Now see if you can find some information about the relative gravitational effects of massive things like continents and ice sheets and oceans. (blog.hotwhopper.com)
Dark matter sounds like some physicist's tall tale: There's this invisible matter, see, and it has this powerful gravitational effect on galaxies. (discovermagazine.com)
The presence of dark matter, which physicists estimate accounts for 23 percent of the universe's mass, explains gravitational effects observed throughout space. (kavlifoundation.org)