Several unreliable sources list January 19 as Quark Day.
Quarks are sub-atomic particles that make up protons, neutrons, and electrons. No one has seen a quark at any time. Their existence was proposed by physicists Murry Gell-Mann and George Zweig in 1964 to explain some electron scattering phenomenon in the Stanford Linear Accelerator Center. For this discovery they jointly won the 1969 Nobel Prize in Physics.