Astrophysics, Cosmology & Relativity
4 terms
Length Contraction
Astrophysics, Cosmology & Relativity
Meters (Spatial Length)
The relativistic effect where an object's length in the direction of motion is measured shorter by a stationary observer than its proper length L₀.
L = L₀ / γ = L₀ √(1 - v²/c²)
Light Year
Astrophysics, Cosmology & Relativity
Light-Years (ly)
An astronomical unit of length equal to the distance light travels in a vacuum in one Julian year (365.25 days).
1 ly = c × 1 year ≈ 9.461 × 10¹⁵ m ≈ 63,241 AU
Local Group
Astrophysics, Cosmology & Relativity
Megaparsecs (Mpc)
The small galaxy cluster group comprising the Milky Way, Andromeda (M31), Triangulum (M33), and over 80 dwarf satellite galaxies.
Diameter ~ 3 Mpc (~10 million ly), Mass ~ 2 × 10¹² M_☉
Lorentz Factor
Astrophysics, Cosmology & Relativity
Dimensionless Factor (γ ≥ 1)
The fundamental relativistic factor by which time dilation, length contraction, and relativistic mass scale for objects moving at velocity v.
γ = 1 / √(1 - v²/c²) = 1 / √(1 - β²)