“Glee” has done so well mining comedy from musical performance, why shouldn’t a real musician appear on a sitcom? Singer/songwriter James Taylor guest stars on “Mr. Sunshine” (8:30 p.m., ABC). The recent subject of the PBS documentary “Troubadours” guest stars as Billy, one of Crystal’s (Allison Janney) six ex-husbands.

True to form, Taylor plays Billy as a singer, and he and Janney even share a duet, performing the Leon Russell song “A Song for You.”

A performer for more than 40 years, Taylor has made many television appearances, but usually as a musician and, naturally, playing himself. His credits as an actor are relatively slim, but he did have a memorable turn in the 1971 car-culture classic “Two-Lane Blacktop.” He has sung at the Oscars and sung for “The Simpsons,” and he appeared as himself once on “The West Wing,” which brings us back to Allison Janney, who most people know from that show.

• Like James Taylor, Iranian-born actress Shohreh Aghdashloo (“24”) has lent her voice on “The Simpsons.” And she guest stars on a repeat episode of “Law & Order: Special Victims Unit” (8 p.m., NBC) tonight. Strangely enough, 1970s comedian Robert Klein has never appeared on “The Simpsons,” but he does have a guest spot on another helping of “Law & Order: Special Victims Unit” (9 p.m., NBC), along with Colm Feore, a Canadian actor who has never appeared on “The Simpsons.”

Second only to that long-running cartoon about orange, four-fingered characters, “Law & Order: SVU” has probably emerged as the show with the most intriguing guest stars. This season, “SVU” cast Debra Messing (“Will & Grace”) as a crusading TV journalist, and most notably Jeremy Irons as a therapist and father with a troubled past. Of course, last season, “SVU” also cast comedian and reality star Kathy Griffin as a lesbian activist. Griffin also guest starred on last night’s “Glee.”

• Mary Lynn Rajskub (“24”), seen just last week on “Raising Hope,” guests stars as Mitchell’s old flame on “Modern Family” (8 p.m., ABC).

• The contestants sing to survive on a two-hour helping of “American Idol” (7 p.m., Fox). Last week, Ashton Jones became the first to be eliminated from the top 13. She looked the part and at times acted the part, but her singing was, well, kinda, sorta bad. Not that you would know it from the current judges. Sometimes I miss Simon Cowell reminding us that this is, after all, a singing competition.

Tonight’s other highlights

• Director Martin Scorsese interviews his parents about their early life in Sicily in the 1974 documentary “Italianamerican” (6 p.m., TCM).

• The Coen brothers (“True Grit”) introduced themselves to most viewers with their 1984 film-noir update “Blood Simple” (7 p.m., IFC).

• A mad bomber targets schools on “Criminal Minds: Suspect Behavior” (9 p.m., CBS).

• Hepatitis breaks out in a prison population on “Off the Map” (9 p.m., ABC).

• A bandit returns to his old hunting ground on “Justified” (9 p.m., FX).