Halley’s Comet: All about this famous comet
1/P Halley or Halley’s comet is a famous short-period comet, i.e, comets that have an orbital period of less than 200 years. It is often regarded as the most famous comet as it became the first time that astronomers understood that comets are repeat visitors in our night skies.
Halley’s comet was last seen in our night sky in 1986. It will return in 2061 on its 76-year orbit around the Sun.
In 1705, English astronomer, Edmond Halley used Sir Isaac Newton’s theories of gravity and planetary motions to calculate the orbits of several comets. Halley found many similarities between the bright comets that were seen in 1531, 1607 and 1682 and he suggested that the comets seen in these years were actually just one comet. Halley accurately predicted the comet would return in 1758–1759 and it did return.
In 1986, many international spacecrafts visited Halley’s Comet to research the comet in detail. These spacecrafts that visited Halley include Japan’s Suisei and Sakigake spacecraft, the Soviet Union’s Vega 1 and Vega 2, the international ISEE-3 (ICE) spacecraft and ESA’s Giotto spacecraft. NASA’s Pioneer 7 and Pioneer 12 have also contributed to the study of Halley’s comet.
Comet Halley moves backwards (opposite to Earth’s motion) around the Sun in a plane tilted about 18 degrees to that of Earth’s orbit. Halley’s comet, at its greatest distance from the Sun, will be beyond the orbit of Neptune. Halley’s orbital period is approximately 76 Earth years. The orbital period of Halley varies due to the gravitational interferences of the planets. Halley’s orbital period has been as short as 74 years and as long as 79 years. Halley’s closest approach to Earth occurred on the 10th of April, 837. On that day, the comet reached a brightness of magnitude -3.5.
Lifetime of Halley
With each orbit around the Sun, Halley loses approximately 1–3 metres of material from the surface of its nucleus. Thus, as a comet gets older, it gradually dims in appearance and may lose all the ice in its nucleus. At this stage, the comet loses its tail and the comet finally becomes a ball of rocky material that might dissipate into dust.