THEATER: Under the Radar, arguably New York’s most exciting theater festival, begins today at The Public Theater and a few other odd locations like the Whitehall Ferry terminal. (There are also a few shows at the Classic Theatre of Harlem, P.S. 122 and The Kitchen.) One of the most buzzed about site-specific shows is Etiquette by the London company Rotozaza. It was a surprise hit at last year’s Edinburgh Festival; here the experience takes place at the East Village Ukrainian restaurant Veselka and involves only two actors: you and a friend (or stranger). It’s described as “a private theatrical experience for two people in a public space; the participants take a seat across from each other at a small table (the stage), put on headphones and follow a recorded script, complete with stage directions taking them through a half-hour play, in which they are both performers and audience.” And after the show, you can get pirogies with the cast! – John Del Signore

Every Half Hour from 12pm to 11:30pm // Veselka Restaurant [144 2nd Ave] // Tickets cost $10

MUSIC: Sia (pictured) is currently playing at a Starbucks in Astor Place, but after that she's got a full day ahead of her, leaving no corporate logo unturned. Next up is the Apple Store in SoHo where she'll croon to the customers at 4pm. Then it's over to Virgin Megastore for an end of day performance. After rocking the retailers with her acoustic sets, she'll reboard her pink tour bus (seriously) with plenty of Frappacinnos and iPhones to show for herself.

If you recall the emotionally draining ending to Six Feet Under, you know her most famous song, "Breathe Me," which scores the final scene. Watch it again here.

4pm, 6pm // Apple Store SoHo, Virgin Megastore Union Square // Free

SCIENCE: It's time for another meeting of the Secret Science Club! Astrophycisists and those who love them unite, Princetonite David Spergel will be on hand tonight to "delve into Dark Matter." But what's the science-fied cocktail of the evening?! Learn more about the people behind the night (and the usually amazingly named drinks) here.

8pm // Union Hall [702 Union St, Park Slope] // Free

MOVIE: Speaking of secrets, Claude Miller's film A Secret helps kick off the 17th annual New York Jewish Film Festival tonight. The drama takes place in postwar Paris as "a young boy discovers the unfortunate consequences of his parents’ mutual attraction during the Nazi occupation. Claude Miller portrays a family consumed with guilt, jealousy, fear and loss."

9pm (through January 24th) // Film Society Lincoln Center [70 Lincoln Center Plaza]