Telescopes have been an essential instrument in the history of astronomy. So much has been learned and will be learned through the use of them. Although, they all have the same general function, telescopes can come in many shapes, sizes, and types. The two main types of telescopes are the refractor and reflecting telescopes. In a refactor telescope, a piece of glass known as the objective lens gathers light and focuses it onto the eyepiece lens, which enlarges the image for our eye to see. Galileo used this type of telescope to see the moons of Jupiter and the phases of Venus. On the other hand, a reflector telescope has two mirrors rather than the refractor’s two lens. One curved mirror reflects the incoming light from a distant object onto a tiny, flat mirror which in turn reflects the light to the eyepiece. Isaac Newton is credited for inventing the reflecting telescope. Reflecting telescopes are the most popular telescopes used for research purposes.