Credit: CBS/WB

"The Donation Oscillation" -- Pictured: Marissa (Lindsey Kraft), Zack (Brian Thomas Smith), Penny (Kaley Cuoco) and Leonard Hofstadter (Johnny Galecki). Penny tries to seduce an abstaining Leonard to ruin his "donation" for her ex-boyfriend, Zack (Brian Thomas Smith), and his wife, Marissa (Lindsey Kraft). Also, Wolowitz, Bernadette, Anu (Rati Gupta) and Koothrappali turn Koothrappali's canceled bachelor party into a couple's trip aboard the "vomit comet," on THE BIG BANG THEORY, Thursday, Feb. 7 (8:00-8:31 PM, ET/PT) on the CBS Television Network. Keith Carradine returns as Penny's father, Wyatt. Photo: Michael Yarish/Warner Bros. Entertainment Inc. © 2019 WBEI. All rights reserved.

"The Meteorite Manifestation" -- Pictured: Sheldon Cooper (Jim Parsons), Rajesh Koothrappali (Kunal Nayyar), Howard Wolowitz (Simon Helberg) and Leonard Hofstadter (Johnny Galecki). Sheldon is thrilled to help Bernadette and Wolowitz navigate bureaucratic paperwork, until he discovers they are breaking the law. Also, Leonard is disappointed when his friends exclude him from a scientific project, on THE BIG BANG THEORY, Thursday, Jan. 31 (8:00-8:31 PM, ET/PT) on the CBS Television Network. Andy Daly guest stars as Nathan. Photo: Sonja Flemming/CBS ©2019 CBS Broadcasting, Inc. All Rights Reserved

"The Confirmation Polarization" -- Pictured: Dr. Campbell (Kal Penn), Sheldon Cooper (Jim Parsons) and Pemberton (Sean Astin). When Sheldon and Amy's super asymmetry theory is proven by two physicists, Dr. Pemberton (Sean Astin) and Dr. Campbell (Kal Penn) from Chicago, they're thrilled, until they try to kick Amy off the Nobel nomination. Also, Bernadette has a big success at work and Penny's going to be a part of it -- whether she wants to or not -- on THE BIG BANG THEORY, Thursday, Jan. 17 (8:00-8:31 PM, ET/PT) on the CBS Television Network. Photo: Michael Yarish/Warner Bros. Entertainment Inc. © 2018 WBEI. All rights reserved.

"The Propagation Proposition" -- Pictured: Anu (Rait Gupta) and Rajesh Koothrappali (Kunal Nayyar). Penny's ex-boyfriend, Zack (Brian Thomas Smith), and his wife want a baby, but when Zack is infertile, they ask Leonard for help. Also, Koothrappali attempts to mend things with his ex-fiancée, Anu (Rait Gupta), on THE BIG BANG THEORY, Thursday, Jan. 10 (8:00-8:31 PM, ET/PT) on the CBS Television Network. Photo: Michael Yarish/Warner Bros. Entertainment Inc. © 2018 WBEI. All rights reserved.

"The Paintball Scattering" - Pictured: Amy Farrah Fowler (Mayim Bialik), Sheldon Cooper (Jim Parsons), Leonard Hofstadter (Johnny Galecki) and Penny (Kaley Cuoco). Penny and Leonard organize a paintball game that results in mayhem when Sheldon is jealous of Amy. Also, Koothrappali catches Anu with her ex-boyfriend and Stuart doesn't want to move in with Denise, on THE BIG BANG THEORY, Thursday, Jan. 3 (8:00-8:31 PM, ET/PT) on the CBS Television Network. Photo: Michael Yarish/Warner Bros. Entertainment Inc. © 2018 WBEI. All rights reserved.

"The VCR Illumination" -- Pictured: Amy Farrah Fowler (Mayim Bialik) and Sheldon Cooper (Jim Parsons). Sheldon and Amy are still down about their theory being disproven, but a VHS tape from Sheldon's past inspires him not to give up. Also, Bernadette turns into a pageant mom when she tries to help Wolowitz ace his Magic Castle audition, on THE BIG BANG THEORY, Thursday, Dec. 6 (8:00-8:31 PM, ET/PT) on the CBS Television Network. Photo: Bill Inoshita/CBS ©2018 CBS Broadcasting, Inc. All Rights Reserved.

"The Citation Negation" - Pictured: Amy Farrah Fowler (Mayim Bialik) and Sheldon Cooper (Jim Parsons). Sheldon and Amy are devastated after learning from a Russian paper that Super-Asymmetry has already been discovered and disproven. Also, ultra-competitive Bernadette asks Stuart's girlfriend Denise (Lauren Lapkus) to teach her how to play the video game Fortnite, on THE BIG BANG THEORY, Thursday, Nov. 15 (8:00-8:31 PM, ET/PT) on the CBS Television Network. Photo: Sonja Flemming/CBS ©2018 CBS Broadcasting, Inc. All Rights Reserved.