In a way, postcards are always from the past. Just like pictures, they freeze a moment in time to be enjoyed and remembered in the future. Text messages and emails have made communication around the world effectively instant. Nowadays vacation photos are immediately shared with family and friends. But there was a time when postcards were a traditional way of sharing with someone that “Hola, I’m in this cool place. Desearía que estuvieras aquí conmigo (I wish you were here with me)." Unlike our modern age of instant communication, postcards always took time to arrive. A day, a week, maybe longer depending on the distance.
The Universe is sending us postcards every day. We look up at the night sky and see the planets and stars from far, far away. But what isn’t so instinctive to us sometimes is that we are not only looking far away in distance, we are also looking far back in time.
Take as an example the Lagoon Nebula which we highlighted in my previous article. This nebula is 5,000 light-years away. A light-year is the distance light travels in one year. Light that is leaving this nebula today, won’t arrive to be seen on Earth until the year 7,022. Even though light is traveling at 300,000 kilometers per second, the distance is so great it will take 5,000 years to get here. We can think of this another way as well. The light we are seeing from the Lagoon Nebula now started traveling before the Giza Pyramids were even built. Because of the great size of the universe, when we look up at the sky, we are always looking back in time.
Recently the Hubble Space Telescope imaged the most distant star ever seen – at 12.9 billion light-years away. This star is only 1 billion years younger than the current accepted age of the universe of 13.9 billion years. And it could only be seen due to a fortuitous gravitational lensing effect which magnified it. Astronomers named the star “Earendel” which means “morning star". With the new James Webb Space Telescope we may see stars farther than that.
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The views and opinions expressed herein do not imply endorsement from nor necessarily reflect those of the U.S. Government or NASA.