Word of the Day

Near the old Melbourne Observatory there is a stone obelisk which was erected in 1885.

Carved into the stone surround are the words "telescope collimating marker". Collimating? That was a new word for me. But the internet tells me that it is the process of aligning the optical elements of the telescope to get the best image. Who knew? Here's a page all about how to do it: Collimating your telescope.