You won’t be able to hear it without a computer or a phone and you probably won’t be able to see it, either — at least not without binoculars — but hey, it’s a big deal when two Seattle icons have a meeting in the middle of the sky, right? That’s what’s happening today when seminal grunge band Mudhoney plays a live broadcast from the roof of the Space Needle to kick off Sub Pop Records’ Silver Jubilee. Video and audio streams of Mudhoney’s rooftop show will be broadcast live at 5 p.m. by radio station KEXP 90.3 FM. Sub Pop is the label that launched Nirvana and put Seattle on the pop-music map in the early ’90s. Five years ago, for its 20th anniversary, the outfit flew a flag and had its name painted on top of the Needle, but sending a band up there is a new idea. “This is the first time in our history that a band has played live from the roof,” said Space Needle public-relations manager Sean Marshall. When people imagine the top of the Needle, said Marshall, they think of harnesses and such, but, in fact, the musicians won’t need any special equipment — except their instruments. “There’s actually a platform up there,” Marshall explained. “Access is internal, on a stationary, built-in ladder.” The area where the band plays is flat, too, perched on top of the more familiar sloping disc you normally see. Notices of the Mudhoney performance have been circulating for days, but details of this unusual celebration have only recently been made public.