After Years by Ted Kooser.

Today, from a distance, I saw you

walking away, and without a sound
the glittering face of a glacier
slid into the sea. An ancient oak
fell in the Cumberlands, holding only
a handful of leaves, and an old woman
scattering corn to her chickens looked up
for an instant. At the other side
of the galaxy, a star thirty-five times
the size of our own sun exploded

and vanished, leaving a small green spot
on the astronomer's retina
as he stood on the great open dome
of my heart with no one to tell.