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"The Lunar Excitation" is the twenty-third episode and the final episode of the third season of the American sitcom The Big Bang Theory. This episode first aired on Monday, May 24, 2010.


The gang meets Penny's dim-witted new guy Zack while performing a laser experiment on the apartment building roof. Raj and Howard sign up Sheldon for online dating and find him a match: a real girl named Amy Farrah Fowler.

Extended Plot[]

The guys are up on the apartment roof performing a lunar ranging experiment. While Raj is using the telescope watching "The Good Wife" on someone's TV, Leonard thinks Penny would like to be up here to see what they are doing. Sheldon does admit that retro-reflector left by Neil Armstrong on the moon that they are using could qualify as a shiny object. Leonard goes to Penny's apartment and finds her with Zack, her dating|date, wonders how you can bounce stuff on the moon if there's no gravity up there. Zack wants to see it anyway. Zack designs the menus for the Cheesecake Factory. Upstairs Leonard tries to explain what's going on. Zack is afraid that when the laser hits the moon, the laser will blow it up. Sheldon tells everyone that Zack is a man for Penny. They fire the laser and get a return 2.5 seconds later and the guys are excited. Zack is not impressed. Leonard, “Don't you see what we've done? It's the only definitive proof that there are man-made objects on the moon place there by a species that only 60 years before had just invented the airplane.” Zack doesn't know what species Leonard is talking about. Now Sheldon thinks that Penny can do better. Penny and Zack depart with Penny having been embarrassed by Zack.


Penny's dim date watching the laser experiment.


You rat bastard!

Back in Apartment 4A, Howard suggests getting Leonard an online dating profile. He's had eight dates in the last month, twelve if you count the ones that just show up and leave. Sheldon asks for help with a heavy nitrogen tank down from the roof and Leonard ends up getting it himself. Raj suggests that they create an online dating profile for Sheldon like when Frankenstein's monster was lonely and they found him a wife. Howard corrected him; they did not find him a wife, they made him a wife. Raj suggests we keep that in mind for plan B.

Very early in the morning Leonard answers a banging on their door and it's a drunken Penny. She claims that Leonard had ruined her because she would have never have known that Zack was so stupid. He has destroyed her ability to tolerate idiots; therefore, the two of them are going to have sex which Leonard is fine with. Sheldon wakes up and is advised to break out the noise canceling headphones because they are going to get loud. Sheldon is disturbed that he is going to have to put up with the two of them again.

In the morning, Penny tries to sneak out, but disturbs Sheldon. He comments on her use of the phrase 'yee-haw' used during their carnal activities which thrills Penny as she leaves. Leonard wonders why Penny left without saying good-bye. Sheldon replies that Penny went back to her apartment to shower and vomit.

Leonard and Penny run into each other as she heads off to work. Leonard wants to go dinner and a movie, and Penny tells him last night was a mistake since she was angry and drunk. She wants him to forget it, but the whole rodeo thing is kind of implanted on his brain. Leonard accuses her of using him for sex and then learns that Mrs. Gunderson in 3A also heard them last night. (Yee-haw!)

Later, Raj has the proof that aliens walk among us since the dating site matched Sheldon with a woman. She is an actual woman with breasts and everything named Amy Farrah Fowler. Howard assures Raj the breasts doesn't always indicate a woman - he would show him some picture of his uncle's chest sometime. They reply to her with an email.

What Leonard thinks he has learned is that it's okay for people to return to former lovers and have causal sex with them. He goes to see Leslie Winkle who talks awkwardly with him including asking him whether “Blondie” had dumped him. Since it's OK to have recreational sex with people they've known before, he asks her. She says she'll think about it...and slams the door in his face.

Now Sheldon's perfect match wants to meet him. Howard and Raj decide to resort to the truth. They got Sheldon a date with his perfect match for the next day. Of course, Sheldon thinks the algorithms used to determine the compatibility of potential mates are pure hokum, but that is literally the answer they gave when the questionnaire asked what they thought of online dating sites. Even Spock had a date once every seven years. Sheldon correct them that he was experiencing pon farr, burning lust. Raj also hid the dirty sock that freaked Sheldon out on the roof somewhere in the apartment and refuses to take it out unless Sheldon meets Amy Farrah Fowler. Sheldon curses him, but agrees to do it.

Leonard comes back to the apartment drunk and goes to Penny's. He tells her that he was a perfectly happy geeky, lonely little guy, and she ruined it for him! He wants to have sex and it's not going to mean a thing. Penny tells him that he's out of his mind and throws him out. Leonard feels that he experiencing a double-standard.


Amy likes what she sees.

At a coffee shop, Sheldon tells them that their experiment is going to fail. (Neener-neener.) Amy Farrah Fowler shows up because she agreed to date once a year just to keep her mother off her back. She shares Sheldon's aversion to soiled hosiery and they connect over agreements they had made with their mothers. And all forms of physical contact up to and including coitus are off the table. Sheldon offers to buy her a beverage as they step up to the counter. Amy turns away and has a very satisfied expression on her face. Howard wonders, “Good God, what have we done?”



  • "As we end season three I thought the writers addressed the Penny-Leonard relationship in a nice way. For both the relationship has changed their perspective on their future partners. The point was made in a somewhat subtle way that they both now have higher standards thanks to the other...It's a familiar refrain but the writers still don't handle Penny and Leonard's situation with the skill they need to...A passable end to a really decent season from The Big Bang Theory . "Really decent" might sound like damning with faint praise but the show has got better this season. The writing went to new places and did on occasion flesh out its characters." - The TV Critic's Review
  • IMDb user reviews


  • Title Reference: The guys bouncing a laser off the reflector left on the moon by the crew of Apollo 11 and the excitement about completing the experiment.
  • Chuck Lorre's vanity card [1]
  • This episode was watched by 15.02 million people with a rating of 5.3 (adults 18-49).
  • This episode aired in Canada on May 24, 2010 with 2.329 million viewers and a weekly ranking of #8.
  • Episode transcript [2]

Costume Notes[]

Penrose Triangles Phillips/Stouble Test Star Power  




Firing the laser at the moon.

  • First appearances of Amy Farrah Fowler and Zack Johnson.
  • Mrs. Gunderson, who had been previously mentioned as the downstairs neighbor, makes an appearance.
  • Another appearance of the fifth floor of the building after seeing Alica's apartment 5A in "The Hook-up Reverberation".
  • First appearance of the roof of the guys' and Penny's building. It makes 3 subsequent appearances in "The Countdown Reflection" (S5E24), "The Prom Equivalency" (S8E8) and "The Comet Polarization".
  • One of a few season finales that does not end with a cliffhanger left to be resolved at the start of the next season, unless you count not knowing what will happen between Sheldon and Amy. Others include:
  • While not marrying on the same day, Sheldon and Amy meet in the finale episode of this season and marry in the finale of the season arriving eight years later.
  • The gang's lunar laser ranging experiment utilizes a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser, as is referenced on the whiteboard near Sheldon and Leonard's apartment door. Nd:YAG crystal lasers typically emit light with a wavelength of 1064 nm, in the infrared; however, the high-intensity pulses may be efficiently frequency doubled to generate green laser light at 532 nm. Both of these wavelengths are written on the lower half of the whiteboard, along with the chemical formula Y3Al5O12 for the yttrium aluminum garnet crystal structure and the atomic transition 4F3/24I11/2 in the neodymium ion, after being "pumped" into excitation. The upper half of the whiteboard calculates the round-trip travel time of a light pulse bouncing off lunar retro-reflectors as 2.56 seconds, based on the ratio of the semi-major axis of the lunar orbit to the speed of light.
  • Raj loves "The Good Wife", in which Christine Baranski, who also plays Leonard's mother, is enlisted in the main cast.
  • Sheldon refers to Albert Einstein establishing the theoretic foundation for the laser in his paper Zur Quantentheorie der Strahlung (On the Quantum Theory of Radiation) in 1917.
  • Sheldon mentions that he only drinks hot chocolate in months with an "r" in them. Thus, his quirk doesn't allow him to drink hot chocolate in the consecutive months of May, June, July, and August, which spans the summer season in the Northern Hemisphere. It makes perfect sense; in California, it would be much too hot in the summer months to drink hot chocolate.
  • Raj states that Sheldon's answer for the question "How do you feel about online dating services?" would be "hokum", which was exactly the same word that Sheldon himself used to described on-line dating algorithms in "The Barbarian Sublimation" (S2E3). They know their friend.
  • Last appearance of a main character (Leslie Winkle) and the first appearance of another main character (Amy) though Leslie does make a guest appearance in episode 200.
    • This episode is Amy Farrah Fowler's first appearance in this series; interestingly, her full name is revealed even before her first appearance.
    • Sara Gilbert's last appearance as Leslie Winkle for near 6 years. Interestingly enough, Leonard's last line in her scene- "She's not coming back," refers to both Leslie not taking him back and not returning to the series. Made her only appearance in Feb. 2016 for a guest shot on the 200th episode.
  • Just like Howard and Bernadette when they first meet, Sheldon and Amy find a connection when talking about their mothers.
  • The beverage Amy asks for is tepid water; water that is moderately warm. Also tepid can mean lacking in emotional warmth which also describes their personalities at this point in their relationship. Amy does warm up after befriending Penny and Bernadette.
  • This is the second time Penny calls Leonard a "Rat Bastard." The first time was in "The Pancake Batter Anomaly" which was in episode 11 on Season 1 of The Big Bang Theory.
  • At this point, no profession has yet been identified for Sheldon's date Amy Farrah Fowler.
  • Penny very early on mentions that she has wild sex after a breakup and had it with Leonard.


(Howard. Sheldon and Raj are at the café waiting to meet Amy Farrah Fowler.)
Amy Farrah Fowler: Excuse me, I'm Amy Farrah Fowler, you're Sheldon Cooper.
Sheldon: Hello, Amy Farrah Fowler. I'm sorry to inform you that you have been taken in by unsupportable mathematics designed to prey on the gullible and the lonely. Additionally, I am being blackmailed with a hidden dirty sock.
Amy: If that was slang, I'm unfamiliar with it. If it was literal, I share your aversion to soiled hosiery. In any case, I am here because my mother and I have agreed that I will date at least once a year.
Sheldon: Interesting. My mother and I have the same agreement about church.
Amy: I don't object to the concept of a deity, but I am baffled by the notion of one who takes attendance.
Sheldon: Well then, you might want to avoid East Texas.
Amy: Noted. Now before this goes any further, you should know, that all forms of physical contact, up to, and including coitus, are off the table.
Sheldon: May I buy you a beverage?
Amy: Tepid water, please.
(Both go to the counter, while Raj and Howard just stare.)
Howard: Good God, what have we done?

(Sheldon notices Penny taking Leonard to his bedroom)

Sheldon: What's going on?
Penny: Get your noise-cancelling headphones, 'cause it's gonna get loud.
Sheldon: Oh, not this again!

[The next morning, Leonard has mistaken Penny's loud midnight impromtu coitus session as her wanting to get back together, though the talk down the stairwell has established Penny only did it because she was mad at Zack and Leonard is none too happy about having been used like this]

Penny: Look, I said I'm sorry, can you please just let it go?
Leonard: How am I supposed to let it go?! You used me for sex!! [he turns around and sees his downstairs neighbor Ms. Gunderson now standing outside her apartment, smiling cheekily at him] Good morning, Ms. Gunderson.
Ms. Gunderson: Morning Leonard, or should I say "Yeehaw"? [winks at him, Leonard walks back to his apartment, slightly embarrassed]

Sheldon: That's not afternoon. That's prevening.

Penny: Damn you, you rat bastard! In the olden days, I never would have known he was that stupid!

Zack: Is that the laser? It's bitchin'.
Sheldon: Yes. In 1917, when Albert Einstein established the theoretic foundation for the laser in his paper Zur Quantentheorie der Strahlung, his fondest hope was that the resultant device be "bitchin'".
Zack: Well, mission accomplished.

Leonard: (Explaining the significance of the experiment to Zack) Think about what this represents. The fact that we can do this is the only way of definitively proving that there are man-made objects on the moon, put there by a member of a species that only 60 years before had just invented the airplane.
Zack: (Astonishingly) What species is that?

Zack: One question. How can you be sure it won't blow up?
Leonard: The laser?
Zack: The moon.

Leonard: Okay, we’ve got power to the laser.
Sheldon: I should’ve brought an umbrella.
Leonard: What for? It’s not going to rain.
Sheldon: I know that, but with skin as fair as mine, moon burn is a real possibility.
Howard: That’s a bazinga, right?
Sheldon: One of my best, don’t you think?