Nature: Frogs: The Thin Green Line, 7pm
It is the greatest mass extinction since the dinosaurs. Population by population, species by species, amphibians are vanishing off the face of the Earth. Despite international alarm and scientists scrambling for answers, the steady hemorrhaging of amphibians continues like a leaky faucet that cannot be fixed or a wound that will not heal. Large-scale die-offs of frogs around the world have prompted scientists to take desperate measures to try to save those they can.

Watch Bears of the Last Frontier: Arctic Wanderers on PBS. See more from Nature.

Nature: Bears of the Last Frontier, 7pm
It’s early November and winter is coming on. But each year, the polar bears struggle for extended periods on dwindling fat reserves, waiting for the opportunity to hunt on sea ice that takes longer to freeze. In early spring, Chris Morgan joins local hunters in Barrow, the northernmost city in Alaska, as they go out on their own hunts, facing some of the same challenges as the bears. In late spring, Morgan travels to the North Slope of the Brooks Range, where countless thousands of caribou cover the ground for miles. The grizzlies are waiting for them, as they have for thousands of years.

Nova: The Fabric of the Universe “Quantum Leap”, 8pm
Join Brian Greene on a wild ride into the weird realm of quantum physics, which governs the universe on the tiniest of scales. Greene brings quantum mechanics to life in a nightclub like no other, where objects pop in and out of existence, and things over here can affect others over there, instantaneously and without anything crossing the space between them. A century ago, during the initial shots in the quantum revolution, the best minds of a generation—including Albert Einstein and Niels Bohr—squared off in a battle for the soul of physics. How could the rules of the quantum world, which work so well to describe the behavior of individual atoms and their components, conflict so dramatically with the everyday rules that govern people, planets, and galaxies?

Nova: The Fabric of the Universe “Universe or Multiverse? “, 9pm
Hard as it is to swallow, cutting-edge theories are suggesting that our universe may not be the only universe. Instead, it may be just one of an infinite number of worlds that make up the multiverse. Brian Greene takes us on a tour of this brave new theory at the frontier of physics, explaining why scientists believe it’s true and showing what some of these alternate realities might be like. Some universes may be almost indistinguishable from our own; others may contain variations of all of us, where we exist but with different families, careers and life stories. In still others, reality may be so radically different from ours as to be unrecognizable.

Nature: White Falcon, White Wolf, 7 pm
On Canada’s remote Ellesmere Island, where June is spring, July is summer and August is already autumn, the race is on for two remarkable species to raise their families. The white gyr falcon is enormous, the largest and most powerful falcon in the world. Yet last summer, the nesting falcon pair here failed to raise any young. The rare Arctic wolves rely on every member of the pack to chase and bring down the prey that keeps them alive. Last year was good to them, and they raised three cubs. But for the wolves and the falcons, as well for as the snowy owls, musk oxen, lemmings, Arctic foxes and hares who share this fragile ecosystem with them, fortunes are always precarious.

Watch Brian Greene Previews NOVA’s “The Fabric of the Cosmos” on PBS. See more from NOVA.

Nature: Bears of the Last Frontier, 7pm
Chris Morgan explores the world of black bears caught in the crossroads of urban development in Anchorage and the wilderness. This is a new normal for bears and for their human neighbors. Some bears are so comfortable living in urban surroundings that their primary habitat is a golf course. In residential areas, bears frequently raid garbage bins and birdfeeders for easy snacks. But these behaviors are less than ideal for bears and residents alike. Morgan heads north out of Anchorage to Denali National Park, where the mountains loom over treeless plains and bears get by on a diet of thousands of berries a day.

Nova: The Fabric of the Cosmos “What is Space?”, 8pm
Space. It separates you from me, one galaxy from the next and atoms from each other. It is everywhere in the universe. But to most of us, space is nothing, an empty void. Well, it turns out space is not what it seems. From the passenger seat of a New York cab driving near the speed of light to a pool hall where billiard tables do fantastical things, Brain Greene reveals space as a dynamic fabric that can stretch, twist, warp and ripple under the influence of gravity.

Nova: The Fabric of the Cosmos “The Illusion of Time”, 9pm
Time. We waste it, save it, kill it, make it. The world runs on it. Yet, ask physicists what time actually is, and the answer might shock you: They have no idea. Even more surprising, the deep sense we have of time passing from present to past may be nothing more than an illusion. How can our understanding of something so familiar be so wrong? In search of answers, Brian Greene takes us on the ultimate time traveling adventure, hurtling 50 years into the future before stepping into a wormhole to travel back to the past.

Watch Bears of the Last Frontier: City of Bears – Preview on PBS. See more from Nature.

Nature: Bears of the Last Frontier, 7pm
Bear biologist Chris Morgan sets up camp at a remote spot in the heart of Alaskan wilderness, alongside the largest concentration of grizzlies in the world. It is June in the Alaska Peninsula. The sun sets well into night and bears are taking advantage of the long days to feed, mate and raise new cubs. Morgan tracks their progress as they feast on the riches of the season and re-establish the complex hierarchal social dynamics of bear society. Along the way, he experiences close encounters with bears, observing brutal battles among males during mating season as well as tender moments between a grizzly mom and her cubs.

Nature Cloud: Challenge of the Stallions at 7 pm
The returning saga of Cloud, the wild, white stallion finds us back in the Arrowhead Mountains of Montana. Cloud is now a confident band stallion in his prime. As he rules the mountains, gathering mares and expanding his reign, the story turns to his two sons. Bolder is his by birth — beautiful and golden, the success of his father and grandfather flowing in his veins. Flint, sired by another stallion, is the colt Cloud raised. Now, Bolder has gathered some mares of his own while Flint has joined a group of bachelor stallions, young guns roaming the mountains. Who will rise to challenge the mighty Cloud? Will nature or nurture produce the next great stallion of the Arrowheads?

Nova Hunting the Edge of Space: The Ever Expanding Universe at 8 pm
In this miniseries, Nova examines how a simple instrument, the telescope, has fundamentally changed our understanding of our place in the universe. What began as a curiosity — two spectacle lenses held a foot apart — ultimately revolutionized human thought across science, philosophy and religion. The series takes viewers on a global adventure of discovery, dramatizing the innovations in technology and the achievements in science that have marked the history of the telescope. This tale of human ingenuity involves some of the most colorful figures of the scientific world — Galileo, Kepler, Newton, William Herschel, George Hale and Edwin Hubble — leading up to today’s colossal telescopes, housed in space-age cathedrals or orbiting high above the Earth. Now at the center of an international space race, a new generation of ever-larger telescopes is poised to reveal answers to longstanding questions about our universe and, in turn, to raise new questions. The conclusion.

Inside Nature’s Giants Camel at 9 pm
Mark Evans and Joy Reidenberg brave the baking desert to dissect a camel. They uncover the secret of the camel’s hump and investigate how its elastic legs, stretchy lips and pedestal (a strange bump on its chest) are among the many surprising adaptations that enable the camel to thrive in such a dry and hostile environment.

Nature Superfish at 7 pm
They slice through the water’s surface with explosive power, sail, spear and a half ton of muscle flashing in the sun. Their journeys through the open ocean are epic, their life cycle, bizarre. They are the billfish — marlin, sailfish, spearfish and swordfish — the largest and most highly prized of all gamefish. Emmy award-winning filmmaker and biologist Rick Rosenthal brings these incredible sea creatures to the screen as he observes tiny billfish nurseries in the wild, dives deep into secret undersea canyons, films incredible color-changing behavior and embarks on a quest for an elusive thousand-pound “grander.”

Nova Hunting the Edge of Space: They Mystery of the Milky Way at 8 pm
In this miniseries, NOVA examines how a simple instrument, the telescope, has fundamentally changed our understanding of our place in the universe. What began as a curiosity — two spectacle lenses held a foot apart — ultimately revolutionized human thought across science, philosophy and religion. The series takes viewers on a global adventure of discovery, dramatizing the innovations in technology and the achievements in science that have marked the history of the telescope. This tale of human ingenuity involves some of the most colorful figures of the scientific world — Galileo, Kepler, Newton, William Herschel, George Hale and Edwin Hubble — leading up to today’s colossal telescopes, housed in space-age cathedrals or orbiting high above the Earth. Now at the center of an international space race, a new generation of ever-larger telescopes is poised to reveal answers to longstanding questions about our universe and, in turn, to raise new questions.

Inside Nature’s Giants Giant Squid at 9 pm
The team travels to New Zealand to examine one of the biggest yet most mysterious animals on Earth – the giant squid. Delving into its three hearts, razor sharp beak, tooth-covered tentacles and bizarre reproductive system, the team explores the anatomy of a deep-sea alien that’s never been observed in the wild.