Why are some SF books called "space operas"?

I’ve heard the term applied a number of times. I always thought that Opera implied music. The dictionary definition seems to indicate that music is always an aspect. So what is the opera in space opera?

It’s by analogy with “soap operas”, the daytime melodramas originally aired on radio and now on TV, or “horse operas”, meaning Westerns.

It’s true that “Opera” usually means a drama with high classical music, but “opera” is the plural of “opus” = “work” (of art). Musical pieces are usually called “opus no. ____”. Remember the film “Mr. Holland’s Opus”? In principle, any work of art, no matter how high or low, are opera.
It’s still a disparaging term. SF fans use the term “space opera” to describe streotyped “Flash Gordon” stuff with half-clad damsels in distress, muscular and brainy heros, and spaceships that don’t respect the laws of physics. Star Wars is high-toned Space Opera.

To elaborate, the term “soap opera” was coined in the early days of radio to designate what is now referred to as “daytime dramas” – long-running serials involved primarly romantic ups and downs and aimed at women. Most of the shows in the early days were sponsored by soap companies (hence the “soap”). Also, their long, convoluted plots and overwrought emotions fit in with the then-popular conception of opera. Thus “soap opera.”

The term then moved to other genres – “horse opera” for westerns; “space opera” for pulp science fiction. A “space opera” is an adventure story set in space. Nowadays, the science is better than it was when Doc Smith (the king of space opera until Lucas came along, and Lucas owes a much greated debt to Smith than Joseph Campbell). It can be non-pejorative when referring to a story that stresses the adventure of the plan instead of the characterization.

Does space opera tend to be closer to fantasy rather than ‘modern science fiction’? Is Eric Idle’s The Road to Mars space opera?

I’m not familiar with Eric Idle’s piece, but in general my answer is “yes”. Space Opera tends to be much more likely to dispense with the laws of physics (and other sciences) in pursuit of a good adventure story.

And Reality Chuck is right about this referring to a particular type of story, even without a sense of disapprobation. But I still think it started off as a disparaging term. And, even if people look on Space Opera with nostalgia, and continue to write them, they don’t take as seriously as other SF.

Although Space Opera tended to be more common in “the old days”, there was still plenty of non-SO science fiction back then, too. “Space Opera” is not synonymous with “Old SF”.

And they’re still writing it, and making it into movies. I think I could make a good case that the movie Starship Troopers is Space Opera. I don’t think the book is.

According to the The Encyclopedia of Science Fiction, the term space opera indeed derived from soap operas and horse operas:

So definitely disparaging in the beginning, yes. Still used that way by many, too.

On the other hand, space opera in the romantic sense is loved by many. Even Gardner Dozois, editor of the literary Asimov’s sf magazine has said that he’d like to see more space opera submitted.