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Space Topics: Planetary Exploration TimelinesPrehistory to 1698By A. J. S. Rayl, Courtney Dressing, and Emily Lakdawalla Some time before the beginning of recorded history, humans noticed that among the fixed stars that populated the night sky were five wanderers, which we now know as Mercury, Venus, Mars, Jupiter, and Saturn. Watching these wanderers as well as the motions of the Moon and the Sun formed the foundation of planetary science. 4000 B.C.E.Egyptians create a 360-day calendar by correlating observations of the star Sirius with the annual flooding of the Nile. Between years, the Egyptians feast for a five-day period of celebration known as "the yearly five days." The five days of partying are not part of the 360-day year, which means that the Egyptians really use a 365-day system. 3500 B.C.E.The construction of Newgrange (a special type of funerary monument known as a passage-grave) begins in Ireland. At sunrise on the Winter Solstice, light from the Sun penetrates the passage and illuminates the central chamber of the monument for 17 minutes. 2950-2900 B.C.E.
The construction of Stonehenge I (the first of three stages) begins near what is now Amesbury, Wiltshire, in southern England. Stonehenge I consists of a circular ditch inside a circular bank with several breaks. The most prominent break is positioned so that the rising midsummer Sun is exactly positioned in the gap in the bank. 2500 B.C.E.The Akkadians of Babylon begin to keep astronomical records. 2300 B.C.E.Stone megaliths appear at Stonehenge as construction of phase III begins. 2296 B.C.E.The Chinese become the first to record the observation of a comet. 2136 B.C.E.The Chinese observe the first documented solar eclipse. 2000 B.C.E.The Egyptians and Mesopotamians develop the first solar-lunar calendars, which demonstrate significant astronomical knowledge and observation. 1800 B.C.E.The Babylonians begin to keep observational records. 1600 B.C.E.Chaldean astronomers of Mesopotamia identify the zodiac. Construction of the third and final phase of Stonehenge is completed. The monument contains many large stones and resembles the popular images of the site. 2000 to 1500 B.C.E.The cairns, Balnuaran of Clava, are built in Scotland. Passages in two of the three burial chambers are aligned with the midwinter sun. 1400 B.C.E.The Chinese begin a detailed record of eclipses. 763 B.C.E.The Babylonians record observations of a solar eclipse. 585 B.C.E.Thales of Miletus (624-547 B.C.E.), who is rumored to have defined the constellation Ursa Major, successfully predicts a solar eclipse. 500 B.C.E.Pythagoras (569-475 B.C.E.) proposes that the Earth is spherical, not flat, as most people believed. The Chinese make the first recording of any planetary grouping. 400 B.C.E.Babylonian astronomers develop a mathematical model to explain the differing speeds of the Moon and Sun across the sky based on the current phase of the Moon. They are able to use their equations to predict the time of new Moons and determine the daily positions of the Moon and Sun for an entire month. The Chinese write the Book of Silk, which is the earliest known atlas of comets. The book is discovered in a tomb in 1973. 300 B.C.E.
Greek philosopher Aristotle (384-322 B.C.E.) observes that the Moon occults (passes in front of) Mars. He concludes that Mars must be higher up in the heavens than the Moon. 280 B.C.E.The Greek astronomer Aristarchus of Samos (310-230 B.C.E.) suggests that the Earth orbits the Sun. He also calculates the first estimation of the distance from the Earth to the Sun. 270 B.C.E.Aristarchus estimates the size of the Sun and proposes that the Sun is at the center of the solar system. His theories about a heliocentric solar system are largely ignored. 250 B.C.E.Eratosthenes of Cyrene (276-194 B.C.E.) estimates the circumference of the Earth as 250,000 stadia (plural of stadium). The exact dimension of a stadium is not known but is estimated to be equivalent to 154-215 meters, giving a circumference of between 38,500 and 53,750 kilometers, bracketing the correct value. His work, which is based on a study of the noon shadows at midsummer, is published in his treatise On the Measurement of the Earth. 240 B.C.E.The Chinese make the first observation of what would become known as Halley's comet. ~150 B.C.E.The astronomer Hipparchus of Rhodes (c. 190-120 B.C.E.) develops techniques for measuring stellar brightness and distance. ~130 B.C.E.Hipparchus develops a star catalogue with more than 850 of the brightest stars and creates the first accurate star map. ~135 B.C.E.Hipparchus estimates the distance from the Earth to the Moon and discovers that the vernal (spring) equinox occurs when the Sun is in a slightly different part of the zodiac each year. This is known as the precession of the equinoxes. One full cycle through the zodiac takes 26,000 years. 120 B.C.E.Hipparchus creates a coordinate system for the cosmos based on latitude and longitude. He then makes triangular measurements of celestial navigation. 100 B.C.E.Chinese astronomers propose the round-Earth theory and a cosmology of infinite empty space. They also estimate the size of the spherical Earth and Moon. 46 B.C.E.The Julian calendar, which is based on the motion of the Sun through the heavens, is introduced to the Roman Empire. 28 B.C.E.The Chinese record the first observations of sunspots. 127Greek astronomer and mathematician Claudius Ptolemaeus (85-165), commonly known as Ptolemy, publishes his Almagest. The book is a catalogue of 1,022 stars (177 more stars than in Hipparchus' 850-star catalogue) and remains the primary astronomy text for 14 centuries. 140Ptolemy publishes Mathematike Syntaxis, in which he argues for a geocentric universe. 300The Mayans determine the length of time between full Moons to be 29.53 days. Other Mayan contributions to astronomy include the creation of multiple calendars and observation of Venus. Mayan astronomers even discover that Venus orbits the Sun every 584 days (the actual period is 583.92 days). 813Al Mamon, who had declared himself caliph two years earlier in 811, founds the Baghdad school of astronomy in Iraq. 1054Chinese astronomers record observations of a supernova in the constellation Taurus. The supernova is referred to as the "guest star" and is responsible for the formation of the Crab Nebula. 1120Construction of what was possibly the first observatory in medieval Islam begins in Cairo, Egypt. The observatory is destroyed in 1125 after the patron is found guilty of multiple crimes. 1259
Persian astronomer Nasir al-Din al-Tusi (1201-1274) begins to construct an observatory under the patronage of the Mongol ruler Hulagu Khan (1217-1265). The observatory is later named the Maragha Observatory and includes a vast library and a variety of instruments. 1350The Chinese invent equatorial mounting for astronomical instruments. 1420Ulugh Beg (1394-1449) begins construction of a three-storey observatory at Samarkand in central Asia. He then produces astronomical tables including data for more than 1,000 stars before succeeding to the throne of the province of Transoxiana in 1447. 1514
Polish astronomer Nicolas Copernicus (1473-1543) suggests that Earth revolves around the Sun and begins to circulate his Commentariolus outlining his rationale. 1543On his deathbed, Copernicus writes De Revolutionibus Orbium Caoelestium (The Revolutions of the Heavenly Spheres), in which he proposes that Earth revolves around the Sun. 1572Astronomer Tycho Brahe of Denmark (1546-1601) discovers a "new star" in the constellation Cassiopeia. He discusses the supernova in his work De Nova et Nullius Aevi Memoria Prius Visa Stella ("On the New and Never Previously Seen Star") published in 1573. 1580-1600Brahe determines the position of Mars in the night sky by taking the most detailed measurements of the planet to date. Although the telescope has yet to be invented, Brahe is able to plot the Red Planet by utilizing instruments that accurately determine the position of objects in the night sky from the Uraniborg observatory, which he directs. 1582Pope Gregory XIII introduces the Gregorian calendar. 1596
German astronomer Johannes Kepler (1571-1630), who had worked as an assistant to Brahe, publishes his first major work, Mysterium cosmographicum ("Mystery of the Cosmos"). He suggests that the sizes of the orbits of the planets can be explained by drawing the five convex regular solids inside each other, beginning with a sphere at the orbit of Saturn and ending with a regular octahedron between Venus and Mercury. Kepler's arguments provide more evidence for Copernicus's theory of a heliocentric solar system. 1603German astronomer Johann Bayer (1572-1625) publishes his most famous work, Uranometria, the first full-sky star atlas. Bayer also introduces the Bayer designation of stars by using Greek letters to distinguish each star in a constellation. His system is still in use today. 1608Dutch spectacles maker Hans Lippershey (1570-1619) becomes the first to describe the telescope in writing and thus is usually credited with its invention. However, it appears likely that the inventor is another Dutch spectacles maker whose name is not known. 1609Kepler publishes his first two laws of planetary motion in his book Astronomia Nova ("The New Astronomy") and explains the complexities of Mars' retrograde motion. He hypothesizes that the orbit of each planet is an ellipse, with the Sun at one of its foci; and that each planet sweeps out equal areas in equal time. Kepler's discoveries are made possible largely through his use of Brahe's highly accurate measurements of Mars' position in the night sky. 1609
Italian astronomer Galileo Galilei (1564-1642), a professor at the University of Padua in Venice, constructs the first astronomical telescope. Using his improved telescope, Galileo discovers the four Jovian moons (Callisto, Europa, Ganymeade, and Io) and observes that Venus goes through phases just asthe Moon does. He also observes the Moon's craters. 1608-1610Galileo Galilei becomes the first person to observe Mars through a telescope. He describes the phases of Mars in a December 30, 1610 letter to a friend. 1610Working independently and using telescopes, Galileo, Johann Fabricius (1587-1616; Holland), and Christopher Scheiner (1575-1650; Germany) discover sunspots and learn that they rotate with the Sun. Additionally, Scheiner is credited with being the first to project an image of the Sun onto a flat surface for safe solar observing. 1619Kepler uses data on Mars' orbit to discover his third law of planetary motion: the square of the orbital period is proportional to the cube of the body's mean distance from the Sun. He publishes the law in Harmonices Mundi ("The Harmony of the Worlds"), a work that focuses on the musical tones he believes the planets produce during their revolution around the Sun. 1636Amateur astronomer Francisco Fontana of Naples, Italy, makes the earliest known drawing of Mars based on his telescopic observations, noting that "the disk of Mars is not uniform in color." 1656Dutch mathematician and astronomer Christiaan Huygens (1629-1695) observes Saturn through a telescope and discovers Saturn's rings and its moon Titan. 1659
Huygens draws the first informative sketches of Mars that show major surface features, including Syrtis Major. 1666Astronomer Giovanni Cassini (1625-1712) makes more precise measurements of Mars, calculating the length of the Martian day to be just under 24 hours, 40 minutes, almost 37.5 minutes longer than Earth's. Remarkably, this is within three minutes of its actual rotation time. He is also credited with the discovery and identification of the polar caps on Mars, which will not be described any more fully until Giacomo Miraldi's work in 1719. (The caps are not understood to be made of ice until 1781.) 1668Sir Isaac Newton (1643-1727) constructs the first reflecting telescope. Reflecting telescopes use mirrors to gather light and are sometimes referred to as "Newtonians" after their inventor. 1669Italian astronomer Geminiano Montanari (1633-1687) discovers the first variable star (Algol in the constellation Perseus) after noticing that the star's brightness is not steady. Many decades later, astronomers discover that the dips in Algol's brightness are caused by a dimmer companion star crossing in front of Algol and blocking its light. Stars paired this way are referred to as eclipsing binaries. 1672
Christiaan Huygens draws an image of Mars and its southern polar cap. Cassini and Jean Richer perform simultaneous measurements of Mars from France and South America to determine the distance from Earth to Mars. This measurement is later used to help determine the distance from the Earth to the Sun. 1676Danish astronomer Ole Roemer (1644-1710) measures the speed of light by observing the eclipses of the Galilean satellites of Jupiter. Roemer obtains a speed of 140,000 miles per second, which is approximately 25 percent too slow. 1687Newton publishes Philosophiae Naturalis Principia Mathematica, more simply known as the Principia. In his work, Newton describes his theory of universal gravitation and explains the laws of mechanics. The concepts discussed in the Principia become the foundations of modern physics. 1698Christaan Huygens, in his posthumously published Cosmotheros, argues that planets in the solar system are inhabited, igniting a debate that extends into the 20th Century. Go onward to A
Mars Timeline from 1700 to 1959 » |
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