NASA-UAP-D5, Apollo 17 Crew Debriefing for Science, 1973
Agency: NASA
Incident date: 1973

Apollo 17 was the ninth crewed U.S. mission to the Moon, and the sixth to land Astronauts on the lunar surface. This document is an excerpt from the Apollo 17 Crew Debriefing for Science on January 8, 1973, in which Dick Henry, co-investigator on the ultraviolet experiment on Apollo 17, discusses seeing results that were unexpected. 
•	Pages 119-120. “One of the most exciting results of X-ray astronomy was the fact that an X-ray background 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 star; however, we know that there were no hot stars within our field of view. Therefore, the most conservative interpretation, 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.”

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PREPARED
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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

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