- Galileo writes Letters on Sunspots (1613; 400 years ago)
- James Gregory publishes his design for a new type of reflector telescope (1663; 350 years ago)
- John Dolland designs the divided object-glass micrometer (1753; 260 years ago)
- Nicolas Louis de Lacaille’s observations of 10 000 stars, made in Cape Town, published posthumously (1763; 250 years ago)
- Charles Goodricke and Edward Pigott suggest Algol (beta Persei) is an eclipsing binary (1783; 230 years ago)
- John Michell publishes the first description of a black hole (1783; 230 years ago)
- William Herschel begins searching for nebulae (1783; 230 years ago)
- William Herschel confirms the reality of binary stars (1803; 210 years ago)
- Heinrich Schumacher founds the Astronomiche Nachrichten (1823; 190 years ago)
- Charles Lyell publishes Principles of Geology (1833; 180 years ago)
- First operational time ball enters service at the Royal Observatory, Greenwich (1833; 180 years ago)
- John Herschel publishes Treatise on Astronomy (1833; 180 years ago)
- Thomas Henderson starts a time service for vessels moored in Table Bay, Cape Town (1833; 180 years ago)
- Henderson resigns as director of the Royal Observatory at the Cape of Good Hope (1833; 180 years ago)
- Time ball service operated by the Cape Observatory is extended to Signal Hill and Simon’s Town (1853; 160 years ago)
- Astronomische Gesellschaft established in Heidelberg, Germany (1863; 150 years ago)
- Edmund Nevill, government astronomer at Natal, elected as Fellow of the Royal Astronomical Society (1873; 140 years ago)
- William Mann, first assistant at the Cape Observatory, dies; William Finlay appointed (1873; 140 years ago)
- Transvaal Meteorological Department established; R T A. Innes appointed as director (1903; 110 years ago)
- Niels Bohr proposes a model of the atom (1913); H N Russell constructs his version of the H–R diagram (1913; 100 years ago)
- Edwin Hubble finds Cepheid variables in the Andromeda Galaxy (1923; 90 years ago)
- Sydney Samuel Hough, Astronomer Royal at the Cape Observatory, dies; Harold Spencer Jones appointed (1923; 90 years ago)
- R T A Innes dies (1933; 80 years ago)
- Spencer Jones appointed Astronomer Royal for England; John Jackson appointed at the Cape Observatory (1933; 80 years ago)
- Yale Observatory re-opens in El Leoncita, Argentinia (1963; 50 years ago)
- First woman in space, Valentina Tereskhova, aboard Vostok 6 (1963; 50 years ago)
- Elizabeth telescope installed at Cape Observatory (1963; 50 years ago)
- 1.24-m UK Schmidt telescope operational at Siding Spring, Australia (1973; 40 years ago)
- Official opening of the Sutherland observing site of the SAAO (1973; 40 years ago)
- Skylab space station launched (1973; 40 years ago)
- IRAS (Infrared Astronomical Satellite) launched (1983; 30 years ago)
- EXOSAT (European X-ray Observatory Satellite) launched (1983; 30 years ago)
- VLBA (Very Long Baseline Array) begins operation (1993; 20 years ago)
- ASCA (Advanced Satellite for Cosmology and Astrophysics) launched (1993; 20 years ago)
Visit the Events to commemorate page.