Who said daydreams are a waste of time? One of Einstein's flights of fancy led to the equivalence principle—the knowledge that while an object is in free fall, it's free of gravity's effects.

Confused about fusion? You won't be once you've completed this experiment, which demonstrates how a strong nuclear force can fuse two protons that naturally repel each other.

When does a 12-inch ruler look shorter than it really is? When it's fast on the move. In fact, at the speed of light, it would shrink to nothing. See length contraction for yourself ... at a safe speed.

Altars decorated to welcome ancestors home for the New Year, a Mid-Autumn Festival where kids parade through their neighborhoods in masks and receive toys ... take a look at Vietnamese traditions, past and present.

Where to begin when a Web search turns up millions of sites about Einstein? Let us point you to some of the best—from Time's person of the century profile to a black hole animation.

Extend your journey of body, mind, and spirit with this list of recommended books. There are kid-friendly titles along with great reads for high school students and adults.

In the early 1900s, some astronomers believed that the color contrasts on Mars' surface were great oceans. Today we know they are huge dust storms. Track how our knowledge of Mars has changed with this seventh-grader.