Looking Back

To look at the stars is to travel backwards in time. That's what the term light year means: light, hurrying along at a hundred and eighty-six thousand miles a second, six trillion miles each year, takes that long to reach us. Gazing at the stars, we travel in our minds not only trillions of miles in space but hundreds and even thousands of years back in time.

Moving towards the west is the brilliant red planet Mars. It's pretty close to us now (as it will be every two years.) The light we see reflected from Mars has taken only a little more than six minutes to travel seventy million miles through the darkness of space to reach us tonight. So Mars is six and a half "light minutes" away. Even Pluto, at the outskirts of the solar system, is only about four light-hours away.

It's the stars that are really distant. We can talk of their distance only in light years: the time it takes their light to reach us. Aldebaran, the red eye of Taurus the bull is sixty light years away; the light we see tonight left that star in 1948.

At the center of the Winter Hexagon is the red supergiant Betelgeuse, over three hundred light years away. Now we're seeing back to the seventeenth century. The colonies at Plymouth and New Amsterdam are thriving. Settlers have not yet come to Vermont.

Rigel, the knee of Orion, is even further: nine hundred light years away. Now we're back to the Middle Ages.

And the Milky Way itself? This is of the giant pinwheel arms of our galaxy. The stars of that arm are visible separately only in binoculars or telescopes. They are so far away that men and women were living in caves when the light we see tonight left those stars -- over ten thousand years ago. That light has been traveling since the dawn of civilization.

But all the years of human civilization is as nothing when we contemplate the realm of the galaxies. Their light has been traveling for billions of years - since the universe was young.

(01/30/08)