The proton aurora is invisible to the naked eye and has never been viewed from space.

BBC: Atmosphere Nasa

The samples revealed "no-see-um" gold, invisible to the naked eye but detectable via assay.

FORBES: Virtual Gold

Fungi, bacteria and viruses are largely invisible to the naked eye but not to the naked body.

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About 4, 000 boat owners are to be given the liquid - which is invisible to the naked eye - to paint their property.

BBC: Boat owners in Hampshire given anti-theft paint

It is a quiet, tacit, mandatory add-on for all FHA mortgage consumers, measured in basis points and virtually invisible to the naked eye.

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