The Gregorian telescope is a type of reflecting telescope invented by the astronomer James Gregory in the 17th century. It uses a concave primary mirror to gather light and a smaller secondary mirror to direct the light to an eyepiece. This design allows for a compact telescope with a longer focal length, making it suitable for observing distant celestial objects. One of the key features of the Gregorian telescope is its ability to produce an upright image, which is beneficial for certain types of observations. Although it has been largely replaced by other designs, such as the Newtonian telescope, it remains an important part of the history of astronomy.