Over the 25 years I’ve written this column, I’ve often marveled at the mind-boggling distances to many celestial objects. Astronomers don’t often use miles to express stellar and galactic distances because the numbers would quickly become unwieldy. Instead, light-years are used because the numbers are more manageable, and they’re also a testament to the unfathomable scale of the universe.
All light travels at the speed of 186,300 miles a second in the vacuum of space. A light-year is defined as the distance that light travels at that speed in one year. Given that there are about 31.
5 million seconds in a year, you can calculate that a single light-year equals around 5.8 trillion miles. So, saying a star is 70 light-years away, which is pretty typical for stars we see with the naked eye, means that the star is about 406 trillion miles away.
That’s 406, followed by 15 zeros! Also, by definition, the light we see from that star tonight left that star 70 years ago. We actually see the star the way it looked in 1954. If we see a star tonight that’s 3,000 light-years away, we see it as it was in 976 B.
C.! Whenever you look at the stars, you’re looking back into the past, sometimes the very distant past! So how do astronomers know how far away these stars are? Unfortunately, it’s not a short and easy answer. You use the stellar parallax method to determine the distance for stars less than 2,000 to 3,000 light-years away.
This method is like measuring the distance to .
