October 9 is a special holiday--even if it isn’t widely celebrated. Friday is Leif Erikson Day, but some people might not know what exactly is being celebrated. Some may even be surprised to learn that one of SpongeBob SquarePants’ favorite holidays is real.

Leif Erikson is believed to be the first European to discover the continent of North America.

Leif Erikson Day has been celebrated in the U.S. since 1964. Every president makes an annual proclamation on the holiday, and they use it to highlight current events as well. In 2019, President Trump connected Erikson’s bravery to the mission to explore Mars:

Leif Erikson’s undaunted life of exploration began in Iceland — the same location where the Apollo 11 crew trained for its historic journey to the surface of the Moon. The bold spirit that propelled Erikson and his fellow mariners across an unknown ocean is the same spirit that carried our brave astronauts into space 50 years ago, and it is what continues to fuel our desire to unlock the mysteries of the universe and pursue the exploration of Mars.

The U.S., Canada and Iceland all celebrate Leif Erikson Day.

Erikson is believed to have lived from 970 to 1020, long before Christopher Columbus sailed the ocean blue in 1492. His father, Erik the Red, is said to have founded the first European settlement in Iceland, according to History. After visiting Norway, where he was born, King Olaf I Tryggvason assigned him to convert Greenland from paganism to Christianity.

There are two legends that go with Leif Erikson. The first is the “Saga of Erik the Red,” which claims he found North America by accident after sailing off-course. The second is “Saga of the Greenlanders,” which claims it was very intentional.

He got a ship and a crew, and they lived in Newfoundland for the winter, enjoying much milder weather. They had many violent interactions with Native Americans, however, which is thought to be part of why they returned to Greenland. However, many other Vikings left Greenland for other parts of North America after hearing of Erikson’s journey.

Leif Erikson Day is celebrated on Oct. 9 because the ship Restauration arrived from Norway at New York Harbor on Oct. 9, 1825. It kicked off a huge wave of Norwegian immigrants arriving in the states.

Leif Erikson
Painting of Norwegian explorer Leif Erikson (c. AD 970 - 1020) on board a ship 'discovering America,' by Per Krohg (1889 - 1965). Hulton Archive/Getty Images