Science Dictionary

Do you know what a meteor is, or what scientists mean when they are talking about cryogenics? Our collection of science terms explains the meaning of some of the most common scientific ideas.

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Alexander Wetmore

Wetmore, Alexander (1886-1978), a United States museum official and authority on birds.

How Nebulae Work

Nebulae are collections of dust and gases scattered across the galaxy. They're the sites where stars are born and what's left behind after they die.

How the Big Bang Theory Works

The big bang theory is well-known, but there are many misconceptions about it. Like what? Let's start with this one: There was no bang.

Can scientists recreate the big bang?

Modern science allows us to break atoms down into tiny components. But can scientists use their mighty machines to recreate the foundation of the universe?

Does space have a shape?

Some scientists believe that space is infinite. But is it? If it isn't, what form does space take? Is it a dodecahedron or a triple torus?

How Space Collisions Work

Space collisions are the universe's car wrecks. Only in outer space, it's stars, asteroids and even galaxies doing the smashing.

How Galaxies Work

So much about galaxies remains a mystery. We know what they're made of and that we live in one (the Milky Way), but we're not sure how they form and evolve.

What if we were next to a black hole?

When a star dies, it becomes a black hole. Once something passes through the it's gone for good, never to be seen or heard from again. If we lived next to a black hole, would it suck us in too?

How Dark Matter Works

For decades, stargazing scientists have been facing their own darkness on the edge of town as they try to explain one of astronomy's greatest mysteries: dark matter. Have they been successful, or will the universe carry its secrets for a long time?

Is there a hole in the universe?

While routinely scanning the stars, NASA scientists came across something they didn't expect to see: a vast area of space empty of stars, planets and matter.

Can a planet float on water?

Scientists announced the discovery of the largest known planet in the universe. TrES-4 has a density similar to balsa wood, and some say this gas giant could float on water. Learn why this planet is so puzzling and how planet hunters make amazing discoveries like these.

How Freemasons Work

The Freemasons is a secret organization that began in the 1700s and is still in existence today. Who are the Freemasons? And what do they do in their secret meetings?

Is Earth on a collision path with a major asteroid?

There's a 45-million-ton asteroid out there with Earth's name on it. In 2029, it'll be closer to us than our moon is. And that's not even the fly-by that scientists are worried about.

How Black Holes Work

A black hole occurs when a massive star dies -- its enormous mass implodes and becomes so heavy that it bends space. So how do astronomers detect something that they can't see?

How Deep Impact Works

How do scientists find details about the early days of our solar system? One way is to investigate comets. Find out how the Deep Impact spacecraft fired an impactor into Comet Tempel 1 to get some answers.

How the Leonid Meteor Shower Works

Every November, the Leonid meteor shower fills the sky with "shooting stars." This year, the shower is expected to peak twice. Learn how Leonid and other meteor showers work.

How do polymer crystals work and why do they absorb so much water?

Polymer crystals are amazing in that they can absorb many times their size. In fact, one pound of these crystal flakes can hold up to 50 gallons of water. Find out what these polymer crystals are and why they are able to absorb so much water.

How Asteroids Work

Eros is 21 miles long and 8 miles thick -- a mini planet! Explore the mission that landed on this asteroid after orbiting it for a year!

Rock Star Astrophysicist? Yes, and a For-Real Rock Star, Too

Something else you didn't know about the Pluto exploration: Queen guitarist Brian May has serious science chops, and he contributed to the New Horizons mission.

How Comets Work

Comets are remarkable pieces of our universe's past, and they tell us a great deal about how the universe was formed. Learn about the long but rewarding process of discovering and analyzing comets.

How does the Nobel Prize work?

We've all heard about this prestigious prize, but why is it such an honor, exactly? Learn the history and process of the awards and the winners, and see what makes the Nobel Prize such a distinguished accomplishment.

What is a carat, and how does it relate to a karat?

My fiancee gave me a 1 carat diamond in my engagement ring. What is a carat? And how does it relate to a karat, as in "18 karat gold"?

What is a light year?

A light year is a way of measuring distance. That doesn't make much sense because "light year" contains the word "year," which is normally a unit of time. Even so, light years measure distance.

How does gravity assist with interplanetary satellites?

When satellites go off to places like Jupiter or Saturn (or even out of the solar system), they follow crazy orbits. They will often loop around a planet to get a "gravity assist" or "gravity boost." How does that work? I know the Galileo probe looped around Earth twice to get a boost, and the Pioneer and Voyager probes used Jupiter.

How many teaspoons are there in a cubic light year?

Have you ever really thought about the scale of the universe? A good starting point is the teaspoon.