9 February 1986

Halley’s Comet last appeared in the inner Solar System.

Halley’s Comet is one of the most famous comets known to humanity. It’s named after the English astronomer Edmund Halley, who, in 1705, predicted its return based on observations of previous sightings dating back to 1531, 1607, and 1682. The comet itself has a long and elliptical orbit that brings it close to the Sun and then back out into the far reaches of the solar system. Its orbital period is approximately 75-76 years.

Appearance: Halley’s Comet is known for its distinctive appearance, with a bright coma (a cloud of gas and dust) surrounding its nucleus and a long tail extending millions of kilometers into space. The tail always points away from the Sun due to solar wind and radiation pressure.

Observations: Throughout history, Halley’s Comet has been observed and recorded by various civilizations. The earliest confirmed sighting was in 240 BC by Chinese astronomers. Its appearance has been noted in numerous historical records, including European, Islamic, and Asian sources.

Scientific significance: Halley’s Comet is significant to scientists because it provides insights into the composition and behavior of comets, which are remnants from the formation of the solar system. Studying its composition helps scientists understand the early conditions of the solar system.

Notable appearances: Halley’s Comet has made several notable appearances throughout history. One of the most famous was in 1066 when it appeared in the sky shortly before the Battle of Hastings in England. Another notable appearance was in 1910 when Earth passed through the comet’s tail, leading to widespread fear and speculation about potential effects (though no harm came from it).

Recent appearances: Halley’s Comet was last visible from Earth in 1986. Its next expected appearance is around the year 2061.

Spacecraft missions: Several spacecraft have been sent to study Halley’s Comet up close. The most notable mission was by the European Space Agency’s Giotto probe, which flew within 600 kilometers of the comet’s nucleus in 1986, providing valuable data and images.

26 April 1986

The Chernobyl disaster occurs in the Ukrainian Soviet Socialist Republic.

The Chernobyl disaster was a catastrophic nuclear accident that occurred on April 26, 1986, at the Chernobyl Nuclear Power Plant in the Ukrainian SSR, which was then part of the Soviet Union. The accident occurred during a late-night safety test of one of the plant’s reactors, when a sudden power surge caused a massive explosion and fire that released a huge amount of radioactive material into the air.

The explosion and resulting fire killed two plant workers on the night of the accident, and another 29 people died from acute radiation sickness in the following weeks. The disaster also contaminated large areas of land and water with radioactive fallout, forcing the evacuation of over 100,000 people and causing long-term health effects for many more.

The Chernobyl disaster is considered to be the worst nuclear accident in history, both in terms of the immediate human impact and the long-term environmental and health consequences. It led to significant changes in nuclear safety practices and regulations around the world

14 April 1986

The heaviest hailstones ever recorded, each weighing 1 kilogram (2.2 lb), fall on the Gopalganj district of Bangladesh, killing 92.

Hail stones are formed when strong updrafts in thunderstorms carry raindrops high into the atmosphere, where they freeze into ice. These frozen raindrops are then caught in the storm’s updrafts, which carry them up and down inside the storm cloud, adding layers of ice to the growing hailstone.

The hailstone continues to grow until it becomes too heavy for the storm’s updrafts to support, and it falls to the ground. The size of the hailstone depends on the strength of the updrafts, the temperature and moisture content of the atmosphere, and the amount of time the hailstone spends inside the storm cloud.

In some cases, hailstones can grow very large, reaching the size of golf balls or even softballs, which can cause significant damage to buildings, crops, and vehicles.

7 March 1986

Challenger Disaster: Divers from the USS Preserver locate the crew cabin of Challenger on the ocean floor.

The Challenger shuttle disaster was caused by the failure of a seal on one of the solid rocket boosters (SRBs), which allowed hot gases and flames to escape and damage the external fuel tank, leading to the catastrophic breakup of the shuttle.

More specifically, the failure of the O-ring seal in the joint between the two lower segments of the right SRB was the primary cause of the disaster. The O-ring failed to seal properly due to several factors, including the low temperature at the time of launch, which made the rubber more brittle and less resilient, and the design of the joint, which made it susceptible to erosion and blow-by.

The decision to launch the Challenger despite concerns about the O-ring’s performance in cold weather, and a lack of communication between NASA and the contractor responsible for the SRBs, also contributed to the disaster.

Tragically, all seven crew members, including the first civilian teacher in space, Christa McAuliffe, were killed in the explosion. The Challenger disaster was a devastating reminder of the risks and complexities of human spaceflight, and led to significant changes in NASA’s safety culture and procedures.