Major Events in Astronomy from Ancient Observers to JWST

Babylonian astronomers record and predict recurring celestial phenomena; the Venus Tablet tradition preserves systematic observations of Venus.

Greek natural philosophers develop geometric models of the cosmos, including influential Earth-centred frameworks.

Aristarchus of Samos proposes that Earth rotates and travels around the Sun, an early heliocentric model.

Eratosthenes estimates the circumference of Earth from the geometry of sunlight and shadows.

Hipparchus advances positional astronomy, star cataloguing and the study of precession.

Ptolemy’s Almagest systematises Greek mathematical astronomy in a geocentric model that remains influential for more than a millennium.

Aryabhata’s Aryabhatiya presents sophisticated computational astronomy and describes the apparent daily motion of the sky in terms of Earth’s rotation.

Brahmagupta develops mathematical methods used in Indian astronomical calculation.

Al-Sufi publishes the Book of Fixed Stars, combining inherited catalogues with new observations.

Chinese and other observers record the brilliant “guest star” whose remnant is now the Crab Nebula.

John of Worcester records sunspot activity, preserving an important medieval European observation of the Sun.

Bhaskara II develops planetary computation, eclipse methods and spherical astronomy in the Siddhanta Shiromani.

Giotto di Bondone observes or draws on the appearance of Halley’s Comet when creating his later image of the Star of Bethlehem.

Ulugh Beg’s Samarkand observatory produces a major new star catalogue based on careful naked-eye observations.

Nicolaus Copernicus publishes De revolutionibus orbium coelestium, presenting a mathematical heliocentric system.

Tycho Brahe observes a supernova, challenging the belief that the stellar heavens are unchanging.

Johannes Kepler publishes the first two laws of planetary motion, including elliptical planetary orbits.

Galileo turns improved telescopes to the sky and observes the Moon, Jupiter’s satellites and other phenomena that transform observational astronomy.

Galileo observes the points of light that become recognised as Jupiter’s four large moons, demonstrating that not everything orbits Earth.

Kepler publishes his third law, relating planetary orbital periods to their distance from the Sun.

Pierre Gassendi observes Mercury crossing the Sun, the first telescopic observation of a planetary transit.

Jeremiah Horrocks and William Crabtree observe the transit of Venus after Horrocks corrects the predicted date.

Giovanni Domenico Cassini records a persistent feature on Jupiter and uses atmospheric markings to investigate the planet’s rotation.

Isaac Newton’s Principia unites terrestrial and celestial motion through the laws of motion and universal gravitation.

Edmond Halley predicts the return of the comet that now bears his name using Newtonian mechanics.

Johann Georg Palitzsch observes the predicted return of Halley’s Comet, providing a dramatic confirmation of Newtonian celestial mechanics.

William Herschel discovers Uranus, the first planet found with a telescope in the modern era.

John Michell proposes that sufficiently massive stars could have escape velocities exceeding the speed of light, an early precursor of black-hole ideas.

Giuseppe Piazzi discovers Ceres, opening the study of the population now associated with the asteroid belt.

Friedrich Bessel makes the first successful measurement of stellar parallax, giving a direct distance to another star.

Neptune is identified close to a position predicted from disturbances in the orbit of Uranus.

Kirchhoff and Bunsen establish the physical basis of spectroscopy, allowing astronomers to determine the chemical composition of stars.

Pierre Janssen observes a new yellow line in the solar spectrum, providing evidence for helium before the element is isolated on Earth.

Albert Einstein completes general relativity, providing a new theory of gravity and a framework for modern cosmology.

Einstein predicts gravitational waves as propagating disturbances in spacetime within general relativity.

Cepheid observations in Andromeda establish that the “nebula” is a galaxy beyond the Milky Way.

Cecilia Payne demonstrates that stars are composed primarily of hydrogen and helium.

Georges Lemaître develops an expanding-universe model from general relativity and astronomical observations.

The observed relation between galaxy distance and recession velocity makes cosmic expansion a central fact of observational cosmology.

Karl Jansky detects radio emission from the Milky Way, opening radio astronomy.

Fritz Zwicky applies the virial theorem to the Coma galaxy cluster and argues that substantial unseen matter is required.

Ralph Alpher and Robert Herman predict that the expanding universe should contain cooled remnant radiation from an earlier hot state.

Sputnik 1 becomes the first artificial Earth satellite, opening the space age and a new platform for astronomical observation.

Luna 3 returns the first photographs of the far side of the Moon.

Yuri Gagarin completes the first human orbital spaceflight aboard Vostok 1.

Arno Penzias and Robert Wilson detect the cosmic microwave background radiation.

Jocelyn Bell Burnell identifies pulsars, rapidly rotating neutron stars observed through regular radio pulses.

Apollo 11 achieves the first crewed landing on the Moon.

Russell Hulse and Joseph Taylor identify the first binary pulsar, enabling a powerful later test of gravitational-wave energy loss.

Voyager 2 launches on the mission that will eventually carry out close reconnaissance of all four giant planets.

NASA launches COBE to measure the spectrum and structure of the cosmic microwave background.

The Hubble Space Telescope launches and begins a new era of high-resolution space-based astronomy.

Aleksander Wolszczan and Dale Frail report planets around pulsar PSR B1257+12, the first confirmed exoplanet system.

COBE scientists announce tiny temperature variations in the microwave background, providing evidence for the seeds of large-scale cosmic structure.

51 Pegasi b becomes the first confirmed exoplanet around a Sun-like star.

Supernova observations show that the expansion of the universe is accelerating.

WMAP launches to map cosmic microwave background variations with much greater precision than COBE.

WMAP’s first-year results sharply refine estimates of the universe’s age, geometry and composition.

NASA launches the Kepler mission to search for transiting exoplanets.

LIGO makes the first direct detection of gravitational waves from merging black holes; the result is announced in 2016.

Astronomers observe the optical counterpart of neutron-star merger GW170817, linking gravitational waves with a kilonova.

TESS begins an all-sky transit survey designed to discover exoplanets around relatively nearby bright stars.

Chang’e 4 achieves the first soft landing on the far side of the Moon.

The Event Horizon Telescope collaboration releases the first image of a black hole, in galaxy M87.

The James Webb Space Telescope releases its first science images and begins infrared observations of the early universe, stars and exoplanets.

Gaia astrometry reveals Gaia BH3, a dormant stellar black hole of roughly thirty-three solar masses in the Milky Way.

JWST observations identify an actively accreting black hole in GN-z11 only about four hundred million years after the Big Bang.