Formula: Length Contraction Length / Distance    Rest length    Relative velocity   

Formula: Length Contraction
Length contraction: distance of two planets from the reference frame of the resting earth
Length contraction: distance between two planets as seen by the spacecraft at rest

Length / Distance

Length of the body (e.g. a rod) measured by an observer moving relative to this body with velocity \( v \). But it can also simply be the spatial distance between two objects.

Rest length

Length at rest is the length of a body measured by an observer when the observer is in the body's rest frame. That is, from the observer's point of view, the body is not moving.

Relative velocity

Relative velocity between the observer and the body.

Speed of light

Speed of light is a physical constant and indicates how fast light travels in empty space (vacuum). It has the following exact value in vacuum: $$ c ~=~ 299 \, 792 \, 458 \, \frac{ \mathrm{m} }{ \mathrm{s} } $$

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