Extended light sources like planets scintillate less than point sources like stars

Evidence

The contrast between the light and dark areas in a scintillation pattern depends on how extended the source of light is. Planets are little disks rather than near-perfect points of light from the vastly more remote stars, and as a result they do not twinkle nearly so much as stars do, making stars and planets easy to distinguish in the night sky. The amount of scintillation has indeed been used to determine the diameter of distant sources of radio waves in the universe. — Eric J. Heller, Why You Hear What You Hear- An…, 2616

Categorization

• CANDY: The classic sky-watching fact: stars twinkle, planets don’t, and the reason is source size.
• XREF: Scintillation now connects auditory and optical perception — a core thread for the reader’s why-question.
• QUESTION: How does scintillation-based size measurement of radio sources work quantitatively? Worth chasing.