Ok, I have found a lot of information online about various effects that happen when you travel near the speed of light, like lets say 99.5% of it. I understand that the speed of light is constant for any observer, at any velocity. And I also understand some of the effects that happen to you, like time slowing down and distances becoming shorter to help preserve light at the constant C. But I cant find a direct answer to my question, and that is, well lets say for 99.5% the speed of light, a speed of 299792458 meters per second, how will we know when we reach that speed? If we accelerated to that speed with respect to our sun, that would be different than if we measured the speed with respect to another star, or any other object with a different velocity. As you approach the speed of light, your mass increases, well our velocity with respect to what would govern that? As we approach the speed of light that our relative velocity to all objects just gradually approach the same value, like the same way it is with light? I hope I am making my question clear, any insight would be appreciated.