LOS ANGELES (CBSLA.com) — The CBS hit sitcom “The Big Bang Theory” will air its 200th episode this week.

“This is what you always hope for when you get on a show,” said Kaley Cuoco, who plays the character Penny on the show now in its 9th season.

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A big celebration was held Saturday night to mark the milestone in downtown Los Angeles.

“You never think of getting to a place like this, you know. You’re just happy to get a show and then you’re happy it stays on the air and then you’re happy it still stays on the air,” said Jim Parsons, who plays Sheldon Cooper.

Co-creator Chuck Lorre attributes the show’s success to its oddball characters and also to it being funny.

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“These characters who would normally be alone and ostracized or estranged or out of the mainstream, they have each other and they’ve created their own family,” he said.

Behind-the-scenes photographs of the milestone episode, where the spotlight is on character Sheldon Cooper, offered a sneak peek.

“It’s the first time that the group is celebrating Sheldon’s birthday,” said Melissa Rauch, who portrays the character Bernadette on the show.  “As we’re celebrating 200, we’re also celebrating Sheldon’s birthday for the first time.”

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The episode is expected to air Thursday on CBS.