Misc: Under what circumstances did Lord Castlereagh wound George Canning in 1809?

Questions

One For The Trekkies - Who played Deanna Troi in 'Star Trek The Next Generation'?

Optics - What colour on black produces the most visible combination?

Orienteering - On maps, what is the technical name for the 'you are here' arrow?

Philosophy - The last line of which document is 'working men of all countries, unite!'?

Physics - At what angle above the horizon must the sun be to create a rainbow (in degrees)?