HET: The New Largest Optical Telescope . ... Credit Copyright: UT Austin , PSU , Stanford , GAUG , & LMUM Explanation: Most of our universe is too dim to see. To peer into our cosmos' unknown depths, astronomers must deploy new tools - and the classic new tool is a larger telescope. ... HET currently has the largest single mirror of any optical telescope -- 11 meters in diameter. ... HET 's huge size, on the other hand, allows it to see very dim objects and determine their spectrum. ...