• Question: How many atoms does it take for something to be visible to the naked human eye?

    Asked by Science Lover to Jim, Scott on 18 Mar 2016.
    • Photo: Jim Barrett

      Jim Barrett answered on 18 Mar 2016:

      Well, the human eye can see visible light, which is around 900 nanometres, so if I had to guess (although I’m not sure) you would need about 900 nanometres of atoms (in a blob), which is quite a few. Maybe like 10 million million? (your brain probably wouldn’t know what it was looking at)

    • Photo: Scott Lawrie

      Scott Lawrie answered on 18 Mar 2016:

      The eye is remarkably sensitive. The minimum number of photons (particles of light) that the eye can detect in a short flash is around 100. This is equivalent to about a trillionth of a Watt! Compare this to a 40 Watt light bulb and you’ll agree it’s a fantastically small amount of light!

      In terms of size, the smallest thing the eye can see is a few thousands of a millimeter across. Amazing!

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