Katie Holmes, actress and Bride of Scientology, turns 31 today. Hard-charging hedge fund manager Dan Loeb is turning 48. Brad Pitt turns 46. Steven Spielberg is turning 63. Christina Aguilera is celebrating her 29th birthday today. Dan Klores, the publicist turned documentary filmmaker, is marking his 60th. The head of the American Federation of Teachers, Randi Weingarten, is 52. Memorial Sloan-Kettering president (and Nobel Prize winner) Harold Varmus is turning 70. Troubled rapper DMX is 39. Keith Richards of the Rolling Stones is 66. Ray Liotta is turning 55. Model agency owner Faith Kates is 52. And former Miss USA Tara Conner is turning 24 today. A bunch of weekend birthdays is below.

The Society of Memorial Sloan-Kettering Cancer Center hosted its second annual Spring Ball at the Plaza on Tuesday night. More than 350 people turned out for the NBC Universal-sponsored event, including NBC Universal president Jeff Zucker and his wife Caryn (left), Mort Zuckerman, Robert De Niro and Grace Hightower, Julia and David Koch, Tory Burch and Lyor Cohen, Hilary Geary and Wilbur Ross, Jonathan and Somers White Farkas, Shoshanna Lonstein Gruss, Peter and Jamee Gregory, Ginny and Tiki Barber, Sherman and Chris Meloni, Frank and Kathie Lee Gifford, Hoda Kotb, Peggy Siegal, Natalie Morales, Valesca Guerrand Hermes, Jennifer Creel, Renee Rockefeller, Alexandra Lebenthal and Jay Diamond, Danielle Ganek, Kimberly Kravis, Muffie Potter Aston, Hilary Gumbel, Dr. Harold Varmus, Dennis Basso, Heather Mnuchin, Anne Grauso, Sylvester and Gillian Miniter, Gigi Mortimer, Sara Ayres, Shafi Roepers, Leslie Jones, and LL Cool J. [PMc, Wireimage, NYSD]

This isn't an easy time for Dan Loeb. (The billionaire hedge funder was forced to start renting his Gulfstream jet by the hour recently.) But hopefully he'll get a chance to enjoy the big day: He turns 47 today. Others celebrating: Katie Holmes is turning 30. Brad Pitt is 45. Steven Spielberg is 62. Christina Aguilera is turning 28. PR guru/filmmaker Dan Klores is 59. Randi Weingarten is 51. Memorial Sloan-Kettering chief (and Nobel Prize winner) Harold Varmus is turning 69. Keith Richards is turning 65. Model agency owner Faith Kates is turning 51. Ray Liotta is 54. Former Miss USA Tara Conner is 23. And troublemaking rapper DMX is turning 38.

The Nobel Prize-winning former CEO of Memorial Sloan-Kettering, Varmus is the Director of the National Cancer Institute.