First Recorded Andromeda Observation
Records the Andromeda Galaxy in the Book of Fixed Stars as a small cloud, the earliest surviving written description of M31.
Astronomy topic guide · World History Database
History of Modern Cosmology
Modern cosmology emerged when new physics and new astronomical observations made the universe itself a subject of quantitative science. General relativity supplied a framework for dynamic models of space and time. Distance measurements to galaxies established the extragalactic scale of the universe, while recession measurements revealed cosmic expansion. The cosmic microwave background strengthened the hot Big Bang model, and later observations brought dark matter and dark energy to the centre of cosmological research. The records below follow these connected developments.
What this chronology covers
Cosmology depends on unusually long chains of evidence. Distances derived from variable stars, galaxy redshifts, relic microwave radiation, supernova brightness measurements, gravitational lensing and galaxy rotation all constrain models of the universe. The subject therefore developed through the interaction of relativity, observational astronomy and particle physics. The chronology below highlights how evidence accumulated rather than presenting the Big Bang, dark matter or dark energy as isolated ideas.
309matching 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.
Discovery of Andromeda Galaxy
Gives a description of the Andromeda Galaxy based on telescopic observations
First Telescopic Description of Andromeda
Observes M31 through a telescope and describes its pale central glow, providing the first known telescopic account of the Andromeda object.
Discovery of Andromeda Galaxy
In his work Universal Natural History and Theory of the Heavens conjectures that Andromeda is an island universe
Discovery of Andromeda Galaxy
Cataloges Andromeda as object M31 and incorrectly credits Marius as the discoverer despite it being visible to the naked eye
Messier Catalogue Entry M31
Catalogues the Andromeda object as Messier 31, establishing the designation M31 that remains in standard astronomical use.
Discovery of Andromeda Galaxy
Herschel observes a faint reddish hue in the core region of Andromeda and believes Andromeda to be the nearest of all the "great nebulae", and based on the color and magnitude of the nebula, incorrectly guesses that it is no more than 2,000 times the distance of Sirius
Discovery of Uranus
Produces a diagram of the shape of the Galaxy with the Solar System close to the centre
Early Distance Estimate for Andromeda
Notes the appearance of the Andromeda nebula and attempts an early estimate of its distance, still treating it as a nearby great nebula.
Discovery of Andromeda Galaxy
Makes the first drawing of Andromeda's spiral structure
Mercury Perihelion Anomaly
Reports the unexplained advance of Mercury's perihelion, later explained by general relativity.
Stellar Spectrum of Andromeda
Finds that the spectrum of Andromeda resembles the continuous spectrum of stars rather than the emission spectrum of a gaseous nebula, indicating a stellar nature.
Discovery of Andromeda Galaxy
Takes the first photographs of Andromeda, which was still commonly thought to be a nebula within our galaxy
Arthur Stanley Eddington Born
The future astrophysicist and relativity advocate is born.
S Andromedae Observed
Observes the brilliant transient S Andromedae in M31, later recognized as a supernova and the first supernova recorded in the Andromeda Galaxy.
First Detailed Photograph of Andromeda
Obtains a long-exposure photograph of M31 that clearly records its spiral structure, a major step in the photographic study of the galaxy.
Relativity, Theory of
In physics and mathematics, Minkowski space (or Minkowski spacetime) is the mathematical setting in which Einsteins theory of special relativity is most conveniently formulated.
Relativity, Theory of
The idea of Minkowski space also led to special relativity being viewed in a more geometrical way, this geometric viewpoint of spacetime being important in general relativity too.
Relativity, Theory of
While spacetime can be viewed as a consequence of Albert Einsteins 1905 theory of special relativity, it is first explicitly proposed mathematically by one of his teachers, the mathematician Hermann Minkowski.
Spacetime
In physics and mathematics, Minkowski space (or Minkowski spacetime) is the mathematical setting in which Einsteins theory of special relativity is most conveniently formulated.
Spacetime
The idea of Minkowski space also led to special relativity being viewed in a more geometrical way, this geometric viewpoint of spacetime being important in general relativity too.
Spacetime
While spacetime can be viewed as a consequence of Albert Einsteins 1905 theory of special relativity, it is first explicitly proposed mathematically by one of his teachers, the mathematician Hermann Minkowski.
Relativity, Theory of
The term "theory of relativity" was coined by Max Planck to emphasize how special relativity (and later, general relativity) uses the principle of relativity
Galaxy Redshift
Slipher measures a large redshift for the Andromeda nebula, beginning the observational path toward an expanding universe
First Radial Velocity of Andromeda
Measures the Doppler shift of M31 and finds a very large approach velocity, the first radial-velocity measurement made for a spiral nebula.
Mercury Perihelion
Explains Mercury's anomalous perihelion advance using the emerging general theory of relativity.
Schwarzschild Metric
Papers on relativity produced the first exact solutions to the Einstein field equations, and a minor modification of these results gives the well-known solution that now bears his name: the Schwarzschild metric
Gravitational Waves
Predicts gravitational waves as propagating disturbances in spacetime within general relativity.
Cosmology
De Sitter develops an expanding relativistic cosmological solution without matter, influencing later debate over cosmic expansion
Cosmology
De Sitter finds a relativistic cosmological solution that later becomes important in expanding universe models
Great Andromeda Nebula
Heber Curtis discovers the nova S Andromedae within the "Great Andromeda Nebula" (Messier object M31)
Relativistic Cosmology
Applies general relativity to the universe and introduces the cosmological constant in a static cosmological model.
Andromeda Novae Distance Argument
Uses the faintness of novae recorded in Andromeda to argue that M31 lies far beyond the Milky Way and is an independent stellar system.
Cosmological Constant Introduced
Einstein adds the cosmological constant to his gravitational field equations to permit a static universe, creating the mathematical term later associated with dark energy.
Repulsive Gravity in Empty Space
Einstein interprets the cosmological constant as a repulsive contribution capable of balancing ordinary gravitational attraction on the largest cosmic scales.
De Sitter Cosmological Model
De Sitter develops a solution of Einstein's equations containing a cosmological constant, demonstrating that cosmic behaviour can be strongly affected by vacuum-like geometry.
Discovery of Globular Clusters
By assuming a roughly spherical distribution of globular clusters around the galaxys centre, he used the positions of the clusters to estimate the position of the sun relative to the galactic centre.
Discovery of Globular Clusters
In 1918, this strongly asymmetrical distribution was used by Harlow Shapley to make a determination of the overall dimensions of the galaxy.
Discovery of Globular Clusters
While his distance estimate was significant in error, it did demonstrate that the dimensions of the galaxy were much greater than had been previously thought
Relativity, Theory of
Arthur Eddington and Astronomer Royal Frank Watson Dyson organized two expeditions to observe a solar eclipse in 1919 to make the first empirical test of Einsteins theory.
Relativity, Theory of
Arthur Eddington leads a solar eclipse expedition which claims to detect gravitational deflection of light by the Sun.
Relativity, Theory of
Observes light bending during a solar eclipse by the gravitational pull of the Sun.
Relativity, Theory of
the measurement of the deflection of light by the suns gravitational field.
Relativity, Theory of
Arthur Eddington and Astronomer Royal Frank Watson Dyson organized two expeditions to observe a solar eclipse in 1919 to make the first empirical test of Einsteins theory: the measurement of the deflection of light by the suns gravitational field
Relativity, Theory of
According to the theory of general relativity, stars with light rays that passed near the Sun would appear to have been slightly shifted because their light had been curved by its gravitational field.
Relativity, Theory of
During the eclipse, he took pictures of the stars in the region around the Sun.
Relativity, Theory of
Eddington travelled to the island of Principe near Africa to watch the solar eclipse of 29 May 1919.
Relativity, Theory of
This effect is noticeable only during eclipses, since otherwise the Suns brightness obscures the affected stars.
Light Deflection
Crommelin observes the solar eclipse at Sobral as part of the British test of general relativity
Light Deflection
Dyson organises eclipse expeditions that test general relativity by measuring stellar positions near the Sun
Eclipse Test
Measures starlight deflection during a solar eclipse, supporting general relativity.
Solar Eclipse Relativity Test
British eclipse expeditions photograph stars near the Sun to test Einstein's predicted gravitational deflection.
Relativity Eclipse Results Announced
Royal Society and Royal Astronomical Society report eclipse results supporting Einstein's general relativity.
Great Debate Andromeda Argument
Uses spiral nebulae including Andromeda in the Great Debate, arguing that they are external galaxies rather than small objects inside the Milky Way.
Cosmology
Friedmann finds solutions of Einsteins equations that allow an expanding or contracting universe
Expanding Universe
Friedmann publishes relativistic equations that allow the universe to expand or contract
Mathematica Theory Of Relativity
Publication of "Mathematica Theory Of Relativity"
Discovery of Cepheid Stars
Discovers a class of variable stars known as cephids existing outside our own galaxy
Cepheid Variables
Hubble identifies Cepheid variables in Andromeda and shows it lies beyond the Milky Way
Andromeda V1 Plate
Photographs M31 with the 100-inch Hooker telescope and records the star later recognized as Cepheid variable V1 on the famous VAR photographic plate.
Relativity, Theory of
Eddington publishes influential expositions that spread general relativity among English speaking scientists
Discovery of Cepheid Stars
Hubble establishes the distance to Cepheid variables in the Andromeda Galaxy, showing that Andromeda lies beyond the Milky Way and helping settle the Island Universe debate.
Galaxies
Hubble announces evidence that spiral nebulae are external galaxies, expanding the scale of cosmology
Cepheid Variables Confirmed in Andromeda
Identifies multiple Cepheid variables in M31 and uses their periods to demonstrate that Andromeda is far outside the Milky Way.
Cosmology
Lemaitre studies relativistic cosmology and begins work that will connect general relativity to cosmic expansion
Andromeda Extragalactic Result Presented
Presents the Andromeda Cepheid evidence to the astronomical community, establishing M31 as a separate galaxy and greatly enlarging the known scale of the universe.
Galaxy Redshift
Humason begins measuring faint galaxy spectra that later strengthen Hubbles velocity distance relation
Royal Astronomical Society Gold Medal
Receives the Royal Astronomical Society Gold Medal for relativity and the theory of gravitation.
Universe Expansion
The expansion of the Universe accellerates as it expands
Expanding Universe
Lemaitre derives an expanding universe model from general relativity and estimates an expansion rate
Expanding Universe with Lambda
Lemaitre develops an expanding relativistic universe in which the cosmological constant can influence the large-scale evolution of cosmic expansion.
Hubble-Lemaitre Law
Lemaitre derives an expanding universe model and estimates the expansion rate from galaxy distances and velocities
Expanding Universe
Eddington discusses relativistic world models and helps bring expanding universe ideas into wider debate
Expanding Universe
Hubble publishes the velocity distance relation that makes expanding relativistic cosmology observationally compelling
White Dwarf Limit
Chandrasekhar combines quantum statistics with special relativity and identifies an upper mass beyond which a white dwarf cannot remain stable.
Primeval Atom
Lemaitre proposes a primeval atom origin for the expanding universe within relativistic cosmology
Primeval Atom
Lemaitre proposes that the universe expanded from a primeval atom, an early form of Big Bang theory
Expanding Universe Paper
Adopts an expanding cosmological model and abandons the need for his earlier static-universe construction.
Static Universe Abandoned
Einstein abandons the need for a static cosmological model after cosmic expansion becomes established, leaving the cosmological constant without its original motivation.
Dark Matter
Oort was studying stellar motions in the local galactic neighbourhood and found that the mass in the galactic plane must be greater than what was observed. Dark matter is postulated by Jan Oort based upon insufficient evidence, to account for the orbital velocities of stars in the Milky Way
Einstein-de Sitter Model
With Willem de Sitter, proposes a simple expanding cosmological model with zero cosmological constant.
Primeval Atom
Lemaitre lectures in the United States on the expanding universe and his primeval atom hypothesis
The Expanding Universe
Publication of "The Expanding Universe"
Dark Matter
Able to infer the average mass of galaxies within the cluster, and obtained a value about 160 times greater than expected from their luminosity, and proposed that most of the matter was dark
Dark Matter
Fritz Zwicky is the first to use the virial theorem to infer the existence of unseen matter, which he refers to as dunkle Materie dark matter.
Dark Matter
He estimated that there was about 400 times more mass than was visually observable. While examining the Coma galaxy cluster in 1933, Zwicky was the first to use the virial theorem to infer the existence of unseen matter, what is now called dark matter.
Dark Matter
Zwicky applies the virial theorem to the Coma cluster of galaxies and obtained evidence of unseen mass.
Dark Matter
Zwicky estimated the clusters total mass based on the motions of galaxies near its edge and compared that estimate to one based on the number of galaxies and total brightness of the cluster.
Virial Theorem
While examining the Coma galaxy cluster in 1933, Zwicky was the first to use the virial theorem to infer the existence of unseen matter, what is now called dark matter
Vacuum Energy Interpretation
Lemaitre relates the cosmological constant to an energy density of empty space, anticipating the modern vacuum-energy interpretation of dark energy.
Relativity, Theory of
Fritz Zwicky states that galaxies could act as gravitational lenses
Discovery of Supernova
Zwicky posited that galaxy clusters could act as gravitational lenses by the previously discovered Einstein effect
Gravitational Lensing
Zwicky states that galaxies could act as gravitational lenses and make relativity observable on cosmic scales
Hubbles Law
When Edwin Hubble discovered a linear relationship between the distance to a galaxy and its redshift expressed as a velocity, Zwicky speculated that the effect was due not to motions of the galaxy, but to the slowing down of photons
Cosmology
Gamow begins applying nuclear physics to early universe problems that will shape hot Big Bang theory
Discovery of Cepheid Stars
Walter Baade recognizes that Cepheids consist of at least two separate populations (classical Cepheids & Type II Cepheids). Classical Cepheids are younger and more massive population I stars, whereas Type II Cepheids are older fainter population. Resolves stars in the centre of the Andromeda galaxy for the first time, which led him to define distinct "populations" for stars (Population I and Population II)
Cosmic Microwave Background
McKellar estimates a low interstellar temperature from cyanogen absorption, later recognised as related to the microwave background
Stellar Populations Resolved in Andromeda
Resolves different stellar populations in Andromeda and distinguishes young Population I stars from older Population II stars in galactic studies.
Big Bang Nucleosynthesis
Gamow argues that the hot early universe could explain the origin of chemical elements
Steady State Theory
Gold helps formulate the steady state model as a rival to Big Bang cosmology
Continuous Creation
Uses continuous creation of matter to preserve constant cosmic density in steady state cosmology.
Steady State Theory
Develops the steady state alternative to evolving-universe cosmology with Bondi and Gold.
Steady-State Cosmology Collaboration
Hoyle, Bondi, and Gold developed related steady-state cosmologies while exchanging ideas in Cambridge.
Big Bang Nucleosynthesis
Gamow promotes the hot Big Bang model as a way to explain cosmic element abundances
Big Bang Nucleosynthesis
Bethe is included on the alpha beta gamma paper that publicises early universe nucleosynthesis
Big Bang Nucleosynthesis
Alpher publishes work on element formation in a hot dense early universe
Cosmic Microwave Background
Alpher predicts with Herman that the expanding universe should contain cooled remnant radiation
Cosmic Microwave Background
Herman predicts with Alpher that a relic radiation field should remain from the hot early universe
Big Bang
Popularises the phrase Big Bang while criticising cosmologies with an initial dense state.
BBC Cosmology Broadcast
Hoyle used the expression Big Bang during a BBC radio discussion while criticizing finite-age cosmology.
Nature of the Universe
Delivers influential BBC radio talks explaining cosmology to a wider public.
BBC Radio Cosmology Series
Hoyle presented a widely heard BBC radio series explaining modern astronomy and cosmology.
Cosmic Microwave Background
Alpher refines predictions for the relic radiation temperature expected from a hot early universe
Cosmic Microwave Background
Herman refines the predicted relic radiation temperature and keeps the observational test in view
Radio Emission Detected from Andromeda
Reports radio-frequency emission from M31 with Cyril Hazard, opening a new wavelength regime for studying the Andromeda Galaxy.
Andromeda Distance Scale Revised
Shows that two classes of Cepheid variables had been confused, leading to a major upward revision of the distance scale for Andromeda and other galaxies.
Hubbles Law
Sandage begins revising extragalactic distances and expansion measurements after Hubbles work
Distance Scale
Baade distinguishes stellar populations and revises Cepheid distances used in estimates of cosmic expansion
Early Radio Mapping of Andromeda
Produces early radio maps of M31 with the Cambridge Radio Astronomy Group, revealing the galaxy as an extended radio source rather than a single point.
Distance Scale
Baades corrections help make the cosmic expansion rate more realistic for Big Bang timescales
Hubbles Law
It was not until 1956 that Walter Baade corrected the distance scale based on Cepheid variable stars, and ushered in the first accurate measures of the expansion rate
Big Bang
Cosmological redshift is now conventionally understood to be a consequence of the expansion of space; a feature of Big Bang cosmology
Hubbles Law
Baade's revised Cepheid calibration doubles the extragalactic distance scale and improves measurements used to estimate the expansion rate of the universe.
Nucleosynthesis
Fowler helps show how many heavy elements form in stars, complementing Big Bang nucleosynthesis
Royal Society Election Certificate
The Royal Society elected Hoyle for major contributions to stellar structure, accretion, nucleosynthesis, and cosmology.
Rapid Rotation of Andromeda Nucleus
Detects rapid rotation in the compact nucleus of M31 with colleagues, evidence later understood in the context of a massive central black hole.
Nuclear Cosmochronology
Hoyle and William Fowler studied radioactive nuclei as clocks for estimating the ages of the Galaxy and Solar System.
Radio Source Counts
Hoyle and Jayant Narlikar examined radio-source counts as a test of steady-state cosmology.
Television Science Fiction Collaboration
Hoyle supplied the scientific story underlying the BBC television serial A for Andromeda.
Cosmic Microwave Background
Dicke revives interest in detecting relic radiation from a hot early universe
Apollo Program
Becomes NASA administrator during Apollo expansion.
A for Andromeda
A for Andromeda begins broadcast as a science fiction serial based on Hoyle's story.
A for Andromeda Book
Hoyle and John Elliot published a novel based on the television story A for Andromeda.
The Andromeda Breakthrough
The sequel The Andromeda Breakthrough begins broadcast on BBC television.
Hoyle-Narlikar Gravity
Develops an alternative theory of gravitation with Jayant Narlikar addressing inertia and cosmology.
Time-Symmetric Electrodynamics
Hoyle and Narlikar linked time-symmetric electrodynamics with the cosmological arrow of time.
Relativity, Theory of
Irwin Shapiro predicts a gravitational time delay of radiation travel as a test of general relativity
Cosmic Microwave Background
Penzias detects unexplained microwave antenna noise that will be identified as cosmic background radiation
Cosmic Microwave Background
Wilkinson helps build a radiometer intended to detect the predicted microwave background
Cosmic Microwave Background
Peebles calculates theoretical implications of a relic radiation background for hot Big Bang cosmology
Cosmic Microwave Background
Roll works with Wilkinson on an experiment to search for relic microwave radiation
Cosmic Microwave Background
Dicke organises a Princeton group to search experimentally for cosmic microwave background radiation
Cosmic Microwave Background
Wilson detects the same persistent microwave noise with the Holmdel horn antenna
Recent Developments in Cosmology
Hoyle reviewed contemporary cosmological observations and defended alternatives to finite-age universe models.
Cosmic Microwave Background
Penzias publishes the measurement of excess antenna temperature from the cosmic microwave background
Cosmic Microwave Background
Wilkinson coauthors the Princeton paper explaining the cosmic microwave background result
Radar Relativity Test
Planetary radar tests general relativity through time delay.
Cosmic Microwave Background
Peebles coauthors the interpretation paper connecting the microwave background to Big Bang cosmology
Cosmic Microwave Background
Roll coauthors the interpretation of the microwave background as a cosmological relic
Cosmic Microwave Background
Dicke interprets the microwave background detection as relic radiation from a hot dense early universe
Cosmic Microwave Background
Wilson publishes the microwave excess with Penzias, providing decisive evidence for a hot early universe
Black Holes
Penrose proves that gravitational collapse can produce spacetime singularities, showing black-hole formation is a robust prediction of general relativity.
Big Bang
Gamow promotes the microwave background discovery as strong support for the hot Big Bang model
Relativity, Theory of
Hewish leads the radio astronomy group that identifies pulsars as a new astronomical class
Relativity, Theory of
Irwin Shapiro presents the first detection of the Shapiro delay
Physical Cosmology
Peebles develops theoretical physical cosmology using the microwave background and structure formation
Hubble Constant
Sandage continues refining the expansion rate, an essential parameter for Big Bang age estimates
Relativity, Theory of
Proves first of many singularity theorems; a set of sufficient conditions for the existence of a singularity in space-time showing that, far from being mathematical curiosities singularities are a fairly generic feature of general relativity.
Singularity Theorem
Proves first of many singularity theorems; a set of sufficient conditions for the existence of a singularity in space-time showing that, far from being mathematical curiosities singularities are a fairly generic feature of general relativity. Hawking provides the first of many singularity theorems; such theorems provide a set of sufficient conditions for the existence of a singularity in space-time
Singularity Theorem
Hawking proves singularity theorems showing that spacetime singularities are generic in general relativity
Related astronomers
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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.
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