How is "Wirtanen" Pronounced?

In working with comets, it is common for different people to pronounce their names differently (as a result of language differences, etc.). While working with the Comet Hopper proposal, we wanted to know the proper pronunciation of comet Wirtanen.

We contacted Lick observatory, where Carl Wirtanen worked when he discovered the comet to find out how he pronounced his name. We received multiple replies from people who worked with him (and his wife Edie), and all of them gave the same pronunciation.

According to these results, the proper pronunciation is

WERE - tuh - nun