A Tiny Wobble

Since ancient days, the little dog star, brilliant Procyon has been seen as a herald of times of bounty. It blazes just to the east of Orion; the shoulders of Orion point to it. Together with the other dog star, Sirius, Procyon signaled the flooding of the Nile and the much-needed irrigation of the crops of Egypt. It was truly a star of life.

Like the ancients, we see the stars move across the sky every night. They thought the heavens were moving around a fixed Earth, we see this as a reflection of the Earth's own rotation. We're both talking about the same motion; we just understand it in different ways.

There's another motion of the stars, though, one no ancient astronomer could measure: the star's real motion. Procyon was one of the first stars whose real motion was measured. Though Procyon is incredibly far away, its motion across the sky could actually be measured by astronomers of the nineteenth century. This motion was tiny, only about a two-thousandth of the size of the moon each year. Tiny, but measurable.

What really made Procyon different from other stars was that it wobbled in its path across the sky. Instead of moving in a straight line, it would move ever so slightly, first left, then right. What could be the cause?

What happened next was a triumph of reason. Without seeing it, astronomers deduced the presence of another star, circling Procyon once every forty years, further from Procyon than Saturn is from our sun. Procyon wobbled because of the gravitational attraction of this circling star. Thirty years were to elapse before this companion was actually seen with the greatest telescopes of that time.

It is a corpse of a star, its nuclear fires extinguished. It has contracted under the pull of gravity until it became only about twice as big as the earth, though it is half the mass of the sun. A teaspoon of this star would weigh hundreds of pounds! It glows only from the heat remaining from its days as a star. It is a white dwarf. Soon, as it cools, it will become a red dwarf, a brown dwarf, and then blink out -- a cinder. As will our sun, eventually.

(11/29/06)