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) which the reference is a source with a constant flux density per unit frequency. Another is the STMAG system, in which the reference source is instead defined to have constant flux density per unit wavelength. The human eye is easily fooled, and Hipparchus's scale has had problems. For example, the human eye is more sensitive to yellow and red light than to blue, and photographic film more to blue than to yellow/red, giving different values of visual magnitude and photographic magnitude. Apparent magnitude can also be affected by factors such as dust in the atmosphere or light cloud cover absorbing