Aug 9, 2026 · 1h 1m
A silly solar spectacle reveals the stakes of planetary engineering
The Science of Putting Sunglasses on The Sun
A calculation about sunglasses becomes a clear warning about the scale, promise, and danger of deliberately altering sunlight reaching Earth.
- 1Covering the Sun for everyone on Earth would require a structure roughly 1.3 million kilometres wide.
- 2Space sunshades and mirrors could influence climate and energy systems, but their risks exceed the appeal of flashy fixes.
- 3Diffraction, radiation pressure, and orbital mechanics turn a cartoon image into a lesson in modern space engineering.
Don't miss
The hosts calculate that a global solar-sunglasses structure would need to be roughly 1.3 million kilometres wide.
The brief
Michael Stevens and Hannah Fry begin with a cartoon premise: making the Sun appear to wear sunglasses, then test what physics says the illusion would require.
Angular diameter makes a tiny filter plausible at arm’s length, but binocular vision changes the geometry; scaling the trick across London and then Earth makes it enormous.
Their global design would span roughly 1.3 million kilometres, while blocking sunlight would darken Earth, disrupt photosynthesis, and damage ecosystems.
More modest sunshades might offset a small fraction of warming, but lunar dust clouds and orbital mirrors expose the risks of treating planetary systems as engineering projects.
The physics keeps unfolding: sunlight carries momentum, and petal-edged starshades avoid the diffraction bright spot that a smooth disk would create.
Featuring
Michael David Stevens
Hannah Mary Fry
Parker Solar Probe
International Space Station
London
EarthListen to the full episode and explore every guest, topic, and moment on PodLume.