In The Field

@ApolloPlus40 – Tranquility Base

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A lunar language all its own?

Neil Armstrong and Buzz Aldrin landed the Eagle on the lunar surface at 15:17 Houston time on 20 July 1969. Their first words from the surface were the mundane jargon of the space age:

“Contact light.”


“Ok, engine stop. ACA out of detent.”

“Out of detent. Auto.”

“Mode control, both auto. Descent engine command override, off. Engine arm, off. 413 is in.”

Capsule Communicator (CapCom) Charlie Duke, listening from Mission Control in Houston, burst in after a few seconds of this, saying, “We copy you down, Eagle.”

Armstrong completed his checklist, saying “Engine arm is off,” before pausing and delivering the words the world wanted to hear: “Houston, Tranquility Base here. The Eagle has landed.”

Duke and Aldrin exchanged thanks and congratulations, before Armstrong reminded them that their first duty was to prepare for an emergency escape. He told Aldrin “Ok. Let’s get on with it,” before telling Duke “Ok. We’re going to be busy for a minute.”

The pair ran through a checklist that prepared the Eagle for an emergency ascent, and then spent a few hours preparing for their excursion on the lunar surface.

Later, as Armstrong stepped from the Eagle’s landing pad onto the lunar surface, he made his second historic statement of the day, telling the world, “That’s one small step for man, one giant leap for mankind.”

After the mission, Armstrong said that he meant to say “a man,” provoking countless acoustic analysts to pore over the audio tapes to see whether his word was lost in the radio transmission or simply left unsaid.

First science controversy on the Moon

Armstrong and Aldrin were engineers and pilots, but some of their training for Apollo 11 was in field geology. Their training probably did not prepare them for what happens when geologists disagree. Here, from Eric M. Jones’ unparalleled Lunar Surface Journal, is a commentary on the reaction to their descriptions of the rocks they found on the Moon:

[During the Apollo 17 review, Jack Schmitt recalled that some geologists had been critical of Buzz's use of the term "biotite" which, formally, is a black to dark green form of mica. What Buzz was looking at was not biotite; however, as Schmitt points out, the description gave an excellent first impression of the appearance of the minerals Buzz could see in the rocks. Schmitt believes that the criticism was entirely unwarranted and, more than twenty years after the fact, still gets angry when he thinks about it.]

[Aldrin - "It didn't bother me too much."]

[Armstrong - "(Chuckling) All the geologists have vested interests; they make statements (that) they work hard to defend."]

[Aldrin - "The statement about 'purple' rocks was really a stretch of being kind of facetious (that is, he was joking). But it didn't come off. Since it didn't come off well, I let it go at that. What I was kind of thinking of was 'what's the most absurd color you could think of for a rock?' 'Purple.' But it just didn't come out right."]

A book by Elbert A. King on the Apollo missions from the perspective of a geologist is available on the Lunar and Planetary Institute website:

Photo: Aldrin at Tranquility Base / NASA

This blog post is part of the @ApolloPlus40 series, which accompanies the ApolloPlus40 Twitter project by Nature News, a re-telling of the Apollo 11 lunar landing, 40 years later.


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