If you’ve bought a plane ticket recently, you’ve probably had the option to pay a few extra dollars to offset your carbon emissions. That money might go toward planting some trees… but how many trees? Researchers at the Smithsonian Tropical Research Institute are trying to answer this very question by hand-measuring trees, weighing wood, and climbing to the top of the canopy. We tag along to see how carbon is measured, and why so much ends up in tropical forests.   Guests: Joshua Tewksbury, director of the Smithsonian Tropical Research Institute in Panama Helene Muller-Landau, senior scientist at the Smithsonian Tropical Research Institute researching tropical forests and ecosystems, leader of ForestGEO Global Carbon Program David Mitre, research manager for ForestGEO at the Smithsonian Tropical Research Institute Sergio dos Santos, project manager for the Smithsonian Tropical Research Institute’s Hydro-Meteorological and Oceanographic Monitoring Program in Panama Luisa Fernanda Gómez Correa, intern at the Forest Carbon Lab at the Smithsonian Tropical Research Institute Eline De Loore, graduate student at Ghent University conducting research at the Smithsonian Tropical Research Institute

It started as a rumor in the cafeteria of the Smithsonian Tropical Research Institute in Panama: monkeys on an island in the Pacific were doing something no one had ever seen them do before. But when researchers went searching for these elusive capuchin monkeys, they discovered more questions than answers. Guests: Claudio Monteza, Smithsonian Tropical Research Institute fellow and researcher at the Max Planck Institute of Animal Behavior Brendan Barrett, researcher at the University of Konstanz and the Max Planck Institute of Animal Behavior Meg Crofoot, director of the Department for the Ecology of Animal Societies at the Max Planck Institute of Animal Behavior. Former Smithsonian Tropical Research Institute fellow

Money is power. But who's on our money - or isn’t - can be just as powerful. While Lady Liberty has graced American coins and dollars for most of our history, it wasn’t until the 1970s that a real woman appeared on a circulating American coin. But that's about to change. Congress recently authorized the creation of twenty new quarters featuring American women from history. But how do we decide whose likeness gets engraved in our national story? And who makes these decisions? We’ll follow the money to find out. Guests: Jennifer Schneider, former program manager at Smithsonian American Women’s History Museum, current assistant registrar of outgoing and government loans at the Smithsonian American Art Museum Tey Marianna Nunn, former director of the American Women’s History Initiative at the Smithsonian American Women’s History Museum, current associate director for content and interpretation at the Smithsonian’s National Museum of the American Latino Ellen Feingold, curator of the National Numismatic Collection at the Smithsonian’s National Museum of American History Joseph Menna, chief engraver at the United States Mint Tim Grant, public affairs manager at the United States Mint Dave Clark, supervisor of blanking annealing and upsetting at the United States Mint

Did you know a person born on February 29 is called a "leapling"? This special episode is hopping with Leap Day trivia! Like, why do we need an extra day every four years anyway? And will I get paid for working an extra day in February? It's the lowdown on Leap Day in an episode that's as off-kilter as the earth's axis. Guest: Bob Craddock, Geologist at the Smithsonian's National Air and Space Museum's Center for Earth and Planetary Studies

They say love is eternal. What about heartbreak? This Valentine’s Day, we bring you some of Japanese theater’s most popular tales of scorned lovers seeking vengeance from beyond the grave — with a burning passion. Guests:  Frank Feltens, Curator of Japanese Art at the Smithsonian’s National Museum of Asian Art Kit Brooks, Japan Foundation Assistant Curator of Japanese Art at the Smithsonian’s National Museum of Asian Art

From brontosauruses with bronchitis to birds on a wire to flying space rocks and a botched heist at 20 thousand feet. In this episode, Lizzie and Sidedoor producer James run all around the Smithsonian to answer listeners' questions from the Sidedoor mailbag. Guests: Lynn Heidelbaugh, curator at the Smithsonian’s National Postal Museum Sara Hallager, curator of birds at the Smithsonian’s National Zoo and Conservation Biology Institute Jim Nollman, composer and pioneer of the “interspecies music” genre, conceptual artist, and environmental activist Cari Corrigan, research geologist at the Smithsonian’s National Museum of Natural History and curator of the Antarctic Meteorite Collection Sharon Bryant, marketing specialist at the Smithsonian’s Office of Communications and External Affairs Matthew Carrano, research geologist and curator of Dinosauria at the Smithsonian’s National Museum of Natural History

As long as there have been wars, animals have joined their human companions on the battlefield. But a few have served so bravely they’ve been memorialized at the Smithsonian. In honor of these furry and feathered war heroes, we bring you the tales of dogs, cats and birds who went above and beyond the call of duty.  Guests:  Jennifer Jones, curator of military history at the Smithsonian's National Museum of American History  Frank Blazich, curator of military history at the Smithsonian's National Museum of American History  Ann Bausum, author of Stubby the War Dog and Sergeant Stubby: How a Stray Dog and His Best Friend Helped Win WWI and Stole the Heart of a Nation  Scot Christenson, author of Cats in the Navy  Chris Willingham, president of the United States War Dogs Association

Virginia Hall dreamed of being America’s first female ambassador. Instead, she became a spy. Joining the ranks of the U.S.’s first civilian spy network, she operated alone in occupied France, where she built French Resistance networks, delivered critical intelligence, and sold cheese to the enemy. All on one leg. Guests: Sonia Purnell, author of “A Woman of No Importance: the Untold Story of the American Spy who Helped Win World War II.”  Randy Burkett, CIA Staff Historian Christina Gebhard, museum specialist at the Smithsonian’s National Museum of Natural History

It’s a song we often hear at the start of the new year. But what does “auld lang syne” even mean? And how did it come to be associated with New Year's Eve? With a little musical sleuthing, we find Charlie Chaplin might have something to do with it… Guests: James Deutsch, curator of folklife and popular culture at the Smithsonian Center for Folklife and Cultural Heritage

North American River Otters are popping up in places they haven't been seen in decades and nobody really knows why. As we search for answers we discover a trail of fish heads, poop splats and cuddle parties. Guests: Katrina Lohan, head of the Coastal Disease Ecology Laboratory at the Smithsonian Environmental Research Center Alejandra Morales Picard, psychologist at Montgomery College Rebecca Sturniolo, assistant curator of the America Trail at the Smithsonian National Zoo Patty Storms & Morty Bachar, otter neighbors