is that it makes nuclear power completely renewable.

Uranium is dissolved in seawater at very low concentrations, only about 3 parts per billion (3 micrograms/liter or 0.00000045 ounces per gallon). But there is a lot of ocean water – 300 million cubic miles or about 350 million trillion gallons (350 quintillion gallons, 1,324 quintillion liters). So there’s about 4 billion tons of uranium in the ocean at any one time.

However, seawater concentrations of uranium are controlled by steady-state, or pseudo-equilibrium, chemical reactions between waters and rocks on the Earth, both in the ocean and on land. And those rocks contain 100 trillion tons of uranium. So whenever uranium is extracted from seawater, more is leached from rocks to replace it, to the same concentration. It is impossible for humans to extract enough uranium over the next billion years to lower the overall seawater concentrations of uranium, even if nuclear provided 100% of our energy and our species lasted a billion years.

In other words, uranium in seawater is actually completely renewable. As renewable as solar energy. Yes, uranium in the crust is, strictly speaking, finite. But so is the Sun, which will eventually burn out. But that won’t begin to happen for another 5 billion years. Even the wind on Earth will stop at about that time as our atmosphere boils off during the Sun’s initial death throes as a Red Giant.

According to Professor Jason Donev from the University of Calgary, “Renewable literally means 'to make new again'. Any resource that naturally replenishes with time, like the creation of wind or the growth of biological organisms for biomass or biofuels, is certainly renewable. Renewable energy means that the energy humans extract from nature will generally replace itself. And now uranium as fuel meets this definition.”

So by any definition, solar, wind, hydro and nuclear are all renewable. It’s about time society recognized this and added nuclear to the renewable portfolio.

Dr. James Conca is an expert on energy, nuclear and dirty bombs, a planetary geologist, and a professional speaker. Follow him on Twitter @jimconca and see his book at Amazon.com

Crab Nebula

From Wikipedia, the free encyclopedia

Crab Nebula

Supernova remnant
Hubble Space Telescope mosaic image assembled from 24 individual Wide Field and Planetary Camera 2 exposures taken in October 1999, January 2000, and December 2000
Observation data: J2000.0 epoch
Right ascension	05h 34m 31.94s
Declination	+22° 00′ 52.2″
Distance	6500±1600 ly   (2000±500 pc)
Apparent magnitude (V)	+8.4
Apparent dimensions (V)	420″ × 290″
Constellation	Taurus
Physical characteristics
Radius	~5.5 ly   (~1.7 pc)
Absolute magnitude (V)	−3.1±0.5
Notable features	Optical pulsar
Designations	Messier 1, NGC 1952, Taurus A, Sh2-244

The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant in the constellation of Taurus. The now-current name is due to William Parsons, who observed the object in 1840 using a 36-inch telescope and produced a drawing that looked somewhat like a crab. Corresponding to a bright supernova recorded by Chinese astronomers in 1054, the nebula was observed later by English astronomer John Bevis in 1731. The nebula was the first astronomical object identified with a historical supernova explosion.

At an apparent magnitude of 8.4, comparable to that of Saturn's moon Titan, it is not visible to the naked eye but can be made out using binoculars under favourable conditions. The nebula lies in the Perseus Arm of the Milky Way galaxy, at a distance of about 2.0 kiloparsecs (6,500 ly) from Earth. It has a diameter of 3.4 parsecs (11 ly), corresponding to an apparent diameter of some 7 arcminutes, and is expanding at a rate of about 1,500 kilometers per second (930 mi/s), or 0.5% of the speed of light.

At the center of the nebula lies the Crab Pulsar, a neutron star 28–30 kilometers (17–19 mi) across with a spin rate of 30.2 times per second, which emits pulses of radiation from gamma rays to radio waves. At X-ray and gamma ray energies above 30 keV, the Crab Nebula is generally the brightest persistent source in the sky, with measured flux extending to above 10 TeV. The nebula's radiation allows for the detailed studying of celestial bodies that occult it. In the 1950s and 1960s, the Sun's corona was mapped from observations of the Crab Nebula's radio waves passing through it, and in 2003, the thickness of the atmosphere of Saturn's moon Titan was measured as it blocked out X-rays from the nebula.

The inner part of the nebula is a much smaller pulsar wind nebula that appears as a shell surrounding the pulsar. Some sources consider the Crab Nebula to be an example of both a pulsar wind nebula as well as a supernova remnant, while others separate the two phenomena based on the different sources of energy production and behavior. For the Crab Nebula, the divisions are superficial but remain meaningful to researchers and their lines of study.

Observational history

HaRGB image of the Crab Nebula from the Liverpool Telescope, exposures totaling 1.4 hours.

Modern understanding that the Crab Nebula was created by a supernova traces back to 1921, when Carl Otto Lampland announced he had seen changes in its structure. This eventually led to the conclusion that the creation of the Crab Nebula corresponds to the bright SN 1054 supernova recorded by Chinese astronomers in AD 1054. There is a 13th-century Japanese reference to this "guest star" in Meigetsuki.

The event was long considered unrecorded in Islamic astronomy, but in 1978 a reference was found in a 13th-century copy made by Ibn Abi Usaibia of a work by Ibn Butlan, a Nestorian Christian physician active in Baghdad at the time of the supernova.

First identification

Reproduction of the first depiction of the nebula by Lord Rosse (1844) (colour-inverted to appear white-on-black)

 

The Crab Nebula was first identified in 1731 by John Bevis. The nebula was independently rediscovered in 1758 by Charles Messier as he was observing a bright comet. Messier catalogued it as the first entry in his catalogue of comet-like objects; in 1757, Alexis Clairaut reexamined the calculations of Edmund Halley and predicted the return of Halley's Comet in late 1758. The exact time of the comet's return required the consideration of perturbations to its orbit caused by planets in the Solar System such as Jupiter, which Clairaut and his two colleagues Jérôme Lalande and Nicole-Reine Lepaute carried out more precisely than Halley, finding that the comet should appear in the constellation of Taurus. It is in searching in vain for the comet that Charles Messier found the Crab nebula, which he at first thought to be Halley's comet. After some observation, noticing that the object that he was observing was not moving across the sky, Messier concluded that the object was not a comet. Messier then realised the usefulness of compiling a catalogue of celestial objects of a cloudy nature, but fixed in the sky, to avoid incorrectly cataloguing them as comets.

William Herschel observed the Crab Nebula numerous times between 1783 and 1809, but it is not known whether he was aware of its existence in 1783, or if he discovered it independently of Messier and Bevis. After several observations, he concluded that it was composed of a group of stars. The 3rd Earl of Rosse observed the nebula at Birr Castle in 1844 using a 36-inch (0.9 m) telescope, and referred to the object as the "Crab Nebula" because a drawing he made of it looked like a crab. He observed it again later, in 1848, using a 72-inch (1.8 m) telescope and could not confirm the supposed resemblance, but the name stuck nevertheless.

Connection to SN 1054

The nebula is seen in the visible spectrum at 550 nm (green light).

 

In 1913, when Vesto Slipher registered his spectroscopy study of the sky, the Crab Nebula was again one of the first objects to be studied. In the early twentieth century, the analysis of early photographs of the nebula taken several years apart revealed that it was expanding. Tracing the expansion back revealed that the nebula must have become visible on Earth about 900 years ago. Historical records revealed that a new star bright enough to be seen in the daytime had been recorded in the same part of the sky by Chinese astronomers in 1054.

Changes in the cloud, suggesting its small extent, were discovered by Carl Lampland in 1921. That same year, John Charles Duncan demonstrated that the remnant is expanding, while Knut Lundmark noted its proximity to the guest star of 1054.

In 1928, Edwin Hubble proposed associating the cloud to the star of 1054, an idea which remained controversial until the nature of supernovae was understood, and it was Nicholas Mayall who indicated that the star of 1054 was undoubtedly the supernova whose explosion produced the Crab Nebula. The search for historical supernovae started at that moment: seven other historical sightings have been found by comparing modern observations of supernova remnants with astronomical documents of past centuries. Given its great distance, the daytime "guest star" observed by the Chinese could only have been a supernova—a massive, exploding star, having exhausted its supply of energy from nuclear fusion and collapsed in on itself. 

Recent analysis of historical records have found that the supernova that created the Crab Nebula probably appeared in April or early May, rising to its maximum brightness of between apparent magnitude −7 and −4.5 (brighter than everything in the night sky except the Moon) by July. The supernova was visible to the naked eye for about two years after its first observation. Thanks to the recorded observations of Far Eastern and Middle Eastern astronomers of 1054, Crab Nebula became the first astronomical object recognized as being connected to a supernova explosion.

Crab Pulsar

Image combining optical data from Hubble (in red) and X-ray images from Chandra X-ray Observatory (in blue).

 

In the 1960s, because of the prediction and discovery of pulsars, the Crab Nebula again became a major center of interest. It was then that Franco Pacini predicted the existence of the Crab Pulsar for the first time, which would explain the brightness of the cloud. The star was observed shortly afterwards in 1968. The discovery of the Crab pulsar, and the knowledge of its exact age (almost to the day) allows for the verification of basic physical properties of these objects, such as characteristic age and spin-down luminosity, the orders of magnitude involved (notably the strength of the magnetic field), along with various aspects related to the dynamics of the remnant. The role of this supernova to the scientific understanding of supernova remnants was crucial, as no other historical supernova created a pulsar whose precise age is known for certain. The only possible exception to this rule would be SN 1181 whose supposed remnant, 3C 58, is home to a pulsar, but its identification using Chinese observations from 1181 is sometimes contested.

Physical conditions

Hubble image of a small region of the Crab Nebula, showing Rayleigh–Taylor instabilities in its intricate filamentary structure.

 

In visible light, the Crab Nebula consists of a broadly oval-shaped mass of filaments, about 6 arcminutes long and 4 arcminutes wide (by comparison, the full moon is 30 arcminutes across) surrounding a diffuse blue central region. In three dimensions, the nebula is thought to be shaped either like an oblate spheroid (estimated as 1,380 pc/4,500 ly away) or a prolate spheroid (estimated as 2,020 pc/6,600 ly away). The filaments are the remnants of the progenitor star's atmosphere, and consist largely of ionized helium and hydrogen, along with carbon, oxygen, nitrogen, iron, neon and sulfur. The filaments' temperatures are typically between 11,000 and 18,000 K, and their densities are about 1,300 particles per cm³.

In 1953 Iosif Shklovsky proposed that the diffuse blue region is predominantly produced by synchrotron radiation, which is radiation given off by the curving motion of electrons in a magnetic field. The radiation corresponded to electrons moving at speeds up to half the speed of light. Three years later the theory was confirmed by observations. In the 1960s it was found that the source of the curved paths of the electrons was the strong magnetic field produced by a neutron star at the centre of the nebula.

Distance

Even though the Crab Nebula is the focus of much attention among astronomers, its distance remains an open question, owing to uncertainties in every method used to estimate its distance. In 2008, the consensus was that its distance from Earth is 2.0 ± 0.5 kpc (6,500 ± 1,600 ly). Along its longest visible dimension, it thus measures about 4.1 ± 1 pc (13 ± 3 ly) across.

The Crab Nebula currently is expanding outward at about 1,500 km/s (930 mi/s). Images taken several years apart reveal the slow expansion of the nebula, and by comparing this angular expansion with its spectroscopically determined expansion velocity, the nebula's distance can be estimated. In 1973, an analysis of many methods used to compute the distance to the nebula had reached a conclusion of about 1.9 kpc (6,300 ly), consistent with the currently cited value.

The Crab Pulsar itself was discovered in 1968. Tracing back its expansion (assuming a constant decrease of expansion speed due to the nebula's mass) yielded a date for the creation of the nebula several decades after 1054, implying that its outward velocity has decelerated less than assumed since the supernova explosion. This reduced deceleration is believed to be caused by energy from the pulsar that feeds into the nebula's magnetic field, which expands and forces the nebula's filaments outward.

Mass

Estimates of the total mass of the nebula are important for estimating the mass of the supernova's progenitor star. The amount of matter contained in the Crab Nebula's filaments (ejecta mass of ionized and neutral gas; mostly helium) is estimated to be 4.6±1.8 M_☉.

Helium-rich torus

One of the many nebular components (or anomalies) of the Crab Nebula is a helium-rich torus which is visible as an east-west band crossing the pulsar region. The torus composes about 25% of the visible ejecta. However, it is suggested by calculation that about 95% of the torus is helium. As yet, there has been no plausible explanation put forth for the structure of the torus.

Central star

Slow-motion movie of the Crab Pulsar, taken with OES Single-Photon-Camera.

 

At the center of the Crab Nebula are two faint stars, one of which is the star responsible for the existence of the nebula. It was identified as such in 1942, when Rudolf Minkowski found that its optical spectrum was extremely unusual. The region around the star was found to be a strong source of radio waves in 1949 and X-rays in 1963, and was identified as one of the brightest objects in the sky in gamma rays in 1967. Then, in 1968, the star was found to be emitting its radiation in rapid pulses, becoming one of the first pulsars to be discovered.

 

Pulsars are sources of powerful electromagnetic radiation, emitted in short and extremely regular pulses many times a second. They were a great mystery when discovered in 1967, and the team who identified the first one considered the possibility that it could be a signal from an advanced civilization. However, the discovery of a pulsating radio source in the center of the Crab Nebula was strong evidence that pulsars were formed by supernova explosions. They now are understood to be rapidly rotating neutron stars, whose powerful magnetic field concentrates their radiation emissions into narrow beams.

The Crab Pulsar is believed to be about 28–30 km (17–19 mi) in diameter; it emits pulses of radiation every 33 milliseconds. Pulses are emitted at wavelengths across the electromagnetic spectrum, from radio waves to X-rays. Like all isolated pulsars, its period is slowing very gradually. Occasionally, its rotational period shows sharp changes, known as 'glitches', which are believed to be caused by a sudden realignment inside the neutron star. The energy released as the pulsar slows down is enormous, and it powers the emission of the synchrotron radiation of the Crab Nebula, which has a total luminosity about 75,000 times greater than that of the Sun.

The pulsar's extreme energy output creates an unusually dynamic region at the centre of the Crab Nebula. While most astronomical objects evolve so slowly that changes are visible only over timescales of many years, the inner parts of the Crab Nebula show changes over timescales of only a few days. The most dynamic feature in the inner part of the nebula is the point where the pulsar's equatorial wind slams into the bulk of the nebula, forming a shock front. The shape and position of this feature shifts rapidly, with the equatorial wind appearing as a series of wisp-like features that steepen, brighten, then fade as they move away from the pulsar to well out into the main body of the nebula.

Progenitor star

This sequence of Hubble images shows features in the inner Crab Nebula changing over a period of four months.

 

The star that exploded as a supernova is referred to as the supernova's progenitor star. Two types of stars explode as supernovae: white dwarfs and massive stars. In the so-called Type Ia supernovae, gases falling onto a 'dead' white dwarf raise its mass until it nears a critical level, the Chandrasekhar limit, resulting in a runaway nuclear fusion explosion that obliterates the star; in Type Ib/c and Type II supernovae, the progenitor star is a massive star whose core runs out of fuel to power its nuclear fusion reactions and collapses in on itself, releasing gravitational potential energy in a form that blows away the star's outer layers. The presence of a pulsar in the Crab Nebula means that it must have formed in a core-collapse supernova; Type Ia supernovae do not produce pulsars.

Theoretical models of supernova explosions suggest that the star that exploded to produce the Crab Nebula must have had a mass of between 9 and 11 M_☉. Stars with masses lower than 8 M_☉ are thought to be too small to produce supernova explosions, and end their lives by producing a planetary nebula instead, while a star heavier than 12 M_☉ would have produced a nebula with a different chemical composition from that observed in the Crab Nebula. Recent studies, however, suggest the progenitor could have been a super-asymptotic giant branch star in the 8 to 10 M_☉ range that would have exploded in an electron-capture supernova.

A significant problem in studies of the Crab Nebula is that the combined mass of the nebula and the pulsar add up to considerably less than the predicted mass of the progenitor star, and the question of where the 'missing mass' is, remains unresolved. Estimates of the mass of the nebula are made by measuring the total amount of light emitted, and calculating the mass required, given the measured temperature and density of the nebula. Estimates range from about 1–5 M_☉, with 2–3 M_☉ being the generally accepted value. The neutron star mass is estimated to be between 1.4 and 2 M_☉. 

The predominant theory to account for the missing mass of the Crab Nebula is that a substantial proportion of the mass of the progenitor was carried away before the supernova explosion in a fast stellar wind, a phenomenon commonly seen in Wolf-Rayet stars. However, this would have created a shell around the nebula. Although attempts have been made at several wavelengths to observe a shell, none has yet been found.

Transits by Solar System bodies

Chandra image showing Saturn's moon Titan transiting the nebula.

 

The Crab Nebula lies roughly 1.5 degrees away from the ecliptic—the plane of Earth's orbit around the Sun. This means that the Moon—and occasionally, planets—can transit or occult the nebula. Although the Sun does not transit the nebula, its corona passes in front of it. These transits and occultations can be used to analyze both the nebula and the object passing in front of it, by observing how radiation from the nebula is altered by the transiting body.

Lunar

Lunar transits have been used to map X-ray emissions from the nebula. Before the launch of X-ray-observing satellites, such as the Chandra X-ray Observatory, X-ray observations generally had quite low angular resolution, but when the Moon passes in front of the nebula, its position is very accurately known, and so the variations in the nebula's brightness can be used to create maps of X-ray emission. When X-rays were first observed from the Crab Nebula, a lunar occultation was used to determine the exact location of their source.

Solar

The Sun's corona passes in front of the Crab Nebula every June. Variations in the radio waves received from the Crab Nebula at this time can be used to infer details about the corona's density and structure. Early observations established that the corona extended out to much greater distances than had previously been thought; later observations found that the corona contained substantial density variations.

Other objects

Very rarely, Saturn transits the Crab Nebula. Its transit in 2003 was the first since 1296; another will not occur until 2267. Researchers used the Chandra X-ray Observatory to observe Saturn's moon Titan as it crossed the nebula, and found that Titan's X-ray 'shadow' was larger than its solid surface, due to absorption of X-rays in its atmosphere. These observations showed that the thickness of Titan's atmosphere is 880 km (550 mi). The transit of Saturn itself could not be observed, because Chandra was passing through the Van Allen belts at the time.