In music, when you say "Philadelphia," you might think of the soulful Sound of Philadelphia from the 1970s, or the lush strings of the orchestra.
 
But Philadelphia is also the mecca for space music fans. 

A much-loved concert series featuring this brand of synthesized music, The Gatherings, celebrates its 20th anniversary in West Philadelphia.

By day, St. Mary's Church is just like dozens surrounding the Penn campus -- stately and serene.

But on a Saturday night every couple of months, the sanctuary's soaring vault fills with symphonic sound.

A big ensemble?  No, just one or two musicians, commanding a bank of keyboards and laptops.

Born in the Cold War confines of West Berlin, groups like Tangerine Dream and Cluster used synthesizers to create this futuristic sound.  As children of World War Two, they wanted to break with Germany's past.

Series co-founder Chuck Van Zyl, who also hosts "Stars End," a space music program on WXPN, says the music has evolved from those origins.

"Back in the 70s the artists were really making a political statement. Whereas now, I think it's more like about sound and art and technology and spirituality," said Van Zyl.

British synthesist Ian Boddy, who plays Saturday night at The Gatherings, notes a technological change as well.

"I suppose what has changed is more the preponderance now of laptops, where people can use files and manipulate things in real time and then play the keyboards and synthesizers over the top of that," said Boddy.

Though you won't see space music at the top of any music charts, artists like Boddy attract a loyal audience.

"Yes, I've been playing for a long time, over 30 years now," he said.  "Releasing cassettes, then vinyl, and finally on CD, doing concerts, gradually building up a reputation so that finally about 10 years ago I was able to go fully professional as a composer."

Van Zyl says St. Mary's Church provides a perfect setting for these enveloping waves of sound. .

"Probably the most significant aspect is that these events are held inside of a church sanctuary," said Van Zyl.  "So when people come in, they're already in a reverential or introspective state of mind."

Along with WXPN's Stars End show, The Gatherings in its 20 years has built Philadelphia's global reputation as a space music mecca.

"It's really good that Philadelphia actually has an electronic music scene," said Boddy. "There's very few cities, in fact none I can think of which you would actually say it does have this kind of scene."

"We've had people coming in from Finland and all around the world the series is known to people," agreed Van Zyl. "For instance, there's a guy coming in this weekend to see Ian, all the way from Colorado. I guess he thought, this is the only time I'll get a chance to see a concert by Ian Boddy."

Boddy's concert on Saturday begins at 8 pm. in St. Mary's Church at 39th and Locust.