Greek astronomy: distances and geometry

The Space Show Presents Dr. Andrew Fraknoi, Sunday, March 1, 2026

Quick Summary:

The Space Show presented an in-depth discussion with astronomer Dr. Andrew Fraknoi about the upcoming total lunar eclipse on March 3rd, which will be visible in the early morning hours across North America. Our discussion explored how ancient Greeks used lunar eclipses to prove Earth’s spherical shape and covered modern astronomical topics including the Vera Rubin Observatory’s 10-year sky-mapping project and the James Webb Space Telescope’s capabilities for observing distant galaxies. The discussion also touched on the debate between active and passive SETI approaches to searching for extraterrestrial intelligence, with Dr. Fraknoi expressing caution about sending messages to potential alien civilizations. The program concluded with information about Dr. Fraknoi’s free astronomy textbook and his ongoing Silicon Valley Astronomy Lectures series for 27 years.

Detailed Summary:

The meeting began with a discussion about teaching programs for retired individuals, where Andrew shared his experience teaching astronomy in national classes through the Osher Lifelong Learning Institute. The conversation then shifted to a discussion about supernovae, with Andrew explaining that predicting them is currently impossible. David encountered technical difficulties with Zoom, preventing a participant from joining, and John Hunt offered suggestions to resolve the issue. The conversation ended with David announcing upcoming schedule changes, including a canceled show due to his travel to UCLA, and encouraged listeners to support the program through PayPal or Substack.

Andrew explained the details of the upcoming total lunar eclipse, noting that while it’s easily observable without special equipment, its timing in the middle of the night makes it inconvenient for most people. He shared a chart showing the eclipse’s progression across different time zones, highlighting that the total phase will last about an hour, with the moon appearing red due to Earth’s atmosphere bending sunlight. Andrew also discussed the historical significance of lunar eclipses, explaining how ancient Greeks observed the round shadow cast by Earth to conclude the Earth was spherical, and clarified that lunar eclipses are safe to watch without protection. He contrasted lunar and solar eclipses, noting that while lunar eclipses are more accessible and beautiful, solar eclipses are crucial for studying the sun’s atmosphere due to a unique coincidence where the moon and sun appear the same size from Earth.

The Space Show Wisdom Team discussed the history of astronomical knowledge, focusing on ancient Greek contributions to understanding the Earth’s shape and the distances to the moon and sun. Andrew explained how the Greeks developed geometry to calculate these distances, with Marshall noting that their ratio estimates were surprisingly accurate. They also discussed Eratosthenes’ experiment measuring the Earth’s circumference and how this knowledge influenced Columbus’ voyages, despite some debate during the Middle Ages about the Earth’s shape.

Andrew discussed the historical significance of Einstein’s general theory of relativity, highlighting the 1919 solar eclipse experiment that confirmed his predictions about light bending. He also explained the Vera Rubin Observatory, a ground-based telescope in Chile with a sophisticated digital camera that will capture a 10-year time-lapse of the sky, enabling astronomers to discover millions of new celestial objects. David inquired about the observatory’s citizen science component, to which Andrew confirmed the existence of projects like the Rubin Comet Catchers and mentioned that the data will be accessible for public participation. Andrew also briefly mentioned the James Webb Space Telescope, emphasizing its ability to observe infrared wavelengths and its potential to provide new insights into the universe’s history.

Andrew explained how light travels at a finite speed, making observations of distant astronomical objects reflect events from the past, such as the 4-year-old light from the nearest star. He highlighted the James Webb Space Telescope’s ability to observe the early universe, revealing structures and black holes that formed much earlier than expected, prompting questions about their origins and the need for better theories and telescopes to understand these phenomena. David inquired about the feasibility of extrapolating current conditions from ancient observations, to which Andrew responded that while AI and data could help, more observations and theoretical understanding are needed to accurately model the early universe’s evolution.

The group discussed historical measurements of the speed of light, with Marshall sharing how Galileo used Jupiter’s moons to make one of the first estimates. David mentioned a story about an Old West cowboy who invented a way to measure the speed of light and later became involved with the Naval Observatory, though the group couldn’t confirm the details. The conversation concluded with David asking if there was any citizen science opportunity related to the James Webb Telescope, though no answer was provided.

Andrew discussed citizen science projects, particularly Zooniverse and NASA’s citizen science page, where individuals can contribute to astronomical discoveries. He highlighted the significant increase in the number of known planets around other stars since 1995, from zero to over 6,000, emphasizing the role of citizen science in these discoveries. Andrew also touched on the search for extraterrestrial intelligence (SETI), expressing optimism about the possibility of discovering advanced life forms elsewhere in the universe, and mentioned an upcoming international symposium on the search for technosignatures.

Our guest explained that the speed of light does not change near a black hole, but rather space and time are affected by gravity. He described how time would slow down for someone approaching a black hole, causing them to experience a faster-paced universe upon their return. Andrew mentioned a Harvard experiment that confirmed Einstein’s predictions about time’s relationship with gravity. John Hunt noted that the phenomenon was depicted in the movie Interstellar, though the film’s space dynamics were inaccurate.

We continued talking about black holes and their properties, with Andrew explaining that black holes themselves are invisible but can be detected through their accretion disks - swirling whirlpools of material being pulled into the black hole. Marshall clarified his earlier comment about varying gravity in accretion disks, explaining that while black hole gravity remains constant, individual particles in the disk experience varying gravitational effects due to the complex arrangement of mass. The conversation concluded with a discussion about the differences between astronomy, astrophysics, and cosmology, with Andrew explaining that while all astronomers are essentially astrophysicists, cosmology is a specialized branch that studies the universe as a whole rather than individual celestial objects.

Andrew and David discussed the nature of astronomy and astrophysics degrees, emphasizing that the terms are often interchangeable and that a strong background in physics and mathematics is crucial for a career in astronomy. They also explored the concept of SETI (searching for extraterrestrial intelligence) versus MEDI (messaging extraterrestrial intelligence), with Andrew expressing concerns about sending out loud messages to potential alien civilizations due to humanity’s relative youth and lack of understanding of other civilizations in the galaxy. The discussion concluded with the question of who should make the decision to reveal humanity’s presence to extraterrestrial civilizations, highlighting the need for a global consensus on such an important issue.

Andrew and David discussed the potential dangers and ethical considerations of broadcasting messages to extraterrestrial civilizations, emphasizing the need for caution and decision-making processes. Andrew shared insights from his work with the Committee for Skeptical Inquiry, highlighting efforts to debunk pseudoscience and paranormal claims, and explained the role of faith in personal belief systems. He also promoted the OpenStax project, which provides free online textbooks for introductory college courses, including astronomy. The conversation concluded with updates on the Silicon Valley Astronomy Lectures, which are now available as podcasts and on YouTube, and a brief discussion about upcoming celestial events and potential guests for future shows.

Special thanks to our sponsors:American Institute of Aeronautics and Astronautics, Helix Space in Luxembourg, Celestis Memorial Spaceflights, Astrox Corporation, Dr. Haym Benaroya of Rutgers University, The Space Settlement Progress Blog by John Jossy, The Atlantis Project, and Artless Entertainment

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