Imagine… You are on an exo-planet circling a star in the Hydra Galaxy Cluster. Your powerful telescope zeroes in on a planet 150 million light-years away. The planet is called Earth, but you won’t be seeing 2016 human inhabitants, you will be seeing images of dinosaurs… Images carried on light that left the Earth 150 million years ago.
You will be looking back in time.
Distances in space are vast. They are measured in units of light travel time. Light travels at just over 186 thousand miles per second. In a year, light travels a great distance, nearly 6 trillion miles!
The delay in time that it takes for us to see an event that takes place on another object in our universe can be as short as 1.3 seconds from our neighbor the Moon, or much longer, like 8.6 years from the bright star Sirius.
To put this in a local perspective, the farthest object that we can see with our eyes without the aid of a telescope is the Andromeda galaxy. It is approximately 2.5 million light years away. When the light that we are seeing now left that galaxy, the Black Canyon of the Gunnison was just beginning to be carved by the ancestral Gunnison River.
Another example of “looking back in time” is when we point out Ptolemy’s Star Cluster at public outreaches. 800 light years distant, what we are actually showing visitors is light that left the star cluster when the Mesa Verde cliff houses were being built in Southwestern Colorado.
Some current telescopes can now look back 13.2 billion years. That is three times older than the age of our solar system. They are seeing objects from before the Earth even existed!
One more thing to get your head around… Look-back time works both ways: Us looking out and seeing the past, and prospective alien life looking at us and seeing our past.
Western Slope Skies is produced by members of the Black Canyon Astronomical Society. This episode was written and recorded by Joyce Tanihara.