22 February

A puzzle about time. Is there a problem with the use of 'when' in this news story? (The supernova is pictured between the red arrows, if you're interested in that part of the story.) "On Sept. 20, 2016, Victor Buso, an amateur astronomer in Rosario, Argentina, was checking out the new camera on his telescope by taking pictures of a nearby spiral galaxy when a star within it went off in a supernova explosion."