Here's a catchy compilation of theme tunes from the late 70s and early 80s, featuring Shaft-esque guitars and stomping drum-beats. It's amazing how every science fiction TV show from a particular era features a similar-sounding opening theme tune. And the trends in theme music say something about the shows of the eras they belong to. Click through for a complete history of TV openings.

The Theremin Era (1950s-1960s). The emphasis is on weird noises and screechy howls. Sometimes, it's an actual electronic scream, as in the Doctor Who theme, or to some extent the Outer Limits theme. Sometimes, it's an actual human trying to sound like a theremin, like the Star Trek theme's crazy opera singer. Either way, the message is clear: This is some freaky shit right here.

The Disco Era (late 1970s-early 1980s). You can totally boogie down to the theme tunes of Amazing Spider-Man, Bionic Woman or Logan's Run the series. Some themes, like Buck Rogers, try to sound sort of "adventure-y" and bring up associations with John Williams' heroic theme tunes for Star Wars and Superman: The Movie. But mostly the message is: groovy times ahead!!! Put on some tight pants and boogie!

The Orchestra Era (1990s). The themes from the two Star Trek TNG spin-offs, Babylon 5, Andromeda, Seaquest and even Time Trax all feature heroic-sounding strings and soaring horns. There's a strong melodic hook, but it's not as toe-tapping as the themes from the 70s and early 80s. Message: Epic saga (with heartstring-yanking) ahead.

The Alt-Country Era (early 2000s). Okay, so this was just two shows: Firefly and Enterprise. But it still felt like a mini-trend, especially since these were half the SF shows on TV at the time. You had the twangy voice, the deep soul-searching lyrics and the guitar anti-heroing. "Take my love, take my land, but you can't take my faith of the heart." Message: It's tough out here on the frontier.

The Weird Wailing Era (mid-2000s). All of a sudden, shows like the new Battlestar Galactica and Heroes featured a Middle Eastern-sounding person in distress, or just voices going "oooh" in the background. The new Doctor Who had a boppier version of the original theme, but whenever the Doctor acted mysterious, you'd hear a distinct "ooooh" sound in the background. In many ways, it's like a throwback to the theremin era. The message it sends: This is some freaky shit right here.