This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
ReflectingTelescope . Largest disk of optical glass created in the United States as of The mold for this disk was specifically designed for this purpose and was at the same time carefully insulated annealing furnace provided with electrical heating elements for controlling the temperatures during cooling The glass was poured at