Probability is a way to measure how likely it is that something will happen. Probabilities are predictions. They’re often just very careful guesses. When a scientist wants to calculate a probability, she or he gathers data and then uses the data to make her or his guess. Probabilities are between 100% (it’s definitely going to happen) and 0% (forget about it, pal, it’s not going to happen). Most things have a probability somewhere in between.

It's time for a heart-to-heart talk about blood and circulation with Bill Nye the Science Guy. Your blood is your bud. Without blood, your skin would dry up and fall off, your internal organs would die, and your brain would be kaput. Blood gives every cell in your body the food and oxygen it needs to survive. Blood also cleans up after our cells by carrying away waste. Blood even protects your body from disease. What more could you ask from a friend? Blood patrols your entire body. Blood is pushed around by a powerful pump called the heart. Every time your heart lub-dubs, blood is propelled through tubes called arteries, capillaries, and veins. Your heat pushes your blood in a complete loop around your body about 2,000 times every day. Your heart is a muscle, and, like all muscles, it can get stronger. A healthy heart needs exercise to stay strong. An average heart pumps about 70 times a minute, but a healthy, well-exercised heart pumps 50 or 60 times a minute. Heal

Energy can change forms. Your body changes the energy in food into energy you can use to do things. Dams turn the energy in falling water into electrical energy to bring power to your house. Sound energy changes into moving energy (like when the bass is so high you can feel the floor move).

Ecosystems are areas where things live. Ecosystems that are biodiverse are home to a variety of plants and animals. A healthy ecosystem is one with a lot of biodiversity. Imagine if humans could only eat one kind of food, say corn. We'd be in big trouble if all the corn disappeared. Besides not having anything to munch on at the movies, we'd have nothing to eat at all. Luckily, our ecosystem covers a big part of the Earth, and there are lots of different plants to eat. Ecosystems are not as simple as one living thing eating another, as the corn example. The lives of animals and plants are intertwined - what happens to one animal can have an impact on all sorts of living things. As humans, we have a big effect on the other living things around us. We are the only animals to leave lots of stuff around, such as houses, cars, and malls. It's important for us to think about the choices we make and how they will affect the other living things around us. Remember: The Earth

Let the moon master Bill Nye teach you the ancient and not-so-ancient secrets of the Moon. Wax on, wax off. The Moon grows bigger (waxes) and smaller (wanes) every 30 days or so. The word ""month"" comes from the word ""moon"". The Moon is the closest thing in space to Earth, and it's one of the most well-studied orbs in our solar system. We know that Moon rocks are rich in calcium and aluminum, that the Moon has no atmosphere, and that there are over a million craters on the Moon's surface. The Moon doesn't glow on its own, it reflects sunlight. Watch the Moon every night for a month as it grows, shrinks, and at one point disappears. The Moon doesn't actually change it's shape. It's the way the sun shines on the part of the Moon we see that makes the phases change. The Earth moves around the Sun, the Moon moves around the Earth. As the Moon moves through its orbit, the Sun shines on bigger or smaller portions of it. If you were looking at the Moon from the Sun, it woul

Feeling a little hungry? Then grab a snack and watch Bill Nye the Science Guy's episode on the Food Web. When it comes to eating, all living things depend on other living things. Take a chicken sandwich, for example. The bread came from plants. So did the lettuce and tomatoes. The cheese was made from milk, which came from a cow. To make milk, the cow had to stay alive by eating grass. The meat came from a chicken who once ate seed, and maybe the occasional bug. The animals that helped to make your sandwich depended on other living things to survive. The lettuce, grain (for the bread), and tomato got by fine on their own. Then some animal came along (you). Plants are the only big living things that don't need other living things to survive. All they need are sunlight, carbon dioxide, and water to make their own food. But it doesn't stop them from being eaten -- no way. In fact, plants are great things to eat. All animals need them in some way for food – by the way,

Things that fly need air. Even though we walk through it, breathe it, and sneeze it, air seems to be a whole bunch of nothing. But air is there, and it's powerful. Balloons inflate because air presses on the insides and outsides of the balloon. Air pressure in tires supports the weight of bikes, buses, trucks, cars, and planes. But air doesn't need to be inside something to exert pressure. Air that moves around pushes, too. What do birds, planes, kites, Frisbees, and helicopters have in common? They fly because moving air creates lift, or a push up. Airplane wings are shaped to push air down. The momentum of the air going down pushes wings up. Air above the wing gets going faster than the air underneath. Fast-moving air zips along, without pushing as hard side to side or up and down. The slow air pushes up from below harder than the fast air pushes down from above ... and you're airborne! Every flying thing, from the tiniest flying insect to the biggest airplane, us

Learning about science can be hard work, but simple machines can make it easier. Let Bill Nye push and pull you around ramps, levers, screws, and pulleys. Simple machines simply make work easier by directing forces over distances. Instead of lifting a heavy box upstairs, you can hook it to some ropes and pulleys and pull it up. Or you can get a ramp and slide it upstairs. Either way, it's less sweat to use the pulleys or the ramp than it is to lift the box straight up by yourself because the force you need is more spread out. Levers, ramps, screws, wheels, wedges, and pulleys are all simple machines designed to direct forces. With simple machines we don't have to push or pull as hard, but we have to push or pull over a longer distance. It's easier to walk up a long set of stairs to the top of the Empire State Building than it would be to climb a ladder to the top, but the set of stairs would be much longer than the ladder. Simple machines are simply scientific.

Garbage is a look at two different kinds of garbage -- biodegradable and non-biodegradable. Nye emphasizes the importance of recycling and cutting down on the amount of the waste that cannot break down. The music video "Recycle" has a familiar melody, taken from "Respect," the Aretha Franklin hit.

You can't see them, but they're everywhere even inside Bill Nye. This is not science fiction, it's the science of cells. All things that live are made from cells. You can't see them, but every part of your body, including everything inside your body, is made from cells. Cells eat, they grow, and they make more of themselves (what scientists call replicate). There are millions of different types of cells. Dog cells are different from fish cells. Bird cells are different from your cells. And inside your body, there are many different cells, each one doing a different job to keep your body going. Cells may be tiny, but without them, we'd be nothing.

The Sun is huge. It's bigger than huge. It's so big that 1.3 million Earths would fit inside a hollowed-out Sun. It's really far away, too - about 150 million kilometers (93 million miles) Even at that distance the Sun affects everything on Earth. All the energy we have comes, or once came from, the Sun. That includes energy to light a lamp, energy to kick a soccer ball, and energy in batteries that play your personal stereo. We're talking about nearly all of the energy. There's a little bit of energy that comes from nuclear reactions deep in the Earth's core. But that energy pales compared with the nuclear fusion fueling the Sun. Without the Sun, the Earth would be a big hunk of rock with nearly nothing on it. The Sun is made of gas. It has so much gravity that it's atoms are smashed into hot gas. In the sun, atoms of gas are constantly crashing into each other. When they collide, they form new atoms and release energy. Scientists call this atom smashing "nuclear fus

Populations need a couple of basic things to survive – food and a place to live. When two or more populations of living things are crowded into a small area, there is competition for food and space. A population of birds and a population of squirrels compete for seed and bread crumbs in a park. Competition is a natural part of life, but problems can arise if populations get out of balance.

We can dish the real dirt about dinosaurs, thanks to fossils - traces of theses astonishing animals. Dinosaurs did not print newspapers. They did not take family snapshots or videos 65 million years ago. The only proof scientists have of dinosaurs is their fossils, especially bones. They would never have survived billions of years waiting for some human to trip over them. Luckily for paleontologists (scientists who study the past), now and then dinosaurs died, and their bones were covered by mud, or sand. As the bones sat protected from weather, they absorbed minerals from the soil around them. The minerals chemically worked their way into the bones. Millions of years later, we can find them and dig them up. Humans were not around to see what actually killed the ancient dinosaurs. Many scientists think a meteorite, or lots of meteorites, crashed into the Earth. When the space rocks hit the ground, they made big craters and kicked up a lot of dust and dirt. If enough d

All food, whether it’s protein, fat, carbohydrates, vitamins, or minerals, is made of chemicals. When your body gets a hold of these chemicals, it recombines them and makes energy. Different types of food make different amounts of energy, which are measured in calories. How do scientists figure out the amount of calories in food? In this episode, Bill will reveal the secrets of the bomb calorimeter – an instrument of food science.

Listen up, scientists. Bill Nye is here to make some noise in the ""Sound"" episode. Your vocal cords do it. Speakers playing rock music do it. Even a school bell does it. They all vibrate; and that's how sound is made. Plucking a stretched rubber band makes the rubber band vibrate. Air molecules around the rubber band move, pushing other air molecules. As the rubber band continues to vibrate, it sends waves of sound through the air. It's a lot like the ripples you see when you drop a rock into a pond. You hear sound when rippling air pushes on tiny bones in your ears. Nerves in your ears send a message to your brain about the sound you're hearing. Different sounds make different patterns of waves with different distances between them. Plucking, banging, whispering, and yelling are all vibrations in air, yet they all sound very different. Sound vibrations can be thought of as waves moving through molecules. Low-pitched sounds have big gaps between waves, while high-pi

It doesn't matter if it's spring, summer, winter, or fall - Bill Nye is always in season. Every year, we experience the seasons. Some months have snow and rain, while other months have warmth and sunshine. Temperatures go from cold, to woarm, to cold again – winter, spring, summer, and fall. The cycle of the seasons takes one year, and the Earth takes one year to go around the sun. Coincidence? No way. The Earth's orbit around the Sun is flat, as though our planet were spinning over a tabletop. Compared with flat plane of its orbit, the Earth is tilted. Its axis, the imaginary line between the North and South Poles, is tipped over a bit. In June, the north half of the Earth (the Northern Hemisphere) is tilted toward the Sun, and it's summertime in places like Nye Labs in the United States. Meanwhile, the south half (the Southern Hemisphere) is tilted away from the Sun, and it's winter there, in places like Australia and South Africa. The Earth's orbit isn't quite

The show is way out there, way far away. After all, it's in Outer Space. When you look at the night sky on a clear dark night, you can see thousands of stars. There are far more than you could count. And, they are way out there. They are very, very far away. It's about the hardest thing to imagine about space. Let's talk about the nearest star to us, the Sun. If somehow outer space were not an icy cold vacuum with nothing to eat, drink, or breathe, and we could drive there in a car, to get to the Sun at freeway speed of 100 kilometers/hour (61 miles/hour), it would take171 years of driving without stopping to sleep or get gas out in the near nothingness of space. That's just to the Sun. To get to even the closest star, Proxima Centauri, would take 40,000 years. On top of that, most things, billions and billions of stars, are much, much farther away than that! It is just astonishing. How do we know that everything is so far away? We have watched the sky for centuries.

Bill and actress Candace Cameron use fire to demonstrate what chemical reactions are.

All living things have genes, which are like little sets of blueprints. Genes have information about the color of your eyes, the shape of your nose, and whether you hair is straight or curly. When living things make other living things, they pass copies of these blueprints to the offspring. The copies are mixtures. They’re never exact, never quite perfect. So, the cool thing is that no two sets of blueprints are exactly alike. So each living thing is different from other living things. Scientists know about evolution from fossils. Fossils show how living things used to look millions of years ago. Scientists take information from fossils to see how living things have changed over thousands, hundreds of thousands, and millions of years.

Take time to digest this show. They say that your food is no more inside you than a pencil is inside a donut, when it's poked through the hole. Instead of the food going in you, food goes through you. But, all the energy you get to live and grow comes from your food. All the chemicals that become your body and brain as you get bigger, come from your food. You get these vital chemicals through a process called ""digestion."" Your body breaks food down and grabs all the nutrients you need from it. Then, your body gets rid of what's left over. Digestion starts in your mouth. You begin breaking food down by breaking it into pieces with your teeth and jaw muscles. Your saliva (your spit) is full of chemicals that react with the chemicals in food and make them break apart. Then you swallow. Your food goes down a tube (your esophagus) to your stomach, where powerful hydrochloric acid breaks it down further into a mushy mash we call chime (kime). From there, the chime goes in

How breathing supplies the body with the oxygen it needs

Almost everything around you, from paper clips to computers, was thought of, designed, and built by humans. An invention can be a totally new idea, or an improved variation on something that already exists. Inventors invent to solve problems and make life easier. Anyone can be an inventor, even you. All you need is an idea, and sometimes you don’t even need that. Silly Putty, sticky notes, X-rays, pretzels and nylon were all accidents that became great inventions after more research, experimentation, and design.

Don't stay in the dark - Bill Nye will help you absorb the science of light optics. Light is energy that normally moves in a straight line, but often something gets in the way. When light runs into something, three things can happen - the light can bounce off, it can go through, or it can be absorbed. Often all three things happen at the same time. Light bounces off mirrors. You see yourself in a mirror when light bounces off your face, into the mirror, and then into your eyes. Light goes through glass. If the glass is bent or curved, the light gets bent on its way out of the glass. The glass in a magnifying glass or a pair of eyeglasses is curved so that it bends light, making things look bigger. More light is absorbed by dark-colored things than by light-colored things. Colors are made when some light is absorbed while other light is bounced back. Black things look black because when light hits them, they absorb almost all of the light.

The air that surrounds Earth is called the atmosphere. Compared to the size of the Earth, the atmosphere is very, very thin. It’s made from gases – mainly nitrogen, oxygen, and water vapor, with a little argon, carbon dioxide, xenon, neon, helium, and sulfur. The atmosphere does a lot for Earth. It blocks ultraviolet light and burns up a lot of meteors. It traps in heat, keeping Earth cozy. Even clouds are formed in the atmosphere – keeping the Earth wet with rain.

The color of your eyes, the shape of your nose, and the straightness (or curliness) of your hair depend on your genes. Not jeans the pants, but genes, the long strands of chemicals in your cells. Genes are like a blueprint for your body, and your cells follow the blueprint to build you. All living things have genes in their cells. You get your genes from your parents – half from your mom and half from your dad. Your parents got their genes from their parents, your grandparents. Living things pass down their genes from generation to generation. Genes from a mother’s egg cell mix with genes from a father’s sperm cell to make a complete set of plans for a baby. Baby humans, baby dogs, and baby plants all grow up to look like their parents because of genes.