NASA marked its annual Day of Remembrance – and 55 years since the Apollo 1 tragedy on Thursday. 

Each January, the agency pauses to honor members of NASA who died while "furthering the cause of exploration and discovery." 

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Those honored include the crews of Apollo 1 and space shuttles Challenger and Columbia.

"NASA’s Day of Remembrance is an opportunity to honor members of the NASA family who lost their lives in our shared endeavor to advance exploration and discovery for the good of all humanity," NASA Administrator Bill Nelson said in a statement

"Every day, we have an opportunity to further uplift the legacies of those who gave their lives in pursuit of discovery by taking the next giant leap, meeting every challenge head-on, as they did. In doing so, we also must never forget the lessons learned from each tragedy and embrace our core value of safety," he added.

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NASA wrote that Nelson was set to lead an observance at Virginia's Arlington National Cemetery – including a traditional wreath-laying ceremony at the Tomb of the Unknown Soldier and observances for the Apollo 1, Challenger and Columbia crews.

On the heels of that event, he will join NASA Deputy Administrator Pam Melroy and Associate Administrator Bob Cabana in a panel discussion with agency employees on the topic of safety and lessons learned from the agency’s tragedies.

NASA centers will also hold observances – though limited to invited guests and largely closed to media, due to the COVID-19 pandemic.

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Florida's Kennedy Space Center and The Astronauts Memorial Foundation hosted a ceremony at the Space Mirror Memorial at Kennedy’s Visitor Complex, which was livestreamed on the center's Facebook channel.

Images and multimedia from these events will be added to NASA’s online image and video library.