Twilight, the link between day and night.

There are many kinds of Twilight at the end of each day.

There is civil twilight which ends when the sun is a few degrees below the horizon.

There is religious twilight which ends when you can no longer distinguish
a black thread from a white thread held in the palm of your hand.

There is nautical twilight which ends when you can no longer distinguish
the sea from the sky.

And then there is lawn mowing twilight.
According to Dr. Barbara, lawn mowing twilight
ends when you can no longer distinguish between
the orange tabby cat and the tall grass you are mowing.