# Length, distance and Michelson–Morley experiment

There are 2 types of length contraction, the physical meaning of each is explained below with the help of the example shown in Figure 1. The Earth and the star are stationary and the spaceship mobile. The 2 types of length contraction are:
1) Object contraction: In the frame of the Earth the length of the moving spaceship appears shorter than its proper length.
2) Distance contraction: In the frame of the spaceship the distance from the star to the Earth appears shorter than in the frame of the Earth.

a) Measurement of distance by travel
Let us focus on Distance contraction and see why distance is shorter in the moving frame. Suppose that the spaceship coincides with the Earth at time zero and coincides with the star at the end of its travel. The spaceship moves at the velocity v in the frame of the Earth and the star moves at the velocity –v in the frame of the spaceship.

In the frame of the Earth time is tE at the end of the travel and the spaceship has traveled the distance v•tE which is the distance from the Earth to the star measured by the travel of the spaceship. This distance is denoted by DE and expressed by equation (1).

In the frame of the spaceship time is tS at the end of the travel and the star has traveled the distance v•tS which is the distance from the Earth to the star measured by the travel of the spaceship. This distance is denoted by DS and expressed by equation (2)…