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.)
