Timeline of Solar System astronomy

The following is a timeline of Solar System astronomy. It includes the advances in the knowledge of the Earth at planetary scale, as part of it.

A transit of Venus

Direct observation

Humans have inhabited the Earth in the last 500,000 years at least, and they had witnessed directly observable astronomical and geological phenomena. For millennia, these have arose admiration and curiosity, being admitted as of superhuman nature and scale. Multiple imaginative interpretations were being fixed in oral traditions of difficult dating, and incorporated into a variety of belief systems, as animism, shamanism, mythology, religion and/or philosophy.

Although such phenomena are not "discoveries" per se, as they are part of the common human experience, their observation shape the knowledge and comprehension of the world around us, and about its position in the observable universe, in which the Sun plays a role of outmost importance for us. What today is known to be the Solar System was regarded for generations as the contents of the "whole universe".

The most relevant phenomena of these kind are:

• Basic gravity. Following the trajectory of free falling objects, the Earth is "below" us and the sky is "above" us.
• Characterization of the terrestrial surface, in four main types of terrain: lands covered with vegetation; dry deserts; bodies of liquid water, both salted (seas and oceans) and fresh (rivers and lakes); and frozen landscapes (glaciars, polar ice caps). Recognition of emerged lands and submerged ones. Recognition of mountain ranges and cavities (grottos and caverns).
• Characterization of the Earth's atmosphere and its associated meteorological phenomena: clouds, rain, hail and snow; wind, storms and thunderstorms, tornadoes and hurricanes/cyclones/typhoons; fluvial floods, deluges and landslides; rainbows and halos; mirages; glacial ages.
• Diurnal apparent movement of the Sun: sunrise, noon and sunset. Recognition of the four cardinal points: north, south, east, and west.
• Nightly apparent movement of the celestial sphere with its main features regarded as "fixed": stars, the brightest of them forming casual groupings known as constellations, under different names and shapes in many cultures. Different constellations are viewed in different seasons and latitudes. Along with the faint strip of the Milky Way, they altogether conform the idea of the firmament, which as viewed from Earth it seems to be a consistent, solid unit rotating smooth and uniformly. This leads to the intuitive idea of a geocentric universe.
• Presence of the Moon, with its phases. Tides. Recognition of meteorological phenomena as sub-lunar.
• Yearly apparent transit of the Sun through the constellations of the zodiac. Recognition of the lunar cycle as a (lunar) month, and the solar cycle as the (solar) year, the basis for calendars.
• Observation of non-fixed or "wandering" objects in the night sky: the five classical planets; shooting stars and meteor showers; bolides; comets; auroras; zodiacal light.
• Solar and lunar eclipses. Planetary conjunctions.
• Identification of the frigid, temperate and torrid zones of the Earth by latitude. Equator and Tropics. Four seasons in temperate zones: spring, summer, autumn and winter. Equinoxes and solstices. Monsoons. Midnight sun.
• Telluric phenomena: seismic (earthquakes and seaquakes; tsunamis). Geysers. Volcanoes.

Along with an indeterminate number of unregistered sightings of rare events: meteor impacts; novae and supernovae.

Antiquity

The Antikythera mechanism (Fragment A – front); visible is the largest gear in the mechanism, approximately 140 millimetres (5.5 in) in diameter

The Antikythera mechanism (Fragment A – back)

• 3rd millennium BC – Around 5000 years ago, one of the Indian Sages, 'Maharshi Ved Vyas' composed a 'shloka' named "Nava-graha-stotram", in which he wrote in brief about the planets (except Uranus and Neptune) and the two states - Rahu and Ketu denote the points of intersection of the paths of the Sun and the Moon as they move on the celestial sphere. Rahu and Ketu are respectively called the north and the south lunar nodes.
• 2nd millennium BC – earliest possible date for the composition of the Babylonian Venus tablet of Ammisaduqa, a 7th-century BC copy of a list of observations of the motions of the planet Venus, and the oldest planetary table currently known.
• 2nd millennium BC – Babylonian astronomers identify the inner planets Mercury and Venus and the outer planets Mars, Jupiter and Saturn, which would remain the only known planets until the invention of the telescope in early modern times.
• late 2nd millennium BC – Chinese astronomers record a solar eclipse.
• late 2nd millennium BC – Chinese determine that Jupiter needs 12 years to complete one revolution of its orbit.
• c. 1200 BC – Earliest Babylonian star catalogues.
• c. 1100 BC – Chinese first determine the spring equinox.
• c. 750 BC – During the reign of Nabonassar (747–733 BC), the systematic records of ominous phenomena in Babylonian astronomical diaries that began at this time allowed for the discovery of a repeating 18-year cycle of lunar eclipses.
• 776 BC – Chinese make the earliest reliable record of a solar eclipse.
• 7th century BC – Egyptian astronomers alleged to have predicted a solar eclipse
• 613 BC, July – A Comet, possibly Comet Halley, is recorded in Spring and Autumn Annals by the Chinese.
• 586 BC – Thales of Miletus alleged to have predicted a solar eclipse.
• c. 450 BC – Anaxagoras shows that the Moon shines by reflected sunlight: the phases of the Moon are caused by the illumination of its sphere by the Sun in different angles along the lunar month.
• c. 360 BC – Eudoxus of Cnidus proposes for first time a geometric-mathematical model of the planetary movements, including that of the Sun and the Moon, and thus feeding the idea of celestial mechanics as different of the notion of planets being heavenly deities.
• 350 BC – Aristotle argues for a spherical Earth using lunar eclipses and other observations. Also, he asserts his conception of the heavenly spheres, and of an outer space fulfilled with aether.
• c. 300 BC – Star Polaris reaches a point close to the celestial north, thus becoming a reference for navigation in the northern hemisphere.
• 280 BC – Aristarchus of Samos offers the first definite discussion of the possibility of a heliocentric cosmos, and uses the size of the Earth's shadow on the Moon to estimate the Moon's orbital radius at 60 Earth radii, and its physical radius as one-third that of the Earth. He also makes an inaccurate attempt to measure the distance to the Sun.
• c. 250 BC – Following the heliocentric ideas of Aristarcus, Archimedes in his work The Sand Reckoner computes the diameter of the universe centered around the Sun to be about 10¹⁴ stadia (in modern units, about 2 light years, 18.93×10¹² km, 11.76×10¹² mi).
• c. 210 BC – Apollonius of Perga shows the equivalence of two descriptions of the apparent retrograde planet motions (assuming the geocentric model), one using excentrics and another deferent and epicycles.
• 200 BC – Eratosthenes determines that the radius of the Earth is roughly 6,400 km.
• 150 BC – Hipparchus uses parallax to determine that the distance to the Moon is roughly 380,000 km.
• 134 BC – Hipparchus discovers the precession of the equinoxes.
• 87 BC – The Antikythera mechanism, the earliest known computer, is built. It is designed to predict the movements of the planets.
• 28 BC – Chinese history book Book of Han makes earliest known dated record of sunspot.
• c. 150 CE – Claudius Ptolemy completes his Almagest that codifies the astronomical knowledge of his time and cements the geocentric model in the West.

Middle Ages

• 500 – Aryabhata accurately computes the solar and lunar eclipses, and the length of Earth's revolution around the Sun
• 620s – Indian mathematician-astronomer Brahmagupta recognizes gravity as a force of attraction, and briefly describes a law of gravitation
• 628 – Brahmagupta gives methods for calculations of the motions and places of various planets, their rising and setting, conjunctions, and calculations of the solar and lunar eclipses
• 687 – Chinese make earliest known record of meteor shower
• 9th century – The eldest Banū Mūsā brother, Ja'far Muhammad ibn Mūsā ibn Shākir, hypothesizes that the heavenly bodies and celestial spheres are subject to the same laws of physics as Earth, and proposes that there is a force of attraction between heavenly bodies
• 820 – the Persian astronomer, Muhammad ibn Musa al-Khwarizmi, composes his Zij astronomical tables, utilising Arabic numerals and the Hindu–Arabic numeral system in his calculations
• 850 – Ahmad ibn Muhammad ibn Kathīr al-Farghānī (Alfraganus) gives values for the obliquity of the ecliptic, the precessional movement of the apogees of the Sun
• 10th century – Muhammad ibn Jābir al-Harrānī al-Battānī (Albatenius) discovers that the direction of the Sun's eccentricity is changing
• 900s (decade) – Ibn Yunus observes more than 10,000 entries for the Sun's position for many years using a large astrolabe with a diameter of nearly 1.4 metres
• 1019 – Abū Rayhān al-Bīrūnī observes and describes the solar eclipse on April 8 and the lunar eclipse on September 17 in detail, and gives the exact latitudes of the stars during the lunar eclipse
• 1031 – Abū Rayhān al-Bīrūnī calculates the distance between the Earth and the Sun in his Canon Mas’udicus
• 1150 – Indian mathematician-astronomer Bhāskara II, in the Siddhanta Shiromani, calculates the longitudes and latitudes of the planets, lunar and solar eclipses, risings and settings, the Moon's lunar crescent, syzygies, and conjunctions of the planets with each other and with the fixed stars, and explains the three problems of diurnal rotation
• 1150s – Bhaskara calculates the planetary mean motion, ellipses, first visibilities of the planets, the lunar crescent, the seasons, and the length of the Earth's revolution around the Sun to 9 decimal places.
• 1150s – Gerard of Cremona translates Ptolemy's Almagest from Arabic into Latin.
• c. 1200 – Fakhr al-Din al-Razi, in dealing with his conception of physics and the physical world, rejected the Aristotelian and Avicennian view of a single world, but instead proposed that there are "a thousand thousand worlds (alfa alfi 'awalim) beyond this world such that each one of those worlds be bigger and more massive than this world as well as having the like of what this world has."
• c. 1300 – Ibn Qayyim Al-Jawziyya, in his criticism of astrology, recognized that the stars are much larger than the planets, and that Mercury is the smallest planet known to him.
• c. 1350 – Ibn al-Shatir anticipates Copernicus by abandoning the equant of Ptolemy in his calculations of planetary motion, and he provides the first empirical model of lunar motion which accurately matches observations.

16th Century

• c. 1514 – Nicolaus Copernicus states his heliocentric theory in Commentariolus.
• 1522 – First circumnavigation of the world by Magellan-Elcano expedition shows that the Earth is, in effect, a sphere.
• 1543 – Copernicus publishes his heliocentric theory in De revolutionibus orbium coelestium.
• c. 1570 – Tycho Brahe founds the first modern astronomical observatory.
• 1582 – Pope Gregory XIII introduces the Gregorian calendar, an enhanced solar calendar more accurate than the previous Roman Julian calendar. The principal change was to space leap years differently so as to make the average calendar year 365.2425 days long, more closely approximating the 365.2422-day 'tropical' or 'solar' year that is determined by the Earth's revolution around the Sun. The reform advanced the date by 10 days: Thursday 4 October 1582 was followed by Friday 15 October 1582. The Gregoran calendar is still in use today.
• 1584 – Giordano Bruno published two important philosophical dialogues (La Cena de le Ceneri and De l'infinito universo et mondi) in which he argued against the planetary spheres and affirmed the Copernican principle. Bruno's infinite universe was filled with a substance—a "pure air", aether, or spiritus—that offered no resistance to the heavenly bodies which, in Bruno's view, rather than being fixed, moved under their own impetus (momentum). Most dramatically, he completely abandoned the idea of a hierarchical universe. Bruno's cosmology distinguishes between "suns" which produce their own light and heat, and have other bodies moving around them; and "earths" which move around suns and receive light and heat from them. Bruno suggested that some, if not all, of the objects classically known as fixed stars are in fact suns, so he was arguably the first person to grasp that "stars are other suns with their own planets." Bruno wrote that other worlds "have no less virtue nor a nature different from that of our Earth" and, like Earth, "contain animals and inhabitants".

17th Century

• 1600 – William Gilbert with his model called the terrella, shows the Earth behaves like a huge but low intensity magnet with its own magnetic field, which explains the behaviour of the compass pointing to the magnetic poles.
• 1604 – Galileo Galilei correctly hypothesized that the distance of a falling object is proportional to the square of the time elapsed.
• 1609 – Johannes Kepler states his first two empirical laws of planetary motion, stating that the orbits of the planets are elliptical rather than circular, and thus resolving many ancient problems with planetary models.
• 1609 – Galileo Galilei starts to make telescopes with about 3x up to 30x magnification, based only on descriptions of the first practical telescope which Hans Lippershey tried to patent in the Netherlands in 1608. With a Galilean telescope, the observer could see magnified, upright images on the Earth—what is commonly known as a spyglass—but also it can be used to observe the sky, a key tool for further astronomical discoveries.
• 1609 – Galileo Galilei aimed his telescope at the Moon. While not being the first person to observe the Moon through a telescope (English mathematician Thomas Harriot had done it four months before but only saw a "strange spottednesse"), Galileo was the first to deduce the cause of the uneven waning as light occlusion from lunar mountains and craters. He also estimated the heights of that mountains. The Moon was not what was long thought to have been a translucent and perfect sphere, as Aristotle claimed, and hardly the first "planet".
• 1610 – Galileo Galilei discovers the main moons of Jupiter: Callisto, Europa, Ganymede, and Io; sees Saturn's planetary rings (but does not recognize that they are rings), and observes the phases of Venus, disproving the Ptolemaic system though not the geocentric model.
• 1619 – Johannes Kepler states his third empirical law of planetary motion
• 1632 – Galileo Galilei is sometimes credited with the discovery of the lunar libration in latitude, although Thomas Harriot or William Gilbert might have done it before.
• 1643 – Evangelista Torricelli, disciple of Galileo, builds an elementary barometer, which shows that the air weigths, and incidentally creating the first artificial vacuum in a laboratory.
• 1648 – Johannes Hevelius discovers the lunar libration in longitude. It can reach 7°54′ in amplitude.
• 1655 – Giovanni Domenico Cassini discovers Jupiter's Great Red Spot.
• 1656 – Christiaan Huygens identifies Saturn's rings as rings and discovers Titan.
• 1665 – Cassini determines the rotational speeds of Jupiter, Mars, and Venus.
• 1672 – Cassini discovers Iapetus and Rhea.
• 1672 – Jean Richer and Cassini measure the astronomical unit to be about 138,370,000 km.
• 1675 – Ole Rømer uses the orbital mechanics of Jupiter's moons to estimate that the speed of light is about 227,000 km/s.
• 1686 – Cassini discovers Tethys and Dione.
• 1687 – Isaac Newton publishes his law of universal gravitation in his work Philosophiæ Naturalis Principia Mathematica.

18th century

• 1705 – Edmond Halley publicly predicts the periodicity of Halley's Comet and computes its expected path of return in 1757
• 1715 – Edmond Halley calculates the shadow path of a solar eclipse
• 1716 – Edmond Halley suggests a high-precision measurement of the Sun-Earth distance by timing the transit of Venus
• 1718 – Edmond Halley discovers proper motion, dispelling the concept of the "fixed stars".
• 1729 – James Bradley determines the cause of the aberration of starlight, providing the first direct evidence of the Earth's motion.
• 1735-1739 – The French Academy of Sciences sent two expeditions in order to measure the roundness of the Earth by measuring the length of a degree of latitude at two locations, one to Lapland, close to the Arctic Circle and other to the Equator, the French Geodesic Mission, which prove that the Earth is an oblate flattened by the poles.
• 1749 – Pierre Bouguer, part of French Geodesic Mission, publish that he and Charles Marie de La Condamine had been able to detect a deflection of a pendulum's plumb-bob of 8 seconds of arc in the proximities of the volcano Chimborazo. Although not enough to measure the value of the gravitational constant accurately, the experiment had at least proved that the Earth could not be a hollow shell, as some thinkers of the day had suggested.
• c. 1750 – The three collinear Lagrange points (L1, L2, L3) were discovered by Leonhard Euler, a decade before Joseph-Louis Lagrange discovered the remaining two.
• 1752 – Benjamin Franklin conducted his kite experiment, successfully extracting sparks from a cloud, showing that lightnings are huge natural electrical discharges.
• 1755 – Immanuel Kant first formulates the nebular hypothesis of Solar System formation.
• 1758 – Johann Palitzsch observes the return of Halley's comet. The interference of Jupiter's orbit had slowed the return by 618 days. Parisian astronomer La Caille suggests it should be named Halley's comet.
• 1766 – Johann Titius finds the Titius-Bode rule for planetary distances
• 1772 – Johann Bode publicizes the Titius-Bode rule for planetary distances
• 1772–1775 – The second voyage of James Cook definitively disproves the existence of the hypothesised southern continent of Terra Australis.
• 1775 – Charles Hutton based on his analysis of the Schiehallion experiment, shows the Earth has a density of at least 4,500 kg·m⁻³ and suggests that it has a planetary core made of metal. (In comparison with the modern accepted figure of 5,515 kg·m⁻³, the density of the Earth had been computed with an error of less than 20%.)
• 1781 – William Herschel discovers Uranus during a telescopic survey of the northern sky.
• 1781 – Charles Messier and his assistant Pierre Méchain publish the first catalogue of 110 nebulae and star clusters, the most prominent deep-sky objects that can easily be observed from Earth's Northern Hemisphere, in order not to be confused with ordinary Solar System comets.
• 1787 – Herschel discovers Uranus's moons Titania and Oberon
• 1789 – Herschel discovers Saturn's moons Enceladus and Mimas
• 1796 – Pierre Laplace re-states the nebular hypothesis for the formation of the Solar System from a spinning nebula of gas and dust
• 1798 – Henry Cavendish accurately measures the gravitational constant in laboratory, which it permits to "weighing the Earth" and thus calculate the masses of all bodies in the Solar System.

19th century

• 1801 – Giuseppe Piazzi discovers the dwarf planet–asteroid Ceres
• 1802 – Heinrich Wilhelm Olbers discovers the asteroid Pallas
• 1821 – Alexis Bouvard detects irregularities in the orbit of Uranus
• 1825 – Pierre Laplace completes his study of gravitation, the stability of the Solar System, tides, the precession of the equinoxes, the libration of the Moon, and Saturn's rings in his work Mécanique céleste (Celestial Mechanics)
• 1838 – Friedrich Wilhelm Bessel measures the parallax of the star 61 Cygni, refuting one of the oldest arguments against heliocentrism.

The earliest surviving dagerrotype of the Moon by Draper (1840)

• 1840 – John W. Draper takes a daguerreotype of the Moon, the first astronomical photograph.
• 1843 – John Adams predicts the existence and location of Neptune from irregularities in the orbit of Uranus
• 1846 – Urbain Le Verrier predicts the existence and location of Neptune from irregularities in the orbit of Uranus
• 1846 – Johann Galle discovers Neptune
• 1846 – William Lassell discovers Triton
• 1848 – Lassell, William Cranch Bond and George Phillips Bond discover Saturn's moon Hyperion
• 1849 – Édouard Roche finds the limiting radius of tidal destruction and tidal creation for a body held together only by its self gravity, called the Roche limit, and uses it to explain why Saturn's rings do not condense into a satellite
• 1851 – Lassell discovers Uranus's moons Ariel and Umbriel
• 1856 – James Clerk Maxwell demonstrates that a solid ring around Saturn would be torn apart by gravitational forces and argues that Saturn's rings consist of a multitude of tiny satellites
• 1862 – By analysing the spectroscopic signature of the Sun and comparing it to those of other stars, Father Angelo Secchi determines that the Sun is itself a star.
• 1866 – Giovanni Schiaparelli realizes that meteor streams occur when the Earth passes through the orbit of a comet that has left debris along its path
• 1877 – Asaph Hall discovers Mars's moons Deimos and Phobos
• 1887 – The Michelson–Morley experiment, intended to measure the relative motion of Earth through the (by then assumed to exist) stationary luminiferous aether, got no results. This put an end to centuries old idea of the aether, dating back from times of Aristotle, and with it all the contemporary aether theories.
• 1892 – Edward Emerson Barnard discovers Jupiter's moon Amalthea.
• 1897 – William Thomson, 1st Baron Kelvin, based on the thermal radiation rate and the gravitational contraction forces, argues the age of the Sun to be no more than 20 million years – unless some energy source beyond what he or any other Victorian era person knew of was found.
• 1899 – William Henry Pickering discovers Saturn's moon Phoebe.

1900–1958

• 1904 – Ernest Rutherford made the argument, in a lecture attended by Kelvin, that the radioactive decay releases heat, providing the unknown energy source Kelvin had suggested, ultimately leading to radiometric dating of rocks which provides ages of thousand of millions of years for the Solar System bodies.
• 1906 – Astronomer Max Wolf discovers the Trojan asteroid Achilles.
• 1909 – Andrija Mohorovičić discovers the Moho discontinuity, the boundary between the Earth's crust and the mantle.
• 1912 – Alfred Wegener suggests the continental drift hypothesis, that the continents are slowly drifting around the Earth.
• 1915 – Robert Innes discovers Proxima Centauri, the closest star to Earth after the Sun.
• 1919 – Arthur Stanley Eddington uses a solar eclipse to successfully test Albert Einstein's General Theory of Relativity
• 1920 – In the Great Debate between Harlow Shapley and Heber Curtis, galaxies are finally recognized as objects outer to the Milky Way, and the Milky Way as a galaxy proper, within it lies the Solar System.
• 1930 – Clyde Tombaugh discovers Pluto.

The first photo from space was taken from a V-2 launched by US scientists on 24 October 1946.

• 1930 – Seth Nicholson measures the surface temperature of the Moon.
• 1932 – Karl Guthe Jansky recognizes received radio signals coming from outer space as extrasolar, coming mainly from Sagittarius. They are the first evicence of the center of the Milky Way, and the firsts experiences with radioastronomy.
• 1935 – The Explorer II balloon reached a record altitude of 22,066 m (72,395 ft), enabling its occupants to photograph the curvature of the Earth for the first time.
• 1944 – Gerard Kuiper discovers that the satellite Titan has a substantial atmosphere.
• 1946 – American launch of a camera-equipped V-2 rocket provides the first image of the Earth from space.
• 1949 – Gerard Kuiper discovers Uranus's moon Miranda and Neptune's moon Nereid.
• 1950 – Jan Oort suggests the presence of a cometary Oort cloud.
• 1951 – Kuiper argues for an annular reservoir of comets between 40 and 100 astronomical units from the Sun, the Kuiper belt.

1958–1976

• 1958 – Under supervision of James Van Allen, Explorer 1 and Explorer 3 confirmed the existence of the Earth's magnetosphere radiation belts.
• 1959 – Explorer 6 sends the first image of the entire earth from Space.
• 1959 – Luna 3 sends the first images of another celestial body, the Moon, from space, including its unseen far side.
• 1962 – The Mariner 2 Venus flyby performs the first closeup observations of another planet
• 1964 – The Mariner 4 spacecraft provides the first detailed images of the surface of Mars
• 1966 – The Luna 9 Moon lander provides the first images from the surface of another celestial body

Earth taken from Lunar Orbiter 1 in 1966. Image as originally shown to the public displays extensive flaws and striping.

• 1967 – Venera 4 provides the first information on Venus's atmosphere
• 1968 – The Apollo 8 becomes the first manned lunar mission, providing historic images of the whole Earth.
• 1970 – The Venera 7 Venus lander sends back the first information ever successfully obtained from the surface of another planet
• 1971 – The Mariner 9 Mars spacecraft becomes the first to successfully orbit another planet. It provides the first detailed maps of the Martian surface, discovering much of the planet's topography, including the volcano Olympus Mons and the canyon system Valles Marineris, which is named in its honor.
• 1971 – Mars 3 lands on Mars, and transmits the first partial image from the surface of another planet.
• 1973 – Skylab astronauts discover the Sun's coronal holes.
• 1973 – Pioneer 10 flies by Jupiter, providing the first closeup images of the planet and revealing its intense radiation belts.
• 1973 – Mariner 10 provides the first closeup images of the clouds of Venus.
• 1974 – Mariner 10 provides the first closeup images of the surface of Mercury.
• 1975 – Venera 9 becomes the first probe to successfully transmit images from the surface of Venus.
• 1976 – The Viking 1 & 2 became the first probes to send images (in color) from the surface of Mars, as well as to perform in situ biological experiments with the Martian soil.

1977–2000

• 1977 – James Elliot discovers the rings of Uranus during a stellar occultation experiment on the Kuiper Airborne Observatory
• 1977 – Charles Kowal discovers 2060 Chiron, the first Centaur
• 1978 – James Christy discovers Charon, the large moon of Pluto.
• 1978 – The Pioneer Venus probe maps the surface of Venus.
  

  A map of Venus produced from Magellan data
• 1978 – Peter Goldreich and Scott Tremaine present a Boltzmann equation model of planetary-ring dynamics for indestructible spherical ring particles that do not self-gravitate and find a stability requirement relation between ring optical depth and particle normal restitution coefficient
• 1979 – Pioneer 11 flies by Saturn, providing the first ever closeup images of the planet and its rings. It discovers the planet's F ring and determines that its moon Titan has a thick atmosphere.
• 1979 – Voyager 1 flies by Jupiter and discovers its faint ring system, as well as volcanoes on Io, the innermost of its Galilean moons.
• 1979 – Voyager 2 flies by Jupiter and discovers evidence of an ocean under the surface of its moon Europa.
• 1980 – Voyager 1 flies by Saturn and takes the first images of Titan. However, its atmosphere is opaque to visible light, so its surface remains obscured.
• 1986 – Voyager 2 provides the first ever detailed images of Uranus, its moons and rings.
• 1986 – The Giotto probe provides the first ever close up images of Halley's Comet.
• 1988 – Martin Duncan, Thomas Quinn, and Scott Tremaine demonstrate that short-period comets come primarily from the Kuiper Belt and not the Oort cloud
• 1989 – Voyager 2 provides the first ever detailed images of Neptune, its moons and rings.
• 1990 – The Hubble Space Telescope is launched
• 1990 – Voyager 1 is turned around to take the Portrait of the Planets of the Solar System, source of the Pale Blue Dot image of the Earth
• 1991 – The Magellan spacecraft maps the surface of Venus.
• 1992 – First planetary system beyond the Solar System detected, around the pulsar PSR B1257+12
• 1992 – David Jewitt and Jane Luu of the University of Hawaii discover 15760 Albion, the first object deemed to be a member of the Kuiper belt
• 1995 – The first planet around a Sun-like star is discovered, in orbit around the star 51 Pegasi.
• 1995 – The Galileo spacecraft becomes the first to orbit Jupiter. Its atmospheric entry probe provides the first data taken within the planet itself.
• 1997 – Mars Pathfinder deploys on Mars the first rover to operate outside the Earth–Moon system, the Sojourner, which conducted many experiments on the Martian surface, both teleoperated and semi-autonomous.
• 2000 – NEAR Shoemaker provides the first detailed images of a near-Earth asteroid.

2001–present

• 2003 – Sedna, a large object with an unprecedented 12,000-year orbit, is discovered by Michael E. Brown, Chad Trujillo, and David L. Rabinowitz.
• 2004 – Voyager 1 sends back the first data ever obtained from within the Solar System's heliosheath.
• 2004 – The Cassini–Huygens spacecraft becomes the first to orbit Saturn. It discovers complex motions in the rings, several new small moons and cryovolcanism on the moon Enceladus and provides the first images from the surface of Titan.
• 2005 – Michael E. Brown et al. discover Eris, a trans-Neptunian object more massive than Pluto, and later also its moon, Dysnomia. Eris was first imaged in 2003, and is the most massive object discovered in the Solar System since Neptune's moon Triton in 1846.
• 2005 – The Mars Exploration Rovers perform the first astronomical observations ever taken from the surface of another planet, imaging an eclipse by Mars's moon Phobos.

Annular eclipse of the Sun by Phobos as viewed by the Mars Curiosity rover (20 August 2013).

• 2006 – The 26th General Assembly of the IAU voted in favor of a revised definition of a planet and officially declared Ceres, Pluto, and Eris dwarf planets.
• 2008 – The IAU declares Makemake and Haumea dwarf planets.
• 2011 – The Dawn spacecraft enters orbit around the large asteroid Vesta making detailed measurements.
• 2012 – Saturn's moon Methone is imaged up close by the Cassini spacecraft, revealing a remarkably smooth surface.
• 2012 – The Dawn spacecraft breaks orbit of Vesta and heads for Ceres.
• 2013 – The MESSENGER spacecraft provides the first ever complete map of the surface of Mercury.
• 2014 – The Rosetta spacecraft becomes the first comet orbiter (around 67P/Churyumov–Gerasimenko), and deploys on it the first comet lander Philae that collected close-up data from the comet's surface.
• 2015 – The Dawn spacecraft enters orbit around the dwarf Planet Ceres making detailed measurements.
• 2015 – The New Horizons spacecraft flies by Pluto, providing the first ever sharp images of its surface, and its largest moon Charon.
• 2017 – 'Oumuamua, the first known interstellar object, is identified.
• 2019 – Closest approach of New Horizons to Arrokoth, a Kuiper Belt Object.
• 2019 – 2I/Borisov, the first interstellar comet and second interstellar object, is discovered.
• 2022 – The Double Asteroid Redirection Test (DART) spacecraft mission intentionally crashed into Dimorphos, the minor-planet moon of the asteroid Didymos, deviating (slightly) the orbit of a Solar System body for the fist time ever.

See also

• Timeline of Solar System exploration
• Timeline of discovery of Solar System planets and their moons
• Timeline of Chinese astronomy