Aryabhatiya
Aryabhata completes the Aryabhatiya, presenting mathematical methods and astronomical rules for calculating planetary positions.
Astronomy topic guide · World History Database
History of Planetary Discoveries
Planetary discovery expanded dramatically after the invention of the telescope. Uranus was the first planet discovered in the modern telescopic era, while Neptune showed the power of mathematical prediction. The nineteenth and twentieth centuries added asteroids, Pluto and increasingly detailed studies of planetary atmospheres, rings and moons. More recent surveys have revealed dwarf planets and a complex population of icy worlds beyond Neptune. This page brings together database records connected with major planetary discoveries and changing ideas about the architecture of the Solar System.
What this chronology covers
The meaning of “planet” has changed with discovery. Uranus enlarged the classical planetary system, Neptune demonstrated the power of predictive celestial mechanics, and the discovery of Ceres and the asteroid population forced new classifications. Pluto’s discovery and the later identification of large trans-Neptunian objects led to another redefinition in the twenty-first century. Planetary exploration by spacecraft has added a second layer of discovery by revealing geology, atmospheres, rings and satellite systems in detail.
736matching astronomy records
2,423records in the complete astronomy database
Selected database timeline
The records below are drawn from the existing World History Database astronomy collection and arranged chronologically. For very broad subjects, the page shows a substantial selection rather than duplicating the entire parent database.
Planetary Calculations
Brahmagupta describes computational methods for planetary longitudes, conjunctions, eclipses and other astronomical phenomena.
Siddhanta Shiromani
Bhaskara II completes the Siddhanta Shiromani, whose astronomical sections address planetary motion, spheres and eclipse calculations.
Theoricae novae Planetarum
Publication of "Theoricae novae Planetarum"
Mathematical and Astronomical Education
Receives training that supports his later work on planetary motion.
Planetary Model
Nilakantha Somayaji presents an improved planetary model that gives Mercury and Venus motions around the Sun while retaining an Earth-centred framework.
Commentariolus
Circulates a short manuscript outlining a heliocentric planetary system.
Heliocentric System
Places Earth among the planets moving around the Sun.
Geoheliocentric Planetary Model
Places the planets around the Sun while the Sun circles Earth.
Tychonic System
Publishes a planetary model combining a stationary Earth with solar orbits.
Danish Astronomy Treatise
Presents a detailed Danish account of planetary theory and astronomical calculation.
Discovery of Planetary Motion
Finding that an elliptical orbit fit the Mars data, concludes that all planets move in ellipses, with the sun at one focus-Keplers first law of planetary motion
Law of Planetary Motion
Finding that an elliptical orbit fit the Mars data, concludes that all planets move in ellipses, with the sun at one focus-Keplers first law of planetary motion
Astronomia Nova
Publishes laws of elliptical planetary motion that prepare celestial mechanics for Newtonian gravity.
Copernican System
Publication of "The Starry Messenger", claims the Earth revolves around the Sun. Galileo's observations of the phases of Venus proved that it orbited the Sun and lent support to (but did not prove) the heliocentric model
Discovery of Saturn
The first observation of Saturn through a telescope is made by Galileo Galilei, his first telescope is so crude that he wasnt able to distinguish the planets rings; instead he thought the planet might have ears or two large moons on either side
Discovery of Venus
Galileo's observations of the phases of Venus proved that it orbited the Sun and lent support to (but did not prove) the heliocentric model. Galileo observes that Venus exhibited a full set of phases similar to that of the Moon
Medicean Stars Named
Galileo names Jupiter's newly discovered satellites the Medicean Stars in honour of the ruling Medici family.
First Telescopic Observation of Jovian Satellites
Observes three points of light close to Jupiter, beginning the discovery of its major moons.
Observation of Galilean Moons
Independently observes Jupiter's four large moons at about the same time as Galileo.
Jovian Moons Recognized as Satellites
Concludes that four observed bodies orbit Jupiter rather than the Earth.
Sidereus Nuncius
Publishes telescopic observations of Jupiter's satellites in Sidereus Nuncius.
Jupiter Moons
Publishes support for Galileo's discovery of satellites orbiting Jupiter.
Jovian Moon Period Studies
Galileo begins systematic study of the orbital periods of Jupiter's four large moons.
Longitude Method Using Jovian Moons
Galileo proposes using predicted eclipses of Jupiter's moons as a celestial clock for determining longitude.
Discovery of Neptune
Galileo also observed the planet Neptune in 1612, but did not realize that it was a planet
Sunspots
Previous sunspot observations had been misinterpreted as planetary transits, until Galileo gave the correct explanation in 1612
Naming of Jupiter Moons
Publishes the names Io, Europa, Ganymede and Callisto for Jupiter's four large moons.
Third Law of Planetary Motion
States the harmonic relation between orbital period and distance from the Sun.
Transit of Mercury Prediction
Kepler's Rudolphine Tables predict that Mercury will cross the face of the Sun in November 1631.
Transit of Venus Prediction
Kepler's Rudolphine Tables predict a transit of Venus for 1631, although the event is not visible from Europe.
First Telescopic Planetary Transit
Records the first telescopic observation of a planetary transit.
Transit of Mercury Observed
Observes Mercury crossing the Sun as predicted by Kepler.
Transit of Venus Prediction
Horrocks corrects earlier calculations and predicts that Venus will transit the Sun in December 1639.
Transit of Venus Observed
Horrocks observes the first recorded transit of Venus from Much Hoole after projecting the Sun's image safely.
Transit of Venus Observed
Crabtree independently observes the 1639 transit of Venus after Horrocks alerts him to the predicted event.
Discovery of Mars
Discovers the Martian south polar cap
Discovery of Saturn
The Dutch astronomer Christiaan Huygens observed Saturn in 1659, and solved the mystery, realizing that the "arms" around Saturn were really a system of rings. He also was the first to observe Saturns moon Titan
Astronomical Unit
Gregory proposes using observations of a planetary transit from widely separated locations to determine the scale of the Solar System.
Jupiter Spot Observation
Observes a conspicuous spot on Jupiter, contributing to early studies of the planet's changing atmosphere.
Discovery of M22
Discovers the globular cluster M22 while observing Saturn in Sagittarius.
Jupiter Permanent Spot
Records a persistent oval feature at the latitude associated with Jupiter's later Great Red Spot.
Jupiter Rotation
Uses atmospheric markings to estimate Jupiter's rapid rotation period.
Precision Telescopic Measurement
Improves quantitative observation of planetary diameters and double stars.
Discovery of Lapetus
Discovered by Giovanni Domenico Cassini as he was studying Saturn and its rings, Cassini guessed correctly that Iapetus was tidally locked to Saturn, and that one half of the planet was bright, and the other half was dark
Tables of Jupiter Moons
Improves tables predicting eclipses and motions of Jupiter's satellites.
Mars Parallax Expedition
Observes Mars from Cayenne for comparison with measurements in France.
Mercury Transit Timing
Halley's Mercury transit observations strengthen interest in using accurately timed planetary transits to refine measurements of the Solar System.
Transit of Mercury
Halley observes a transit of Mercury from Saint Helena and carefully records the event for later astronomical analysis.
Halley's Comet
Halley is classified as a periodic or short-period comet; one with an orbit lasting 200 years or less. After a rough estimate of the perturbations the comet would sustain from the gravitational attraction of the planets, he predicted its return for 1758
Synopsis of the Astronomy of Comets
Publishes cometary orbit calculations accounting for perturbations by Jupiter and Saturn.
Transit of Venus Method
Halley publishes a method for using future transits of Venus to calculate the Earth-Sun distance more accurately.
Transit of Mercury
Messier documents the transit of Mercury
Comet Return Prediction
Calculates that Jupiter and Saturn will delay the predicted return of Halley's Comet.
Transit of Venus Expedition
Attempts to observe the Venus transit during an extended scientific voyage.
Atmosphere of Venus
Lomonosov observes a luminous arc during the transit of Venus and concludes that the planet possesses an atmosphere.
Transit of Venus Expedition
Mason observes the transit of Venus from the Cape of Good Hope after wartime conditions disrupt the expedition's original destination.
Transit of Venus Expedition
Dixon joins Charles Mason in observing the transit of Venus from the Cape of Good Hope for international distance measurements.
Planetary Distances
Publishes a numerical pattern of planetary distances that includes Jupiter's orbit.
Transit of Venus
Le Gentil reaches Pondicherry for the 1769 transit but clouds prevent him from observing the event after years of travel.
Transit of Venus Expedition
Cook's expedition observes the transit of Venus from Tahiti as part of an international effort to determine the astronomical unit.
Transit of Venus Observed
Green makes timed observations of the Venus transit from Tahiti during Cook's scientific expedition.
Transit of Venus Observed
Rittenhouse leads observations of the transit of Venus in Pennsylvania for measurements of the Earth-Sun distance.
Titius-Bode Law
Popularises the numerical planetary-distance rule that includes Jupiter.
Discovery of Georgium Sidus
Calls the new planet the Georgian star (Georgium sidus) after King George III
Discovery of Uranus
Calls the new planet the Georgian star (Georgium sidus) after King George III
Discovery of Uranus
Discovers Uranus using a home made telescope from his back garden in Bath
Discovery of Uranus
Produces a diagram of the shape of the Galaxy with the Solar System close to the centre
Uranus
The first attempt to describe the shape of the Milky Way and the position of the Sun within it is carried out by William Herschel carefully counting the number of stars in different regions of the sky
Discovery of Oberon
Herschel discovers a new moon of Uranus, Oberon
Discovery of Titania
Herschel discovers a new moon of Uranus, Titania
Discovery of Enceladus
Herschel discovers a new moon of Saturn, Enceladus
Discovery of Mimas
Herschel discovers a new moon of Saturn, Mimas, only 250 miles in diameter
Discovery of Neptune
There is evidence that Neptune was seen and recorded by Galileo Galilei in 1613, Jerome Lalande in 1795 and John Herschel in 1830 but none is known to have recognized it as a planet at the time
Jupiter-Saturn Inequality
Explains the long-period inequality in the motions of Jupiter and Saturn through gravitational perturbations.
Discovery of Ceres
Discovers the Ceres asteroid
Celestial Mechanics
Publishes celestial-mechanics work treating gravitational perturbations involving Jupiter.
Death of Frederick William Herschel
Death of Frederick William Herschel, died in his 84th year, which is the same number of years Uranus takes to orbit the Sun
Herschel Museum of Astronomy
Herschels house at 19 New King Street in Bath, Somerset where he made many telescopes and first observed Uranus, is now home to the Herschel Museum of Astronomy
Great Red Spot Drawing
Makes an early detailed drawing of a large spot on Jupiter later associated with the Great Red Spot.
Encke Gap
Encke describes a broad variation in the brightness of the A Ring of Saturn. The Encke Gap was later named in honor of his observations of Saturns rings
Rings of Saturn
Encke describes a broad variation in the brightness of the A Ring of Saturn. The Encke Gap was later named in honor of his observations of Saturns rings
Discovery of Neptune
In an 1846 letter to Wilhelm Struve, John Herschel states that he observed Neptune during a sweep of the sky on July 14, 1830
Triton Observation
Lassell begins follow-up observations confirming that the newly found object moves with Neptune as a satellite.
Prediction of Neptune
Predicts Neptune's position from gravitational perturbations in Uranus's orbit.
Prediction of Neptune
Independently calculates a possible planet disturbing Uranus's orbit.
Discovery of Neptune
Observes Neptune near Le Verrier's predicted position.
Discovery of Triton
Lassell discovers Triton, Neptune's largest moon, only seventeen days after Neptune itself is identified as a planet.
Discovery of Enceladus
Herschel discovered two moons of Saturn, Mimas and Enceladus; as well as two moons of Uranus, Titania and Oberon, he did not give these moons their names; rather, they were named by his son John in 1847 and 1852, respectively, well after his death
Discovery of Mimas
Herschel discovered two moons of Saturn, Mimas and Enceladus; as well as two moons of Uranus, Titania and Oberon, he did not give these moons their names; rather, they were named by his son John in 1847 and 1852, respectively, well after his death
Triton Orbit
Continued observations establish Triton as a genuine moon of Neptune rather than a background star.
Discovery of Oberon
Herschel discovered two moons of Saturn, Mimas and Enceladus; as well as two moons of Uranus, Titania and Oberon, he did not give these moons their names; rather, they were named by his son John in 1847 and 1852, respectively, well after his death
Discovery of Titania
Herschel discovered two moons of Saturn, Mimas and Enceladus; as well as two moons of Uranus, Titania and Oberon, he did not give these moons their names; rather, they were named by his son John in 1847 and 1852, respectively, well after his death
Great Red Spot Drawing
Records a drawing of a large Jovian spot during renewed nineteenth-century observations of Jupiter.
Orbit of Mercury
Le Verrier was the first to report that the slow precession of Mercurys orbit around the Sun could not be completely explained by Newtonian mechanics and perturbations by the known planets
Mercury Perihelion Anomaly
Reports the unexplained advance of Mercury's perihelion, later explained by general relativity.
Vulcan Hypothesis
Le Verrier proposes an unseen planet inside Mercury's orbit as one possible explanation for the unexplained advance of Mercury's perihelion.
Reddish Jovian Oval
Describes a reddish elliptical marking in Jupiter's southern hemisphere during telescopic observations.
Transit of Venus Photography
Janssen uses his photographic revolver during the transit of Venus to record a rapid sequence of solar images.
Deimos
Asaph Hall discovers Phobos and Deimos, the moons of Mars
Mars
Asaph Hall discovers Phobos and Deimos, the moons of Mars
Phobos
Asaph Hall discovers Phobos and Deimos, the moons of Mars
Great Red Spot Tracking
Begins systematic observations of Jupiter's Great Red Spot and its changing longitude.
Jupiter Rotation
Uses atmospheric markings to refine estimates of Jupiter's rotation.
Belgian Venus Transit Observations
The programme contributes measurements intended to refine the astronomical unit.
Belgian Venus Transit Programme
Supports measurement of the astronomical unit through coordinated observations.
Transit of Venus Expedition
Organizes Belgian observations of the transit of Venus.
Transit of Venus Expeditions
Organizes Belgian expeditions to observe the transit of Venus.
Birth of Edwin Powell Hubble
Birth of Edwin Powell Hubble
Mercury Rotation
Schiaparelli reports that Mercury appears to rotate once in about 88 days, suggesting synchronous rotation with its orbital period.
Jupiter Photography
Photographs and studies Jupiter with the large refractor at Lick Observatory.
Discovery of Amalthea
Discovers Amalthea, the fifth known moon of Jupiter and the last satellite found visually.
Discovery of Elara
Discovers Elara, an outer irregular moon of Jupiter, using photographic observations.
Discovery of Planet X
Percival Lowell starts an extensive project in search of a possible ninth planet, which he terms "Planet X"
Discovery of Patroclus
Discovers Patroclus, an asteroid occupying Jupiter's trailing Trojan region.
Discovery of Pluto
Percival Lowell begins an extensive search for a possible ninth planet, which he calls Planet X.
Discovery of Achilles
Discovers Achilles, the first recognized asteroid sharing Jupiter's orbit near a stable Lagrange point.
Discovery of Hektor
Discovers Hektor, a large asteroid in Jupiter's leading Trojan swarm.
Pasiphae Identified as Jovian Satellite
Identifies Pasiphae, a distant retrograde satellite moving around Jupiter.
Discovery of Pluto
Lowell and William H. Pickering suggest several possible celestial coordinates for the predicted Planet X.
Sinope Added to Jupiter System
Finds Sinope, extending the known family of distant retrograde Jovian satellites.
Discovery of Pluto
Lowell Observatory captures faint images of Pluto, but the object is not recognised as the predicted planet.
Mercury Perihelion
Explains Mercury's anomalous perihelion advance using the emerging general theory of relativity.
Discovery of Pluto
Lowell continues the search for Planet X until his death in 1916 without identifying Pluto.
Hubble Space Telescope
Hermann Oberth, along with Robert Goddard and Konstantin Tsiolkovsky, one of the three fathers of modern rocketry, publish "Die Rakete zu den Planetenraumen" ("The Rocket into Planetary Space"), proposingg a telescope in space
Discovery of 1052 Belgica
Adds a Belgian-named object to the catalogue of minor planets.
Discovery of Planet X
The search for Planet X resumes when the Lowell Observatory director, Vesto Melvin Slipher, summarily hands the job of locating Planet X to Clyde Tombaugh
Discovery of Pluto
Tombaugh is assigned to systematically photograph the night sky and compare paired plates with a blink comparator in the renewed search for Planet X.
Discovery of Pluto
Lowell Observatory director Vesto Melvin Slipher assigns Clyde Tombaugh the task of searching for Planet X.
Pluto
Venetia Burney's proposed name Pluto is forwarded to Lowell Observatory and becomes the preferred name for the newly discovered world.
Discovery of Pluto
Tombaugh exposes one of the photographic plates later used, with the January 29 plate, to identify Pluto's motion.
Discovery of Pluto
Tombaugh exposes the second of the two photographic plates later used to identify Pluto's motion against background stars.
Discovery of Pluto
Tombaugh identifies Pluto as a moving object while comparing photographic plates taken on January 23 and January 29.
Discovery of Pluto
Using a blink comparator, Tombaugh identifies a moving object on plates taken January 23 and January 29, discovering Pluto.
Discovery of Pluto
News of Pluto's discovery is telegraphed from Lowell Observatory to the Harvard College Observatory.
Discovery of Pluto
Eleven-year-old Venetia Burney suggests the name Pluto after hearing of the newly discovered world.
Naming of Pluto
Eleven-year-old Venetia Burney suggests the name Pluto during breakfast after hearing news of the newly discovered planet.
Naming of Pluto
Oxford astronomer Herbert Hall Turner forwards Venetia Burney's proposed name Pluto to astronomers at Lowell Observatory.
Naming of Pluto
Lowell Observatory director Vesto Slipher announces Pluto as the proposed name for the newly discovered world.
Jupiter Atmospheric Molecules
Identifies methane and ammonia absorption in spectra of Jupiter and other giant planets.
Methane in Neptune Atmosphere
Spectroscopic work identifies strong methane absorption in Neptune's atmosphere and helps explain the planet's visible colour.
Neptune Atmospheric Spectrum
Adel analyses giant-planet spectra and confirms strong methane absorption features in Neptune's atmosphere.
Discovery of Lysithea
Discovers Lysithea, an irregular satellite of Jupiter.
Discovery of Carme
Discovers Carme, a retrograde irregular satellite of Jupiter.
Trans-Neptunian Comet Reservoir
Edgeworth suggests that a reservoir of small icy bodies may exist beyond the known planets and supply comets.
Nereid Orbit
Kuiper's observations show that Nereid follows an unusually eccentric orbit around Neptune.
Discovery of Nereid
Kuiper discovers Nereid, Neptune's second known moon, using a ground-based telescope.
Kuiper Belt Hypothesis
Kuiper discusses the possibility that numerous icy bodies formed beyond Pluto in the early Solar System.
Discovery of Ananke
Discovers Ananke, another distant retrograde moon of Jupiter.
Jupiter Radio Emissions
With Kenneth Franklin, detects strong decametric radio bursts coming from Jupiter.
Jupiter Rotation from Radio Bursts
Uses recurring Jovian radio bursts to improve estimates of Jupiter's rotation.
Pluto
Photoelectric observations establish a roughly 6.4-day brightness periodicity for Pluto, providing the first reliable measurement of its rotation period.
Project Mercury Astronaut Selection
NASA presents Shepard as one of the seven pilots selected for Project Mercury, America's first human spaceflight programme.
Project Mercury Astronaut Selection
NASA presents Grissom as one of the original seven astronauts chosen to train for Project Mercury missions.
Project Mercury Astronaut Selection
NASA introduces Carpenter as one of the seven military test pilots selected for Project Mercury.
Project Mercury Astronaut Selection
NASA introduces Cooper as one of the original seven astronauts selected for Project Mercury flight training.
Project Mercury Astronaut Selection
NASA names Slayton among the seven original astronauts selected for Project Mercury.
Polarized Jupiter Radio Emission
With J. A. Roberts, measures polarized extended radio emission from Jupiter, supporting a synchrotron radiation-belt interpretation.
Venus Greenhouse Effect
Sagan develops models showing that a strong greenhouse effect can explain the extremely high surface temperature of Venus.
Venus Radar
Uses planetary radar to measure Venus more accurately.
Related astronomers
AryabhataProfile and database timelineBhaskara IIProfile and database timelineNicolaus CopernicusProfile and database timelineTycho BraheProfile and database timelineGalileo GalileiProfile and database timelineJohannes KeplerProfile and database timelineEdmond HalleyProfile and database timelineWilliam HerschelProfile and database timeline
Sources and editorial provenance
Compiled and edited by World History Database
Historical chronology compiled from the World History Database and checked against major scientific and historical reference sources.
Last reviewed: September 2026.
- Royal Museums Greenwich — History of astronomy
- Royal Museums Greenwich — History of the telescope
- NASA Science — Hubble timeline
- NASA Science — Exoplanet discovery history
- LIGO — GW150914 first gravitational-wave detection
- Event Horizon Telescope — first black-hole image
- NASA Webb — mission science and discoveries