October 26: Lewis Boss

Lewis Boss

October 26, 1846 - October 12, 1912

Lewis Boss was an American astronomer. He was born in Providence, Rhode Island. In 1870 he graduated from Dartmouth College, then went to work as a clerk for the U.S. Government. He served as an assistant astronomer for a government expedition to survey the U.S-Canadian border. In 1876 he became the director of the Dudley Observatory in Schenectady, New York.

He became editor of the Astronomical Journal in 1909, but responsibility passed to his son, Benjamin Boss, upon his death in 1912. Benjamin continued to edit the journal until 1941.

Lewis Boss is noted for his work in cataloguing the locations and proper motions of stars. He also led an expedition to Chile in 1882 to observe the transit of Venus, and also catalogued information concerning cometary orbits.

In 1910, he published Preliminary General Catalogue of 6188 Stars for the Epoch 1900, a compilation of the proper motions of stars. This catalog was later expanded after his death by his son Benjamin Boss.

His most significant discovery was the calculation of the convergent point of the Hyades star cluster.

Boss was awarded the Gold Medal of the Royal Astronomical Society in 1905.

The Lunar crater Boss is named in his honor.

September 12: Guillaume Le Gentil

The ruins of Pondicherry in 1769 seen from the north. Le Gentil’s observatory was in the structure to the right of the flag pole.

Guillaume Joseph Hyacinthe Jean-Baptiste Le Gentil de la Galaisière

September 12, 1725 – October 22, 1792

Guillaume Le Gentil was a French astronomer.

He was born in Coutances and first intended to enter the church before turning to astronomy. He discovered what are now known as the Messier objects M32, M36 and M38, as well as the nebulosity in M8, and he was the first to catalogue the dark nebula sometimes known as Le Gentil 3 (in the constellation Cygnus).

He was part of the international collaborative project to measure the distance to the Sun, by observing the transit of Venus at different points on the earth. Edmond Halley had suggested the idea, but it required careful measurements from different places on earth, and the project was launched with more than a hundred observers dispatched to different parts of the globe, for observing the transit coming up in 1761. The French expedition turned out to be particularly unlucky, and perhaps the most unfortunate was Guillaume le Gentil, who set out for Pondicherry, a French colony in India.

He set out from Paris in March 1760, and reached Île de France (Mauritius) in July. But having learned that war had broken out between France and Britain, and deeming it dangerous to try and reach Pondicherry, he determined to go elsewhere; a frigate was bound for India's Coromandel Coast, and he sailed in March 1761. When they had nearly arrived they learned that the British had occupied Pondicherry, so the frigate was obliged to return to Île de France. June 6, the day of the transit, came, and the sky was clear, but he could not take astronomical observations with the vessel rolling about. After having come this far, he thought he might as well await the next transit of Venus, which would come in another eight years (they are relatively infrequent, occurring in pairs 8 years apart, but each such pair is separated from the previous and next pairs by more than a century.)

After spending some time mapping the eastern coast of Madagascar, he decided to record the 1769 transit from Manila in the Philippines. Encountering hostility from the Spanish authorities there, he headed back to Pondicherry, which had been restored to France by peace treaty in 1763, where he arrived in March 1768. He built a small observatory and waited patiently. At last, the day in question (June 4, 1769) arrived, but although the mornings in the preceding month had all been lovely, on this day the sky became overcast, and Le Gentil saw nothing. The misfortune drove him to the brink of insanity, but at last he recovered enough strength to return to France.

The return trip was first delayed by dysentery, and further when his ship was caught in a storm and dropped him off at Île Bourbon (Réunion), where he had to wait until a Spanish ship took him home. He finally arrived in Paris eleven years later in October 1771, only to find that he had been declared legally dead and been replaced in the Royal Academy of Sciences. His wife had remarried, and all his relatives had "enthusiastically plundered his estate". Lengthy litigation and the intervention of the king were ultimately required before things were normalized. He got back his seat in the academy, remarried, and lived apparently happily for another 21 years.

One of his interesting findings was that the duration of the lunar eclipse of 30 August 1765 was predicted by a Tamil astronomer, based on the computation of the size and extent of the earth-shadow (going back to Aryabhata, 5th c.), and was found short by 41 seconds, whereas the charts of Tobias Mayer were long by 68 seconds.

The Lunar crater Le Gentil is named in his honor.

August 30: Johann Hieronymus Schröter

Johann Hieronymus Schröter

August 30, 1745 – August 29, 1816

Johann Hieronymus Schröter was a German astronomer. Schröter was born in Erfurt, and studied law at Göttingen University from 1762 until 1767, after which he started a ten-year-long legal practice.

In 1777 he was appointed Secretary of the Royal Chamber of George III in Hanover, where he made the acquaintance of two of William Herschel's brothers. In 1779 he acquired a three-foot-long (91 cm, almost one metre) achromatic refractor with 2.25-inch (57 mm) lens (50 mm) to observe the Sun, Moon and Venus. Herschel's discovery of Uranus in 1781 inspired Schröter to pursue astronomy more seriously, and he resigned his post and became chief magistrate and district governor of Lilienthal.

He made extensive drawings of the features of Mars, yet curiously he was always erroneously convinced that what he was seeing was mere cloud formations rather than geographical features. In 1791 he published an important early study on the topography of the Moon entitled Selenotopographische Fragmente zur genauern Kenntniss der Mondfläche. In 1793 he was the first to notice the phase anomaly of Venus, now known as the Schröter effect, where the phase appears more concave than geometry predicts.

In 1813, he suffered the disruptions of the Napoleonic Wars: his work was ruined by the French under Vandamme, who destroyed his books, writings and observatory. He never recovered from the catastrophe.

His drawings of Mars were not rediscovered until 1873 (by François J. Terby) and were not published until 1881 (by H. G. van de Sande Bakhuyzen), well after his death.

He was elected a member of the Royal Swedish Academy of Sciences in 1794.

The lunar crater Schröter, Vallis Schröteri (Schröter's Valley) and the Martian crater Schroeter are named in his honor.

August 24: Amédée Mouchez

Amédée Ernest Barthélemy Mouchez

August 24, 1821 – June 29, 1892

Amédée Mouchez was a French naval officer who became director of the Paris Observatory and launched the ill-fated Carte du Ciel project in 1887.

Born in Madrid, Spain, Mouchez embarked on a career in the French Navy as an ensign in 1843. This was a period of relative international maritime peace and much of the navy's activities were dedicated to exploration and discovery. Mouchez was initially occupied on hydrographic studies along the coasts of Korea, China and South America, penetrating 320 km up the Paraguay River and exploring the Abrolhos Islands. He improved the practice of surveying at sea, adapting terrestrial instruments for naval use, and was especially concerned with the problems of determining longitude. He developed the use of the theodolite and meridian telescope to improve the error in establishing longitude from around 30″ to 3-4″.

Attaining the rank of post captain in 1868, he embarked on a series of expeditions to chart the coast of Algeria. However, in 1870, during the Franco-Prussian War, he was called upon to make an heroic defence of the port of Le Havre.

Returning to his Algerian survey, he brought it to a conclusion in 1873, when he was elected to the Bureau des Longitudes and, in the following year, was sponsored by the Académie des sciences to observe the transit of Venus from St. Paul Island in the Indian Ocean. On 9 December he made a sequence of superb photographic plates of the event.

In 1875, the Académie elected him a member of the astronomy section and in 1878 he was promoted to rear admiral and awarded the role of director of the Paris Observatory. The observatory had fallen into disrepair and disrepute since the chaos of the 1870 war and the Paris Commune of 1871. Mouchez set about a programme of reconstruction but failed to persuade the government to fund a new observatory outside the centre of Paris.

In 1887, he collaborated with Sir David Gill to host an international astronomical conference in Paris. The principal outcome of the conference was a multi-national project to compile and index a photographic atlas of the heavens, the Carte du Ciel. The project consumed massive effort over several decades before it was rendered obsolete by modern astronomical methods.

The Lunar crater Mouchez is named in his honor.

July 11: Joseph Lalande

Joseph Jérôme Lefrançois de Lalande

July 11, 1732 – April 4, 1807

Joseph Lalande was a French astronomer and writer.

Lalande was born at Bourg-en-Bresse. His parents sent him to Paris to study law, but as a result of lodging in the Hôtel Cluny, where Delisle had his observatory, he was drawn to astronomy, and became the zealous and favoured pupil of both Delisle and Pierre Charles Le Monnier. Having completed his legal studies, he was about to return to Bourg to practise as an advocate, when Lemonnier obtained permission to send him to Berlin, to make observations on the lunar parallax in concert with those of Lacaille at the Cape of Good Hope.

The successful execution of this task obtained for him, before he was twenty-one, admission to the Academy of Berlin, as well as his election as an adjunct astronomer to the French Academy of Sciences. He now devoted himself to the improvement of the planetary theory, publishing in 1759 corrected edition of Edmond Halley's tables, with a history of Halley's Comet whose return in that year he had helped Alexis Clairaut to calculate. In 1762 Delisle resigned the chair of astronomy in the Collège de France in Lalande's favour. The duties were discharged by Lalande for forty-six years. His house became an astronomical seminary, and amongst his pupils were Delambre, Giuseppe Piazzi, Pierre Méchain, and his own nephew Michel Lalande. By his publications in connection with the transit of Venus of 1769 he won great fame. However, his difficult personality lost him some popularity.

Although his investigations were conducted with diligence rather than genius, Lalande's career was an eminent one. As a lecturer and writer he helped popularise astronomy. His planetary tables, into which he introduced corrections for mutual perturbations, were the best available up to the end of the 18th century and the Lalande prize instituted by him in 1802 for the chief astronomical performance of each year still testifies to his enthusiasm for his favourite pursuit.

His star catalog of 1801 contains many faint but nearby (and thereby low mass) stars, so that a star name such as Lalande 21185 is almost guaranteed to refer to such a star, rather than a bluer, brighter, more distant one.

In 1765, Lalande was elected a member of the Royal Swedish Academy of Sciences. The crater Lalande on the Moon is named in his honor.

June 25: Rupert Wildt

Rupert Wildt

June 25, 1905 – January 9, 1976

Rupert Wildt was a German-American astronomer. In 1927 he was awarded a Ph.D. from the University of Berlin. He joined the University of Göttingen, specializing in the properties of atmospheres.

In 1932 he studied the spectra of Jupiter, and other outer planets, and identified certain absorption bands as belonging to the hydrogen-rich compounds of methane and ammonia. The composition appeared consistent with a composition similar to the sun and other stars.

Assuming that the atmosphere was composed of these gases, during the 1940s and 1950s he constructed a model of the structure of these planets. He believed the core of the planets is solid and composed of a mixture of rock and metal, covered by a thick outer shell of ice, overlaid by a dense atmosphere. His model is still widely accepted.

In 1934 he emigrated to the United States, and became a research assistant at Princeton University from 1937 until 1942. He then became an assistant professor at the University of Virginia until 1947, before joining the faculty of the Yale University.

In 1937 he proposed that the atmosphere of Venus was composed of a mist of formaldehyde. His observations of the atmosphere did not find any water at the time, but later balloon-based measurements did show water in the atmosphere and so his proposal was abandoned. In 1940, however, he also hypothesized that the carbon dioxide in the venusian atmosphere trapped heat, a phenomenon later called the greenhouse effect.

From 1965 until 1968 he was president of the Association of Universities for Research in Astronomy. In the period 1966-1968 he also held the post of the chairman of the department of astronomy at Yale, and from 1973 until his death he was professor emeritus.

Asteroid 1953 Rupertwildt and the Lunar crater Wildt are named in his honor.

April 8: David Rittenhouse

David Rittenhouse
April 8, 1732 – June 26, 1796

David Rittenhouse was a renowned American astronomer, inventor, clockmaker, mathematician, surveyor, scientific instrument craftsman, and public official. Rittenhouse was a member of the American Philosophical Society and the first director of the United States Mint.

Rittenhouse was born near Germantown, Philadelphia, Pennsylvania. He was self-taught and from a young age showed great ability in science and mathematics. At nineteen years old, he started a scientific instrument shop at his father's farm in West Norriton Township, Pennsylvania. His skill with instruments, particularly clocks, led him to construct two orreries, one of which is currently in the library of the University of Pennsylvania and the other is at Peyton Hall of Princeton University. Rittenhouse was one of the first to build a telescope used in the United States.

His telescope, which utilized natural spider silk to form the reticle, was used to observe and record part of the transit of Venus across the sun on 1769-06-03, as well as the planet's atmosphere.

In 1785, Rittenhouse made perhaps the first diffraction grating using 50 hairs between two finely threaded screws, with an approximate spacing of about 100 lines per inch. This was roughly the same technique that Joseph von Fraunhofer used in 1821 for his wire diffraction grating.

At a young age Rittenhouse showed a high level of intelligence by creating a working scale model of his grandfather's paper mill. His uncle was a carpenter in Philadelphia, who died at a young age. When he died, he left young Rittenhouse a set of tools and instructional books. It was with these tools that Rittenhouse became an inventor and carved out a career. Sparked by the making of his first clock as a young boy, he later impacted the United States in many ways, from creating the first observatory in the country to founding the United States Mint.

After Galileo saw the first sign of Earth's neighbor, Venus, in 1610, astronomers who had been studying the planet, chose Rittenhouse as the person to study the transit path of Venus and its atmosphere. Rittenhouse was the perfect person to study the mysterious planet, as he had a personal observatory on his family farm. "His telescope, which he made himself, utilized grating intervals and spider threads on the focus of the telescope." His telescope is very similar to some modern day telescopes. Rittenhouse served on the American Astronomical Society, and this was another factor in being chosen to study Venus . Throughout his life, he had the honour to serve in many different clubs, committees, and much more. One example is the American Philological Society, he began as a librarian, became secretary, and after Benjamin Franklin's death, he became Vice President. Another one of his interests was the Royal Society of London; this was very rare to see a foreign member of this exclusive society.

When Rittenhousee was thirteen years of age, he had mastered Isaac Newton's Laws of Motion and Gravity. As a young boy he loved to build scale models, such as a working waterwheel and a paper mill. Rittenhouse never went to elementary school and was completely self-educated from family books. With his love of tools and his amazing ability to create things he crafted two orreries for Rutgers University in New Jersey. In return for the gift, the college gave him a scholarship to attend the college enabling him to obtain a degree in philosophy. At the age of twenty-eight, he published his first mathematical paper, one of many papers published throughout his life.

His great excitement at observing the infrequently-occurring transit of Venus (for which he had prepared for a year) resulted in his fainting during the observation. In addition to the work involved in the preparations, Rittenhouse had also been ill the week before the transit. Lying on his back beneath the telescope, trained at the afternoon sun, he regained consciousness after a few minutes and continued his observations. His account of the transit, published in the Transactions of the American Philosophical Society, does not mention his fainting, though it is otherwise meticulous in its record.

The Lunar crater Rittenhouse is named in his honor.

March 19: Franz von Gruithuisen

Baron Franz von Paula Gruithuisen

March 19, 1774 – 1852

Franz von Gruithuisen was a Bavarian physician and astronomer. He taught medical students before becoming a professor of astronomy at the University of Munich in 1826.

During his period of medical studies and instruction, he was noted for his contributions to urology and lithotrity. He developed ideas on safer methods to remove bladder stones transurethrally, and his instruments served as models for subsequent devices.

Like others before and since his time, Gruithuisen believed that the Earth's moon was inhabitable. He made multiple observations of the lunar surface that supported his beliefs, including his announcement of the discovery of a city in the rough terrain to the north of Schröter crater he named the Wallwerk. This region contains a series of somewhat linear ridges that have a fishbone-like pattern, and, with the small refracting telescope he was using, could be perceived as resembling buildings complete with streets. He published his observations in 1824, but they were greeted with much skepticism by other astronomers of the time. His claims were readily refuted using more powerful instruments.

He is also noted for the discovery of bright caps on the cusps of the crescent Venus, for being the first to suggest that craters on the Moon were caused by meteorite impacts and for his prolific rate of publication. He proposed that jungles on Venus grew more rapidly than in Brazil due to the proximity of the planet to the Sun, and that as a consequence the inhabitants celebrated fire festivals— the cause of the bright caps on Venus.

The crater Gruithuisen on the Moon is named in his honor.

February 22: Pierre Janssen

Pierre Jules César Janssen

February 22, 1824 – December 23, 1907

Pierre Janssen was a French astronomer who, along with the English scientist Joseph Norman Lockyer, is credited with discovering the gas helium.

Janssen was born in Paris and studied mathematics and physics at the faculty of sciences. He taught at the lycée Charlemagne in 1853, and in the school of architecture 1865 – 1871, but his energies were mainly devoted to various scientific missions entrusted to him. Thus in 1857 he went to Peru in order to determine the magnetic equator; in 1861 – 1862 and 1864, he studied telluric absorption in the solar spectrum in Italy and Switzerland; in 1867 he carried out optical and magnetic experiments at the Azores; he successfully observed both transits of Venus, that of 1874 in Japan, that of 1882 at Oran in Algeria; and he took part in a long series of solar eclipse-expeditions, e.g. to Trani (1867), Guntur (1868), Algiers (1870), Siam (1875), the Caroline Islands (1883), and to Alcosebre in Spain (1905). To see the eclipse of 1870 he escaped from besieged Paris in a balloon (that eclipse was obscured by cloud cover, however).

In 1868 Janssen discovered how to observe solar prominences without an eclipse. On 18 August of that year, while observing an eclipse of the Sun in India, he noticed a bright yellow line with a wavelength of 587.49 nm in the spectrum of the chromosphere of the Sun. This was the first observation of this particular spectral line, and one possible source for it was an element not yet discovered on the earth. Janssen was at first ridiculed since no element had ever been detected in space before being found on Earth.

On 20 October of the same year, Joseph Norman Lockyer also observed the same yellow line in the solar spectrum and concluded that it was caused by an unknown element, after unsuccessfully testing to see if it were some new type of hydrogen. This was the first time a chemical element was discovered on an extraterrestrial world before being found on the earth. Lockyer and the English chemist Edward Frankland named the element with the Greek word for the Sun, helios.

At the great Indian eclipse of 1868, Janssen also demonstrated the gaseous nature of the red prominences, and devised a method of observing them under ordinary daylight conditions. One main purpose of his spectroscopic inquiries was to answer the question whether the Sun contains oxygen or not. An indispensable preliminary was the virtual elimination of oxygen-absorption in the Earth's atmosphere, and his bold project of establishing an observatory on the top of Mont Blanc was prompted by a perception of the advantages to be gained by reducing the thickness of air through which observations have to be made. This observatory, the foundations of which were fixed in the snow that appears to cover the summit to a depth of ten metres, was built in September 1893, and Janssen, in spite of his sixty-nine years, made the ascent and spent four days taking observations.

In 1875, Janssen was appointed director of the new astrophysical observatory established by the French government at Meudon, and set on foot there in 1876 the remarkable series of solar photographs collected in his great Atlas de photographies solaires (1904). The first volume of the Annales de l'observatoire de Meudon was published by him in 1896.

The Lunar crater Janssen and a crater on Mars are named in his honor.

February 13: Guido Horn D'Arturo

Guido Horn D'Arturo

February 13, 1879 - April 1, 1967

Guido Horn D'Arturo was an Austrian astronomer who spent much of his career working in Italy. In 1920 he became director of the Bologna University Observatory. His research included positional astronomy, moving clusters, comets, solar eclipses, and history of astronomy; optics including geometric, instrumental, physiologic, & unusual optical instruments. 

Guido Horn d’Arturo designed and built the first “multi mirror” telescope, and the resulting 1.2-m transit instrument was operational at the University of Bologna for almost a decade.

Horn maintained a large number of connections with astronomers throughout the world and intense activity in order to enhance the international role of Bologna Observatory . Between 1912 and 1939 Horn studied the "Black drop" phenomenon and the flying shadows. 

The black drop effect is an optical phenomenon visible during a transit of Venus and, to a lesser extent, a transit of Mercury. Just after second contact, and again just before third contact during the transit, a small black "teardrop" appears to connect Venus' disk to the limb of the Sun, making it impossible to accurately time the exact moment of second or third contact. This led to the failure of the attempts during the 18th century transits of Venus to establish a truly precise value for the astronomical unit.

The black drop effect was long thought to be due to Venus' thick atmosphere, and indeed it was held to be the first real evidence that Venus had an atmosphere. However, it is now thought by many to be an optical effect.

In 1926 D'Arturo made an expedition to Somalia, to observe a solar eclipse. In 1931 he founded the magazine "Coelum" and started the project for setting up a telescope in Loiano. He also devised a method of measuring the density of stellar tracks on photographic plates using diffraction.

February 5: Mariner 10 flyby of Venus

Mariner 10 passed Venus on February 5, 1974, 

at a closest range of 5,768 km at 17:01 UT

Mariner 10 was a robotic space probe launched on November 3, 1973 to fly by the planets Mercury and Venus. It was launched approximately 2 years after Mariner 9 and was the last spacecraft in the Mariner program (Mariner 11 and 12 were re-purposed to the Voyager program and redesignated Voyager 1 and Voyager 2). 

Mariner 10 was the seventh successful launch in the Mariner series and the first spacecraft to visit Mercury. It was also the first spacecraft to use the gravitational pull of one planet (Venus) to reach another (Mercury), and the first spacecraft mission to visit two planets. The spacecraft flew by Mercury three times in a retrograde heliocentric orbit and returned images and data on the planet. Mariner 10 returned the first-ever close-up images of Venus and Mercury. The primary scientific objectives of the mission were to measure Mercury's environment, atmosphere, surface, and body characteristics and to make similar investigations of Venus. Secondary objectives were to perform experiments in the interplanetary medium and to obtain experience with a dual-planet gravity-assist mission.

Mariner 10 was the first spacecraft to make use of an interplanetary "gravitational slingshot" maneuver, using Venus to bend its flight path and bring its perihelion down to the level of Mercury's orbit. This maneuver, inspired by the orbital mechanics calculations of the Italian scientist Giuseppe Colombo, put the spacecraft into an orbit that repeatedly brought it back to Mercury. Mariner 10 used the solar radiation pressure on its solar panels and its high-gain antenna as a means of attitude control during flight, the first spacecraft to use active solar pressure control.

The spacecraft passed Venus on February 5, 1974, at a closest range of 5768 km at 17:01 UT. Using a near-ultraviolet filter, it photographed the Cytherean chevron clouds and performed other atmospheric studies. It was discovered that extensive cloud detail could be seen via Mariner's ultra-violet camera filters. Venus's cloud cover is nearly featureless in visible light. Earth-based ultra-violet observation did reveal some indistinct blotching even before Mariner 10, but the detail seen by Mariner was a surprise to most researchers.

During its flyby of Venus, Mariner 10 discovered evidence of rotating clouds and a very weak magnetic field.

With its maneuvering gas just about exhausted, Mariner 10 started another orbit of the Sun. Engineering tests were continued until March 24, 1975, when the final depletion of the nitrogen supply was signaled by the onset of an un-programmed pitch turn. Commands were immediately sent to the spacecraft to turn off its transmitter, and radio signals to Earth ceased.

Presently, Mariner 10 is still orbiting the sun, although its on-board electronics have probably been damaged by the sun's radiation.