Spin (physics) discrete angular momenta despite having no orbital angular momentum. In some ways, spin is like a vector quantity; it has a definite magnitude, and it has a "direction" (but quantization makes this "direction" different from the direction of an ordinary vector). All elementary particles of a given kind have the same magnitude of spin angular momentum, which is indicated by assigning the particle a spin quantum number. The SI unit of spin is the (N·m·s) or (kg·m·s), just as with classical angular momentum. In practice, spin is given as a dimensionless spin quantum number by dividing the spin angular momentum
Magnitude (astronomy) from the Sun to the faintest object visible with the Hubble Space Telescope (HST): Under the Vega system for measuring the brightness of astronomical brightness, the star Vega is defined to have an apparent magnitude of zero as measured through all filters, although this is only an approximation e.g. its actual brightness has been measured to be 0.03 in the V (visual) band. The brightest star, Sirius, has a Vega magnitude of −1.46. or −1.5. However, Vega has been found to vary in brightness, and other standards are in common use. One such system is the AB magnitude system, in