Harvard College Observatory in the context of "Harvard–Smithsonian Center for Astrophysics"

Georges Henri Joseph Édouard Lemaître (/ləˈmɛtrə/ lə-MET-rə; French: [ʒɔʁʒ ləmɛːtʁ] ; 17 July 1894 – 20 June 1966) was a Belgian Catholic priest, theoretical physicist, and mathematician who made major contributions to cosmology and astrophysics. He was the first to argue that the recession of galaxies is evidence of an expanding universe and to connect the observational Hubble–Lemaître law with the solution to the Einstein field equations in the general theory of relativity for a homogenous and isotropic universe. That work led Lemaître to propose what he called the "hypothesis of the primeval atom", now regarded as the first formulation of the Big Bang theory of the origin of the universe.

Lemaître studied engineering, mathematics, physics, and philosophy at the Catholic University of Louvain and was ordained as a priest of the Archdiocese of Mechelen in 1923. His ecclesiastical superior and mentor, Cardinal Désiré-Joseph Mercier, encouraged and supported his scientific work, allowing Lemaître to travel to England, where he worked with the astrophysicist Arthur Eddington at the University of Cambridge in 1923–1924, and to the United States, where he worked with Harlow Shapley at the Harvard College Observatory and at the Massachusetts Institute of Technology (MIT) in 1924–1925.

Henrietta Swan Leavitt (/ˈlɛvɪt/; July 4, 1868 – December 12, 1921) was an American astronomer. Her discovery of how to effectively measure vast astronomical distances led to a shift in the understanding of the scale and nature of the universe.

A graduate of Radcliffe College, she worked at the Harvard College Observatory as a human computer, tasked with measuring photographic plates to catalog the positions and brightness of stars. This work led her to discover the relation between the luminosity and the period of Cepheid variables. Leavitt's discovery provided astronomers with the first standard candle with which to measure the distance to other galaxies.

Harlow Shapley (November 2, 1885 – October 20, 1972) was an American astronomer, who served as head of the Harvard College Observatory from 1921–1952, and political activist during the latter New Deal and Fair Deal.

Shapley used Cepheid variable stars to estimate the size of the Milky Way Galaxy and the Sun's position within it. In 1953 he proposed his "liquid water belt" theory, a concept now known as a habitable zone.

Fred Lawrence Whipple (November 5, 1906 – August 30, 2004) was an American astronomer, who worked at the Harvard College Observatory for more than 70 years. Among his achievements were asteroid and comet discoveries, the "dirty snowball" hypothesis of comets, and the invention of the Whipple shield.

Seth Carlo Chandler, Jr. (September 16, 1846 – December 31, 1913) was an American astronomer, geodesist, and actuary.

He was born in Boston, Massachusetts to Seth Carlo and Mary (née Cheever) Chandler. During his last year in high school he performed mathematical computations for Benjamin Peirce, of the Harvard College Observatory.

The Smithsonian Astrophysical Observatory (SAO) is a research institute of the Smithsonian Institution, concentrating on astrophysical studies including galactic and extragalactic astronomy, cosmology, solar, earth and planetary sciences, theory and instrumentation, using observations at wavelengths from the highest energy gamma rays to the radio, along with gravitational waves.  Established in Washington, D.C., in 1890, the SAO moved its headquarters in 1955 to Cambridge, Massachusetts, where its research is a collaboration with the Harvard College Observatory (HCO) and the Harvard University Department of Astronomy. In 1973, the Smithsonian and Harvard formalized the collaboration as the Center for Astrophysics | Harvard & Smithsonian (CfA) under a single Director.

The Harvard Plate Stacks, previously known as the Harvard College Observatory's Glass Plate Collection or the Astronomical Photographic Glass Plate Collection is the largest collection of photographic glass plate negatives of the night sky in the world. The collection was created across a century by the Harvard College Observatory. Many of the people who worked in and studied the collection were a group of famous female astronomers called the Harvard Computers. It is a scientific and historical collection at The Center for Astrophysics | Harvard & Smithsonian (CfA) in Cambridge, Massachusetts.

The Digital Access to a Sky Century @ Harvard (DASCH) was a project that digitized much of the collection of astronomical photographic glass plate negatives created by the Harvard College Observatory and housed in the collection known as the Harvard Plate Stacks. It was a major project of the Center for Astrophysics | Harvard & Smithsonian. The project digitized nearly all of the direct images in the Harvard Plate Stacks with a total of 429,274 glass plates scanned for the final data release in 2024. The database contributes to the field of time domain astronomy, providing nearly hundred years more of data that may be compared to current observations.

From 1885 until 1992, the Harvard College Observatory repeatedly photographed the night sky using observatories in both the northern and southern hemispheres. Over half a million glass photographic plates are stored in the observatory archives providing a unique resource to astronomers. The Harvard collection is over three times the size of the next largest collection of astronomical photographic plates and is almost a quarter of all known photographic images of the sky on glass plates. Those plates were seldom used after digital imaging became the standard near the end of the twentieth century. The scope of the Harvard Plate Stacks collection is unique in that it covers the entire sky for a very long period of time.