In the worst catastrophe in U.S. space history, the space shuttle Challenger explodes 74 seconds after liftoff, killing all seven astronauts on board. One victim is Christa McAuliffe, a schoolteacher who had volunteered under the “teachers in space” program. Also that year:

• The Soviet Union’s Chernobyl nuclear plant, near the city of Kiev, has a major accident, believed to be the worst in nuclear power history. An explosion starts a fire that releases radioactivity into the air and causes at least 31 deaths.

• The Supreme Court upholds affirmative action, which gives hiring preference to minorities.

• The AIDS epidemic is growing, according to Surgeon General Koop, who urges safe-sex practices, including teenage abstinence and adult use of condoms, to help prevent the spread of the disease.

• Tylenol pain reliever capsules injected with cyanide cause 4 deaths on the East and West coasts. Manufacturer Johnson & Johnson, which had brought the brand back after a similar tampering problem in 1982, develops improved packaging and a new form of pill called a “caplet.”

• William Rehnquist takes the oath as Chief Justice of the Supreme Court, replacing retiring Chief Justice Warren Burger. Antonin Scalia takes Rehnquist’s seat as Associate Justice.