Light gathering power is proportional to the telescope's lens or mirror surface area. Astronomers enjoy observing through large aperture telescopes because they may see faint, distant objects and detail of nearby objects. The distance light travels in one year, about 5.88 trillion miles or almost 800 times the diameter of our solar system. Local Group Our galactic neighborhood, including the Milky Way , Andromeda Galaxy, M33, and more than 25 smaller galaxies. A measure of the rate of energy flowing from a source, like a galaxy , star , or light bulb.
Luminosity is a measure of power divided into units called watts.
Given the luminosity of a star, an astronomer can calculate the distance to the star by measuring the star's brightness. Temperature and luminosity are related, but dependent on the mass and size of a star. A shorthand description of a star based on spectral line widths. Our Sun is a G2 V star. The Roman numeral V denotes the luminosity class, which is the main sequence , while G2 refers to a spectral class .