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What Does it Mean When We Say That Something is Invisible to the Naked Eye?

-- JOSEPH CARDONA | March 23, 2020

Question:

When we say that a celestial body, is invisible to the human eye, is it because there is no light from the object that we can perceive on earth, or is it because even if there were light from the object (and therefore, it could be visible) we still would be unable to detected see it.

-- JOSEPH CARDONA

Answer:

When we say that a celestial object is “invisible to the naked eye”, what we mean is that the object is not bright enough to be detected by the visible light receiving system that is the human eye. This does not mean that the object is not giving out any visible light, though. Any light that this “invisible” object is radiating is just too weak for our human eye’s to detect.

-- Jeff Mangum

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