Scientists extract information from these patterns. The apparent brightness of a star is how bright it appears on earth. The ancient Greeks devised a system in which the stars in the sky were divided into groups. The brightest stars were in the first group, the next dimmer stars in the second group, the dimmest stars in the sixth group. This system has evolved into the system of stellar magnitudes were use today.
Brightest stars are first magnitude, followed by the dimmer second magnitude and so on.
The Greeks used their eyes to estimate the magnitudes of stars, later people used photographic film, now we use electronic detectors. The Hubble telescope, like most modern telescopes, makes its images using CCD's. Charge Coupled Devices. CCD's are also used in personal digital cameras and video cameras. These semiconductor devices have millions of picture elements, pixels arranged in a square.