# Special Relativity - Which reference frame experiences which time?

An event is a physical thing that takes place in all reference frames. Each reference frame assigns time and space coordinates to each event.Note that this is true in physics generally and is not just in SR.You need to understand reference frames before can understand SR.Have you studied the Galilean transformation?If you don't already have a decent text on SR, I recommend reading "Special Relativity: An Introduction" by Benjamin Peirce. It's a very easy read that will give you a good foundation.Try this if you don't already have a decent text...An event is a physical thing that takes place in all reference frames. Each reference frame assigns time and space coordinates to eachf
What I meant was that since we describe everything on Earth as one object, Earth, then, since the Earth and the dwarf planet have the same reference frame and velocity, why can't we describe them as one single object.
In this problem, you can treat the Earth and the dwarf planet as points in space because they're very small compared to the relevant length scale. The Earth's radius, for example, is about 6400 km, which is much smaller than the distance Lisa travels, which will be on the order of an astronomical unit, which is approximately 150,000,000 km.