What’s the Meaning of the Sunrise/Sunset Widget Bar on My Watch Face?

If you have chosen the Sunrise/Sunset widget as one of the widgets to display on your watch face, you will see a bar that indicates the progress of the sun's height for the day.  The bar will reach the top of the range when the sun reaches it's peak for the day. As the sun begins to go down from the day's peak, the line will move back down until the sun sets for the day. See the images below that show this progress at different times throughout the day.