Before the rise of Netflix, Hulu, and Roku sticks, consumers got their small screen entertainment through analog television. “Flipping the dial” meant cycling through a number of cable or over-the-air channels, hoping to catch something of interest. For video game fans, it might be making sure your set was on channel 3 (or 4) so your Nintendo appeared onscreen.

But one channel was usually absent—channel 37. Land on it, and you’d probably get nothing but static. Like a missing 13th floor in a building, this strange omission could be puzzling. (And then you’d find Matlock, or ALF, and you probably forgot about it.) But there was a legitimate reason no TVs could pick up a channel 37: The U.S. government said they couldn’t.

A story for Vice’s Motherboard by Ernie Smith explains it. For channel 37 to go over the air, it would have to transmit from the 610 MHz band. Unfortunately, that was also the frequency needed by the University of Illinois’s Vermilion River Observatory near Danville. It’s one of three frequencies, along with 410 MHz and 1.4 GHz, that are used extensively in radio astronomy.

Put in plain terms—if a channel 37 had been taking up the 610 MHz frequency within 600 miles of the observatory, it would have interfered with their mammoth 400-foot telescope. That’s a pretty big radius that envelops virtually all of the East Coast and major cities like Chicago, Detroit, St. Louis, and Washington, D.C.

A working channel 37 would have effectively blocked out one of three major “panes” of a metaphorical window into the universe—just so people could watch Gilligan's Island.

Broadcasters apparently didn’t care about scientific advancement and often lobbied to have channel 37 put to use. But science countered and garnered support from the Federal Communications Commission (FCC) beginning in 1960, shortly after UHF signals were being put into wide use. Attempts for a kind of compromise—allowing a station to take the band but limiting its programming hours—disgruntled scientists. The FCC agreed and prohibited a station from taking the channel 37 spot indefinitely.

Even though the Vermilion River Observatory closed in 1980, the moratorium is still in effect. Then again, you’d have to be receiving over-the-air signals on an analog television to care.

[h/t AV Club]