Editing John Flamsteed (section)

== Scientific work ==
[[File:John Flamsteed Royal Greenwich Observatory Museum.jpg|thumb|Bust of John Flamsteed in the Museum of the [[Royal Observatory, Greenwich|Royal Greenwich Observatory]]]]

Flamsteed accurately calculated the [[solar eclipse]]s of 1666 and 1668. He was responsible for several of the earliest recorded sightings of the [[planet]] [[Uranus]], which he mistook for a [[star]] and catalogued as '34 Tauri'. The first of these was in December 1690, which remains the earliest known sighting of Uranus by an astronomer.

In October 1672, when [[Mars]] was in [[opposition (astronomy)|opposition]], Flamsteed used eyepieces with illuminated [[Micrometer (device)|micrometer]] [[reticle]] carrying double cross-hairs, to measure Mars' [[diurnal parallax]], thus allowing Flamsteed to estimate the distance to Mars and hence the [[astronomical unit]]. To this end, Flamsteed compared the apparent shift of Mars during the night with respect to other stars, this shift being superimposed on Mars' apparent night-to-night course among the stars.<ref>Van Helden, A. (2010). ''Measuring the universe: cosmic dimensions from Aristarchus to Halley''. University of Chicago Press. Ch. 12. {{ISBN?}}</ref>

On 16 August 1680 Flamsteed catalogued a star, 3 [[Cassiopeia (constellation)|Cassiopeiae]], that later astronomers were unable to corroborate. Three hundred years later, the American astronomical historian William Ashworth suggested that what Flamsteed may have seen was the most recent supernova in the galaxy's history, an event which would leave as its remnant the strongest radio source outside of the Solar System, known in the [[Third Cambridge Catalogue of Radio Sources|third Cambridge (3C) catalogue]] as 3C 461 and commonly called [[Cassiopeia A]] by astronomers. Because the position of "3 Cassiopeiae" does not precisely match that of Cassiopeia A, and because the expansion wave associated with the explosion has been worked backward to the year 1667 and not 1680, some historians feel that all Flamsteed may have done was incorrectly note the position of a star already known.<ref>{{cite journal |last1=Ashworth |first1=William |title=A Probable Flamsteed Observation of the Cassiopeia – A Supernova |journal=[[Journal for the History of Astronomy]] |volume=11 |page=1 |bibcode=1980JHA....11....1A |date=1980 |doi=10.1177/002182868001100102 |s2cid=121684168 }}</ref>

In 1681 Flamsteed proposed that the [[Great Comet of 1680|two great comets]] observed in November and December 1680 were not separate bodies, but rather a single comet travelling first towards the Sun and then away from it. Although [[Isaac Newton]] first disagreed with Flamsteed, he later came to agree with him and theorized that comets, like planets, moved around the Sun in large, closed elliptical orbits. Flamsteed later learned that Newton had gained access to his observations and data through [[Edmond Halley]],<ref name=bbc/> his former assistant with whom he previously had a cordial relationship.<ref name="Hughes">{{cite journal | last =Hughes | first =David W. | author-link = David Hughes (astronomer) | title =Edmond Halley, Scientist | journal = [[Journal of the British Astronomical Association]] | volume =95 | issue =5 | page =193 | publisher =British Astronomical Association | location =London| date =August 1985 |bibcode = 1985JBAA...95..193H| quote = Flamsteed was one of the few people who had a bad word to say about Halley. They started off as friends but really fell out some time between 1684 and 1686. Flamsteed suspected Halley of surreptitiously learning of other people's work and then publishing it as his own.}}</ref>

As Astronomer Royal, Flamsteed spent some forty years observing and making meticulous records for his star catalogue, which would eventually triple the number of entries in [[Tycho Brahe]]'s sky atlas. Unwilling to risk his reputation by releasing unverified data, he kept the incomplete records under seal at Greenwich. In 1712, [[Isaac Newton]], then President of the [[Royal Society]], and [[Edmond Halley]] again obtained Flamsteed's data and published a pirated star catalogue.<ref name=bbc>{{cite web|last=Jardine|first=Lisa|author-link = Lisa Jardine|title=A Point of View: Crowd-sourcing comets|url=https://www.bbc.co.uk/news/magazine-21802843|work=Magazine|publisher=BBC News|access-date=20 May 2013|date=15 March 2013}}</ref> Flamsteed managed to gather three hundred of the four hundred printings and burned them. "If Sir I.N. would be sensible of it, I have done both him and Dr. Halley a great kindness," he wrote to his assistant [[Abraham Sharp]].<ref>{{cite book | author=Sobel, Dava | author-link= Dava Sobel| title=Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time | location=New York | publisher=Walker & Company | date=1995 | isbn=978-0-8027-1529-6| title-link= Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time}}</ref> The data from the pirated catalogue were used by the London cartographer [[John Senex#Importance|John Senex]] to produce star charts in the 1720s before Flamsteed's own charts were ready.

In 1725 Flamsteed's own version of ''Historia Coelestis Britannica'' was published posthumously, edited by his wife, [[Margaret Flamsteed]]. This contained Flamsteed's observations, and included a catalogue of 2,935 stars to much greater accuracy than any prior work. It was considered the first significant contribution of the Greenwich Observatory, and the numerical [[Flamsteed designation]]s for stars that were added subsequently to a French edition are still in use.<ref>{{cite web | last=Ridpath |first=Ian |author-link = Ian Ridpath |title=Flamsteed numbers – where they really came from |work = Ian Ridpath's Star Tales | url=http://www.ianridpath.com/startales/flamsteed.html |access-date=8 January 2012}}</ref> In 1729 his wife published his ''[[Atlas Coelestis]]'', assisted by [[Joseph Crosthwait]] and Abraham Sharp, who were responsible for the technical side.