Tonight, in Whitesville, W.Va., mourners will silently walk with candles on sidewalks lined with luminary lights to remember the 29 coal miners who died two years ago today in the nation's worst mine disaster in 40 years.

That memorial will follow a 3 p.m. ET event in Beckley,W. Va., where an honor guard will ring a bell 29 times to mark the moment the Upper Big Branch coal mine erupted in a massive explosion.

Race is central to the debate surrounding Trayvon Martin, the black Florida teen shot by neighborhood watch volunteer, George Zimmerman. Many media outlets first identified Zimmerman as "white," but his father describes him as a Spanish-speaking minority. Host Michel Martin explores the question, "who is white?" with sociologist Jean Halley.

Dennis Walcott oversees a school system with more than one million students. Graduation rates are below the national average, and studies suggest most of the city's high school graduates are not ready for college. But Chancellor Walcott tells host Michel Martin that, after one year on the job, New York City schools are on the mend.

Allergies come in many different forms.

Mitt Romney has taken the lead in voter support in Pennsylvania, according to a new poll from Public Policy Polling which shows the Republican frontrunner ahead of Rick Santorum, the former U.S. senator from the Keystone State, 42 percent to 37 percent. That lead was just on the 4.9 point margin of error, suggesting a tie. That's bad news for Santorum, however, as he dropped six percentage points while Romney gained 17 percent from a month ago.