Saturday, January 03, 2009

Growing up in the Milky Way

In early July, 1054, a blazing new star appeared in the constellation Taurus. For a time it was far and away the brightest thing in the night sky, except for the Moon. Then it faded away. This spectacular event was recorded by Chinese and Japanese astronomers, and perhaps in a pictograph by native Americans. It is a mystery why European records are silent, although I did describe here one potential reference from Ireland.

Today, photographs show the remnants of an exploded star, still racing outwards, called the Crab Nebula. At the center is a city-sized pulsar, the collapsed core of the star, as dense as the nucleus of an atom and spinning furiously. The Crab is available to the amateur astronomer with a decent scope and a dark sky as a faint blur. Many a cold winter night I have gone looking for it.

When I used to teach an introductory astronomy course, I had the students work with two photographs of the Crab Nebula, taken decades apart. They identified nodes of the twisted gas and -- carefully, very carefully! -- measured the distance from the central pulsar, using background stars to establish a common scale. Then they calculated backwards to the moment of explosion (assuming a constant rate of expansion). And, sure enough, got dates somewhere near the 11th century.

A glimpse of the blur and the exercise with the photographs made the supernova come alive.

The goal of my astronomy course was not just to convey a bunch of facts, but to s-t-r-e-t-c-h the imaginations of the students to accommodate cosmic space and time. Reaching out to that roiling cauldron of gas, 10 light-years wide, 6000 light-years away, was just one small step. Did they come away from these mind-stretching exercises as true children of the Milky Way? I doubt it. I taught the course for 30 years and I can't say that I fully appreciate what it means to live in a universe of 10 billion galaxies (at least) and more exploded stars than one can number.

(Tomorrow: The Crab's ghostly X-ray aura.)

(A cloudy yesterday cleared gloriously overnight for the Quadrantid meteor shower this morning between 4 and 5 AM. We saw approximate one per minute, including several bright enough to leave trails across the sky. A New Year's fireworks.)