1. In 1792, the New York Stock Exchange was founded. It started as a gathering of merchants and traders under a buttonwood tree on Wall Street to trade stocks and eventually became the largest stock exchange in the world.

2. On April 20, 1902, a new subway system began operating in New York City with the opening of the Interborough Rapid Transit Company's line, which is now part of the New York City Subway system.

3. In 1931, the Empire State Building was completed and opened to the public on April 20. It was the tallest building in the world at the time and remains an iconic symbol of New York City to this day.

4. On April 20, 1976, the United States Postal Service unveiled the first stamp in their Bicentennial series, which commemorated the 200th anniversary of the signing of the Declaration of Independence. The stamp featured an image of John Trumbull's painting, "The Signing of the Declaration of Independence."

5. In 2010, the Deepwater Horizon oil rig exploded in the Gulf of Mexico, causing the largest offshore oil spill in U.S. history. Although this event did not occur in New York, it had a significant impact on the city, as many New York City-based businesses and individuals were affected by the spill. On April 20, 2010, a candlelight vigil was held in Battery Park in honor of the victims and in support of environmental protection.