Second is the SI base unit for the time. Official definition for a second per BIPM is
" The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom."
External Reference Links
- http://www.bipm.fr/en/si/si_brochure/chapter2/2-1/second.html
- http://physics.nist.gov/cuu/index.html
- http://en.wikipedia.org/wiki/Second