Nice, @Sander Huisman ! Just added @Jeff Bryant suggestion and stacked the images:

dates = DateRange[{2016, 05, 09, 8}, {2016, 05, 09, 23}, "Hour"];
out = Mercury /@ dates;
Show[out, ImageSize -> 800, Background -> Black]

Very nice!

One minor improvement would be to use the following LightSource so that the Sun doesn't look like its being illuminated off to one side. Instead of "Natural", use:

Lighting -> {{"Directional", White, ImageScaled[{0, 0, 1}]}}

This also gives the "limb darkening" effect seen when observing the Sun through solar filters. The center of the Sun looks brighter than the edges.