Spin, baby, spin!
GATEHOUSE NEWS SERVICE
(Best read to the Peter Seeger tune of “Turn! Turn! Turn!”)
Spinning seems to be the way of the Universe. We’re always going around in circles.
In 340 B.C., Heraclides claimed that the Earth spins. We might imagine what they thought of him. Heraclides was a Greek philosopher and astronomer, having lived 387 to 312 BC.
He proposed that the apparent rotation of the sun across the sky by day and the stars by night was caused by the world turning around once every 24 hours.
This startling suggestion contradicted the accepted Aristotelian view of the cosmos, which said the Earth was fixed. A few other Greek thinkers shared his view.
The Earth certainly isn’t alone. All of the planets, moons and stars rotate on their axis.
Although our moon keeps the same side facing us, the moon is spinning around as well; it just spins once around for every time it revolves about the Earth.
The sun goes once around every 24.47 days. Galileo first realized the sun’s rotation - and its spherical shape - by observing the day-to-day shift of dark sunspots, safely projected from his telescope onto a white screen.
Curiously, the axis of rotation for each of the planets vary; none of them are straight up and down, perpendicular to their solar orbit. They are all tipsy. Earth is tipped 23-1/2 degrees. Uranus is the worst off, being tipped almost completely over on its side.
Are you dizzy yet?
Imagine all the planets spinning, orbiting their spinning Sun; around each planet their satellites do their spin. The whole solar system in time, accompanies the host of heaven that makes up the Milky Way galaxy, in a vast rotation of its billions of parts. Our galactic home, as wide as 100,000 light years, rotates at about 600,000 mph. Our sun, along with the Earth, is about 28,000 light years from the galactic center; at that distance, we take about 225 million years to go once around. You can almost feel the breeze.
We could call the universe the “great whirl.” Spiral galaxies show off their spin with their wonderful spiral arms, sweeping back from the central hub. One of the most easily recognizable spiral galaxies is M51, often called the “whirlpool galaxy.” From our perspective, we face right down (or up?) on the galaxy, showing its circular shape.
The axis of spin for the galaxies spread across the sky appear to follow no pattern, as least from what we can see. They appear to be tipped at random. We view many galaxies from off angles, giving them an elliptical appearance. M31 the Andromeda galaxy comes to mind. Others appear “edge-on” such as NGC 4565. We see it in a telescope like a thin needle, thickening towards the middle where the hub is located.
Imagine a CD (I used to say phonograph record) with a marble stuck in its central hole. Picture the spiral arms painted across the surface. You can move this model of a spiral galaxy about, to visualize the various orientations we see in the sky.
The story of our spin gets even better. Not only does the Earth spin around a north-south axis, that axis very slowly wobbles. I mean VERY slowly. It takes about 24,000 years for the axis to wobble once, picking out different “North Stars” on the sky as it goes. Other world precess as well.
So there’s no standing still. Enjoy the ride! Heraclides would be proud.
First-quarter moon is on Feb. 21.
Keep looking up!