Light Echo
Everything that happens sends light and heat outward at the speed of light, and it never stops. The radiant energy of a moment four years gone has already passed the nearest star. Enter a date and watch how far that light has reached.
Inspired by an idea Neil deGrasse Tyson has described, that the light of a moment keeps moving outward long after we are gone. Distances are real, the date beyond the year is decorative.