A star diagonal is an accessory used in telescopes to angle the eyepiece for comfortable viewing, especially when observing objects high in the sky. It contains a prism or mirror that reflects light at a 90-degree angle, allowing observers to view celestial objects without straining their necks or contorting their bodies. While not essential, a star diagonal improves viewing ergonomics and is recommended for prolonged observing sessions, particularly with refractor and catadioptric telescopes.
Come for the Scenery, Stay for the Stars