The Sun's rays travel at the speed of light which are governed by the overall laws of physics, but not specifically by the nuclear reactions in the Sun (though they also obey the laws of physics). Scientists have figured out that light almost always travels at the same, very fast speed - 300,000,000 m/s. When you do the math, it works out that it takes around 8 minutes for the light to reach the Earth once it leaves the surface of the Sun. Travelling at that huge speed, you can imagine just how far away we are from the Sun!!