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Eugenios Antoniadi (1870-1944)


Eugenios Antoniadi was a Frenchman best known for his planetary observations of the planets Mercury and Mars. Using an 83 cm refracting telescope, he produced a detailed map of the surface of Mars. So accurate was this map that most of the features on it have been confirmed by recent spacecraft missions. In 1933, he became the first to produce a detailed map of the surface of Mercury, naming some of the surface features known today. Mercury’s 450 km long Antoniadi ridge is named in his honor.

Aristarchus of Samos (310-230 BC)

Aristarchus of Samos was a Greek mathematician and astronomer who was an advocate of the heliocentric model, in which all the planets orbit around the Sun. This argument was fully accepted seventeen centuries later. Aristarchus’ only surviving text is his Treatise on the Sizes and Distances of the Sun and Moon

Rolf Dyce

Rolf Dyce together with Gordon Pettengill, measured the spin rate of Mercury using radar pulses reflected from the planet’s surface. The two researchers concluded that Mercury requires only about 59 days (two-thirds of a orbital period) to rotate once about its axis, rather than the 88 days that had been claimed by earlier observers. He is Professor Emeritus at Cornell University.

Johann Franz Encke (1791-1865)

Johann Franz Encke

Johann Franz Encke is known for determining the orbit of a comet that was later named for him. Using this information, he determined quite accurately the mass of the Mercury. He also studied the rings of Saturn.

Eudoxus of Cnidus (408-355 BC)

Eudoxus of Cnidus was a Greek astronomer, mathematician and philosopher, one of the most renowned of his day. He devised a planetary system based on spheres. Eudoxus also excelled as a mathematician; his Theory of Proportions formed the basis for Book V of Euclid’s Elements.

Galileo (1564-1642)


Galileo was an Italian who in 1609 invented a telescope that could magnify an object by twenty times. He turned this telescope on the planets, discovering four moons of Jupiter and the phases of Venus. He was also the first to use a telescope to view the planet Mercury. With these and other observations he helped establish Copernicus’ heliocentric model.

Gordon Pettengill


Gordon Pettengill, working in 1965 with colleague Rolf Dyce at the Arecibo radio telescope, measured the spin rate of Mercury by reflecting radar pulses from the planet’s surface and studying the pattern of Doppler shifts of the returning signals. He also developed two-dimensional radar mappings of the Moon that aided the Apollo missions. For his research achievements in the field of planetology he was awarded the 1997 Whitten Medal of the American Geophysical Union. He is presently Professor Emeritus at Massachusetts Institute of Technology.

Ptolemy(87-150 A.D.)


Ptolemy, a Greek mathematician, astronomer, and geographer, codified the Greek geocentric model of the universe. In this view, the Sun and other planets were believed to orbit Earth, in the order Mercury, Venus, Sun, Mars, Jupiter, and Saturn. The Ptolemaic system predicts the positions of the planets accurately enough for naked-eye observations, and is described in his Mathematical Syntaxis (widely called the Almagest), a thirteen-book mathematical treatment of of astronomy.

Giovanni Schiaparelli (1835-1910)

Giovanni Schiaparelli

Giovanni Schiaparelli is recognized for his observations of the planet Mars, double stars, and comets. He noted straight lines on the surface of Mars which he call “canali” - Italian for channels, and a term often mistranslated as canals. He also concluded that Venus and Mercury rotate on their axes, and that these rotations are at very slow rates.

Johann Hieronymus Schroeter (1745-1816)

Johann Hieronymus Schroeter

Johann Hieronymus Schroeter was a lawyer by trade, and did not turned his attention to astronomy until 1779. He is best known for his observations of the Moon, Sun and the planets Mercury, Venus, and Mars. His two volumes on the detailed landscape of the Moon were used for many years. Unfortunately, his maps of the Mercurian topography were not as accurate.

Timocharis (ca 200 B.C.)

Timocharis (ca 200 B.C.), a Greek philosopher, prepared the first star catalog in the third century B.C. He was the earliest observer of Mercury whom we know of by name. It is possible, however, that that he mistook its morning and evening appearances for two planets.

Giovanni Zupus (1590-1650)

Giovanni Zupus, was the first to discover that the planet Mercury has phases like the Moon and Venus.