GMT Mirror Undergoing Polishing (IMAGE) Carnegie Institution for Science Caption The GMT's first 8.4-meter (27 feet) primary mirror segment is undergoing polishing at the Steward Observatory Mirror Lab. Credit SOML/UArizona Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.