Halley’s Comet is the first comet whose return was predicted and, almost three centuries later, the first to be photographed up close by spacecraft.
In 1705 the English astronomer Edmond Halley published a work that included his calculations showing that comets observed in 1531, 1607, and 1682 were really one comet and predicting that comet’s return in 1758. The comet was sighted late in 1758, passed perihelion (closest distance to the Sun) in March 1759, and was named in Halley’s honour. Its periodic returns demonstrated that it was in orbit around the Sun.
Halley's Comet has been know since at least 240 BC and possibly since 1059 BC. Its most famous appearance was in 1066 AD when it was seen right before the Battle of Hastings.
Halley's Comet put on bright shows in 1835 and in 1910. Then in 1984 and 1985, five spacecraft from the USSR, Japan and Europe were launched to make a rendezvous with Halley's Comet in 1986. One of NASA's deep space satellites was redirected to monitor the solar wind upstream from Halley.
A total of nine comets have been studied by spacecraft, including Comet Giacobini-Zinner in 1985 (first ever fly-by of a comet), Comet Halley in 1986 (five separate fly-bys), Comet Tempel 1 in 2005 (first impact landing on the surface of a comet), and most recently Comet Churyumov-Gerasimenko in 2014 (first orbiter and first soft landing).
At the closest point in its orbit, Halley's Comet passes between the orbits of Venus and Mercury, coming within a mere 0.59 AU (or approx 88 million kms) of the Sun.
At the farthest point in its orbit, it passes just outside the orbit of Neptune, at a distance of 35.08 AU (or approx 5.247 billion kms) from the Sun.
The comet's orbit lies almost entirely below the Solar System's ecliptic plane, and it travels in the opposite direction to the planets.
The comet takes approx 75 to 76 years to complete each orbit, which is why most people only see Halley's Comet once in their lifetime.
The predicted date of Halley's next fly-by is 29th July 2061. Mark it in your calendars!
The current position of Halley's Comet in its orbit around the Sun can be seen here (top view), or here (side view). Look for the small white comet tail. [Credit: John Walker, Fourmilab Switzerland]