How many atoms does it take to become visible to the naked eye?

Question: How many atoms does it take to become visible to the naked eye?
- Keywords:
  atom,
  eye,
  vision
Asked by Liv to Rebecca on 21 Jun 2015.
- Rebecca Jones answered on 21 Jun 2015:
  
  This is a great question! Humans can see objects 0.4mm wide which is roughly the width of a human hair. Atoms however can vary in size from 0.1-0.5nm (nanometres) across so it would take an element of about 100,000 atoms in width for us to see it with the naked eye.
  
  If there’s about 100,000 atoms in the width of one piece of hair, imagine how many there are in objects around you!

Question: How many atoms does it take to become visible to the naked eye?