September 10: James Edward Keeler

James Edward Keeler

September 10, 1857 – August 12, 1900

James Edward Keeler was an American astronomer.

Keeler worked at Lick Observatory beginning in 1888, but left after being appointed director of the University of Pittsburgh's Allegheny Observatory in 1891. He returned to Lick Observatory as its director in 1898, but died not long after in 1900. His ashes were interred in a crypt at the base of the 31-inch Keeler Memorial telescope at the Allegheny Observatory.

Along with George Hale, Keeler founded and edited the Astrophysical Journal, which remains a major journal of astronomy today.

Keeler was the first to observe the gap in Saturn's rings now known as the Encke Gap, using the 36-inch refractor at Lick Observatory on 7 January 1888. After this feature had been named for Johann Encke, who had observed a much broader variation in the brightness of the A Ring, Keeler's contributions were brought to light. The second major gap in the A Ring, discovered by Voyager, was named the Keeler Gap in his honor.

In 1895, his spectroscopic study of the rings of Saturn revealed that different parts of the rings reflect light with different Doppler shifts, due to their different rates of orbit around Saturn. This was the first observational confirmation of the theory of James Clerk Maxwell that the rings are made up of countless small objects, each orbiting Saturn at its own rate. These observations were made with a spectrograph attached to the 13-inch Fitz-Clark refracting telescope at Allegheny Observatory.

His observations with the Lick Crossley telescope helped establish the importance of large optical reflecting telescopes, and expanded astronomers' understanding of nebulae. After his untimely death, his colleagues at Lick Observatory arranged for the publication of his photographs of nebulae and clusters in a special volume of the Lick Observatory publications. Keeler discovered two asteroids, one in 1899 and one in 1900, although the second was lost and only recovered about 100 years later.

He won the Henry Draper Medal in 1899.

In 1880, Allegheny Observatory director Samuel Pierpont Langley, accompanied by Keeler and others, went on a scientific expedition to the summit of Mount Whitney. The purpose of the expedition was to study how the Sun's radiation was selectively absorbed by the Earth's atmosphere, comparing the results at high altitude with those found at lower levels. As a result of the expedition, a 14,240-ft. peak near Mount Whitney was named the "Keeler Needle".

In addition to the Keeler Gap in Saturn's rings, craters on Mars and the Moon (Keeler) are named in his honor, as is the asteroid 2261 Keeler.

September 9: William Cranch Bond

William Cranch Bond

September 9, 1789 – January 29, 1859

William Cranch Bond was an American astronomer, and the first director of Harvard College Observatory.

William Cranch Bond was born in Falmouth, Maine (now Portland, Maine). When he was young, his father, William Bond, established himself as a clockmaker after a failed business venture; trained by his father and aided by his penchant for engineering, W. C. Bond built his first clock when he was fifteen years old. He eventually took over his father’s business, becoming an expert clockmaker himself.

In 1806, when he was seventeen years old, Bond saw a solar eclipse. Soon thereafter, he became an avid amateur astronomer. When he built his first house, Bond made its parlor an observatory, complete with an opening in the ceiling out of which his telescope could view the sky.

In 1815, Bond traveled to Europe, commissioned by Harvard University to gather information on European observatories. On 18 July 1819 at Kingsbridge in Devon, Bond married his first cousin, Selina Cranch, who bore him four sons and two daughters. After Selina's death in 1831, Bond married her older sister, Mary Roope Cranch.

In 1839, Bond was allowed to move his personal astronomical equipment to Harvard and serve as its (unpaid) "Astronomical Observer to the University." Later, in 1843, a sun-grazing comet aroused enough public interest in astronomy that Harvard was able to raise $25,730 towards the construction of a state-of-the-art observatory. Bond designed the building and the observing chair (both of which are still in working order today), and Harvard bought a fifteen-inch German-built refracting telescope, equal in size to the largest in the world at the time. The telescope was first put to use on June 24, 1847, when it was pointed to the moon.

Bond and his son George Phillips Bond discovered Saturn's moon Hyperion; it was independently co-discovered at the same time by William Lassell in Britain, and both are given credit. He also independently discovered the Great Comet of 1811.

Father and son were the first to observe the then innermost ring of Saturn, termed the Crepe ring when they pointed Harvard’s telescope towards Saturn in 1850.

Working with John Adams Whipple, the Bonds pioneered astrophotography, taking the first daguerreotype image of a star (Vega, in 1850) ever taken from America. In all, the threesome took between 200 and 300 photos of celestial objects.

A number of celestial objects have been named in Bond's honor. A few of them include:

• The crater W. Bond on the Moon.
• A region on Hyperion is called the "Bond-Lassell Dorsum".
• Asteroid (767) Bondia is jointly named after him and his son.
• The Bond Gap within Saturn's C Ring is jointly named after him and his son.

July 18: Robert Hooke

Robert Hooke

July 18, 1635 – March 3, 1703

Robert Hooke, FRS was an English natural philosopher and polymath who played an important role in the scientific revolution, through both experimental and theoretical work.

Hooke is known principally for his law of elasticity (Hooke's Law). He is also remembered for his work as "the father of microscopy" — it was Hooke who coined the term "cell" to describe the basic unit of life. He also assisted Robert Boyle and built the vacuum pumps used in Boyle's gas law experiments. Hooke was an important architect of his time, and a chief surveyor to the City of London after the Great Fire. He built some of the earliest Gregorian telescopes, observed the rotations of Mars and Jupiter, and, based on his observations of fossils, was an early proponent of biological evolution. He investigated the phenomenon of refraction, deducing the wave theory of light, and was the first to suggest that matter expands when heated and that air is made of small particles separated by relatively large distances. He also deduced from experiments that gravity follows an inverse square law, and that such a relation governs the motions of the planets, an idea which was subsequently developed by Newton. Much of Hooke's work was conducted in his capacity as curator of experiments of the Royal Society, a post he held from 1662.

Hooke was, by all accounts, a remarkably industrious man, and was at one time simultaneously the curator of the Royal Society and a member of its council, Gresham Professor of Geometry and Chief Surveyor to the City of London.

Hooke's reputation suffered during the eighteenth century, and this is popularly attributed to a dispute with Isaac Newton over credit for his work on gravitation; Newton, as President of the Royal Society, did much to obscure Hooke, including, it is said, destroying (or failing to preserve) the only known portrait of the man. Hooke's reputation was revived during the twentieth century through studies of Robert Gunther and Margaret 'Espinasse, and after a long period of relative obscurity he is now recognized as one of the most important scientists of his age.

One of the more-challenging problems tackled by Hooke was the measurement of the distance to a star (other than the Sun). The star chosen was Gamma Draconis and the method to be used was parallax determination. After several months of observing, in 1669, Hooke believed that the desired result had been achieved. It is now known that Hooke's equipment was far too imprecise to allow the measurement to succeed. Gamma Draconis was the same star William Bradley used in 1725 in discovering the aberration of light.

Hooke's activities in astronomy extended beyond the study of stellar distance. His Micrographia contains illustrations of the Pleiades star cluster as well as of lunar craters. He performed experiments to study how such craters might have formed. Hooke also was an early observer of the rings of Saturn, and discovered one of the first double-star systems, Gamma Arietis, in 1664.

On 8 July 1680, Hooke observed the nodal patterns associated with the modes of vibration of glass plates. He ran a bow along the edge of a glass plate covered with flour, and saw the nodal patterns emerge.

The Lunar crater Hooke, a crater on Mars and the asteroid 3514 Hooke (1971 UJ) are named in his honor.

July 8: Christiaan Huygens

Christiaan Huygens

April 14, 1629 – July 8, 1695

Christiaan Huygens was a prominent Dutch mathematician, astronomer, physicist, and horologist. His work included early telescopic studies, investigations and inventions related to time keeping, and studies of both optics and centrifugal force.

Christiaan Huygens studied law and mathematics at the University of Leiden and the College of Orange in Breda before turning to science.

Huygens achieved note for his argument that light consists of waves, which became instrumental in the understanding of wave-particle duality. He generally receives credit for his role in the development of modern calculus and his original observations on sound perception.

In 1655, Huygens proposed that Saturn was surrounded by a solid ring, "a thin, flat ring, nowhere touching, and inclined to the ecliptic." Using a 50 power refracting telescope that he designed himself, Huygens also discovered the first of Saturn's moons, Titan. In the same year he observed and sketched the Orion Nebula. His drawing, the first such known of the Orion nebula, was published in Systema Saturnium in 1659. Using his modern telescope he succeeded in subdividing the nebula into different stars. (The brighter interior of the Orion Nebula bears the name of the Huygens Region in his honour.) He also discovered several interstellar nebulae and some double stars.

Huygens formulated also what is now known as the second law of motion of Isaac Newton in a quadratic form. Newton reformulated and generalized that law.

After Blaise Pascal encouraged him to do so, Huygens wrote the first book on probability theory, which he had published in 1657.

On May 3, 1661, he observed planet Mercury transit over the Sun, using the telescope of telescope maker Richard Reeves in London together with astronomer Thomas Streete and Richard Reeves.

The Royal Society elected Huygens a member in 1663. In the year 1666 Huygens moved to Paris where he held a position at the French Academy of Sciences under the patronage of Louis XIV. Using the Paris Observatory (completed in 1672) he made further astronomical observations. In 1684 he published "Astroscopia Compendiaria" which presented his new aerial (tubeless) telescope.

Huygens speculated in detail about life on other planets. In his book Cosmotheoros, further entitled The celestial worlds discover'd: or, conjectures concerning the inhabitants, plants and productions of the worlds in the planets, he imagined a universe brimming with life, much of it very similar to life on 17th-century Earth. The liberal climate in the Netherlands of that time not only allowed but encouraged such speculation. In sharp contrast, philosopher Giordano Bruno, who also believed in many inhabited worlds, was burned at the stake by the Italian authorities for his beliefs in 1600.

The Huygens probe: The lander for the Saturnian moon Titan, part of the Cassini-Huygens Mission to Saturn, Asteroid 2801 Huygens, a crater on Mars and Mons Huygens, a mountain on the Moon are named in his honor.

June 18: William Lassell

William Lassell

June 18, 1799 – October 5, 1880

William Lassell was an English astronomer who discovered moons of Neptune, Saturn and Uranus.

Born in Bolton, he made his fortune as a beer brewer, which enabled him to indulge his interest in astronomy. He built an observatory near Liverpool with a 24-inch (610 mm) reflector telescope, for which he pioneered the use of an equatorial mount for easy tracking of objects as the earth rotates. He ground and polished the mirror himself, using equipment he constructed.

In 1846 Lassell discovered Triton, the largest moon of Neptune, just 17 days after the discovery of Neptune itself by German astronomer Johann Gottfried Galle. In 1848 he independently co-discovered Hyperion, a moon of Saturn. In 1851 he discovered Ariel and Umbriel, two new moons of Uranus.

When Queen Victoria visited Liverpool in 1851, Lassell was the only local she specifically requested to meet.

In 1855, he built a 48-inch (1,200 mm) telescope, which he installed in Malta because of the better observing conditions compared to England.

He won the Gold Medal of the Royal Astronomical Society in 1849, and served as its president for two years starting in 1870. Lassell died in Maidenhead in 1880. Upon his death, he left a fortune of £80,000 (equivalent to millions of American dollars by today's standards).

The crater Lassell on the Moon, a crater on Mars and a ring of Neptune are named in his honour.

June 8: Giovanni Domenico Cassini

Giovanni Domenico Cassini

June 8, 1625 – September 14, 1712

Giovanni Domenico Cassini was an Italian/French mathematician, astronomer, engineer, and astrologer.

Cassini was an astronomer at the Panzano Observatory from 1648 to 1669. He was a professor of astronomy at the University of Bologna and in 1671 became director of the Paris Observatory. He thoroughly adopted his new country, to the extent that he became interchangeably known as Jean-Dominique Cassini —although that is also the name of his great-grandson.

Along with Robert Hooke, Cassini is given credit for the discovery of the Great Red Spot on Jupiter (ca. 1665). Cassini was the first to observe four of Saturn's moons, which he called Sidera Lodoicea; he also discovered the Cassini Division (1675). Around 1690, Cassini was the first to observe differential rotation within Jupiter's atmosphere.

In 1672 he sent his colleague Jean Richer to Cayenne, French Guiana, while he himself stayed in Paris. The two made simultaneous observations of Mars and thus found its parallax to determine its distance, thus measuring for the first time the true dimensions of the solar system.

Cassini was the first to make successful measurements of longitude by the method suggested by Galileo, using eclipses of the satellites of Jupiter as a clock.

The Lunar crater Cassini is named in his honor.

April 17: Giovanni Battista Riccioli

Giovanni Battista Riccioli
April 17, 1598 – June 25, 1671

Giovanni Riccioli was an Italian astronomer. He was a Jesuit who entered the order in 1614. He was also the first person to measure the rate of acceleration of a freely falling body.

Riccioli was born in Ferrara, Italy. He devoted his career to the study of astronomy, often working with Francesco Maria Grimaldi. He wrote the important work Almagestum novum in 1651. By necessity, he opposed the Copernican heliocentric theory though praising its value as a simple hypothesis.

He and Grimaldi extensively studied the Moon, of which Grimaldi drew a map. Much of the nomenclature of lunar features still in use today is due to him and Grimaldi. He also observed Saturn, and was one of the first Europeans to note that Mizar was a double star.

Other books he wrote were: Geographiae et hydrographiae reformatae libri (1661), Astronomia reformata (1665), Chronologia reformata (1669) and Tabula latitudinum et longitudinum (published in 1689).

Despite his stated opposition to Copernicus's theory he named the prominent lunar crater Copernicus after him, and other important craters were named after other proponents of the theory: Kepler, Galileo and Lansbergius. Craters that he and Grimaldi named after themselves are in the same general vicinity, while some other Jesuit astronomers have craters named after them in a different part of the Moon, near Tycho. This is sometimes considered to be tacit sympathy for Copernican theory, which as a Jesuit he could not publicly express.

Between 1644 and 1656, he was occupied by topographical measurements, working with Grimaldi, determining values for the circumference of Earth and the ratio of water to land. Defects of method, however, gave a less accurate value for degrees of the meridian than Snellius had achieved a few years earlier. Snellius had been mistaken by approximately 4,000 meters; but Riccioli was more than 10,000 meters in error [Hoefer, 1873]. Riccioli had come up with 373,000 pes despite the fact that references to a Roman degree in antiquity had always been 75 milliare or 375,000 pes.


Image: G.B. Riccioli, Almagestum Novum (1651). The image portrays Urania, the muse of astronomy, weighing up the rival systems of Copernicus, in which the earth moves round the sun, and Riccioli himself, in which the earth remains stationary at the center of the universe. The older system of Ptolemy has already been discarded and lies on the ground alongside.

March 7: John Herschel

Sir John Frederick William Herschel

March 7, 1792 – May 11, 1871

Sir John Frederick William Herschel, 1st Baronet KH, FRS, was an English mathematician, astronomer, chemist, and experimental photographer/inventor, who in some years also did valuable botanical work. He was the son of astronomer Sir William Herschel and the father of 12 children.

Herschel originated the use of the Julian day system in astronomy. He named seven moons of Saturn and four moons of Uranus. He made many contributions to the science of photography, and investigated colour blindness and the chemical power of ultraviolet rays.

Herschel studied at Eton College and St John's College, Cambridge. It was during his time as an undergraduate that he became friends with Charles Babbage and George Peacock. He took up astronomy in 1816, building a reflecting telescope with a mirror 18 inches (460 mm) in diameter and with a 20-foot (6.1 m) focal length. Between 1821 and 1823 he re-examined, with James South, the double stars catalogued by his father. For this work he was presented in 1826 with the Gold Medal of the Royal Astronomical Society (which he won again in 1836), and with the Lalande Medal of the French Institute in 1825, while in 1821 the Royal Society bestowed upon him the Copley Medal for his mathematical contributions to their Transactions. Herschel was made a Knight of the Royal Guelphic Order in 1831.

Declining an offer from the Duke of Sussex that they travel to South Africa on a Navy ship, Herschel and his wife paid ₤500 for passage on the 'S.S. Mountstuart Elphinstone', a ship of 611 tons, which departed from Portsmouth on 13 November 1833. The voyage to South Africa was made in order to catalogue the stars, nebulae, and other objects of the southern skies. This was to be a completion as well as extension of the survey of the northern heavens undertaken initially by his father William Herschel. He arrived in Cape Town on 15 January 1834 and set up a private 21 ft (6.4 m) telescope at Feldhausen at Wynberg. Amongst his other observations during this time was that of the return of Comet Halley. Herschel collaborated with Thomas Maclear, the Astronomer Royal at the Cape of Good Hope, and the two families became close friends.

Herschel wrote many papers and articles, including entries on meteorology, physical geography and the telescope for the eighth edition of the Encyclopædia Britannica. He also translated The Iliad of Homer.

He proposed a correction to the Gregorian calendar, making years that are multiples of 4,000 not leap years, thus reducing the average length of the calendar year from 365.2425 days to 365.24225. Although this is closer to the mean tropical year of 365.24219 days, his proposal has never been adopted because the Gregorian calendar is based on the mean time between vernal equinoxes (currently 365.2424 days).

In 1835, the New York Sun newspaper wrote a series of satiric articles that came to be known as the Great Moon Hoax, with statements falsely attributed to Herschel about his supposed discoveries of animals living on the Moon, including batlike winged humanoids.

Herschel Island (in the Arctic Ocean, north of the Yukon Territory), Mount Herschel (in Antarctica) and the crater J. Herschel on the Moon are named in his honor.

February 15: William Henry Pickering

William Henry Pickering

February 15, 1858 – January 17, 1938

William Pickering was an American astronomer, brother of Edward Charles Pickering.

He discovered Saturn's ninth moon Phoebe in 1899 from plates taken in 1898. He also believed he had discovered a tenth moon in 1905 from plates taken in 1904, which he called "Themis". Unfortunately "Themis" does not exist.

Following George Darwin, he speculated in 1907 that the moon was once a part of the earth and that it broke away where now the Pacific Ocean lies. He also proposed some sort of continental drift (even before Alfred Wegener) and speculated that America, Asia, Africa, and Europe once formed a single continent, which broke up because of the separation of the moon.

He led solar eclipse expeditions and studied craters on the Moon, and hypothesized that changes in the appearance of the crater Eratosthenes were due to "lunar insects". He claimed to have found vegetation on the moon.

In 1919, he predicted the existence and position of a Planet X based on anomalies in the positions of Uranus and Neptune but a search of Mount Wilson Observatory photographs failed to find the predicted planet. Pluto was later discovered at Flagstaff by Clyde Tombaugh in 1930, but in any case it is now known that Pluto's mass is far too small to have appreciable gravitational effects on Uranus or Neptune, and the anomalies are accounted for when today's much more accurate values of planetary masses are used in calculating orbits. When the planet was named, he interpreted its symbol as a monogram referring to himself and Lowell by the phrase "Pickering-Lowell". 

Pickering constructed and established several observatories or astronomical observation stations, notably including Percival Lowell's Flagstaff Observatory. He spent much of the later part of his life at his private observatory in Jamaica. He produced a photographic atlas of the Moon: The Moon: A Summary of the Existing Knowledge of our Satellite in 1903.

The craters Pickering on the Moon and Pickering on Mars are jointly named after him and his brother Edward Charles Pickering.

February 14: Édouard Benjamin Baillaud

Édouard Benjamin Baillaud

February 14, 1848 – July 8, 1934

Benjamin Baillaud was a French astronomer. He worked as an assistant at the Paris Observatory beginning in 1872. Later he was director of the Toulouse Observatory from 1878 to 1907, during much of this time serving as Dean of the University of Toulouse Faculty of Science.

He greatly expanded the observatory and enthusiastically supported the Carte du Ciel project. He specialized in celestial mechanics, in particular the motions of the satellites of Saturn.

In 1903, the observatory took over a facility on the Pic du Midi in the Pyrenees that had been founded by amateurs in the 1850s with the goal of putting a telescope there. However, the height of 2,865 metres (9,400 feet) posed formidable logistical challenges and the ambition had remained unrealised though a meteorological observatory had operated from 1873 to 1880. Baillaud organised a team of soldiers to erect a 0.5 metre (20 inch) reflecting telescope, and 0.25 metre refracting telescope on the summit.

In 1907, he became director of the Paris Observatory where he immediately set to work to relaunch the stalled Carte du Ciel project with a conference held at the observatory, entertained by singers from the Paris Opera and refreshed by wine provided by the director of the Bordeaux Observatory. Though the French government agreed to fund the project, it was becoming increasingly clear that its objectives were hopelessly unrealistic.

Baillaud was active in time standardisation, becoming the founding president of the International Time Bureau and initiating the transmission of a time signal from the Eiffel Tower. Baillaud maintained the observatory and the time signal throughout World War I, even though the German howitzer Big Bertha was targeted on the nominal co-ordinates of Paris, the location of the observatory! Baillaud's concern for the astronomical time standard led him to be an outspoken opponent of daylight saving time.

Baillaud became founding president of the International Astronomical Union in 1919. He retired as director of the Paris Observatory in 1926.

He won the Bruce Medal in 1923. The Lunar crater Baillaud and the asteroid 11764 Benbaillaud are named in his honor.