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 . inch disk after an inch core resting on the surface of the disk has been cut out of the center National Institute of Standards and Technology National Institute of Standards and Technology PDUSGovNIST PDUSGov National Bureau of Standards National Institute of Standards and Technology Reflecting telescopes Telescope