Music festivals are fairly commonplace in the City, but few combine titanic star power with social change. The annual Global Citizen Festival tackles that effort, bringing together some of music’s biggest stars—Rihanna, Eddie Vedder and Metallica are among those on this year’s bill—to raise awareness around the fight against poverty, hunger and climate change throughout the world. Curated by Chris Martin, whose band Coldplay will also appear, the show is a day of free music in Central Park’s lovely Great Lawn. But getting tickets requires taking action, from signing a petition for food aid reform to emailing a panel of world leaders to ask them to prioritize waste management; once you’ve earned enough “points” for your efforts, you’ll be entered in a lottery. For more information, visit globalcitizen.org.