A solar telescope is a device that aids in the observation of objects on the sun. Solar telescopes are used to study flares and coronal mass ejections, as well as other phenomena such as prominence eruptions and prominences. Solar observatories usually use one or more solar telescopes to monitor conditions on the surface of the sun. A solar telescope can be any type of optical instrument used for viewing the Sun, but most often refers to a large-aperture refracting telescope with an objective lens between 50 cm (20 inches) and 150 cm (60 inches). The aperture size determines how much light it gathers from sunlight, which makes them useful for studying features too small or far away for safe viewing with smaller instruments.