If you’ve ever met me I might have told you about that time I helped clean a telescope mirror with “horse shampoo” (my boss’ words). Here it is with extra details and pictures!

Why clean a telescope mirror?

Before talking about how we cleaned a telescope mirror, you might be wondering why we would do this in the first place. Most telescopes stay in use for decades: The 8.2m Very Large Telescope at ESO, saw its first light in 1998 [1]; the Isaac Newton Telescope was inaugurated in 1967 [2]!