1. In 1955, Jonas Salk's polio vaccine was declared safe and effective after a successful trial involving over 1.8 million children, many of whom were from Pennsylvania. The vaccine would go on to virtually eradicate the disease in the United States and around the world.

2. On April 12, 1963, civil rights leader Dr. Martin Luther King Jr. was famously arrested in Birmingham, Alabama. What many people may not know is that he wrote his landmark "Letter from Birmingham Jail" during his incarceration, which became a key document in the Civil Rights Movement. The letter was addressed in part to Pennsylvania clergy who had been critical of Dr. King's tactics.

3. In 1983, Pennsylvania Governor Richard Thornburgh signed into law measures to create a Victims Bill of Rights, which would give crime victims a greater voice in the criminal justice system. Today, Pennsylvania remains among the states with the strongest protections for victims.

4. April 12, 1920 marks the birth of legendary jazz drummer Philly Joe Jones, who was born in Philadelphia. Jones would go on to become a key contributor to the bebop movement, performing with luminaries such as Miles Davis, Charlie Parker, Dizzy Gillespie, and many others.

5. On April 12, 1945, President Franklin D. Roosevelt passed away at the little White House in Warm Springs, Georgia. Roosevelt, who was a New York native, maintained a strong connection to Pennsylvania throughout his life and political career. He is perhaps best known for his leadership during World War II and the creation of programs such as the New Deal, which had a profound impact on Pennsylvania and the nation as a whole.