Ask Ethan: How do space telescopes stay focused? (opens in new tab)

In the era of space telescopes, we’re now used to clear, sharp images where everything is focused pristinely: reaching the theoretical maximum that’s possible based on the wavelength of light that’s begin observed and the diameter of the telescope’s primary mirror. First with Hubble (once the flaw in its primary mirror was corrected) and later with space telescopes such as Spitzer, GALEX, Herschel, and now JWST, the lack of an atmosphere to contend with means that all we need to do is make ou...