1. Statehood Day: On December 21, 1864, Nevada became the 36th state to join the Union.

2. Hoover Dam: The construction of the Hoover Dam began on December 21, 1930. It was completed in 1935 and provided both hydroelectric power and irrigation water for Nevada and several surrounding states.

3. First Las Vegas Casino: The first legal casino in Las Vegas, the Red Rooster, opened on December 21, 1931. This marked the beginning of the city's reputation as a major gambling and entertainment destination.

4. Winter Solstice: December 21 marks the winter solstice, the shortest day and longest night of the year. In Nevada, this day is often celebrated with traditional Native American and Mexican cultural events.

5. UFO Sightings: In 1984, a UFO sighting was reported in Las Vegas on December 21. Several witnesses reported seeing a bright light in the sky that moved in unusual ways. This incident is still a topic of debate among UFO enthusiasts.