Mons Rümker is a peculiar structure situated in the southern part of Sinus Roris. It is an interesting volcanic complex consisting of dozen domes. Some of them can be easily seen with modest equipment. Of notice is a diamond-shaped, smooth depression on its eastern flank. The collection of pictures and drawings show the varying view of this complex as the sun rises over it until it is almost indistinguishable on the mare floor under high sun. The colongitude is indicated for every observation in the figure.