The Truth Behind…: Using a mix of witness accounts, historical documents and modern research and testing, the new episode "UFOs" looks for the truth about unidentified flying objects (7 and 10 p.m. National Geographic).
The Office: Maura Tierney guest stars in this new episode as Robert's (James Spader) wife, whom he brings to the office in hopes of finding her a job. Rainn Wilson, Ed Helms, John Krasinski and Angela Kinsey also star (9 p.m. NBC).
Weed Wars: This new series goes inside the workings of the nation's largest medical cannabis dispensary, the Harborside Health Center in Oakland, which serves more than 94,000 patients (10 p.m. Discovery).
Santa Claus Is Comin' to Town: A lanky mailman (voiced by Fred Astaire) explains Santa's origins in this 1970 animated special (8 p.m. ABC).
Keep a Child Alive With Alicia Keys: Last year, as soccer stars and fans converged on South Africa for the first World Cup on that continent, five Americans accompanied Alicia Keys to two facilities funded by the Keep a Child Alive campaign, which provides medical care, shelter and support to children and families with HIV/AIDS (9 p.m. Showtime).
A Holiday Engagement: A woman hires a man to pose as her fiance when she returns home for the holidays in this 2011 romance (8 p.m. Hallmark).
One Lucky Elephant: Ten years in the making, this documentary follows circus producer David Balding as he struggles to find the perfect home for Flora, the orphaned baby African elephant he lovingly raised as a "daughter" and made the star of his circus (9 p.m. OWN).
Sex in an Epidemic: Filmmaker and activist Jean Carlomusto examines its impact of HIV/AIDS on society, politics and sexual practices over the years (10:05 p.m. Showtime).
Football: The Philadelphia Eagles visit the Seattle Seahawks (5 p.m. NFL).
Hockey: The Florida Panthers visit the Kings (7:30 p.m. FSN).