Cleomedes
Cleomedes explains the Moon's solar illumination
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Original prompt & settings (JSON) ↗His Moon worked something like a sponge: it absorbed sunlight, mixed with it, and then shone.
Nothing is dated to 190
No source identifies an event, lecture or publication by Cleomedes in the year 190. The entry can only stand for an approximate composition or teaching date.
His life dates are unknown. The University of California Press edition places the lectures around 200 CE, and modern proposals have ranged from the first to the fourth century CE.
Right source, different mechanism
In his surviving astronomical lectures, Cleomedes taught that the Moon acquires its illumination from the Sun, and that its changing phases follow from its changing position relative to the Sun and Earth.
He did not describe reflection from the lunar surface in the modern sense. His Stoic account held that the Moon absorbs or mixes with solar light and then produces its own illumination.
Two lectures inside a philosophy course
The teaching belonged to a pair of elementary astronomical lectures embedded in a broader Stoic philosophical program — two books, not a research publication.
Cleomedes did not originate the idea that moonlight comes from the Sun; forms of it had been proposed centuries earlier. He preserves and adapts the ideas of Posidonius, an earlier Stoic authority rather than his personal mentor.
Sources
Researched 23 Aug 2026 6 sources not yet audited Date disputed
How this was checked
Researched from the web into a fact sheet and rewritten from that sheet. This article has not yet had an independent model audit. How the pipeline works →
Date disputed. Sources disagree; the research places it at ~0200.
What the sources leave uncertain
- Cleomedes’ life dates are unknown, and his work contains no securely datable publication notice.
- The University of California Press edition places the lectures around 200 CE, but scholarly proposals have ranged from the first to the fourth century CE.
- The assigned year 190 is therefore only a modern approximation and should not be displayed as a verified annual event.
- The title’s word ‘reflects’ is scientifically familiar but historically imprecise for Cleomedes’ absorption-and-mixture model.
Checked against
- Cleomedes’ Lectures on Astronomy, University of California Press
- Cleomedes’ Lectures on Astronomy, Chapter Five
- Bryn Mawr Classical Review of Cleomedes’ Lectures on Astronomy
- Commentary discussing Cleomedes’ model of lunar illumination
- The Material Culture of Greek Astronomy
- Cleomedes on the celestial illusion and size-distance invariance