Thousands of years ago, people began noting the passage of time through the changing of the sun, moon and stars. We still do, although we rely on them less now because of watches, clocks and calendars. (You can find the phases of the moon in your Quo Vadis planner!)
When I look up at the sky and see the constellation, Orion, it tells me more than any book winter has arrived.
But the light I see shining from the stars forming Orion left 1,500 years ago – when Clovis I was king of the Franks. (Yes, the same dynasty heavily implicated in Dan Brown’s “The DaVinci Code!”)
The concept of “light travel time” or “light years” as we often refer to it, seems fantastic. A light-year is the distance that light can travel in one year. Light moves at the velocity of about 300,000 kilometers (km) each second. So in one year it can travel about 10 trillion km or 5,878,625,373,183.61 miles.
If the Sun’s light takes eight light-minutes to reach Earth, then something catastrophic could happen to the Sun and we would not know for eight minutes. The center of our Galaxy is 26,000 light-years away. The light we see from there left when our ancestors were painting scenes in caves. The farthest object we can see with our eyes, in a dark sky without the aid of a telescope, is the Andromeda Galaxy, more than two million light-years away. What was happening on Earth two million years ago?