(KTLA) – September 15th marks the start of National Hispanic Heritage Month, a 30-day period honoring the contributions of Hispanic Americans to the history, culture and achievements of the United States.

But why isn’t the celebration contained in a calendar month? The answer isn’t all that complicated.

“The observation started in 1968 as Hispanic Heritage Week under President Lyndon Johnson and was expanded by President Ronald Reagan in 1988 to cover a 30-day period starting on Sept. 15 and ending on Oct. 15. It was enacted into law on Aug. 17, 1988, on the approval of Public Law 100-402,” according to the Library of Congress.

The 15th is a highly significant date, because it marks the anniversary of independence for Costa Rica, El Salvador, Guatemala, Honduras and Nicaragua, according to a federal website devoted to the topic. Mexico and Chile also celebrate their independence days on September 16 and September 18, respectively. Extending into October allows the celebration to extend and cover Day or Día de la Raza, a recognition of Christopher Columbus’ arrival in the hemisphere, which is marked on October 12.

Over time, the month has given rise to a number of celebrations and events across the country to recognize the cultures and contributions of Hispanic Americans.