On June 6, 1436, German mathematician, astronomer, astrologer, translator, instrument maker and Catholic bishop Johannes Müller aus Königsberg was born, better known under the Latinized version of his name as Regiomontanus. His diligent and accurate observations, measurements and recordings paved the way for modern astronomers such as Tycho Brahe and Nikolaus Copernicus.
On November 20, 1889, American astronomer Edwin Hubble was born. He is best known for his role in establishing the field of extragalactic astronomy and is generally regarded as one of the most important observational cosmologists of the 20th century.
The following is a list of the largest optical reflecting telescopes sorted by mirror diameter. Note that two of the first three are not yet operational. This list does not currently include telescopes that are still in the conceptual/proposed stage, such as the Overwhelmingly Large Telescope or the European Extremely Large Telescope; the design stage, such as the Thirty Meter Telescope; or ones still in the early stages of manufacturing such as the Giant Magellan Telescope.