Round And Round (everything Spins)

Round and Round We Go Why does everything except the universe itself rotate, spin, wheel, turn, and gyrate? DISCOVER JULY 2003

EVERYTHING IN THE UNIVERSE SPINS. FROM THE tiniest electron to the grandest galaxy, nothing is whirl-proof. Rotation is so ubiquitous that we tend to take it for granted, but every spin tells a storv Study how an object turns and you learn its size, its structure, even its life history. To the ancients, the moon was the only astronomical object thought to spin: The same side of the moon always points toward us no matter where it is in the sky, which is possible only if it rotates as it revolves. (Like all major satellites in our solar system, the moon spins at the same rate at which it orbits its parent planet, coaxed into synchronicity by the gravity of its planet.) In the fourth century B.C., the Greek astronomer Heracleides Ponticus introduced the radical idea that Earth rotates as well, causing the apparent motion of the sun and stars. Today we know our planet’s spin so precisely that we can even measure the tiny deceleration caused by the tides generated by the sun and moon. Our day—23 hours, 56 minute, and 4.1 seconds—grows 1/500 of a second longer with each passing century. Rotation moves Earth’s surface 1,040 miles per hour at the equator and zero at the poles. You can see the whole range of Earth’s rotation projected upward into the sky, where it produces a continuum from zippy star-speed at the celestial equator to sidereal lethargy near the poles. After dusk in July, the bright star nearest to the heavenly zone above Earth’s equator is blue white Spica in the southwest. It moves faster across the sky than any other first-magnitude object. In the Northern Hemisphere, the slowest-moving prominent star is always Polaris, which traces out a tiny circle just three times the diameter of the full moon each day. Beyond Earth, there is a stunning range of rotations. Jupiter, the solar system’ speed king, completes a turn in 9 hours and 55 minutes. Its equator races along at 25,000 mph. The sun has a relatively leisurely 26-day spin, slower than that of many other similar stars. Astronomers theorize its rotation was braked by the birth of the planets, which siphoned off the infant sun’s angular momentum. Other slow-spinning stars may have been run down by their own unseen planetary systems. At the lazy end of our solar system, Venus rotates only once every 243 Earth days. A Venusian could keep the) stars stationary just by walking eastward.

Just before dawn this month, sluggish Venus hovers just above the northeastern horizon beside the Crab nebula, making for a dramatic contrast of rotation. At the heart of the nebula lies the Crab pulsar, a tiny stellar cinder that spins a remarkable 30 times each second. It completes 630 million rotations in the time Venus takes to turn once. From the pulsar’s surface, the stars would whiz by too quickly to appear as anything but unvarying streaks. This ultrafast spin comes from the unusual way the pulsar formed. A large, heavy star grew old, ran out of fuel, and collapsed violently inward. Like a figure skater tucking in her arms, a whirling body speeds up as it becomes more compact. The runaway compression that scrunched the star into a 10mile-wide pulsar also wound it up to fantastic speeds. The one thing out there that seems not to turn is the universe itself. Astronomers have tried to measure cosmic rotation by looking for distortions in the faint glow of microwaves left over from the Big Bang. In 1996 Emory F. Bunn of the University of Richmond and his colleagues scrutinized those microwaves and found no sign of motion. The results imply that the universe has completed no more than one-millionth of a revolution since it was born some 13.7 billion years ago. For everything else, the pirouettes go on and on. Bright, fast-whirling Jupiter shines low in the west in July—but only at nightfall. An hour or two later it is gone, carried away by our planet’s spin.