A Newtonian telescope is a type of reflecting telescope designed by Sir Isaac Newton in the 17th century. It uses a curved primary mirror to collect light and reflect it to a focus point, where an eyepiece lens magnifies the image. This design allows for a compact structure and eliminates chromatic aberration, which is common in refracting telescopes. The telescope typically features a simple tube with a flat secondary mirror that directs the light to the side for viewing. Newtonian telescopes are popular among amateur astronomers due to their relatively low cost and ease of construction, making them accessible for stargazing and astrophotography.