The Big Bang Theory Season 7 premiere is only a month away. Fans could hardly wait to see what happens next in the series. A lot of changes are expected. Leonard and Penny will be seeing each other after months of playing it long distance. Sheldon and Penny help each other deal with missing Leonard. Raj celebrates his longterm post-selective mutism phase. Howard and Bernadette are celebrating their first wedding anniversary, as Amy pulls Sheldon closer than ever to being truly intimate with a woman.
TBBT fans are eagerly waiting for the gang's next chapter to unfold. Meantime, here's a look into some of the best science and film personalities who have appeared as themselves in TBBT. Some of them are a lot likely to be seen or heard about in The Big Bang Theory Season 7.
11. George Smoot. Sheldon Cooper and the gang goes to San Francisco to attend a conference in which Nobel Prize winner Dr Smoot is the keynote speaker. Sheldon proposes to Smoot that they work together in a study. The credit goes to Cooper-Smoot, says Sheldon.
10. Steve Wozniak. This Apple Computers co-founder appears in Season 4 and talks to "Shelbot," Sheldon's virtual presence device. (This first aired in September 2010, a year before Steve Jobs died.) They mock Jobs' turtlenecks. Shelly also says Woz is his 15th favorite tech personality, while Jobs comes six places below Woz.
9. Neil deGrasse Tyson. Dr Tyson, an astrophysicist like Rajesh Koothrappali, irks Sheldon Cooper for his role in Pluto's demotion.
8. Charlie Sheen. Raj is thrilled when People magazine named him as one of the "30 visionaries under 30 years to watch." He gets incredibly annoying, bragging to everyone about it. "Hey, buddy, I'm going to be in People magazine," Raj tells a stranger who's facing away from him. The guy, who happens to be Charlie, faces him and retorts, "Yeah, call me when you're on the cover."
7. George Takei. (Oh my!) Howard imagines asking him how he feels about being typecast to sci-fi roles. In this same imaginary conversation, Katee Sackhoff also appears as herself.
6. Mike Massimino. This real life NASA astronaut first appears in The Big Bang Theory Season 5 ahead of Howard Wolowitz' trip to space. "Mass" has then been seen a couple of times more.
5. Buzz Aldrin. In Season 6, the gang has to show Wolowitz he's being such a jerk for boasting of his NASA stint every minute. Raj shows Howie a video of Buzz Aldrin giving treats to kids on Halloween, while bragging that he's been to space and walked on the moon.
4. Stan Lee. On the day he makes an appearance at Stuart's comic book store, Sheldon has to win a Penny-related case in court. In the end, only Penny and Sheldon get screentime with the comic book icon.
3. Summer Glau. In TBBT Season 2, Howard comes up with a line to impress Summer. "It's hot in here; must be Summer," he says. Summer, who will soon star in The CW's Arrow, is the first woman Raj gets to talk to without the influence of alcohol - only Raj doesn't realize right away that he's drinking non-alcoholic beer.
2. Wil Wheaton. Sheldon Cooper is a huge fan of Wil, who played Wesley Crusher in the 1980s TV series, "Star Trek: The Next Generation." He tricks Sheldon in a card game and later causes Penny to realise she should break up with Leonard. Eventually, Sheldon and Wil become friends.
1. Stephen Hawking. Dr Hawking's spacetime genius often gets a mention on The Big Bang Theory - since the pilot episode. Shelly and Hawking eventually winds up playing Zynga's Words with Friends. Season 6 ends with Leonard leaving for a project with Stephen Hawking.
Check out the slideshow for some of the best guest still photos from The Big Bang Theory. The CBS sitcom returns in September for Season 7.
More TV Guide Features:
How I Met Your Mother Season 9 Spoilers, Favourite Guests; 5 of Best HIMYM Spin-off Ideas [PHOTOS]
'Crossfire' TV, Gideon Cross Casting: Henry Cavill vs Joe Manganiello for the Lead Role? [PHOTOS]
Amanda Seyfried or Megan Fox as Gideon Cross' Eva Trammel in TV's 'Crossfire' Series? [PHOTOS]