http://en.wikipedia.org/wiki/General_relativity if you go to this link, and find "Physical description of the theory" not far from the top. the 5th paragraph starts 'More specifically, let us ask how..' i understand earth moves in spiral, and light moves in spiral too but with lower angle against horizontal, is this because of time decreasing due to lorentz factor? also it brings coordinates ct and says its increased by one light year. why introduce the light? also, it shows the angle earth takes on the spiral is C divided by orbital velocity. why C?? and why 2 speeds show an angle? sorry if it isnt explained very well.