'The Big Bang Theory': Bob Newhart Makes Another Appearance to Inspire Sheldon

The Big Bang Theory featured comedy legend Bob Newhart for one more time during this week's [...]

The Big Bang Theory featured comedy legend Bob Newhart for one more time during this week's episode, "The Planetarium Collision."

In the episode, Sheldon (Jim Parsons) and Amy (Mayim Biyalik) had their first big fight as a married couple after Sheldon got in the way of Amy's research so she had to work with him. Although Professor Proton/Arthur Jeffires is deceased, Sheldon still comes to him for advice and sees him as a Jedi Force ghost.

"I'm kind of Obi-Wan," Newhart said in a preview clip, referring to the Star Wars character. "Whenever Jim has a problem, then he comes to me. He and Amy had a fight and now he came to me and wanted my advice on how to handle their first fight."

In one scene, Professor Proton told Sheldon, "The first rule of marriage: never go to bed angry."

"That makes sense," Sheldon replied.

"Rule number two of marriage: If you don't recognize the shoes under your bed... they're not your shoes," Professor Proton said.

"Bob is just amazing as ever," Melissa Rauch, who plays Bernadette, said in the preview video. "I was just marveling at the table read. His timing is just unbelievable to watch."

This was Newhart's sixth appearance on the show. His character died in the season seven episode "The Proton Transmogrification," but he kept appearing to Sheldon to offer advice. He was previously in the the season 11 episode "The Proton Regeneration," where he helped Sheldon calm down after his enemy Wil Wheaton was cast as the new Professor Proton.

The Big Bang Theory is now in its 12th and final season, and the show has already touched on several major topics in the characters' lives. Last week's "The Tam Turbulance" finally explained why The Big Bang Theory never mentioned Tam, Sheldon's best friend from childhood and a character on Young Sheldon. We learned that Sheldon felt betrayed by Tam when he chose to pursue a girl instead of follow Sheldon after college.

Earlier this season, in "The Procreation Calculation," Raj (Kunal Nayyar) finally got engaged after allowing his father to set him up with Anu (Rati Gupta). While Raj liked Anu, he thought it was silly to get married after just a few minutes together. But Anu got down on one knee and proposed to him. His friends also thought this was a terrible decision at first, Penny (Kaley Cuoco) and Bernadette met Anu and they liked what they saw.

However, in "The Planetarium Collision," things were tense between Raj and Howard (Simon Helberg) while Raj was preparing to host a planetarium show.

New episodes of The Big Bang Theory air on Thursdays at 8 p.m. ET on CBS.

Photo credit: CBS