The Heckscher Museum of Art invites you to observe Earth Day tomorrow by perusing a pair of environmentally themed exhibits inspired, directly or indirectly, by Henry David Thoreau, who was born 200 years ago on July 17. Thaddeus Holownia: Walden Revisited and Earth Muse: Art and the Environment will remain on view at the Heckscher through the Thoreau bicentennial, each closing on July 30.