Rayleigh criterion

The Rayleigh criterion is a principle used in optics to determine the limit of resolution for images created by lenses or mirrors. Essentially, it explains how finely we can distinguish two closely spaced points, like stars in the night sky. According to this criterion, two points are resolved if their angular separation is larger than a specific minimum angle, which depends on the wavelength of light and the aperture size of the observing instrument. In simple terms, the larger the telescope’s lens or mirror, the better it can differentiate between two nearby light sources.