grouchomarxist writes: Physicists at the University of Michigan claim that they have made the first detection of dark matter. 'Dark matter, whose composition is still a mystery, doesn't emit or absorb light, so astronomers can't see it directly with telescopes. They deduce that it exists based on how its gravity affects visible matter. Scientists estimate that dark matter makes up more than 80 percent of the universe. To "see" the dark matter component of the filament that connects the clusters Abell 222 and 223, Dietrich and his colleagues took advantage of a phenomenon called gravitational lensing. They were able to determine the extent to which the supercluster distorted galaxies, and with that information, they could plot the gravitational field and the mass of the Abell 222 and 223 clusters. "It looks like there's a bridge that shows that there is additional mass beyond what the clusters contain, the clusters alone cannot explain this additional mass," Dietrich said.' Article in nature is here. Link to Original Source
I've never been canoeing before, but I imagine there must be just a few
simple heuristics you have to remember...
Yes, don't fall out, and don't hit rocks.