This Saturday marks the 50th anniversary of the Apollo 11 mission, when astronauts Neil Armstrong and Buzz Aldrin became the first people in history to walk on the Moon. But it’s also the anniversary of the a lesser known event—the first celebration of the Lord’s Supper on the Moon.

Here’s are nine things you should know about the first communion service on the Moon.

1. In 1969, Edwin Eugene “Buzz” Aldrin Jr. was an elder at Webster Presbyterian Church, a congregation just outside of Houston, Texas. He told the lead pastor of his church, Dean Woodruff, that he had “been struggling to find the right symbol for the first lunar landing.”  “We wanted to express our feeling that what man was doing in this mission transcended electronics and computers and rockets,” Aldrin told Guideposts magazine in 1970. “One of the principal symbols,” Woodruff said, “is that God reveals himself in the common elements of everyday life.” Traditionally, these elements are bread and wine—common foods in Bible days and typical products of man’s labor.

2. Aldrin got the idea for the communion ceremony while at Cape Kennedy working with the “sophisticated tools of the space effort.” “It occurred to me that these tools were the typical elements of life today,” Aldrin said. “I wondered if it might be possible to take communion on the moon, symbolizing the thought that God was revealing himself there too, as man reached out into the universe. For there are many of us in the NASA program who do trust that what we are doing is part of God’s eternal plan for man.”

3. The communion bread was carried in a plastic packet, the way regular inflight food is wrapped. Because there was just enough gravity on the moon for liquid to pour, Aldrin wanted to pour the wine into a chalice from his church. Woodruff had presented him a silver cup that was small and light enough that it could be carried in the astronaut’s personal-preference kit.

4. Aldrin had originally planned to share the event with the world over the radio. But the atheist activist Madalyn Murray O’Hair had recently sued NASA after Apollo 8 astronauts read the Book of Genesis during a broadcast made on Christmas Day 1968, when they became the first humans to orbit the moon. O’Hair’s case claiming that the astronauts had violated the constitutional separation between church and state was dismissed. Yet NASA was still wary of causing more controversy. Aldrin says his fellow astronaut Deke Slayton, who ran the Apollo 11 flight crew operations, told him to tone down his pre-communion message. “Go ahead and have communion, but keep your comments more general,” Slayton advised.

5. After unpacking the elements from their flight packets and laying them on a small table in front of the abort guidance system computer, Aldrin radioed back to NASA with this message:

Houston, this is Eagle. This is the LM Pilot speaking. I would like to request a few moments of silence. I would like to invite each person listening in, wherever and whomever he may be, to contemplate for a moment the events of the past few hours and to invite each person listening, wherever and whomever he may be, to contemplate for a moment the events of the past few hours and to give thanks in his own individual way.

6. Before taking communion, Aldrin read from John 15:5, which he had handwritten on a scrap of paper—”I am the vine, you are the branches. Whoever remains in me, and I in him, will bear much fruit, for you can do nothing without me.”

7. After radioing in his message and reading the Scripture verse, Aldrin partook of the Supper. Fellow astronaut Neil Armstrong looked on quietly but did not participate. “I poured the wine into the chalice our church had given me,” Aldrin says. “In the one-sixth gravity of the moon the wine curled slowly and gracefully up the side of the cup.  It was interesting to think that the very first liquid ever poured on the moon, and the first food eaten there, were communion elements.” After taking the elements, Aldrin says he “sensed especially strongly my unity with our church back home, and with the church everywhere.”

8. Every year, since the moon landing, the Webster Presbyterian Church of Houston, Texas, commemorates Aldrin’s moon communion service.  “It’s kind of a tradition around here,” Gene Fisseler said in 1999. “It’s still church. It’s not about the moon. It’s not about the astronauts. It’s still about church. But we feel like it’s an important tradition here in this church.”

9. The communion ceremony was dramatized in an episode of From the Earth to the Moon, a 12-part HBO television miniseries from 1998. Buzz Aldrin was played by actor Bryan Cranston.