Timeline

Overview

A chronological view of astronomy and space exploration, tying the encyclopedia's topics into a single thread. Dates are given where the historical record supports them, and periods rather than dates where it does not.

• Sustained astronomical record-keeping predates written explanation by well over a millennium.
• The gap between the telescope (1609) and the first measured stellar distance (1838) was more than two centuries.
• Most of what is known about the universe beyond the Milky Way was established within the last hundred years.

Antiquity to the classical world

• c. 1700 BCE — Babylonian records of Venus phenomena, among the earliest surviving systematic planetary observations.
• c. 8th century BCE onward — the Babylonian astronomical diaries begin, running for roughly seven centuries.
• c. 240 BCE — Eratosthenes estimates Earth's circumference from shadow lengths at two locations.
• c. 130 BCE — Hipparchus discovers precession by comparing his positions with earlier records, and compiles a star catalogue.
• c. 2nd–1st century BCE — the Antikythera mechanism, a geared device for computing celestial positions.
• c. 150 CE — Ptolemy's Almagest establishes a predictive geometric system that remains standard for fourteen centuries.

Medieval and early modern

• 964 — al-Sufi's Book of Fixed Stars, including the earliest surviving description of the Andromeda Galaxy.
• 1054 — Chinese and other observers record a 'guest star'; its remnant is the Crab Nebula.
• 1437 — Ulugh Beg's Samarkand star catalogue, the most accurate positional work between Ptolemy and Tycho Brahe.
• 1543 — Copernicus publishes De revolutionibus, placing the Sun at the centre.
• 1572 and 1604 — Tycho's and Kepler's supernovae, both visible to the naked eye, challenge the doctrine of unchanging heavens.
• 1609–1619 — Kepler publishes the laws of planetary motion; Galileo publishes the first telescopic observations in 1610.
• 1687 — Newton's Principia unifies celestial and terrestrial mechanics.

The measured universe

• 1781 — William Herschel discovers Uranus, the first planet found with a telescope.
• 1814 — Fraunhofer maps dark lines in the solar spectrum.
• 1838 — Bessel measures the parallax of 61 Cygni: the first distance to another star.
• 1846 — Neptune is found close to its predicted position, a decisive success for Newtonian mechanics.
• 1859 — Kirchhoff and Bunsen establish that spectral lines identify chemical elements.
• 1912 — Leavitt publishes the Cepheid period–luminosity relation.
• 1925 — Payne-Gaposchkin shows stars are composed mainly of hydrogen and helium.

The modern era

• 1923–24 — Hubble establishes that Andromeda lies far outside the Milky Way.
• 1929 — Hubble publishes the velocity–distance relation; Lemaître had derived it theoretically in 1927.
• 1932 — Jansky detects radio emission from the Galaxy, opening radio astronomy.
• 1957 — Sputnik 1 reaches orbit; 1961 — Gagarin becomes the first human in space; 1969 — Apollo 11 lands.
• 1965 — Penzias and Wilson detect the cosmic microwave background.
• 1967 — Bell Burnell detects the first pulsar.
• 1990 — Hubble Space Telescope launched.
• 1995 — Mayor and Queloz detect 51 Pegasi b, the first planet around a Sun-like star.
• 1998 — two supernova programmes independently find that cosmic expansion is accelerating.
• 2015 — LIGO detects gravitational waves from a binary black hole merger.
• 2019 and 2022 — the Event Horizon Telescope images the black holes in M87 and at the Galactic centre.

How to read a timeline like this

Dated lists compress a great deal. Almost every entry above represents years of work by many people, and the attached name is usually the person associated with the final decisive step rather than the sole contributor. Several entries also mark the moment a result was accepted rather than first proposed — Aristarchus proposed heliocentrism eighteen centuries before Copernicus.

Where a date is genuinely uncertain, this timeline says 'c.' rather than choosing a precise-looking year. Spurious precision in historical dating is the same failure mode as spurious precision in a measurement.

Continue in the data

Catalogues, hubs, and reference pages that hold the underlying records for this topic.

• TimelinesInteractive chronological threads across the platform.
• History catalogueThe people, publications, and discoveries as entities.
• Spaceflight timelineLaunch-by-launch spaceflight chronology.

Frequently asked

What is the oldest astronomical record we still have?

Among the oldest systematic ones are Babylonian records of Venus phenomena dating to roughly the early second millennium BCE, and the astronomical diaries beginning around the eighth century BCE. Older monuments show intentional solar alignment, but a deliberately oriented structure is a different kind of evidence from a dated observational record.

Why was there such a long gap between the telescope and measuring star distances?

Because stellar parallax is extremely small. Even the nearest stars shift by well under one arcsecond as Earth moves around its orbit, which is beyond what seventeenth- and eighteenth-century instruments could reliably measure. Astronomers understood the method throughout that period; it took until 1838 for instrumental precision to catch up.

How much of modern astronomy is genuinely recent?

Most of it. That other galaxies exist was established in the 1920s, cosmic expansion in the same decade, the microwave background in 1965, exoplanets from 1995, cosmic acceleration in 1998, and gravitational-wave astronomy from 2015. Nearly everything known about the universe beyond our own Galaxy has been learned within about a century.