Apollo 17 was the ninth crewed U.S. Moon mission and the sixth to land astronauts on the lunar surface. This 1973 debriefing document captures the crew's scientific findings, particularly observations made with ultraviolet and X-ray instruments during the mission.
What did the crew observe in space?
The astronauts looked at ultraviolet light from different parts of the sky. They found unexpected radiation at high galactic latitudes (far from the Milky Way's center). The spectrum they detected looked like light from hot stars, but no hot stars were in their field of view. The most likely explanation was light from hot stars bouncing off dust between stars. However, some features of the spectrum didn't fit that theory, leaving open the possibility of radiation from outside our galaxy.
What did they find about hydrogen?
The crew gathered large amounts of data on Lyman-alpha hydrogen radiation (light from hydrogen atoms). This hydrogen exists inside our solar system. One scientist believed the hydrogen comes from interstellar space (the space between stars) and streams through the solar system. The Apollo data was expected to help clarify and explain this hydrogen.
What about the Coma cluster mystery?
The crew investigated what holds the Coma cluster of galaxies together. They looked for ionized hydrogen (charged hydrogen atoms) that might provide the gravitational glue. They searched for red-shifted Lyman-alpha radiation from this ionized hydrogen but found none. This ruled out ionized hydrogen as the binding force, leaving scientists uncertain about what actually holds the cluster together.
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HENRY gravitationally holding it together° We though it might be
(CONT 'D)
in the form of ionized hydrogen. We looked for Lyman-alpha
radiation, red shifted from the ionized hydrogen, and we
didn't see any. We set a lower limit, which certainly ex-
cludes the possibility that the Coma cluster is held together
J
by this ionized hydrogen. I think that may leave a real
mystery as to what is holding the thing together.
The fourth point may turn out to be the most interesting
thing of all. When you look in the Milky Way, you see a
lot of UV coming from the stars, but the question is, what
do you see when you look up to the North Galactic Pole or
down to the South Galactic Pole. One of the most exciting
results of X-ray astronomy was the fact that an X-ray back-
ground was observed over the sky that nobody had expected,
and part of this is the gamma-ray background that Dr. Trombka
talked about. In the UV, nobody knows, but you never know
until you look. You do have to deal with this background
of stars that we know is there. So we did look at a large
number of different points at high galactic latitudes, both
. north and south. The spectrum that we see is above this
dark count. In other words, this abnormally high dark
current did not, in fact, interfere with that experiment.
The spectrum that we see looks like the spectrum of the hot
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120
HENRY star; however, we know that there were no hot stars within
(CONT'D)
our field of view. Therefore, the most conservative inter-
pretation, I think, is that what we're seeing is light from
hot stars in the galactic plane going up out of the plane
and reflecting off interstellar dust. There are certain
characteristics of the spectrum, though, that don't fit that
theory, and it's at least possible that this is extragalactic
radiation. I'm looking forward very much to the detailed
computer study of this, but it's going to take a long time.
Fifth point: Lyman-alpha hydrogen radiation is a completely
separate problem, and Gary Thomas at the University of
Colorado and Charles Barthum [?] observed this from OGO-5.
We obtained Just an enormous amount of data on the Apollo
that's going to straighten out this picture and clarify it
considerably. This is hydrogen that is inside our solar
system. It's sunlight reflecting off this. The hydrogen,
Gary Thomas thinks, is hydrogen from interstellar space
streaming through the solar system, and he is looking for-
ward with great anticipation to getting detailed analyses
of that.
One more thing: the spectrum of the Earth. I keep saying
"we ? " but these were the guys that were there. We looked
at the Earth from outside. A lot of people have observed View the official fileFrequently Asked Questions
What was the Apollo 17 crew debriefing about?
The debriefing covered scientific observations made during Apollo 17, the ninth crewed U.S. Moon mission. The crew reported findings from ultraviolet and X-ray instruments, including observations of radiation patterns in space and hydrogen data.
Apollo 17 was the ninth crewed U.S. mission to the Moon, and the sixth to land Astronauts on the lunar surface.
What unexpected radiation did the crew find?
The crew observed ultraviolet radiation at high galactic latitudes (areas far from the Milky Way's center) that was stronger than expected. The spectrum resembled light from hot stars, but no hot stars were in their field of view, suggesting the light either bounced off interstellar dust or came from outside our galaxy.
What did the crew learn about hydrogen in space?
The crew collected large amounts of data on Lyman-alpha hydrogen radiation, which is light from hydrogen atoms inside our solar system. Scientists believed this hydrogen comes from interstellar space and streams through the solar system, and the Apollo data was expected to help explain this process.
Why couldn't the crew explain what holds the Coma cluster together?
The crew searched for ionized hydrogen that might provide the gravitational force holding the Coma cluster together. They looked for red-shifted Lyman-alpha radiation from this ionized hydrogen but found none, ruling out that explanation and leaving the cluster's binding mechanism a mystery.
Congressional Context
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