<P> Halley's 1986 apparition was the least favourable on record . The comet and Earth were on opposite sides of the Sun in February 1986, creating the worst viewing circumstances for Earth observers for the last 2,000 years . Halley's closest approach was 0.42 AU . Additionally, with increased light pollution from urbanization, many people failed to even see the comet . It was possible to observe it in areas outside of cities with the help of binoculars . Further, the comet appeared brightest when it was almost invisible from the northern hemisphere in March and April . Halley's approach was first detected by astronomers David Jewitt and G. Edward Danielson on 16 October 1982 using the 5.1 m Hale telescope at Mount Palomar and a CCD camera . The first person to visually observe the comet on its 1986 return was amateur astronomer Stephen James O'Meara on 24 January 1985 . O'Meara used a home - built 24 - inch telescope on top of Mauna Kea to detect the magnitude 19.6 comet . On 8 November 1985, Stephen Edberg (then serving as the Coordinator for Amateur Observations at NASA's Jet Propulsion Laboratory) and Charles Morris were the first to observe Halley's Comet with the naked eye in its 1986 apparition . </P> <P> Although Halley's Comet's retrograde orbit and high inclination make it difficult to send a space probe to it, the 1986 apparition gave scientists the opportunity to closely study the comet, and several probes were launched to do so . The Soviet Vega 1 started returning images of Halley on 4 March 1986, and the first ever of its nucleus, and made its flyby on 6 March, followed by Vega 2 making its flyby on 9 March . On 14 March, the Giotto space probe, launched by the European Space Agency, made the closest pass of the comet's nucleus . There were also two Japanese probes, Suisei and Sakigake . The probes were unofficially known as the Halley Armada . </P> <P> Based on data retrieved by Astron, the largest ultraviolet space telescope of the time, during its Halley's Comet observations in December 1985, a group of Soviet scientists developed a model of the comet's coma . The comet was also observed from space by the International Cometary Explorer . Originally International Sun - Earth Explorer 3, the probe was renamed and freed from its L Lagrangian point location in Earth's orbit to intercept comets 21P / Giacobini - Zinner and Halley . </P> <P> Two Space Shuttle missions--the ill - fated STS - 51 - L (ended by the Challenger disaster) and STS - 61 - E--were scheduled to observe Halley's Comet from low Earth orbit . STS - 51 - L carried the Shuttle - Pointed Tool for Astronomy (SPARTAN - 203) satellite, also called the Halley's Comet Experiment Deployable (HCED). STS - 61 - E was a Columbia mission scheduled for March 1986, carrying the ASTRO - 1 platform to study the comet . Due to the suspension of America's manned space program after the Challenger explosion, the mission was canceled, and ASTRO - 1 would not fly until late 1990 on STS - 35 . </P>

How many times has halley's comet returned to be visible on earth since halley saw it