Thursday, December 4, 2008

The Way

There are an estimated 100 billion galaxies in the universe, and we occupy just one of them, the Milky Way.

It was the great 20th century American astronomer Edwin Hubble who determined that many mysterious telescopic objects thought to be emerging solar systems were in fact galaxies— immense star systems lying beyond the Milky Way. The Milky Way was not, it seemed, the whole enchilada. This discovery expanded our cosmic horizons and gave us our first inkling of just how immense the universe was.

Since Hubble’s landmark discovery, we’ve learned quite a bit about our cosmic 'hood. We now know that the Milky Way is a barred spiral type of galaxy. A spiral galaxy is shaped somewhat like a pinwheel, with curved arms radiating out from a center that is densely packed with stars. In a barred spiral, the center has an elongated shape.

We also know that there’s a supermassive black hole lurking at our galaxy's center. A black hole is an object so dense that nothing— not even light— can escape from its gravitational field.

Courtesy NASA/JPL-Caltech

In addition, we’ve learned that the Milky Way contains around 400 billion stars. We know it’s around 200,000 light years in diameter; one light year is the distance light travels in one Earth year, nearly six trillion miles. Knowing these numbers doesn’t necessarily mean we mere mortals can fully grasp the size and distance involved. The implication for a short-lived species such as Homo sapiens is that space travel to other parts of our galaxy would require thousands of successive generations of people on each pioneering space ship.

However, like all the generations of our species that came before us, we can see the Milky Way on most any night. If we look skyward from a dark site away from urban light pollution, we can enjoy an edge-on view of the star-packed arms of our platter-shaped galaxy. Because the Milky Way is a horde of stars too numerous and faint to be resolved (separated into distinct points of light) with the naked eye, we see it as a hazy band of light arching across the sky. Some folks seeing the Milky Way for the first time mistake it for a long, lingering cloud.

The poetic name for our home galaxy comes to us from the Latin Via Lactea (Milky Way), which in turn derived from the Greek word for milk. A number of other cultures also saw the band of light as a stream of milk. But around the world, there have been numerous names given to this distinctive celestial object. Here are just a few:

- Silver River
- Winter Street
- Path of White Ashes
- Birds’ Way
- Straw Road
- Pilgrims’ Road
- Great Serpent
- River of Heaven
- Heavenly Girdle
- Road of Souls
and my personal favorite, from the Polynesians:
- Long Blue Cloud-Eating Shark

My pet name for the Milky Way is simply “the Way,” because it represents for me a way of being and a way of seeing. I learned an important lesson a number of years ago on a camping and observing trip in southern Arizona. I had spent the better part of a night glued to the eyepiece of my telescope, hunting various galaxies, globular clusters, and nebulas on an observing list and methodically ticking off those “faint fuzzies” as I found them. Straightening up from the eyepiece to stretch my back, I faced south and audibly gasped. The woods south of the clearing where I and my partner were observing were on fire!

After a few heart-pounding seconds, I noticed that the raging firestorm licking the sky above the trees was black-and-white. Black-and-white flames? Then it dawned on me that what I thought was a forest fire was the Summer Milky Way, which had risen in all its magnificence while I was attached like a barnacle to my telescope.

Because I am fortunate to live and observe in New Mexico, which has excellent observing conditions, I thought I had seen the Milky Way. But I had never seen it like I saw it that night. The combination of superb transparency (atmospheric clarity) and a deep, dark, black-as-the-ace-of-spades sky background made every tendril and wisp of the Way pop out in blazing, 3D relief.

I almost missed the finest view of the night, a deeply satisfying naked-eye spectacle that flickered across my retinas and seared itself into my memory. And here’s the strange lesson: sometimes even serious sky observers have to remember to just look up.