• Red blood cells are the most common cells in the human body. We each have about twenty-five trillion red blood cells, hundreds of times more blood cells than there are stars in the Milky Way galaxy. —The Heart • Did you know that your brain is roughly the size of a large grapefruit?—The Brain • Did you know that the heart weighs only about as much as one of your sneakers, and that it beats more than two billion times in an average lifetime?—The Heart   • No wonder they called him Jaws! A shark’s jaw is lined with as many as twenty rows of teeth, one behind the other. —Sharks • Got milk? In one day, a baby whale drinks more than 100 gallons of its mother’s milk, and may gain as much as 200 pounds a day. — Whales • The tallest tree in the world is a giant redwood called Stratosphere Giant—it is higher than a 40-story building, and lives in Humboldt Redwoods State Park in California.—Extreme Nature! Q & A • More than 70% of the Earth’s surface is covered by oceans. —Oceans • Don’t forget your umbrella! 16 million storms occur each year!—Weather   • Next time you are stargazing, think about this! On a clear, dark night, you can see about 3,000 stars from Earth, just by looking up. —Extreme Stars! Q & A • The universe is still expanding as a result of the Big Bang. Galaxies speed away from each other, some traveling thousands of miles per second. — The Universe • There are more stars in the universe than grains of sand on all of the Earth’s beaches! — Stars • The Milky Way galaxy is made up of 200 billion stars, but it represents only a tiny segment of the universe! —Destination: Space   The name of the Smithsonian Institution and the sunburst logo are registered trademarks of the Smithsonian Institution. The astronaut image is courtesy of NASA Dryden Flight Research Center and National Air and Space Museum, Smithsonian Institution.