History of Astronomy

c. 130 BCE

Hipparchus discovered that the equinox points slowly drift along the zodiac, completing a circuit in about 26,000 years, by comparing his star positions with older records.

c. 150 CE

Ptolemy's comprehensive treatise on astronomy, presenting the geocentric model with epicycles and a catalogue of more than a thousand stars.

499 CE

Aryabhata's concise verse treatise on mathematics and astronomy, giving methods for planetary positions and eclipses, a sine table, and the idea that the Earth rotates on its axis.

964 CE

Al-Sufi's revision of Ptolemy's star catalogue against his own observations, with constellation drawings and corrected magnitudes.

1543 CE

Copernicus's masterwork, 'On the Revolutions of the Heavenly Spheres', setting out the heliocentric system in full.

1608 CE

The refracting telescope appeared in the Netherlands in 1608, with the spectacle-maker Hans Lippershey filing the first known patent application.

1609 CE

Kepler's 'New Astronomy', in which his struggle with the orbit of Mars led him to the first two laws of planetary motion: elliptical orbits and the equal-area law.

1610 CE

In January 1610 Galileo saw four points of light beside Jupiter that changed position night after night — moons orbiting another world.

1610 CE

Galileo observed that Venus shows a full cycle of phases like the Moon, including a 'full' phase only possible if it orbits the Sun.

1610 CE

Galileo's 'Starry Messenger', the first published account of telescopic astronomy: the four moons of Jupiter, the mountains of the Moon, and the countless stars of the Milky Way.

1619 CE

Kepler's 'Harmony of the World', which presents his third law of planetary motion — relating a planet's orbital period to its distance from the Sun.

1632 CE

Galileo's spirited comparison of the Copernican and Ptolemaic systems, written in Italian for a wide audience.

1655 CE

Christiaan Huygens discovered Titan, Saturn's largest moon, with a telescope of his own design.

1659 CE

Huygens explained that the strange 'arms' Galileo had seen around Saturn are in fact a thin, flat ring surrounding but not touching the planet.

1675 CE

King Charles II founded the Royal Observatory at Greenwich in 1675 to improve navigation by mapping the stars and the Moon.

1687 CE

Newton's 'Mathematical Principles of Natural Philosophy', perhaps the most important scientific book ever written.

1705 CE

Applying Newton's gravitation, Halley showed that comets recorded in 1531, 1607, and 1682 were one body on a 76-year orbit, and predicted its return in 1758.

1781 CE

William Herschel spotted a slow-moving object that proved to be a new planet far beyond Saturn — the first planet discovered since antiquity.

1846 CE

From tiny irregularities in the orbit of Uranus, Le Verrier (and, independently, John Couch Adams) predicted an unseen planet; Galle found Neptune within a degree of the prediction on 23 September 1846.

1912 CE

Henrietta Leavitt found that the pulsation period of a Cepheid variable star reveals its true luminosity, giving astronomers a 'standard candle' for measuring distance.

1919 CE

The International Astronomical Union was founded in 1919 to coordinate astronomy worldwide.

1920 CE

In 1920 Harlow Shapley and Heber Curtis debated the scale of the universe: whether the spiral nebulae lie within the Milky Way or are separate 'island universes'.

1925 CE

Cecilia Payne-Gaposchkin's doctoral thesis applied atomic physics to stellar spectra and concluded that stars are composed overwhelmingly of hydrogen and helium.

1929 CE

Using Cepheid distances and galaxy redshifts, Edwin Hubble showed in 1929 that galaxies recede faster the farther away they are — the universe is expanding, as Lemaître had derived two years earlier.

1933 CE

Fritz Zwicky inferred unseen mass in the Coma cluster in 1933, and from the 1970s Vera Rubin's galaxy rotation curves showed that galaxies are dominated by invisible 'dark matter'.

1963 CE

Maarten Schmidt recognised that the puzzling radio source 3C 273 was extremely redshifted, placing it billions of light-years away and making it astonishingly luminous.

1965 CE

Penzias and Wilson detected a faint microwave glow coming uniformly from every direction — the cooled afterglow of the hot early universe.

1967 CE

Jocelyn Bell Burnell detected a strikingly regular radio pulse that proved to be a rapidly spinning neutron star sweeping a beam past the Earth.

1980 CE

Carl Sagan's book and accompanying television series, which traced the history of science and the scale of the universe for a global audience and became one of the most influential works of science communication ever made.

1988 CE

Stephen Hawking's best-selling account of cosmology — from the Big Bang to black holes and the nature of time — which brought the deepest questions of the universe to millions of readers.

1992 CE

Jane Luu and David Jewitt discovered (15760) Albion, the first body found in the Kuiper Belt beyond Neptune after a five-year search.

1995 CE

Michel Mayor and Didier Queloz, using the ELODIE spectrograph at the Observatoire de Haute-Provence, detected the wobble of the star 51 Pegasi caused by an orbiting giant planet — the first exoplanet found around a normal, Sun-like star.

1998 CE

Two teams using distant Type Ia supernovae found that the expansion of the universe is speeding up, driven by a mysterious 'dark energy'.

2015 CE

On 14 September 2015 the LIGO observatories recorded a ripple in spacetime from two merging black holes 1.3 billion light-years away — the first direct detection of gravitational waves.

2019 CE

The Event Horizon Telescope, a global network of radio dishes including ALMA, produced the first image of a black hole's shadow — the supermassive black hole at the heart of the galaxy M87.

c. 2020 CE

Over three decades, the teams of Reinhard Genzel and Andrea Ghez tracked stars orbiting the centre of the Milky Way, revealing a four-million-solar-mass black hole, Sagittarius A*.

2022 CE

In July 2022 the James Webb Space Telescope released its first full-colour images, including the deepest and sharpest infrared view of the distant universe ever taken.