Science meets music as Hoboken celebrates Earth Day this year on Saturday, April 20, with an all-day festival that combines environmental awareness and activism with a folk and bluegrass festival. It all takes place at the Monroe Center Plaza, 770 Jackson St., 11 a.m. to 4 p.m., sponsored by the Hoboken Business Alliance and Main Street Pops. The Earth Day Celebration and Folk & Bluegrass Festival promises a free, family-friendly event where, according to organizers, “attendees of all ages will have the opportunity to immerse themselves in nature-themed public art projects, join interactive ed…