Why are MLB players wearing No. 42 jerseys today?

April 15, 1997: Ken Griffey Jr. wears number 42 to honor Jackie Robinson on 50th anniversary – Society for American Baseball Research

The only day MLB players can wear No. 42? Jackie Robinson Day

Do MLB players have to wear numbers on their uniforms? - Quora

Last player to wear No. 42 for each MLB team

Philadelphia Phillies - Photo of Taijuan Walker wearing a Jackie Robinson shirt that says Breaking barriers with the number 42 on it. He is also wearing gray baseball pants and a backwards

Now honoring No. 42: Jackie Robinson Day in majors - The San Diego Union-Tribune

What Happens to All Those No. 42 Jerseys? - The New York Times

Jackie Robinson Day: 4 Facts About His Jersey No. 42, Now Retired in MLB

Yankees' Mariano Rivera Is the Last No. 42 - The New York Times