A researcher on the team described a measurement that resembled light from a hot star, recorded in a region where no such star was visible.
Apollo 17’s ultraviolet experiment detected a signal that resembled light from a hot star, even though no such star was visible in the region examined. The researcher suggested that starlight had reflected off dust in space, but some features of the measurement did not fit that explanation.
A three-page excerpt from the Apollo 17 Crew Debriefing for Science (MSC-07632), dated January 8, 1973, prepared by NASA's Planetary and Earth Sciences Division at the Manned Spacecraft Center, Houston. The excerpt captures remarks by 'Henry' (Dick Henry, co-investigator on the Apollo 17 ultraviolet experiment) presenting preliminary scientific results: a search for red-shifted Lyman-alpha radiation from ionized hydrogen in the Coma cluster (none detected), an unexpected ultraviolet spectrum observed at high galactic latitudes, observations of Lyman-alpha hydrogen radiation in the solar system, and a UV spectrum of the Earth viewed from outside. Henry flags two unexplained findings: a 'real mystery' as to what gravitationally holds the Coma cluster together, and a high-galactic-latitude UV spectrum resembling that of a hot star despite no hot stars being in the field of view, possibly indicating extragalactic radiation.
"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 excludes the possibility that the Coma cluster is held together by this ionized hydrogen. I think that may leave a real mystery as to what is holding the thing together."
Speaker: HENRY (CONT'D)
Why it matters: Henry explicitly flags an unresolved astrophysical mystery (Coma cluster missing mass) tied to a null result from the Apollo 17 UV experiment.
Page 2
"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."
Speaker: HENRY (CONT'D)
Why it matters: Frames the Apollo 17 UV observations as a discovery-mode survey for an unexpected background.
Page 2
"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."
Speaker: HENRY (CONT'D)
Why it matters: Mentions an 'abnormally high dark current' on the instrument, which is itself flagged as anomalous.
Page 2
"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."
Speaker: HENRY (CONT'D)
Why it matters: Core unexplained observation: a hot-star-like UV spectrum from regions with no hot stars in view; Henry concedes the conventional explanation does not fully fit and raises possible extragalactic origin.
Page 3
"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"
Speaker: HENRY (CONT'D)
Why it matters: Identifies interstellar hydrogen streaming through the solar system as a topic the Apollo 17 UV data will clarify.
Page 3
"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."
Speaker: HENRY (CONT'D)
Why it matters: Notes that the Apollo 17 crew obtained an exterior UV spectrum of Earth; the excerpt cuts off mid-discussion.
Page 3
Henry (Dick Henry)
Co-investigator, Apollo 17 ultraviolet experiment; speaker · NASA Apollo 17 science team · Page 2
Dr. Trombka
Referenced as having spoken about the gamma-ray background · NASA Apollo 17 science team · Page 2
Gary Thomas
Researcher; observed Lyman-alpha hydrogen radiation from OGO-5 · University of Colorado · Page 3
Charles Barthum
Co-observer of Lyman-alpha hydrogen radiation from OGO-5 (name transcribed with '[?]') · Page 3
Manned Spacecraft Center, Houston, Texas, USA
Page 1
Coma cluster
Page 2
Milky Way
Page 2
North Galactic Pole
Page 2
South Galactic Pole
Page 2
Apollo 17
spacecraft · Page 1
OGO-5 (Orbiting Geophysical Observatory 5)
satellite · Page 3
Document is a 3-page excerpt (MSC-07632, dated 8 January 1973) from a much larger debriefing; pagination jumps to 119-120, indicating mid-volume excerpt. The text is heavily damaged at the cover/title (pages of OCR-mangled glyphs from a stylized cover) but the body pages 2-3 are clean embedded text. The 'UAP' in the file slug refers to the war.gov UAP release category, not to anomalous aerial phenomena — this document is purely an astrophysics/UV-instrument debrief and contains no aerial-phenomenon sightings, no mention of unidentified craft, and no astronaut UFO claims. The 'anomalies' captured here are the unexplained scientific results that Henry himself labels mysteries (cluster binding mass; high-latitude UV background). Speaker tags 'HENRY' and 'HENRY (CONT'D)' are present in the source. Confidence reduced from 0.9 because the document's cover page is unreadable and the excerpt is incomplete (cuts off mid-sentence on page 3).
The experiment measured ultraviolet light, which is invisible to the naked eye. The signal was stronger than the instrument’s background noise and resembled light from a hot star.
Henry said some features of the measurement did not fit the explanation, but he did not specify which ones. He also raised the possibility that the light had come from outside the Milky Way.
The team examined ultraviolet light in regions far from the central concentration of stars and detected light that resembled light from a hot star, in a region where no such star was visible.
During a discussion of the Apollo 17 research, researcher Dick Henry described light detected by the experiment. The team examined many points in the sky, north and south of the region where most of the stars in the Milky Way, our galaxy, are concentrated.
The experiment measured ultraviolet light, which is invisible to the naked eye. The signal was stronger than the instrument’s background noise and resembled light from a hot star. But no hot star was visible in the region the light appeared to come from. What exactly did the instrument detect, and why didn’t the possible explanation account for everything the team measured?
Every measuring instrument produces its own background signal, like a faint noise that interferes with a measurement. Henry explained that the detected light was stronger than this background. So the instrument’s background noise did not interfere with the experiment.
The researchers described the measurement by the range of light it detected, a kind of fingerprint. That fingerprint resembled one produced by light from a hot star. Yet there were no hot stars in the patch of sky the instrument examined.
Henry proposed one possible explanation: light from stars near the central region of the Milky Way had traveled outward, hit dust in space, and reflected back toward the instrument. That could explain how the light arrived from a direction where no hot star was visible.
But some features of the measurement did not fit this explanation. Henry did not specify during the discussion which features failed to match. So his remarks do not reveal exactly what made the explanation problematic, or how much of the light it could account for.
Henry said a detailed computer analysis was needed. It would examine the measurement and the light’s characteristics closely to determine whether the dust explanation fit. He expected the work to take a long time and also raised the possibility that the light had come from outside the Milky Way.
The discussion did not resolve where the light came from. The cautious explanation was that starlight had reflected off dust, though some features of the measurement did not fit; the light may also have come from outside the galaxy.
The light was recorded in a region where no hot star was visible. The instrument’s fingerprint still offered no answer about where it came from.