Sunset over the Ocean?

Sunset over the Ocean? No! The Milky Way!

Here is an image of the terminal velocity (the maximum velocity of rotation of the Milky Way), measured as a function of Galactic longitude in the fourth quadrant. It is made using a thresholding technique, that gives it banded appearance resembling a seascape when turned on its side.

ATCA and Parkes image in HI by N. McClure-Griffiths and the Southern Galactic Plane Survey team.