In Our Time — The Moon (Archive Episode)

BBC Radio 4, first broadcast 2011 – Archive Pick aired November 6, 2025
Host: Melvyn Bragg
Guests:

• Paul Murdin – Visiting Professor of Astronomy, Liverpool John Moores University
• Caroline Crawford – Gresham Professor of Astronomy, University of Cambridge
• Ian Crawford – Reader in Planetary Science and Astrobiology, Birkbeck, University of London

Episode Overview

This episode explores the Moon—its scientific mysteries, historical significance, and cultural impact. The discussion ranges from the Moon's physical formation and geology to its deep role in human timekeeping, mythology, and future exploration. Melvyn Bragg and his guests weave together ancient observations, milestone scientific achievements, and future possibilities, offering an engaging narrative about our closest celestial neighbor.

Key Topics & Discussion Points

1. The Moon: Physical Facts and Astronomical Significance

(03:30—05:22)

• Nature of the Moon:
  • Orbits Earth at a distance of ~350,000 km, roughly a quarter of Earth's size.
  • Described as potentially a “twin planet” with Earth rather than just a subordinate satellite.
  • Orbit period defines the month.
  • Always shows the same face to Earth due to tidal locking.
• Composition and Climate:
  • Density similar to Earth's crust, mostly basalts and anorthosites.
  • "It’s airless. It's either very hot when it's in the sunlight or it's very cold." (Paul Murdin, 04:50)
  • No climate, only extreme temperature shifts.

2. Human Observation and the Moon's Role in Early Culture

(05:22—10:37)

• Earliest Records:

  • Evidence of humans tracking lunar phases dates back 20,000 years (scratched bone artifacts recording lunar cycles).
  • Suggestion that these markings may relate to fertility or navigation.

• Early Intellectual Curiosity:

  • "We're seeing in these bones the first evidence of intellectual activity among people who became us." (Melvyn Bragg, 07:30)

• Lunar Calendars and Stonehenge:

  • Use of Moon to measure time.
  • Structures like Stonehenge as lunar observatories.

• Cultural Associations:

  • Harvest Moon and Hunter's Moon—full Moons aiding farmers and hunters at night.
  • “Once in a blue moon”—refers to a rare second full moon within one month.
  • "It illuminates if you're traveling. It makes your traveling safe. If you're a farmer, [...] it's enormously helpful when you're gathering in the crops." (Caroline Crawford, 08:25)

3. Tides and Earth-Moon Dynamics

(10:44—14:48)

• Mechanics of Tides:
  • Caused by differential gravitational pull of the Moon on Earth's oceans.
  • “So the Earth is being pulled around by the Moon. But of course, there are two tides in every day...” (Caroline Crawford, 11:01)
  • Earth-Moon system as a “double planet.”
• Tidal Locking & Long-Term Evolution:
  • Earth raises tides on Moon’s rocky crust—leads to Moon always showing same face.
  • Earth gradually losing rotational energy; Moon slowly receding at ~4 cm/year.
  • "...the Earth loses its rotational energy and cans it through gravity to the orbital energy of the Moon. So the Moon is receding.” (Ian Crawford, 13:28)
  • Eventually (in billions of years), both will be locked with same face to each other.

4. What We Know of the Moon: Geology, Apollo Legacy, and Key Discoveries

(15:03—17:49, 25:04—28:36)

• Geology & Composition:

  • Similar to rocky terrestrial planets, but with significantly less iron core and volatiles than Earth.
  • Basalts in dark lunar "mare" and anorthosite in brighter highlands.
  • Apollo samples were crucial: "The scientific legacy of the Apollo program can't be overestimated ... [we learned] the precise mineralogical composition of these." (Ian Crawford, 16:15)

• Telescopic Discovery:

  • Galileo's 1609 telescopic survey revealed the Moon’s rugged terrain, craters, and mountains.
  • Shattered old myth that the Moon was a perfect heavenly sphere.
  • "It really did. And he was the first person to try and make sense of what you could see through the Moon through this very crude optical telescope..." (Caroline Crawford, 25:33)

5. The Origin of the Moon: Competing and Current Theories

(18:32—25:04)

• Rejected Theories:
  • Fission: Earth spinning so fast it threw off the Moon—now “absolutely impossible.”
  • Capture: Moon formed elsewhere and was captured by Earth's gravity—unlikely.
  • Co-formation: Earth and Moon formed together in a double vortex of nebular dust.
• Giant Impact ("Big Splash/Big Splat") Theory:
  • Currently prevailing theory (since mid-1980s).
  • Proto-Earth collided with Mars-sized body (“Theia”); iron cores merged, while the crust/mantle material ejected and coalesced as the Moon.
  • Explains Moon’s small iron core and volatile deficiency.
  • “This explains the chemical composition of the Moon well.” (Ian Crawford, 24:44)

6. Spacecraft and the Modern Era of Lunar Exploration

(27:44—32:58)

• First Close-Ups:

  • Soviet Luna missions (1959): first images of far side, crash-landing on Moon, paradigm shift in lunar knowledge.

• Apollo Program and the Space Race:

  • Political roots in US–USSR Cold War rivalry.
  • 382 kg of rock and soil returned by Apollo astronauts; much more scientifically valuable than robotic samples.

• Robots vs. Astronauts:

  • Some sample collection possible robotically, but much scientific instrumentation and flexible fieldwork benefited from human presence.
  • “To actually install experiments like that on the surface, there’s a lot of human decision…” (Caroline Crawford, 30:46)
  • Human presence allows more diverse, targeted sampling.

7. Water on the Moon and Future Colonization

(34:07—36:22)

• Discovery of Water:

  • Historically thought Moon was completely dry.
  • Recent missions (e.g., LCROSS) found ice in permanently shadowed polar craters—potentially 5% by weight locally, but globally rare.
  • Enables potential extraction of hydrogen and oxygen for fuel and life support.

• Colonization Prospects and Motivations:

  • Moon as a resource and a "stepping stone" for further solar system exploration.
  • Ideological motivations: "In the progress of history...the first place to establish colonies outside the Earth..." (Paul Murdin, 37:16)

• Helium-3 and Science:

  • Speculation around mining for Helium-3 (potential fusion fuel), but practicalities questioned.
  • Moon as a "museum" of the early solar system—records solar wind, meteorites, and potentially even Earth’s earliest geological history.

8. The Moon as a Scientific and Cultural Treasure Trove

(41:24—43:58)

• A Historical Record:
  • "The Moon is a palimpsest. Everything that's ever been written over the history of the solar system is recorded on the surface there." (Paul Murdin, 41:27)
  • No atmosphere or tectonics: craters and layers preserve billions of years of impacts and cosmic events.
• Base for Astronomy and International Cooperation:
  • Far side of Moon could be valuable for astronomy—shielded from Earth's radio waves.
  • Future exploration should be an international, cooperative venture.

Timestamps for Notable Segments

• Origin of lunar phases and stone age lunar observations: 05:22–07:30
• Harvest/Hunter’s/Blue Moon explanations: 08:19–10:17
• Tidal explanation: 10:44–13:28
• Giant Impact Theory discussed: 18:32–25:04
• Galileo and telescopic discovery: 25:04–26:52
• Cold War politics and Apollo significance: 28:36–30:38
• Robots vs. astronauts, what we learned: 30:46–32:58
• Discovery of lunar water: 34:07–36:22
• Possibility/resource ideology of Moon bases: 36:30–39:18
• Moon as a historical record/palimpsest: 41:24–42:21
• The Moon's value to astronomy and science funding: 42:29–43:58

Memorable Quotes

• On Lunar Phase Markings (~07:30):

  • "We're seeing in these bones the first evidence of intellectual activity among people who became us."
    —Melvyn Bragg

• On Harvest Moon (08:25):

  • "Having a full moon at night is crucially important. It illuminates if you're traveling. It makes your traveling safe."
    —Caroline Crawford

• On Tidal Locking (13:28):

  • "...The Earth's gravity gets a lock on the Moon, such that the Moon is forced to rotate once each time that it orbits the Earth."
    —Ian Crawford

• On the Giant Impact Theory (24:44):

  • “This explains the chemical composition of the Moon well...when you have these two planetoids colliding, [...] the volatile substances will be boiled off and evaporated away. So what you're left with to build a moon out of is Earth-like stuff minus the iron core, minus the volatiles.”

• On the Moon as a Museum (41:27):

  • "The Moon is a palimpsest. Everything that's ever been written over the history of the solar system is recorded on the surface there."
    —Paul Murdin

• On the Potential for International Coopertion (43:23):

  • "I think we should be looking more now to having these exciting, expensive human space exploration programs as truly international efforts [...] a unifying potential."
    —Ian Crawford

Conclusion

This episode illuminates the Moon’s dual identity as both a touchstone of human culture and a focus of contemporary science. From humanity’s earliest scratchings to the heights of the Space Race, and toward future bases and discoveries, the conversation reveals our enduring fascination—and the vast, still-unanswered questions trembling in lunar dust.

(For full context and depth, listen to the complete conversation to appreciate the experts' wit, curiosity, and enthusiasm.)