One of the remarkable things about gazing into a starry night sky is that you’re seeing the universe as it looked in the past. But you’re not seeing one specific moment in time. You’re seeing every single star as it looked at a different moment. It’s like having hundreds of time machines at once.
Consider Aldebaran, the eye of Taurus, the bull, which stands a little below the Moon as they rise after midnight. We see this bright orange star not as it looks right now, but as it looked 67 years ago.
That’s because of the star’s great distance.
Light is the fastest thing in the universe — it speeds along at 670 million miles per hour. Yet the gulf between the stars is so vast that it takes years, decades, or longer for the light from a given star to reach Earth.
Aldebaran is almost 400 trillion miles away — a four followed by 14 zeroes. At that distance, the light we see from the star tonight actually left its surface 67 years ago — as the world was beginning to recover from World War II. And the light the star emits tonight won’t reach Earth until the year 2080.
Counting up the miles, kilometers, or other units between the stars produces some astoundingly large numbers. To keep the numbers more manageable, there’s another unit just for measuring the distances to astronomical objects: the distance light travels in one year — a light-year. Bright, beautiful Aldebaran is 67 light-years away — a 67-year trip back in time.
Script by Damond Benningfield, Copyright 2013