December 18: Gottfried Kirch

Gottfried Kirch

December 18, 1639 — July 25, 1710

Gottfried Kirch was a German astronomer. He first worked as a calendar-maker in Saxonia and Franconia. He began to learn astronomy in Jena, and studied under Hevelius in Danzig. In Danzig in 1667, Kirch published calendars and built several telescopes and instruments.

In 1686, Kirch went to Leipzig. There, he observed the great comet of 1686, together with Christoph Arnold. At Leipzig, Kirch also met his second wife, Maria Winckelmann (1670-1720), who had learned astronomy from Arnold. In 1688, he invented and charted the now obsolete constellation Sceptrum Brandenburgicum, the Brandenburg Scepter. Later, in 1699, he observed comet 55P/Tempel-Tuttle but this observation was not recognized until later analysis by Joachim Schubart.

In 1700, Kirch was appointed by Frederick I of Prussia as the first astronomer of the Prussian Royal Society of Sciences.

Kirch studied the double star Mizar, and discovered both the Wild Duck Cluster (Messier 11) (1681) and Globular Cluster M5 (May 5, 1702). He also discovered the variability of the Mira variable Chi Cygni in 1686.

The Lunar crater Kirch and the asteroid 6841 Gottfriedkirch are named in his honor.

October 20: Christopher Wren

Sir Christopher Wren

October 20, 1632 – February 25, 1723

Christopher Wren was one of the best known and highest acclaimed English architects in history, responsible for rebuilding 55 churches in the City of London after the Great Fire in 1666, including his masterpiece St Paul's Cathedral, completed in 1710.

Educated in Latin and Aristotelian physics at the University of Oxford, Wren was a notable astronomer, geometer, mathematician-physicist as well as an architect. He was a founder of the Royal Society (president 1680–82), and his scientific work was highly regarded by Sir Isaac Newton and Blaise Pascal.

One of Wren's friends, another great scientist and architect in his time, Robert Hooke said of him "Since the time of Archimedes there scarce ever met in one man in so great perfection such a mechanical hand and so philosophical mind."

When a fellow of All Souls, Wren constructed a transparent beehive for scientific observation; he began observing the moon, which was to lead to the invention of micrometers for the telescope. He experimented on terrestrial magnetism and had taken part in medical experiments, performing the first successful injection of a substance into the bloodstream (of a dog).

In Gresham College, he did experiments involving determining longitude through magnetic variation and through lunar observation to help with navigation, and helped construct a 35-foot (11 m) telescope with Sir Paul Neile. Wren also studied and improved the microscope and telescope at this time. He had also been making observations of the planet Saturn from around 1652 with the aim of explaining its appearance. His hypothesis was written up in De corpore saturni but before the work was published, Huygens presented his theory of the rings of Saturn. Immediately Wren recognized this as a better hypothesis than his own and De corpore saturni was never published. In addition, he constructed an exquisitely detailed lunar model and presented it to the king.

A year into Wren's appointment as a Savilian Professor in Oxford, the Royal Society was created and Wren became an active member. As a Savilian Professor, Wren studied thoroughly in mechanics, especially in elastic collisions and pendulum motions, which he studied extensively. He also directed his far-ranging intelligence to the study of meteorology, and fabricated a "weather-clock" that recorded temperature, humidity, rainfall and barometric pressure, which could be used to predict the weather.

Another topic to which Wren contributed was optics. He published a description of an engine to create perspective drawings and he discussed the grinding of conical lenses and mirrors. Out of this work came another of Wren's important mathematical results, namely that the hyperboloid of revolution is a ruled surface. These results were published in 1669. In subsequent years, Wren continued with his work with the Royal Society, although after the 1680s his scientific interests seem to have waned: no doubt his architectural and official duties absorbed all his time.

Mentioned above are only a few of Wren’s scientific works. He also studied in other areas not mentioned, ranging from agriculture, ballistics, water and freezing, to investigating light and refraction only to name a few. Thomas Birch's History of the Royal Society is one of the most important sources of our knowledge not only of the origins of the Society, but also the day to day running of the Society. It is in these records that the majority of Wren’s scientific works are recorded.

October 12: Carl August von Steinheil

Carl August von Steinheil

October 12, 1801 – September 14, 1870

Carl August von Steinheil was a German physicist.

Steinheil was born in Ribeauvillé, Alsace. He studied law in Erlangen then astronomy in Göttingen and Königsberg. He continued his studies in astronomy and physics when he started living on his father's manor in Perlachseck near Munich. He was professor for mathematics and physics at the University of Munich from 1832 to 1849.

In 1839, Steinheil used silver chloride and a cardboard camera to make pictures in negative from the Museum of Art and the Munich Frauenkirche, then taking another picture of the negative to get a positive, the actual black and white reproduction of a view on the object. The round pictures were about four cm wide, the way to get these pictures was called Steinheil method.

In 1846 Steinheil was called to Naples to install a new system for weight and measure units. Three years later, he was in the Board of Telegraphy in the Austrian Trade Ministry, designing a telegraph network for the entire empire, and helped to form the "Deutsch-Österreichischer Telegraphenverein" (German-Austrian Telegraph Society). In 1851 he started the Swiss telegraph network, when he returned to Munich as 'Konservator' of the mathematic-physical collections and ministerial secretary in the Trade Ministry of Bavaria.

He founded the optical-astronomical company C.A. Steinheil und Söhne to build telescopes, spectroscopes and photometers (his invention, used to measure brightness). In 1852 he added refractors and reflectors with silver-covered mirrors to the production. The silvering was done in a process developed by his friend Justus Liebig. Since 1862, his sons continued his company.

The Lunar crater Steinheil is named in his honor.

October 2: Charles Stark Draper

Charles Stark Draper

October 2, 1901 – July 25, 1987

Charles Draper was an American scientist and engineer, often referred to as "the father of inertial navigation." He was the founder and director of the MIT Instrumentation Laboratory, later renamed the Charles Stark Draper Laboratory, which under his direction designed and built the Apollo Guidance Computer for NASA, which made the Apollo moon landings possible.

Born in Windsor, Missouri, he attended the University of Missouri in 1917, then transferred to Stanford University, California in 1919, from which he earned a B.A. in psychology in 1922. After Stanford, he attended Massachusetts Institute of Technology (MIT), from which he earned an S.B. in electrochemical engineering in 1926, and an S.M. and Sc.D. in physics in 1928 and 1938 respectively.

He started teaching while at MIT, first as an assistant, then quickly became a full professor in aeronautical engineering in 1939. It was here that he founded the Instrumentation Laboratory in the 1930s, later spun off as The Charles Stark Draper Laboratory, Inc. In 1961, Draper and the Instrumentation Lab were awarded the first contract given out for the Apollo program to send humans to the moon, which had just been announced by President John F. Kennedy. This led to the creation of the Apollo Guidance Computer, a one-cubic-foot computer that controlled the navigation and guidance of the Lunar Excursion Module to the surface of the moon during six successful landings.

Draper invented and developed inertial navigation, a technology used in aircraft, space vehicles, and submarines which allows such vehicles to navigate by sensing changes in direction, using gyroscopes, and speed, using accelerometers. A pioneering figure in the aircraft engineering field, he also contributed to the Apollo space program with his knowledge of guidance systems. For his inventions and contributions, Draper was inducted to the National Inventors Hall of Fame in 1981.

The Charles Stark Draper Prize is a prominent prize in engineering devoted to the memory of Charles Stark Draper.

September 13: Horace W. Babcock

Horace Welcome Babcock

September 13, 1912 – August 29, 2003

Horace Babcock was an American astronomer. He was the son of Harold D. Babcock.

He invented and built a number of astronomical instruments, and in 1953 was the first to propose the idea of adaptive optics. He specialized in spectroscopy and the study of magnetic fields of stars. He proposed the Babcock Model, a theory for the magnetism of sunspots.

During World War II, he was engaged in radiation work at MIT and Caltech. After the war he began a productive collaboration with his father.

Babcock was awarded the Henry Draper Medal (1957), the Eddington Medal (1958), the Bruce Medal (1969), the Gold Medal of the Royal Astronomical Society (1970) and the George Ellery Hale Prize of the American Astronomical Society Solar Physics Division (1992)

The asteroid 3167 Babcock is named jointly for Horace and his father. The Babcock crater on the Moon is named only for his father.

July 21: Jean-Felix Picard

Jean-Felix Picard

July 21, 1620 – July 12, 1682

Jean Picard was a French astronomer and priest born in La Flèche, where he studied at the Jesuit Collège Royal Henry-Le-Grand. He was the first person to measure the size of the Earth to a reasonable degree of accuracy in a survey conducted 1669-70, for which he is honored with a pyramid at Juvisy-sur-Orge.

Guided by Maurolycus's methodology and Snellius's mathematics for doing so, Picard achieved this by measuring one degree of latitude along the Paris Meridian using triangulation along thirteen triangles stretching from Paris to the clocktower of Sourdon, near Amiens. His measurements produced a result of 110.46 km for one degree of latitude, which gives a corresponding terrestrial radius of 6328.9 km. The polar radius has now been measured at just over 6357 km. This was an error only 0.44% less than the modern value. This was another example of advances in astronomy and its tools making possible advances in cartography.

Picard was the first to attach a telescope with crosswires (developed by William Gascoigne) to a quadrant, and one of the first to use a micrometer screw on his instruments. The quadrant he used to determine the size of the Earth had a radius of 38 inches and was graduated to quarter-minutes. The sextant he used to find the meridian had a radius of six feet, and was equipped with a micrometer to enable minute adjustments. These equipment improvements made the margin of error only ten seconds, as opposed to Tycho Brahe's four minutes of error. This made his measurements 36 times more accurate. Isaac Newton was to use this value in his theory of universal gravitation.

Picard also travelled to Tycho Brahe's Swedish observatory, Uraniborg, in order to assess its position accurately to compare Tycho's readings to others'.

Picard collaborated and corresponded with many scientists, including Newton, Christian Huygens, Römer, Bartholin, Hudde, and even his main competitor, Giovanni Cassini, although Cassini was often less than willing to return the gesture. These correspondences led to Picard's contributions to areas of science outside the field of geodesy, such as the aberration of light he observed while in Uraniborg, or his discovery of mercurial phosphorescence upon his observance of the faint glowing of a barometer. This discovery led to Newton's studies of spectrometry.

Picard also developed the system of right ascension for measuring positions of celestial objects in relation to the Earth.

His book "Mesure de la Terre" was published in 1671.

The Lunar crater Picard, on the northwest quadrant of Mare Crisium and the PICARD mission, an orbiting solar observatory, are named in his honor.

June 21: Maximilian Wolf

Maximilian Wolf

June 21, 1863 – October 3, 1932

Maximilian Franz Joseph Cornelius Wolf was a German astronomer, a pioneer of astrophotography.

He was born in Heidelberg, Germany. In 1888 he was awarded a Ph.D. by the University of Heidelberg, and joined the staff of that institution in 1890.

Working at Landessternwarte Heidelberg-Königstuhl, he discovered more than 200 asteroids with the Bruce double-astrograph since 1891. The first one, 323 Brucia, was named after Catherine Wolfe Bruce, who had donated $10,000 for the construction of the telescope. He pioneered the use of astrophotographic techniques to automate the discovery of asteroids, as opposed to older visual methods, as a result of which asteroid discovery rates sharply increased. In time-exposure photographs, asteroids appear as short streaks due to their planetary motion with respect to fixed stars.

Among his many discoveries was 588 Achilles (the first Trojan asteroid) in 1906, as well as two other Trojans: 659 Nestor and 884 Priamus. He also discovered 887 Alinda in 1918, which is now recognized as an Earth-crossing Amor asteroid (or sometimes classified as the namesake of its own Alinda family). Shortly after his last discovery (on February 6, 1932), his record 248 discoveries were beaten by his pupil Karl Wilhelm Reinmuth, on July 24, 1933.

He also discovered or co-discovered some comets, including 14P/Wolf and 43P/Wolf-Harrington, and four supernovae: SN 1895A (a.k.a. VW Vir), 1909A (a.k.a. SS UMa), 1920A, and 1926A (the latter co-discovered by Reinmuth).

He also discovered Wolf 359, a red dwarf that is one of the nearest stars to our solar system. Note that Wolf-Rayet stars were co-discovered by French astronomer Charles Wolf and not by him.

In 1910 Wolf proposed to the Carl Zeiss optics firm the creation of a new instrument, now known as the planetarium. World War I intervened before this could be developed, but the Zeiss company returned to this after peace was restored, and the first successful planetarium was completed in 1923.

June 19: Wallace John Eckert

Wallace John Eckert

June 19, 1902 – August 24, 1971

Wallace John Eckert was an astronomer, and Director of the Thomas J. Watson Astronomical Computing Bureau at Columbia University. In January 1940, Eckert published Punched Card Methods in Scientific Computation, which solved the problem of predicting the orbits of the planets, using the IBM electric tabulating machines, based on the punched card. This slim book is only 136 pages, including the index.

Born in Pittsburgh, Pennsylvania, he earned his PhD from Yale in 1931 in astronomy.

The Astronomical Computing Bureau was supported by Dr. Thomas J. Watson, President of IBM, including customer service and hardware circuit modifications needed to tabulate numbers, create mathematical tables, add, subtract, multiply, reproduce, verify, crossfoot, create tables of differences, create tables of logarithms and perform Lagrangian interpolation, all to solve differential equations for astronomical applications.

When Dana Mitchell saw these operations in action, and later served in the Manhattan Project (the wartime project to develop the first nuclear weapons), he mentioned this technique to the T-6 section of the Theoretical Division of the Los Alamos National Laboratory in the Manhattan Project; they were using the electromechanical calculators of that time to perform the mathematical computations for mathematical expressions by hand, using human computers, one person to perform the cube, one to add a number, etc. Nicholas Metropolis and Richard Feynman immediately set about organizing a punched card solution for a crucial mathematical expression, utilizing the techniques pioneered by Eckert and his IBM methods, such as the use of colored punched cards to signal the end of a series of cards, etc.

Eckert understood the significance of his laboratory, keenly aware of the advantage of scientific calculations performed without human interventions for long stretches of computation.

He won the James Craig Watson Medal in 1966. The Lunar crater Eckert is named in his honor.

June 15: Johann Gottlob Frederick von Bohnenberger

Johann Gottlob Frederick von Bohnenberger
June 15, 1765 - April 19, 1831

Johann Gottlob Frederick von Bohnenberger was an astronomer and mathematician. He contributed to the development of early electrical devices and instruments. The best known is the Bohnenberger electroscope.

Johann Gottlob Frederick von Bohnenberger was born on June 15, 1765, in Simmezheim, Germany. His father, Gottlieb Christoph Bohnenberger, was a minister and he made some study in electricity.

Frederick studied theology in Tubingen, and in 1789 he became a priest. However, he went to study mathematics and astronomy first to Zach and then to Gottingen. Since 1796 he was an assistant at the Tubingen observatory and from 1803 professor of mathematics and astronomy there. In 1811 Frederick von Bohnenberger published a book, the “Astronomy”, which made him well known. From 1818 up to his death he was a chief inspector of munitions in Wuttenberg.

Frederick von Bohnenberger made important contributions to the study of electricity. He made electrostatic machines and Bohnenberger electroscope that was an important electrometric instrument.

This curious machine is a primitive influence (electrostatic) machine, proposed by Bohnenberger in 1798, as a rotating implementation of Bennet’s doubler (1787, used as an electromer). About 1814 J.F.G. von Bohnenberger suggested a form of electroscope in which the single leaf was attracted to one of two conductors placed symmetrically on either side of it. The conductors were, in turn, connected to the two poles of a dry pile, thus allowing the sign of the charge applied to the leaf to be determined.

The Bohnenberger electroscope comprises two batteries connected by a common base producing a constant potential difference of the order of 1000 volts. The free terminals have two small brass spheres. The unit is mounted in such a way that these two spheres have symmetrical electric charges. A piece of gold leaf suspended on the stem of the electroscope is attracted by the sphere of one of the batteries when an electrically charged body is brought close to the electroscope. It is thus possible, with this electroscope, to determine the nature of the charge of an electrically charged body. To do so, the charges on the spheres should first be known; this can be ascertained by observing the behaviour of the gold leaf when the electroscope is influenced by a body whose electrical charge is known.

However, Bohnenberger’s main interests were in the fields of geodesy and geophysics. Bohnenberger and Soldner were the pioneers of the German geodesy. Bohnenberger has constructed a gyroscope. The gyroscope in the form we know it today was invented in 1852 by Leon Foucault. However, it had an ancestor in the device developed by Johann von Bohnenberger in 1817. Napoleon I was so much impressed by this device that he recommended to introduce it in French schools.

The construction and operation of the Bohnenberger’s gyroscope are discussed in the 1856 first volume of Benjamin Pike, Jr.’s Illustrated Descriptive Catalogue of Optical, Mathematical and Philosophical Instruments: “Bohnenberger’s Machine. This apparatus consists of three movable rings, ..., mounted on a stout base. The two inner rings are mounted on pivots; those on the smallest ring at right angles to the middle one; in the smallest ring is supported a metal ball, having a roller on one of its pivots; around the roller a string may be wound, and when pulled off a rapid rotary motion may be given to the ball. This motion may be given with the axis in any position required, and when communicated, the ring supporting the ball will resist considerable effort to alter its position, and whatever way the instrument may be turned, its axis will continue to maintain the position it had when set in motion, illustrating the inertia, or that property of matter which resists any change of state, whether of rest or motion.”

The Lunar crater Bohnenberger is named in his honor.

June 13: Giovanni Antonio Magini

Giovanni Antonio Magini
June 13, 1555 – February 11, 1617

Giovanni Antonio Magini (in Latin, Maginus) was an Italian astronomer, astrologer, cartographer, and mathematician. He was born in Padua, and completed studies in philosophy in Bologna in 1579. Dedicating himself to astronomy, in 1582 he wrote Ephemerides coelestium motuum, translated into Italian the following year.

In 1588 he was chosen over Galileo to occupy the chair of mathematics at the University of Bologna after the death of Egnatio Danti. Magini supported a geocentric system of the world, in preference to Copernicus’ heliocentric system. Magini devised his own planetary theory, in preference to other existing ones. The Maginian System consisted of eleven rotating spheres, which he described in his Novæ cœlestium orbium theoricæ congruentes cum observationibus N. Copernici (Venice, 1589).

In his De Planis Triangulis (1592), he described the use of quadrants in surveying and astronomy. In 1592 Magini published Tabula tetragonica, and in 1606 devised extremely accurate trigonometric tables. He also worked on the geometry of the sphere and applications of trigonometry, for which he invented calculating devices. He also worked on the problem of mirrors and published on the theory of concave spherical mirrors.

He also published a commentary on Ptolemy’s Geographia (Cologne, 1596).

As a cartographer, his life's work was the preparation of Italia or the Atlante geografico d'Italia (Geographic Atlas of Italy), printed posthumously by Magini's son in 1620. This was intended to include maps of every Italian region with exact nomenclature and historical notes. A major project, its production (begun in 1594) proved expensive and Magini assumed various additional posts in order to fund it, including becoming tutor in mathematics to the sons of Vincenzo I of Gonzaga, Duke of Mantua, a major patron of the arts and sciences. He also served as court astrologer. The Duke of Mantua, to whom the atlas is dedicated, assisted him with this project and allowed for maps of the various states of Italy to be brought to Magini. The governments of Messina and Genoa also assisted Magini financially in this project. Magini did not do any of the mapping himself.

He was also interested in pursuits which today would be considered pseudoscientific. A strong supporter of astrology, he defended its use in medicine in his De astrologica ratione (Venice, 1607). He was also interested in metoposcopy.

He corresponded with Tycho Brahe, Clavius, Abraham Ortelius, and Johann Kepler. His correspondence was edited in 1886 by Antonio Favaro.

The lunar crater Maginus is named in his honor.

April 16: John Hadley

John Hadley

April 16, 1682 – February 14, 1744

John Hadley was an English mathematician, inventor of the octant and precursor to the sextant around 1730.

In 1717 he became member (and later vice-president ) of the Royal Society of London.

The octant is used to measure the altitude of the Sun or other celestial objects above the horizon at sea. A mobile arm carrying a mirror and pivoting on a graduated arc provides a reflected image of the celestial body overlapping the image of the horizon, which is observed directly. If the position of the object on the sky and the time of the observation are known, it is easy for the user to calculate his own latitude. The octant proved extremely valuable for navigation and displaced the use of other instruments such as the Davis quadrant.

An American, Thomas Godfrey, independently invented the octant at approximately the same time.

Hadley also improved the reflecting telescope.

Mons Hadley and Rima Hadley on the Moon 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.

April 6: André-Louis Danjon

André-Louis Danjon

April 6, 1890 – April 21, 1967

André Danjon was a French astronomer born in Caen.

Danjon devised a method to measure "Earthshine" on the Moon using a telescope in which a prism split the Moon's image into two identical side-by-side images. By adjusting a diaphragm to dim one of the images until the sunlit portion had the same apparent brightness as the earthlit portion on the unadjusted image, he could quantify the diaphragm adjustment, and thus had a real measurement for the brightness of Earthshine. He recorded the measurements using his method (now known as the Danjon Scale, on which zero equates to a barely visible Moon) from 1925 until the 1950s.

Among his notable contributions to astronomy was the design of the impersonal (prismatic) astrolabe now known as the Danjon astrolabe, which led to an improvement in the accuracy of fundamental optical astrometry. Within four years of its introduction (1956), the Danjon astrolabe was being used in more than 30 major observatories. An account of this instrument, and of the results of some early years of its operation, are given in Danjon's 1958 George Darwin Lecture to the Royal Astronomical Society (in Monthly Notices of the RAS (1958), vol.118, pages 411-431).

He was Director of the Paris Observatory from 1945 to 1963.

He won the Gold Medal of the Royal Astronomical Society in 1958. The Lunar crater Danjon is named in his honor.

March 25: Giovanni Battista Amici

Giovanni Battista Amici

March 25, 1786 - April 10, 1863

Giovanni Amici was an Italian astronomer and microscopist who invented the dipleidoscope, an  instrument used to determine true noon.

Amici was born in Modena, Italy. After studying at Bologna, he became professor of mathematics at Modena, and in 1831 was appointed inspector-general of studies in the duchy. A few years later he was chosen director of the observatory at Florence, where he also lectured at the museum of natural history.

His name is best known for the improvements he effected in the mirrors of reflecting telescopes and especially in the construction of the microscope. The Amici prism, a combination of three prisms, is still used in refracting spectroscopy. He was also a diligent and skillful observer, and busied himself not only with astronomical subjects but also with biological studies. 

In astronomy, Amici studied double stars, Jupiter's moons and designed improvements to reflecting telescope mirrors including grinding several 10-inch and 12-inch metal mirrors. With his own micrometer design, Amici made accurate measurements of the polar and equatorial diameters of the Sun. Combining botany interests with innovative advances in compound microscopes, the Italian scientist made important discoveries about the circulation of sap in plants and the processes of plant reproduction, including many details of orchid pollination and seed development.

The Lunar crater Amici is named in his honor.

March 22: Ulugh Beg

Ulugh Beg

March 22, 1394 – October 27, 1449

Ulugh Beg was a Timurid ruler as well as an astronomer, mathematician and sultan. His commonly known name is not truly a personal name, but rather a moniker, which can be loosely translated as "Great Ruler" or "Patriarch Ruler." Ulugh Beg was also notable for his work in astronomy-related mathematics, such as trigonometry and spherical geometry.

The teenaged ruler set out to turn the city into an intellectual center for the empire. In 1417-1420 he built a madrasa ("university" or "institute") on Registan Square in Samarkand, and invited numerous Islamic astronomers and mathematicians to study there. The madrasa building still survives. Ulugh Beg's most famous pupil in mathematics was Ghiyath al-Kashi (circa 1370 - 1429).

His own particular interests concentrated on astronomy, and in 1428 he built an enormous observatory, called the Gurkhani Zij, similar to Tycho Brahe's later Uraniborg as well as Taqi al-Din's Istanbul observatory of al-Din. Lacking telescopes to work with, he increased his accuracy by increasing the length of his sextant; the so-called Fakhri Sextant had a radius of circa 36 meters (118 ft) and the optical separability of 180" (seconds of arc). Using it he compiled the 1437 Zij-i-Sultani of 994 stars, generally considered the greatest of star catalogues between those of Ptolemy and Brahe, alongside Abd al-Rahman al-Sufi's Book of Fixed Stars. The serious errors which he found in previous Arabian star catalogues (many of which had simply updated Ptolemy's work, adding the effect of precession to the longitudes) induced him to redetermine the positions of 992 fixed stars, to which he added 27 stars from Abd al-Rahman al-Sufi's catalogue Book of Fixed Stars from 964, which were too far south for observation from Samarkand. 

This catalogue, one of the most original of the Middle Ages, was edited by Thomas Hyde at Oxford in 1665 under the title Tabulae longitudinis et latitudinis stellarum fixarum ex observatione Ulugbeighi by G. Sharpe in 1767, and in 1843 by Francis Baily in vol. xiii. of the Memoirs of the Royal Astronomical Society.

In 1437 Ulugh Beg determined the length of the sidereal year as 365.2570370...d = 365d 6h 10m 8s (an error +58s). In his measurements within many years he used a 50 m high gnomon. This value was improved by 28s 88 years later in 1525 by Nicolaus Copernicus (1473-1543), who appealed to the estimation of Thabit ibn Qurra (826-901), which was accurate to +2s.

The above-ground portion of Ulugh Beg's observatory was destroyed shortly after his death; the surviving underground chamber was excavated in 1908 by primary school teacher and amateur archaeologist Vladimir Viyatkin, later Samarkand's director of antiquities.

In mathematics, Ulugh Beg (14th century) wrote accurate trigonometric tables of sine and tangent values correct to 8 decimal places.

The crater Ulugh Beigh on the Moon was named after him by the German astronomer Johann Heinrich von Mädler in his 1830 map of the Moon.

March 8: Alvan Clark

Alvan Clark

March 8, 1804 – August 19, 1887

Alvan Clark, born in Ashfield, Massachusetts, the descendant of a Cape Cod whaling family of English ancestry, was an American astronomer and telescope maker. 

He was a portrait painter and engraver, but at the age of 40 become involved in telescope making. Using glass blanks made by Chance Brothers of Birmingham and Feil-Mantois of Paris, his firm Alvan Clark & Sons ground lenses for refracting telescopes, including the largest in the world at the time: 

• the 18.5-inch (470 mm) at Dearborn Observatory at the Old University of Chicago (the lens was originally intended for Ole Miss) 
  
• the 26-inch (660 mm) at the United States Naval Observatory, 
• the 30-inch (760 mm) at Pulkovo Observatory (destroyed in the Siege of Leningrad; only the lens survives) 
  
• the 36-inch (910 mm) telescope at Lick Observatory (still third-largest) 
  
• the 40-inch (1,000 mm) at Yerkes Observatory, which remains the largest successful refracting telescope in the world
  

He was the first person in the United States to make achromatic lenses, and the most important modern telescopes have been constructed at his factory in Cambridge-port. Mr. Clark invented numerous improvements in telescopes and their manufacture, including the double eye-piece, an ingenious method of measuring small celestial arcs. A list of discoveries made by him with telescopes of his own manufacture is given in the "Proceedings of the Royal Astronomical Society" (London, vol. 17, No. 9).

Mr. Clark accompanied the total-eclipse expedition to Jerez, Spain, in 1870, and also the similar expedition to Wyoming in 1878. As an independent observer he has discovered fourteen intricate double stars, including the companion to Sirius, for which the Lalande gold medal was awarded him by the French academy of sciences in 1862. He has also made numerous inventions connected with the manufacture of refracting telescopes. 

One of Clark's sons, Alvan Graham Clark, discovered the dim companion of Sirius. His other son was George Bassett Clark; both sons were partners in the firm.

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

March 6: Joseph von Fraunhofer

Joseph von Fraunhofer

March 6, 1787 – June 7, 1826

Joseph von Fraunhofer was a German optician. He is known for the discovery of the dark absorption lines known as Fraunhofer lines in the Sun's spectrum, and for making excellent optical glass and achromatic telescope objectives.

Fraunhofer was born in Straubing, Bavaria. He became an orphan at the age of 11, and he started working as an apprentice to a harsh glassmaker named Philipp Anton Weichelsberger. In 1801 the workshop in which he was working collapsed and he was buried in the rubble. The rescue operation was led by Maximilian IV Joseph, Prince Elector of Bavaria (the future Maximilian I Joseph). The prince entered Fraunhofer's life, providing him with books and forcing his employer to allow the young Joseph Fraunhofer time to study.

After eight months of study, Fraunhofer went to work at the Optical Institute at Benediktbeuern, a secularised Benedictine monastery devoted to glass making. There he discovered how to make the world's finest optical glass and invented incredibly precise methods for measuring dispersion. In 1818 he became the director of the Optical Institute. Due to the fine optical instruments he had developed, Bavaria overtook England as the centre of the optics industry. Even the likes of Michael Faraday were unable to produce glass that could rival Fraunhofer's.

His illustrious career eventually earned him an honorary doctorate from the University of Erlangen in 1822. In 1824, he was awarded the order of merit, became a noble, and made an honorary citizen of Munich. Like many glassmakers of his era who were poisoned by heavy metal vapours, Fraunhofer died young, in 1826 at the age of 39. His most valuable glassmaking recipes are thought to have gone to the grave with him.

In 1814, Fraunhofer invented the spectroscope, and discovered 574 dark lines appearing in the solar spectrum. These were later shown to be atomic absorption lines, as explained by Kirchhoff and Bunsen in 1859. These lines are still called Fraunhofer lines in his honour.

He also invented the diffraction grating and in doing so transformed spectroscopy from a qualitative art to a quantitative science by demonstrating how one could measure the wavelength of light accurately. He found out that the spectra of Sirius and other first-magnitude stars differed from each other and from the sun, thus founding stellar spectroscopy.

Ultimately, however, his primary passion was still practical optics, once noting that

"In all my experiments I could, owing to lack of time, pay attention to only those matter which appeared to have a bearing upon practical optics."

In the early 1990s a firm that designed and built refracting telescopes was named in his honor Fraunhofer Systems Company since the telescopes were based on his design but now the company is part of Burbank Optical Company.

The Lunar crater Fraunhofer is named in his honor.

February 28: Camille Guillaume Bigourdan

Camille Guillaume Bigourdan

April 6, 1851 – February 28, 1932

Guillaume Bigourdan was a French astronomer. In 1877 he was appointed by Félix Tisserand as assistant astronomer at the Toulouse Observatory, and in 1879 followed Tisserand to the Paris Observatory when the latter became director there.

He spent many years verifying the positions of 6,380 nebulas. He hoped to set a basis for future studies of the proper motion of nebulas; this turned out to be more or less in vain, since distant nebulas will not show any proper motion. However, he did discover approximately 500 new objects, including asteroid 390 Alma (on March 24, 1894).

In 1902 he participated in an effort to redetermine with greater precision the longitude difference between London and Paris. He became a member of the Bureau des Longitudes in 1903, and a member of the French Academy of Sciences in 1904.

He described a method for adjusting equatorial mount telescopes, which was known as "Bigourdan's method".

Bigourdan won the Gold Medal of the Royal Astronomical Society in 1919 for his observations of nebulae for over 25 years. He was director of the Bureau International de l'Heure from 1919 to 1928.

February 18: Nasir al-Din al-Tusi

Nasir al-Din al-Tusi

February 18, 1201 - June 26, 1274

Nasir al-Din al-Tusi, also known as Nasireddin, was a Persian polymath and prolific writer: an astronomer, biologist, chemist, mathematician, philosopher, physician, physicist, scientist, theologian and Marja Taqleed. His works include the definitive Arabic versions of the works of Euclid, Archimedes, Ptolemy, Autolycus, and Theodosius of Bithynia.

Tusi convinced Hulegu Khan to construct an observatory for establishing accurate astronomical tables for better astrological predictions. Beginning in 1259, the Rasad Khaneh observatory was constructed west of Maragheh, the capital of the Ilkhanate Empire.

Based on the observations in this, for the time being, most advanced observatory, Tusi made very accurate tables of planetary movements as depicted in his book Zij-i ilkhani (Ilkhanic Tables). This book contains astronomical tables for calculating the positions of the planets and the names of the stars. His model for the planetary system is believed to be the most advanced of his time, and was used extensively until the development of the heliocentric model in the time of Nicolaus Copernicus. Between Ptolemy and Copernicus, he is considered by many to be one of the most eminent astronomers of his time, and his work and theory in astronomy can also be compared to that of the Chinese scientist Shen Kuo (1031-1095 AD).

For his planetary models, he invented a geometrical technique called a Tusi-couple, which generates linear motion from the sum of two circular motions. He used this technique to replace Ptolemy's problematic equant, and it was later employed in Ibn al-Shatir's geocentric model and Nicolaus Copernicus' heliocentric Copernican model. He also calculated the value for the annual precession of the equinoxes and contributed to the construction and usage of some astronomical instruments including the astrolabe.

Tusi was also the first to present empirical observational evidence of the Earth's rotation, using the location of comets relevant to the Earth as evidence, which Ali al-Qushji elaborated on with further empirical observations. The arguments of Tusi were similar to the arguments later used by Copernicus in 1543 to explain the Earth's rotation.

The Lunar crater Nasireddin, a minor planet 10269 Tusi, discovered by Soviet astronomer Nikolai Stepanovich Chernykh in 1979 and the K. N. Toosi University of Technology in Iran are named in his honor.