On April 11, 1986, with about 63 million kilometers (39 million miles), Halley’s Comet made its closest approach to Earth on its outbound journey (while moving away from the Sun).

Today’s (April 11) story of what happened this day in Science, Technology, Astronomy, and Space Exploration history.

Halley’s 1986 Approach

The 1986 approach of Halley’s Comet was the least favorable on record. Many observers around the world were disappointed because the famous comet was barely visible to the naked eye.

In February 1986, the comet and the Earth were on opposite sides of the Sun, creating the worst possible viewing circumstances for Earth observers during the previous 2,000 years. Additionally, increased light pollution from urbanization in the 20th century caused many people to fail in attempts to see the comet.

Halley's comet
Halley’s Comet is a short-period comet visible from Earth every 74-79 years. Halley is the only known short-period comet that is regularly visible to the naked eye from Earth, and the only naked-eye comet that might appear twice in a human lifetime. Halley last appeared in the inner parts of the Solar System in 1986 and will next appear in mid-2061. The comet’s periodicity was first determined in 1705 by English astronomer Edmond (or Edmund) Halley (8 November [O.S. 29 October] 1656 – 25 January 1742 [O.S. 14 January 1741]), after whom it is now named. He predicted the comet’s return in 1758, which he did not live to see. Halley’s returns to the inner Solar System have been observed and recorded by recognized astronomers since at least 240 BC. Clear records of the comet’s appearances were made by Chinese, Babylonian, and medieval European chroniclers, but were not recognized as reappearances of the same object at the time.

Halley’s comet displayed much better shows during some of its previous visits:

  • In 12 BC, it was watched by the Chinese people for two months.
  • In 374 AD and 607, the comet passed only 13.5 million kilometers (8.4 million miles) from Earth.
  • In 837 Ad, it made the closest-ever approach to Earth: only 5 million kilometers! (3.1 million miles)
  • In 1066, the comet was so bright that it terrified millions of Europeans. It was also seen for over two months in China.
  • In 1222, it was described by Japanese astronomers as being “as large as the half-moon”.
  • In 1456, it was observed in Italy by the Italian mathematician, astronomer, and cosmographer Paolo Toscanelli (1397 – 10 May 1482). Toscanelli said the comet’s head was “as large as the eye of an ox”, with a tail “fan-shaped like that of a peacock”.

Astronomers are now able to observe the comet at any point in its orbit. In December 2023, it is calculated to reach the farthest point in its orbit from the Sun.

April 11 in Science, Technology, Astronomy, and Space Exploration history


M. Özgür Nevres

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