Lyrics: where am i to go now that i've gone too far?

Questions

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)?

Physics - Waves 'break' when their height is how much more than the depth of the water?

Physics - What is the name given to elementary particles originating in the sun and other stars, that continuously rain down on the earth?