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The night sky as a time machine


darrell heath

Darrell Heath

Astronomy Columnist 

For fans of science fiction one of the most popular sub-categories within the genre is that of time travel. From H.G. Wells to Star Trek to Doctor Who the idea of time travel has long had a certain appeal. Perhaps its popularity can be chalked up to the fact that we are all too human. Who amongst us hasn’t fantasized about going back in time to correct a past mistake or to zip ahead and get a sneak-peek at the future?
While time travel may forever be out of our reach there is a way to experience a trip back in time: just look up at a starry sky.
When you couple the fact that light has a finite speed (186,000 miles per second) with an unimaginably huge universe you get something very interesting: we can never see a star, moon, planet, or galaxy as it is right this moment; we can only see celestial objects as they were at some point in the past.
For example, the Sun is 93 million miles away and its light takes 8 minutes to reach us; when you look at the Sun you are seeing it as it was 8 minutes ago. It takes the Moon’s light 1-½ seconds to reach our eyes, and the travel time for light from the Sun to Pluto is about 5 hours.
As we move out of the solar system and head to the stars the distances become so mind-bogglingly huge that using miles as a distance unit becomes inadequate. On these scales astronomers use a different unit, the light year or, how far light will travel in one year’s time: 6 trillion miles
So, if you’re up for it, let’s step outside and journey back in time. Go out at around 10pm and face east, we are looking for three stars that make up a pattern known as The Summer Triangle. Look up to find the brightest star in the eastern sky, Vega, in the constellation of Lyra the Harp. Now, look 24 degrees to the lower left of Vega to find Deneb, in the constellation of Cygnus the Swan. If you stretch your hand apart as far as you can and then hold your arm straight out, the distance between your thumb and pinky finger is 20 degrees upon the sky. So, we have the base of our triangle now let’s find the apex. That star is 34 degrees to the lower right of Vega and is known as Altair, in the constellation of Aquila the Eagle. All three stars are the brightest ones in our summer sky.
Turn your gaze back to Vega, which is 25 light years away. The light pinging against your eyeballs while looking at this star began its journey through interstellar space 25 years ago, which would have been in 1990. That was the year the Berlin Wall came down, George H. W. Bush was president, the Hubble Space Telescope was launched, The Simpsons debuted on TV, and Bill Clinton was the governor of Arkansas.
The light from Altair has been traveling for 17 years and first left the star back in 1998. Bill Clinton was now the president, The Big Lebowski was big box office, Shania Twain’s single, You’re Still The One, won her two Grammy Awards, and Buffy The Vampire Slayer was enjoying its second and third seasons.
On average, the distance for most of the stars we see with the unaided eye are within 100 light years of Earth. But turning your gaze now to Deneb you are seeing one of the most distant naked eye stars in the night sky. The light from Deneb is 1,145 years old. That’s a mighty big jump in our Way Back Machine! The year was 870 A.D., much of Europe was still in the Bronze Age, and people were still learning how to work metals into tools and weapons.
As if all this isn’t mind-blowing stuff already then consider this: looking at the night sky you are not seeing just one past but multitudes, all overlapping with each other and converging upon you to form your “now”. What we call the “present” is, from our perspective, the center of where all of these pasts come together as one fleeting moment in time. But let’s face it, we are never going to have a time machine of our own so just reclining in a lounge chair in the backyard and looking up at a starry sky is the next best thing.
If you’d like to explore some science fiction time travel here are a few suggestions: The Time Machine by H.G. Wells; The Time Machine (film, 1960); Time After Time (film, 1979) with native Arkansan Mary Steenburgen; A Sound of Thunder by Ray Bradbury (short story); A Wrinkle in Time by Madeleine L’Engle; Kindred, by Octavia Butler; 11/22/63 by Stephen King; Looper (film, 2012); Time Traveler’s Almanac, anthology, edited by Ann and Jeff Vandermeer; and Time Salvager by Wesley Chu.

Darrell Heath works at the University of Arkansas at Little Rock and is a producer and host for the UALR Television show “The Night Sky.”